[GMCnet] ~ Final Drive ~

[J A Holland]

I have a '78 Eleganza II that came with
the 403 Motor /307 Final Drive set up ~

After years struggling up slight hills
I changed out the 307 for a 370 and got
more pulling power, more gas mileage
and better overall performance .

A fellow GMC Motorhome owner has asked
the following question;

What About Installing A 410 Final Drive
On THE 403 MOTOR with 307 Final Drive" ?

So Now I Am Asking For Your Input ~

What would be the advantage of the 410
VS
What would be the advantage of the 370

~ Joe ~
--
/_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
O----------OO--]* ~ '78 TZE168V100234 ""
" Joe & Lavelle " ""
'sweet home alebamy'

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[Matt Colie]

jaholland wrote on Thu, 12 September 2013 19:42

> I have a '78 Eleganza II that came with the 403 Motor /307 Final Drive set up ~
>

> After years struggling up slight inclines while pulling our towd caused me to change out my 307 final drive for a 370 and I got much more pulling power, more gas mileage and better overall performance .
> ~> {my only regret is no Posi-Traction}
>
> A fellow GMC Motorhome owner recently asked me the following question;
>
> "What About Installing A 410 Final Drive On THE GMC Motorhome 403 MOTOR and 307 Final Drive Setup" ?

>
> So Now I Am Asking For Your Input ~
>
> What would be the advantage of the 410
> VS
> What would be the advantage of the 370
>
> ~ Joe ~

Joe,

I was an automotive engineer a lot of my working life.

The plan is to get the expected road speed to land the engine in the middle of its torque curve. Hitting a little high is no big thing, but problem is that John Q Public has been convinced buy pre-WWII data that slower turning engines are more efficient and last longer.

That may have been true then, but I do know it is not now. What really tears up an engine is lugging. (Translation: Asking an engine for maximum torque below its peak torque crankshaft speed.)

I do not have all the information I would like to have. (It seldom that an engineer actually does.) But, from what I know, I would have to think that a 403 would love a 4.10. That would put road speed in the middle of the only 403 torque curve I have ever seen. That would lower the required BMEP (the average cylinder pressure that makes the torque) and lower the load on the piston rings (they would last longer) and the additional speed would make the bearings last longer (and they wouldn't get hammered either).

If there is an actual advantage a 4.10 has over a 3.70, I would have to see real numbers to confirm it, but I can pretty much assure you that it would not hurt anything.

The only advantage that I can see that a 3.70 would have is that JimK has supplied a whole bunk of them and not had problems.

Matt
--
Matt & Mary Colie
'73 Glacier 23 Chaumière (say show-me-air)
Now with 4 working Rear Brakes
SE Michigan - Twixt A2 and Detroit

[A.]

[quote title=Matt Colie wrote on Thu, 12 September 2013 19:46... from what I know, I would have to think that a 403 would love a 4.10. That would put road speed in the middle of the only 403 torque curve I have ever seen. ...[/quote]What's "road speed"?
--
'73 23' Sequoia For Camping
'73 23' CanyonLands For Sale
UA (Upper Alabama)
"Time is money. If you use YOUR time, you get to keep YOUR money."

[J A Holland]

Bob Dunahugh wrote
Messages: 153

Registered: October 2010
Location: Cedar Rapids, IA
Senior Member


{quote }
Have a 78 Royale, 403, and the 3:70.
Sometimes my GVW is in the 20,000 lbs range.
Depending on the trailer I'm pulling.
You've herd about how the short stroke,
big bore 403 comes into it's own above 3,100 rpm's.
So, so true, When I got the 3:70 in 2004.
Best change that I ever made to that GMC.
The 4:10 wasn't out yet. Engine, and trans run cooler,
and my mileage went up. ( Not a lot )
Thinking of selling the 3:70. And going to the 4:10.
Most 1 ton trucks run 3:70 tops, to 4:88.
You could keep it above 3,100 RPM,s more of the time.
When I'm in the mountains. I shift it down. And run it up to 4,500 RPM's. And just leave it there.
The trans at that point is running a lot of fluid to that cooler.
And the load on pistons, rings, and bearings is reduced.
There is 145,000. miles on the clock.
Runs great.
Bob Dunahugh
GMCMI Member
78 Royale4 Yenko Chevrolet's (unquote}

--
/_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
O----------OO--]* ~ '78 TZE168V100234 ""
" Joe & Lavelle " ""
'sweet home alebamy'

[J A Holland]

-----Original Message-----
From: Bob Dunahugh

Have a 78 Royale, 403, and the 3:70. Sometimes my GVW is in the 20,000 lbs range. Depending on the trailer I'm pulling. You've herd

about how the short stroke, big bore 403 comes into it's own above 3,100 rpm's. So, so true, When I got the 3:70 in 2004. Best

change that I ever made to that GMC. The 4:10 wasn't out yet. Engine, and trans run cooler, and my mileage went up. ( Not a lot )
Thinking of selling the 3:70. And going to the 4:10. Most 1 ton trucks run 3:70 tops, to 4:88. You could keep it above 3,100 RPM,s

more of the time.When I'm in the mountains. I shift it down. And run it up to 4,500 RPM's. And just leave it there. The trans at

that point is running a lot of fluid to that cooler. And the load on pistons, rings, and bearings is reduced. There is 145,000.
miles on the clock. Runs great.
Bob

------------------------------------------------------
__From: Rob Mueller <mailto:robmu...@iinet.net.au>
Date: 09/13/2013 7:51 AM (GMT-06:00)
To: mailto:gmc...@temp.gmcnet.org
Subject: Re: [GMCnet] Final Drive. 4:10

Bob,

The 403 has a shorter stroke than the 455. I can't remember what the stroke of both engines is off the top of my head and I'm too
lazy to look it up at the moment. The shorter stroke of the 403 means you can rev it higher with no negative effect.

However, IMO if you run a 455 at the same RPM ranges as the 403 you will be operating the engine at piston speeds that are not
conducive to long term wear / reliability.

Regards,
Rob M.______________

[Matt Colie]

A Hamilto wrote on Thu, 12 September 2013 22:21

> Matt Colie wrote on Thu, 12 September 2013 19:46
> > ... from what I know, I would have to think that a 403 would love a 4.10. That would put road speed in the middle of the only 403 torque curve I have ever seen. ...

> What's "road speed"?

A,

Road speed is a term used loosely in automotive engineering to describe the velocity of a particular vehicle in its expected service. One would not use the same design speed for a Corvette that one might use for a C3500 chassis.

For most of us with old GMCs, road speed is probably 60~65, but if you have a twin turbo Cadillac, it might just be 80~85 and in that case, I thing a high numerical final drive might be ill-advised.

Matt
--
Matt & Mary Colie
'73 Glacier 23 Chaumière (say show-me-air)
Now with 4 working Rear Brakes
SE Michigan - Twixt A2 and Detroit

[78gmc-royale]

Good Morning
Not sure if my new tach is calibrated correctly, but with the 403 & 3:70 last night on the way to our destination at 70 mph the tach said 4000 rpm.  Seems high to me but the ole 403 seemed to like it and just purr'd along.  I will check it with another tach when we get back.  Thoughts on the 4000 rpm?  I run the larger 245 tires so my 3:70 is more like a 3:55.
Ray

Sent from my Galaxy S®III

[A.]

Matt Colie wrote on Sat, 14 September 2013 08:18

> A,
>
> Road speed is a term used loosely in automotive engineering to describe the velocity of a particular vehicle in its expected service. One would not use the same design speed for a Corvette that one might use for a C3500 chassis.
>
> For most of us with old GMCs, road speed is probably 60~65, but if you have a twin turbo Cadillac, it might just be 80~85 and in that case, I thing a high numerical final drive might be ill-advised.
>
> Matt

65 is a good speed. Even in the places where the speed limit is 70 or 75 I just go 65 in the slow lane in the car. Gas mileage in passenger cars drops off a cliff at speeds higher than that. On a 700 mile trip, it adds up to almost 20% more for fuel in the CFO's Ford Freestyle.

Geared the way it is, it would not surprise me if the GMC got about the same at 70 or 75 as it does at 65.

--
'73 23' Sequoia For Camping
'73 23' CanyonLands For Sale
UA (Upper Alabama)
"Time is money. If you use YOUR time, you get to keep YOUR money."

[James Hupy]

Another thing to consider when regearing the GMC is driving into constant
headwinds. With my 78 Royale that is quite heavy and equipped with 3:07
gearing battling headwinds would sometimes require that I shift into 2nd to
maintain 55 mph. Running from Fresno to Weed California, a trip that we
take frequently, that would just suck the fuel down. Now with the 3:70
gearing, I can maintain 60 - 65 mph into the wind and still run on the
primaries at about 12 - 14 inches of vacuum. Way better fuel mileage to be
sure. Same thing with the Columbia Gorge in Oregon. Headwinds there are
frequently 50 - 60 MPH. 200 miles in that stuff ain't fun. My overall fuel
economy is the same or slightly better with the lower gearing, and the
driveability is much improved.
Jim Hupy
Salem, OR
78 GMC Royale 403

[J A Holland]

~> 307 / 410 Final Drive <~

I have an extra 307 Final Drive
and would like to change it into
a limited slip 410 Final Drive and
install it in our 78 Eleganza II ~

Dumb me wants to know just what all
I will need to accomplish this since
I seem to have more time than money ?

~ Joe ~

--
/_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
O----------OO--]* ~ '78 TZE168V100234 ""
" Joe & Lavelle " ""
'sweet home alebamy'

[James Hupy]

You will need a case spreader, and a carrier holding fixture to hold the
carrier stationary while you torque the cap screws holding the ring gear.
Probably also will need some different shims to adjust ring gear to pinion
clearance. Might also need to shim the pinion depth. Dial indicator,
prussian blue or white lead to check tooth contact. Knowledge on how to do
all this stuff is also helpful. Some cases will need to be ground slightly
to clear the new ring gear and carrier assembly. Other than that, it's a
piece of cake. Oh, I forgot, you need to r & r the final drive.
Jim Hupy
Salem, Or
78 gmc Royale 403.

[John Wright]

Better work on the money part as the parts will cost you almost as much as the finished product and thats if Jim K would sell them to you separately and you will still have no warrantee also. The warrantee is pretty darn good!

JR Wright

JR Wright
GMC Great Laker MHC
GMC Eastern States
GMCMHI
78 Buskirk 30' Stretch
1975 Avion (Under Reconstruction)
Michigan

[jim kanomata]

We have supplied the 4.10 gear assembly to 20 people.
They call out the ratio and I sold it to them.
Only reason I do not push that ratio is the possibility of noise.
The final drive unit is bolted to the engine and your riding on top.
I have 2 locations that assemble them and it is not as easy to do when it comes to doing it so you do not end up with a noisy unit.
One can see that the ratio is a great ratio for driving between 55-65mph.
Maybe we will put in a 4.10 with limited slip unit on our 403 powered unit and try it out on our own and see how it works and noise issue.
--
Applied/GMC, Fremont, CA
1-800-752-7502
ji...@appliedgmc.com
www.appliedgmc.com

[Jim Galbavy]

Back in my college days, I had a '57 Chevy Nomad that sported a 265 ci V/8 and a 4:11 rear. Great for towing stock cars but high revving on the highway topping out about 65mph.

jim galbavy
'73 x-CL ANNIE
Lake Mary, Fl

[Johnny Bridges]

Take a look at what Go-Mads are selling for these days.....

--johnny\

--------------------------------------------

On Wed, 10/9/13, Jim Galbavy <j.ga...@att.net> wrote:

Subject: Re: [GMCnet] ~ Final Drive ~

To: gmc...@temp.gmcnet.org
Date: Wednesday, October 9, 2013, 1:20 PM

[D C _Mac_ Macdonald]

My '50 Ford convertible with 239 cid V-8 had a 4.10 or 4.11 rear end and 3-spd w/ overdrive tranny. It would hit the 100 mark on the speedo and continue past 100 and across the blank area back zero! No tach, of course, but valves didn't seem to float in those flathead engines.


~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
______________
*[ ]~~~[][ ][|\
*--OO--[]---O-*



> To: gmc...@temp.gmcnet.org
> From: j.ga...@att.net
> Date: Wed, 9 Oct 2013 08:20:09 -0500

> Subject: Re: [GMCnet] ~ Final Drive ~
>

[J A Holland]

jim kanomata wrote on Wed, 09 October 2013 01:50

> We have supplied the 4.10 gear assembly to 20 people.
> They call out the ratio and I sold it to them.
> Only reason I do not push that ratio is the possibility of noise.
> The final drive unit is bolted to the engine and your riding on top.
> I have 2 locations that assemble them and it is not as easy to do when it comes to doing it so you do not end up with a noisy unit.
> One can see that the ratio is a great ratio for driving between 55-65mph.
>
> Maybe we will put in a 4.10 with limited slip unit
> on our 403 powered unit and try it out on our own
> and see how it works and noise issue.

+ + + + + + + + + +

OR

Since I like the 2 lane hiways/biways and most of my
driving is in ehe 55-65mph range
JUST MAYBE
we could work out some kind of a test deal with the
Master 'Kanomaters' by putting in the 4.10 with limited
slip unit on our 403 powered Eleganza II
and I could try it out to see how it works ~

~ JOE ~

--
/_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
O----------OO--]* ~ '78 TZE168V100234 ""
" Joe & Lavelle " ""
'sweet home alebamy'

[Rob Mueller]

Joe,

Just click on the link below and you'll find the chart that shows the change in engine RPM at various speeds between all the
available ratios: http://www.appliedgmc.com/level.itml/icOid/482

As far as the limited slip diff goes a number of people have noted that is works great!

Regards,
Rob M.

-----Original Message-----
From: J A Holland

jim kanomata wrote on Wed, 09 October 2013 01:50
> We have supplied the 4.10 gear assembly to 20 people.
> They call out the ratio and I sold it to them.
> Only reason I do not push that ratio is the possibility of noise.
> The final drive unit is bolted to the engine and your riding on top.
> I have 2 locations that assemble them and it is not as easy to do when it comes to doing it so you do not end up with a noisy
unit.
> One can see that the ratio is a great ratio for driving between 55-65mph.
>
> Maybe we will put in a 4.10 with limited slip unit
> on our 403 powered unit and try it out on our own
> and see how it works and noise issue.


+ + + + + + + + + +

OR

Since I like the 2 lane hiways/biways and most of my
driving is in ehe 55-65mph range
JUST MAYBE
we could work out some kind of a test deal with the
Master 'Kanomaters' by putting in the 4.10 with limited
slip unit on our 403 powered Eleganza II
and I could try it out to see how it works ~

~ JOE ~

[Emery Stora]

On Oct 8, 2013, at 4:21 PM, J A Holland wrote:

>
>
> ~> 307 / 410 Final Drive <~
>
> I have an extra 307 Final Drive
> and would like to change it into
> a limited slip 410 Final Drive and
> install it in our 78 Eleganza II ~
>
> Dumb me wants to know just what all
> I will need to accomplish this since
> I seem to have more time than money ?
>
> ~ Joe ~
>

Use it as a core and swap it with Jim Kanomata to get his ready built one.
You would probably use more money to try to do it yourself and I don't think you would find the gears. Jim K. has them made for him.

Emery Stora

[anthony ezzo]

I will say this my 67 Eldo is 3:21.At 100mph I am at almost 4000rpm.I wish I had fourth gear in the trans.4:10/11 is for Drag Racing.As far as limited slip,it is already!
If one gets stuck going up an icy hill,kitty litter one wheel and the other will spin,and If I really floor it and hold it down both tires will spin,however this is at the end of its rope when its spinning both tires and I don't advise 4500 rpm burnouts.When one has that kind of power it is difficult not to use it,wisely or unwise.Like having a suzuki hyabusa and going 20 through a school zone.If they had it full posi it would burn the tire every time you make a turn,early versions of the gm FWD had tortional dampeners in the driveshaft to take up the slack instead
of burning the tire,cost too much for them to keep using it so the tire burns as it is!
--
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo

[Jim Galbavy]

Johnny, it hurts every time I think about that Nomad. ...who knew. Back then it was just a 2 door station wagon. ...and station wagons weren't cool. :(

[J A Holland]

~ Jim;

I ordered a new Black 57 Chevy Bel Air 2 dr hardtop
with all available bells and whistles - Power Pac,
Power Glide, Power Steering, Adoonized Body Trim,
Fender Skirts, Red/Black Interior - I traded in my
Hemi Powered Tri-Colored '56 Dodge D-500 On It ~
BUT
WHO KNEW ~

--
/_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
O----------OO--]* ~ '78 TZE168V100234 ""
" Joe & Lavelle " ""
'sweet home alebamy'

[Johnny Bridges]

I sold my '68 Hemi Roadrunner in 1969 for, if memory serves, about 2400 dollars. Because the insurance was going to kill me. I bought it from McConnell in Montgomery for something just over 3 Large - becuase the engine/trans added about 800 to the sticker. They're now bringing obscene amounts of monery. We grow too soon old and too late smart. Face it, our Moms all had wagons, who wanted to be seen on a date in one?

--johnny
'76 23' transmode norris
'76 palm beach

--------------------------------------------

On Thu, 10/10/13, Jim Galbavy <j.ga...@att.net> wrote:

Subject: Re: [GMCnet] ~ Final Drive ~

To: gmc...@temp.gmcnet.org
Date: Thursday, October 10, 2013, 3:25 AM

[D C _Mac_ Macdonald]

These days, there are a few wagons that are NOT uncool. The Dodge Magnum wagon is/was (IMNHO) pretty cool and we have gotten compliments from "the younger set" that our 2012 Ford Flex is a "swag mobile." The 355 hp, twin turbo, and paddle shift six-speed tranny just add to the package!

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
______________
*[ ]~~~[][ ][|\
*--OO--[]---O-*

> Date: Thu, 10 Oct 2013 05:45:04 -0700
> From: jhbr...@ymail.com
> To: gmc...@temp.gmcnet.org

[J A Holland]

Cadillackeeper wrote on Wed, 09 October 2013 14:31

> I will say this my 67 Eldo is 3:21.At 100mph I am at almost 4000rpm.
> I wish I had fourth gear in the trans.4:10/11 is for Drag Racing.
> As far as limited slip,it is already!
> If one gets stuck going up an icy hill,kitty litter one wheel
> and the other will spin,and If I really floor it and hold it
> down both tires will spin,
> however this is at the end of its rope when its spinning both
> tires and I don't advise 4500 rpm burnouts.
> When one has that kind of power it is difficult not to use it,
> wisely or unwise.
> Like having a suzuki hyabusa and going 20 through a school zone.
> If they had it full posi it would burn the tire every time you

> make a turn.
> Early versions of the gm FWD had tortional dampeners in the driveshaft

> to take up the slack insteadof burning the tire,

> cost too much for them to keep using it
> so the tire burns as it is!

= = = = = = = = = = = = = = = = = = = =

~ That is probally why GM called it a Limited Slip ~
BTW
Does the '67 Eldo come with the Switch Pitch Tranny ? ~

~ Jie ~

--
/_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
O----------OO--]* ~ '78 TZE168V100234 ""
" Joe & Lavelle " ""
'sweet home alebamy'

[J A Holland]

jaholland wrote on Thu, 10 October 2013 11:38

> Cadillackeeper wrote on Wed, 09 October 2013 14:31
> > I will say this my 67 Eldo is 3:21.At 100mph I am at almost 4000rpm.
> > I wish I had fourth gear in the trans.4:10/11 is for Drag Racing.
> > As far as limited slip,it is already!
> > If one gets stuck going up an icy hill,kitty litter one wheel
> > and the other will spin,and If I really floor it and hold it
> > down both tires will spin,
> > however this is at the end of its rope when its spinning both
> > tires and I don't advise 4500 rpm burnouts.
> > When one has that kind of power it is difficult not to use it,
> > wisely or unwise.
> > Like having a suzuki hyabusa and going 20 through a school zone.
> > If they had it full posi it would burn the tire every time you
> > make a turn.
> > Early versions of the gm FWD had tortional dampeners in the driveshaft
> > to take up the slack insteadof burning the tire,
> > cost too much for them to keep using it
> > so the tire burns as it is!
>
>
>
>
> = = = = = = = = = = = = = = = = = = = =
>
> ~ That is probally why GM called it a Limited Slip ~
> BTW

> Did Your '67 Eldo Come With The Switch-Pitch Tranny ? ~
>
> ~ Joe ~

[anthony ezzo]

Yes it does!!

--
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo

[Charles Wood]

I had a 56 2door HT, Nomad, & sedan delivery.
Didnt have time for them then...
--
CBWood
77 Kingslay
MWC OK
ONLINE PARTS PROGRAM
http://cbwoodsr.no-ip.org/GMCParts/index.asp

[Hal StClair]

Some wagons are cool-I have a 1965 Olds Vista Cruiser with a LS1 and 4l60e auto, 4 wheel discs, all modern suspension. Get lots of thumbs up when running down the road.
Hal

[Rob Mueller]

G'day,

For the record the 3.21 to 1 planetary gear final drive and switch pitch transmission came in 66 and 67 Toronados.

I have a 3.21 to 1 planetary gear final drive in Double Trouble and I have one to go into The Blue Streak.

For Double Trouble I had Manny build me a switch pitch transmission with a power drive chain gears which results in a 3.66 to 1
ratio.

Since Australia is pretty flat I decided to stay with the 3.21 to 1 and no power drive.

Anthony noted that the 3.21 FD in his Eldo acts like a limited slip diff and I have "heard" that the 3.21 final drive acts like a
limited slip in a GMC can anyone with a 3.21 in a GMC verify that.

Regards,
Rob M.

[Larry]

Robert Mueller wrote on Thu, 10 October 2013 20:03

I have the 3.21 FD and it has a "tendency" to pull like a posi. But if you really push it by putting one wheel on gravel and the other on pavement, the gravel tire will spin first while the pavement wheel wants to do some pulling. On wet grass, both will pull till one or the other looses traction, then Just one will spin. Pulls better than the spider gear set-up, but not as good as a posi. Just what I've observed.
--
Larry :)
78 Royale w/500 Caddy
Menomonie, WI.

[Bob Heller]

I've heard some people say the 3.21 has 'posi' characteristics but having had one apart to replace bearings and now running it on the GMC I can't see how it's any different from any other open diff. There is nothing in the 3.21 to couple the two outputs in any way. A LSD has something, like clutches, to allow some additional torque to be applied to the 'stuck' wheel instead of letting the spinning wheel determine the max amount of power available. The 3.21 has nothing like that, it's an open diff that just happens to use a planetery gear set instead of the more traditional spider gears like everything else. From what I can see, the 3.21's only 'advantage' is that it's narrower but in our application there is plenty of room so the 'narrowness' doesn't matter.

On my GMC the 3.21 spins the tires easier than the 3.07, probably due to the gear ratio multiplying the torque a bit more. It really sucked when I was at Speed World and, where with the 3.07 I got good consistent launches with minimal wheelspin, now with the 3.21 the tires go up in smoke far too easily. With the 3.21, flooring the pedal with the gear lever in '1' results in a tire spinning, the speedometer at 44mph, and the engine making some noises I don't feel comfortable with (it's the original engine and I don't like to float the valves on it). Even in normal driving when it's wet out the tires (actually one tire) spin(s) with less pedal than before. Since I don't tow and mostly drive in Florida I'm ready to put the 3.07 back in.

SO, tell me again, how is the 3.21 the better diff, other than the ratio?
--
Bob Heller
1974 X-Canyonlands 26ft
Winter Springs FL

[Bob Heller]

Joe,

If you are seriously considering the 4.1 ratio do a test forst to see if you can live with it.

According to the rpm chart on Jim K's site the 4.1 will have the engine turning 3000 at 60 mph and 3250 at 65 mph. Here's what you do:

Assuming you've got a tachometer in your GMC, get the GMC on an open road at about 50 mph to start with and put the gear lever in 'S'. Bring the rpms to about 3100 to 3200 (if I remember correctly that's about the rpms/mphs with a 3.07 ratio). 3100 to 3200 is about the rpms you would be running with the new 4.1 ratio in high gear on any kind of open road. After about an hour of listening to the engine running at 3200 rpms decide if the 4.1 is really the right ratio for you. I tried this on my GMC and can tell you there is a big difference between cruising at 2500 rpm and cruising at 3200 rpm. If you're constantly climbing mountains with a car in tow then it might be acceptable, but maybe there are better choices for your needs.

Storytime:
Years ago a co-worker bought a new 1983 Volkswagen Rabbit GTI and was really proud of it's performance, especially compared to the Mustangs and Camaros of the day. One ride in it and I could see how they got the 90-or-so horsepower engine to accelerate the car to 60 mph so well - it's all in the gears. The car magazines gushed about the performance of the GTI, what the car magazines didn't tell you was that you would go nuts listening to that engine screaming while trying to drive on the interstate. It wouldn't have been so bad if VW had put a 'proper' 5th gear in it. At least the Mustangs and Camaros had 'proper' gear ratios and much better sounding engines, even if they didn't have that much horsepower.

[Todd Sullivan]

I had a 321 with chain reduction working out to a 366 in The War Pig. I drove only about 4-500 miles with this drive which came to me in the coach. All of my driving has been with a heavy enclosed trailer. I recently installed a 355 limited slip in its place since I had to replace the engine as the lim slip was on my to do list If I needed to have everything out anyway. I just got back from coos bay and have put close to 1000 miles on the 355. My observation is that the 355 lim slip and the 321 w chain reduction offer very similar traction. However, the new motor built by Jim Hupy is a much stronger motor than the one I had pushing the 321. I have never driven with the stock 307

Todd Sullivan

Sully
77 royale
Seattle

[Howard Nielsen]

We run 4:70 and never have had a tire spin problem
No posi.
Unless I stand on it.
We returned today from Coos Bay returning the long way back on US 395 eastern Sierra.
Snow north of Bishop on the passes over 6,000.
Never a tire slipping/spin problem.
Howard
Alpine Ca
74 Canyon Lands
455 not quite stock running 3:70 final drive.

All is well with my Lord

[J A Holland]

Bobby;
~ My '73 Canyonlands 26 footer with the 455/307 set up
was used in Wisconsin, Illinois, Indiana, Michigan and
Ohio without ever towing.

After we purchased our '78 Eleganza II with the 403/307
setup we have always pulled a TOWD.
Our best fuel mileage with that factory setup is around
the 75mph mark and I much prefer driving on the hi ways
(with the towd) in the 55/60 mph range.

We now do a lot of Hilly and Mountain driving and we also
have a very steep curved drive that the '78 with a 403/307
setup can not pull with the Towd if I drop below 10mph ~

This is my concerns about installing the 4.10 limited slip
final drive and a switch pitch tranny ~

*(just in the thinking stage about the switch pitch tranny)

~ Joe ~
--
/_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
O----------OO--]* ~ '78 TZE168V100234 ""
" Joe & Lavelle " ""
'sweet home alebamy'

[lenze middelberg]

Is there any way to possetivly establish witch FD is installed?
I have read there should be stamped a number, but is not there where it should be

--
Appie
eleganza 76
Volvo v70
Denmark

[Rob Mueller]

Larry,

Thanks for the info.

Regards,
Rob M.

-----Original Message-----

[anthony ezzo]

This was a few years back,My neighbor is a video nut and also is a Mecedes Master Tech.This was after my hood blew up one day cause the tire stuck and twisted the
car a bit to release the latch.I wanted to see the tire spin,he made it fast and slow so I could see.Like i said If I was to really floor it and hold it down the other tire will spin as well.I just think it does it cause the gears are ready to blow to bits at that time and are all stuck together at those high rpm,about 6000 !!!I have the CPP adjustable roller rocker shafts and heavy double springs.

http://www.youtube.com/watch?v=TVZQ5NY_dnI&list=FL-v-xtvsXHUS795jZL3Ln8Q&feature=mh_lolz

--
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo

[Rob Mueller]

Appie,

Very simple; crawl under the coach and count the number of bolts in the FD cover, if it has 10 bolts it's a 3.07 if it's 9 then it's
a 3.21.

It is also possible that a PO installed an aftermarket ratio if it is a 3.07; to determine that you would have to compare the speed
and engine rpm to the chart on Gene's website.

http://gmcmotorhome.info/front.html#RATIO

Regards,
Rob M.


-----Original Message-----

From: lenze middelberg

Is there any way to possetivly establish witch FD is installed?
I have read there should be stamped a number, but is not there where it should be

--
Appie

[Rob Mueller]

Bob,

Thanks for the info.

I don't think anyone has said there IS anything other than the lower gear ratio that makes the 3.21 BETTER.

I too have had a 3.21 apart and pondered why people note is has 'posi' characteristics. If one examines the way JimK's limited slip
FD works it might provide some insight into answering that question.

http://www.appliedgmc.com/products/full/876.jpg

There are two alloy blocks with springs in between them pressing on the spur gears that the drive flange splines go into. This
"connects" the left and right wheels yet allows them to turn at different speeds when going around a corner. Without those parts
both axle flanges are connected to spur gears which would have the same resistance to turning.

Below is a link to an exploded view of the parts of a 3.21 FD.

http://www.gmcmhphotos.com/photos/member-galleries/p33111-3-21-final-drive.html

Note that one drive flange engages with item 24 - CASE AND COVER and the second with item 25 - CARRIER. The carrier has the three
planetary gears inside it

Unlike the 3.07 FD we now have drive flanges attached to different parts and if the resistance to turning between item 24 and 25
were different it seems to me would provide some "limited slip characteristics."

I run AT tires and I don't have any problems with tire spin when it's wet.

Regards,
Rob M.


-----Original Message-----

From: Bob Heller

I've heard some people say the 3.21 has 'posi' characteristics but having had one apart to replace bearings and now running it on
the GMC I can't see how it's any different from any other open diff. There is nothing in the 3.21 to couple the two outputs in any
way. A LSD has something, like clutches, to allow some additional torque to be applied to the 'stuck' wheel instead of letting the
spinning wheel determine the max amount of power available. The 3.21 has nothing like that, it's an open diff that just happens to
use a planetery gear set instead of the more traditional spider gears like everything else. From what I can see, the 3.21's only
'advantage' is that it's narrower but in our application there is plenty of room so the 'narrowness' doesn't matter.

On my GMC the 3.21 spins the tires easier than the 3.07, probably due to the gear ratio multiplying the torque a bit more. It really
sucked when I was at Speed World and, where with the 3.07 I got good consistent launches with minimal wheelspin, now with the 3.21
the tires go up in smoke far too easily. With the 3.21, flooring the pedal with the gear lever in '1' results in a tire spinning,
the speedometer at 44mph, and the engine making some noises I don't feel comfortable with (it's the original engine and I don't like
to float the valves on it). Even in normal driving when it's wet out the tires (actually one tire) spin(s) with less pedal than
before. Since I don't tow and mostly drive in Florida I'm ready to put the 3.07 back in.

SO, tell me again, how is the 3.21 the better diff, other than the ratio?
--
Bob

[Rob Mueller]

Bob / Joe,

Manny has noted on MANY occasions not to put the transmission in "S" above 40 mph!

Regards,
Rob M.

-----Original Message-----
From: Bob Heller

Joe,

If you are seriously considering the 4.1 ratio do a test forst to see if you can live with it.

According to the rpm chart on Jim K's site the 4.1 will have the engine turning 3000 at 60 mph and 3250 at 65 mph. Here's what you
do:

Assuming you've got a tachometer in your GMC, get the GMC on an open road at about 50 mph to start with and put the gear lever in
'S'. Bring the rpms to about 3100 to 3200 (if I remember correctly that's about the rpms/mphs with a 3.07 ratio). 3100 to 3200 is
about the rpms you would be running with the new 4.1 ratio in high gear on any kind of open road. After about an hour of listening
to the engine running at 3200 rpms decide if the 4.1 is really the right ratio for you. I tried this on my GMC and can tell you
there is a big difference between cruising at 2500 rpm and cruising at 3200 rpm. If you're constantly climbing mountains with a car
in tow then it might be acceptable, but maybe there are better choices for your needs.

Storytime:
Years ago a co-worker bought a new 1983 Volkswagen Rabbit GTI and was really proud of it's performance, especially compared to the
Mustangs and Camaros of the day. One ride in it and I could see how they got the 90-or-so horsepower engine to accelerate the car to
60 mph so well - it's all in the gears. The car magazines gushed about the performance of the GTI, what the car magazines didn't
tell you was that you would go nuts listening to that engine screaming while trying to drive on the interstate. It wouldn't have
been so bad if VW had put a 'proper' 5th gear in it. At least the Mustangs and Camaros had 'proper' gear ratios and much better
sounding engines, even if they didn't have that much horsepower.
--
Bob

[Larry]

appie wrote on Fri, 11 October 2013 01:55

> Is there any way to possetivly establish witch FD is installed?
> I have read there should be stamped a number, but is not there where it should be

Look at this for the differences between the 3.21 and others (3.07, 3.50, 3.70, etc)
http://www.gmcmhphotos.com/photos/g4399-fd-visual-differences-3-07-vs-3-21.html

--
Larry :)
78 Royale w/500 Caddy
Menomonie, WI.

[Matt Colie]

Robert Mueller wrote on Fri, 11 October 2013 09:10

> Larry,
> Thanks for the info.
> Regards,
> Rob M.
> -----Original Message-----
> From: Larry
>
> I have the 3.21 FD and it has a "tendency" to pull like a posi. But if you really push it by putting one wheel on gravel and the other on pavement, the gravel tire will spin first while the pavement wheel wants to do some pulling. On wet grass, both will pull till one or the other looses traction, then Just one will spin. Pulls better than the spider gear set-up, but not as good as a posi.
> Just what I've observed.
> --
> Larry :)

Rob and Larry,

The story about the planetary differential being somewhat like a limited slip (at the time often referred to as a "No Spin") is that the internal friction of the gear set was high when the load was asymetric. This depended on many things and the most important was the lubricant used in the system. Also relayed to me in a personal note from one of the engineers importance of the finish of the internal components. This presented and issue as they lost some of the equalizing capability as the parts wore smooth.

So, with very limited first hand experience (mine didn't work), I would guess that the planetary would beat nothing but not be as good as any real locker or limited slip. I was able to change mine out for a Dana PwrLok.

Matt
--
Matt & Mary Colie
'73 Glacier 23 Chaumière (say show-me-air)
Now with 4 working Rear Brakes
SE Michigan - Twixt A2 and Detroit

[Emery Stora]

On Oct 11, 2013, at 7:46 AM, Rob Mueller <robmu...@iinet.net.au> wrote:

> Bob,
>
> Thanks for the info.
>
> I don't think anyone has said there IS anything other than the lower gear ratio that makes the 3.21 BETTER.

Rob
Doesn't the inherent strength of the planetary gear system in the 3.21 make it a stronger design than the 3.07 and others?

Emery Stora
77 Kingsley
Frederick, CO

[Rob Mueller]

Emery,

Matt mentioned in another thread that back in the 60's, 70's, and 80's things in the automotive world seemed to be overdesigned; I
agree with him on that point. .

When I removed the cover of the 3.21 FD to put in Double Trouble I was amazed at how beefy all the parts were in comparison to the
spur gear 3.07. I "heard" that they were "bulletproof." I agree from what I saw that they were tougher than the spur gear FD's.

I also "heard" that they stopped making them because they cost a lot of money to manufacture in comparison to the spur gear FD.

Obviously this is shear conjecture as I have not seen any endurance testing, however I can tell you that jet engine air starters
have planetary reduction gears in them to reduce the turbine speeds from around 10,000 rpm to 3,000 at the output shaft. The ones
for large hi-bypass engines put out 700 ft lb of torque.

Regards,
Rob M.

-----Original Message-----

From: Emery Stora

Rob
Doesn't the inherent strength of the planetary gear system in the 3.21 make it a stronger design than the 3.07 and others?

Emery

[anthony ezzo]

My car is almost 500 horse and almost 600ft/lbs on the chassis dyno at 4500 rpm aprox.

--
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo

[anthony ezzo]

A link...
http://www.gmcmhphotos.com/photos/member-galleries/p46127-side-shot-done.html

[anthony ezzo]

High Rpm setup...
http://www.gmcmhphotos.com/photos/member-galleries/p46124-the-animal.html

[anthony ezzo]

Here I am at work the other day.I had no road rage that day!!!
http://www.gmcmhphotos.com/photos/member-galleries/p51282-no-road-rage.html

[Carl Stouffer]

Here is a neat little graphic of how the Detroit True Track differential works:

http://www.jegs.com/p/Detroit-Locker/Detroit-Truetrac-Differentials/1032953/10002/-1

Reviews are mixed on this unit. This has really nothing to do with the 3.21. other than having a similar planetary gear design. This one, however, transfers torque to the wheel with the best traction. I don't believe the GMC's 3.21 does that, but this might be the source of the belief that it does.
--
Carl S.
'75 ex Palm Beach
Tucson, AZ.

[Rob Mueller]

Carl,

Never seen anything like this before going to have to watch that video a few times to understand how the thing works that's for
sure!

Regards,
Rob M.

-----Original Message-----

From: Carl Stouffer

Here is a neat little graphic of how the Detroit True Track differential works:

http://www.jegs.com/p/Detroit-Locker/Detroit-Truetrac-Differentials/1032953/10002/-1

Reviews are mixed on this unit. This has really nothing to do with the 3.21. other than having a similar planetary gear design.
This one, however, transfers torque to the wheel with the best traction. I don't believe the GMC's 3.21 does that, but this might
be the source of the belief that it does.
--
Carl

[Carl Stouffer]

Rob,

Magic! :twisted:

--
Carl S.
'75 ex Palm Beach
Tucson, AZ.

[Howard Nielsen]

Carl
Has anyone used this in our GMC's
If so how was the revue?
Thanks
Howard

All is well with my Lord

> On Oct 11, 2013, at 14:01, Carl Stouffer <carl...@yahoo.com> wrote:
>
>
>
> Here is a neat little graphic of how the Detroit True Track differential works:
>
> http://www.jegs.com/p/Detroit-Locker/Detroit-Truetrac-Differentials/1032953/10002/-1
>
> Reviews are mixed on this unit. This has really nothing to do with the 3.21. other than having a similar planetary gear design. This one, however, transfers torque to the wheel with the best traction. I don't believe the GMC's 3.21 does that, but this might be the source of the belief that it does.

[Carl Stouffer]

hnielsen2 wrote on Fri, 11 October 2013 16:10

Howard,

There is not one made for our application. AFAIK, there is no option for a posi in a GMC final drive other than Jim K's. There is no room in the final drive case for anything else. As narrow as that case is, it's a minor miracle that Jim's team came up with the design they did. I have Jim K's limited slip 3.70 and IT works great.

[Rob Mueller]

Howard,

If you plug 1975 Oldsmobile into:

Narrow Results for Detroit Truetrac Differentials

You get this:

Detroit Truetrac Differential
1971-89 GM Car
1972-89 GM Truck
28-Spline Axles
8.5'' Diameter Ring Gear
Fits 2.73 & Up Gear Ratios
Rear Only

If we could get them made for the Toronado it would be Magic!

When I was checking on getting a locking diff made by a company in Australia I was told that the 3.07 case was too small, I suspect
that's the case with this also.

Regards,
Rob M.
USAussie - Downunder

-----Original Message-----
From: Howard Nielsen

Carl
Has anyone used this in our GMC's
If so how was the revue?
Thanks
Howard

[Kosier]

Rob,

It is quite possible to put a Truetrac in a GMC final drive.
In fact, it has already been done. The problem is that
there is not room for our axle shafts. Making and using
undersize axle shafts is feasible on a one-off autocross
car, but no good on a 12.000# motorhome.

Gary Kosier
77 PB w/500 Cad
Newark, Oh

[Howard Nielsen]

Rob, Gary
I saw the information
Rear only.
Not a good idea to use the undersized axle
Then I stay off the grass and soft soil.
Thanks guys
Howard
Alpine Ca

All is well with my Lord

> On Oct 11, 2013, at 20:07, "Kosier" <gko...@roadrunner.com> wrote:
>
> Rob,
>
> It is quite possible to put a Truetrac in a GMC final drive.
> In fact, it has already been done. The problem is that
> there is not room for our axle shafts. Making and using
> undersize axle shafts is feasible on a one-off autocross
> car, but no good on a 12.000# motorhome.
>
> Gary Kosier
> 77 PB w/500 Cad
> Newark, Oh
>
> -----Original Message-----
> From: Rob Mueller
> Sent: Friday, October 11, 2013 8:30 PM
> To: gmc...@temp.gmcnet.org
> Subject: Re: [GMCnet] ~ Final Drive ~
>

[Rob Mueller]

Gary,

You jogged my memory, I had communicated with the guy that built that FD:

*******************************************************************************************
Wayne,

I think I've got it now.

An Eaton posi for a 9" Ford diff can be adapted and made to fit in an Olds Toronado final drive by:

Make a ring gear spacer
Make two carrier bearing sleeves
Make you two new stub axles to fit the 31 splines

Regards,
Rob

*******************************************************************************************
Rob

Correct, It is however a smaller unit than what olds uses on the other hand 9" ford units are used in very fast drag cars. I beat
the hell out of mine in AX and after over 250 runs and 450 hp it is still working as installed, but the car and me weigh only 2400
lbs let me know what you end up with.

Wayne

*******************************************************************************************

Wayne,

Hmmm maybe I better forget about this, the GMC Motorhomes built between 1973 and 1978 weigh 12,500 pounds fully loaded.

I will contact Eaton and see what I can find out regarding how much of a load it can handle.

Thanks,
Rob

*******************************************************************************************

I never bothered contacting Eaton because JimK sells the limited slip unit and I'm sure this would cost WAAAAY more to build!

Regards,
Rob M.

-----Original Message-----

From: Kosier

Rob,

It is quite possible to put a Truetrac in a GMC final drive. In fact, it has already been done. The problem is that there is not
room for our axle shafts. Making and using undersize axle shafts is feasible on a one-off autocross car, but no good on a 12.000#
motorhome.

Gary