[GMCnet] Switch pitch transmissions. A want or a need?

[Scott Nutter]

Any switch pitch tranny owners out there with operational knowledge? Would this be a upgrade that would be a must? More moving parts to brake? Any
reason to go, or stay away from the switch pitch tranny? Would be used with a 455 with a 3.21, towing a tracker.
Thanks, Scott
--
Scott Nutter
1978 455 Royale Center Kitchen, Quad bags.
Houston, Texas

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[Todd Sullivan]

Scott,
I have had a gmc with a standard (not manual 😜) trans and my current coach
with a switch. I am almost always towing when I am using the motorhome and
I live in the hilly Pacific Northwest. And I love the switch pitch. As far
as I know there are no additional parts to fail however synthetic trans
fluid must be used and a trans temp gauge is a good idea since trans temps
climb while in switch mode under load.

Sully
77 eleganza 2
Seattle

[Larry]

Scott Nutter wrote on Tue, 13 December 2016 22:05

> Any switch pitch tranny owners out there with operational knowledge? Would this be a upgrade that would be a must? More moving parts to brake? Any
> reason to go, or stay away from the switch pitch tranny? Would be used with a 455 with a 3.21, towing a tracker.
> Thanks, Scott

When I brought our coach home in 2002 from point of purchase, (Houston) the transmission went out as I was backing it into the driveway. I then
rebuilt it to a S/P. I have had a switch pitch since 2005 when we first started driving it again. I would say that the SP is a weak want, and not a
need to have. I don't use it as much as I thought. Probably use it more in reverse than in any of the forward gears as we have a steep drive that I
need to back into. So...yes it can be used in any gear including reverse. I will use it occasionally when towing and I feel the need to come off of a
stop light fairly quick, or need to get up to speed fairly quick on a interstate on ramp. I have used it climbing mountain grades, but it should be
noted that trans fluid temp builds much faster than if I were using it in low stall and just shifted down a gear. If you already have a 3.21 FD then
IMO you might consider the 3;50 power drive chain and sprocket set sold by Manny giving you an efffective 3.70 gearing. JMHO
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

[Pete Smith]

Can you the Manny chain and sprocket without pulling the engine/transmission?
--
Cary, NC

No Coach yet but trending towards mid kitchen Rolaled, 77 or 78, 403, hopefully with good original Imron paint.

[John Wright]

You have to remove the transmission to put the different chain drive assembly.

JR Wright
Michigan
Frozen

[Emery Stora]

You would have to pull the transmission. You can do this without pulling the engine or final drive.

Emery Stora
77 Kingsley
Frederick, CO

[Larry]

thesmith wrote on Wed, 14 December 2016 17:50
> Can you fit the Manny chain and sprocket without pulling the engine/transmission?

No. Gotta pull the trans to do it. Take off the chain and sprocket back cover to change the parts out and put the trans back in. The other option is
to change out the final drive from your 3.21 to one of Jimmy K's 3.70's. That way you wouldn't have to drop the trans. Problem is, that 3.21 is a
strong bullet proof unit. As I said before, the 3.50 sprocket set with the 3.21 FD gives you an effective 3.70. IIRC price on the sprocket set is
about the same as a 3.70, but IMO that 3.70 FD is a somewhat weaker unit than the 3.21. Some have said that the sprocket set puts more strain on the
transmission, but I personally have not seen evidence to support that. Most who have a 3.70 gear ratio...be it the combo 3.21 FD with 3.50 gear set,
or the 3.70 FD have been very pleased with performance and no change in gas milage...even though the engine is spinning more rpm's per mile. Either
way, towing through the mountains is significantly easier with the 3.70. JMHO

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

[Jim Kanomata]

To benefit from the 3.70 final drive, one does not need to be pulling or
climbing hills.
There is enough wind drag putting load on the engine at lower rpm which the
3.07 gives you.

--
Jim Kanomata
Applied/GMC, Fremont,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[Rob Mueller]

Larry,

Thanks for the memory tweak, I promised to talk to Manny about the reliability of the power drive when I visited him on my return to
Sydney in August. I did and he advised he had installed numerous power drives (I can't remember the number he noted) and he's only
had one problem.

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Larry
Sent: Thursday, December 15, 2016 12:11 PM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Switch pitch transmissions. A want or a need?

thesmith wrote on Wed, 14 December 2016 17:50
> Can you fit the Manny chain and sprocket without pulling the engine/transmission?

No. Gotta pull the trans to do it. Take off the chain and sprocket back cover to change the parts out and put the trans back in. The
other option is to change out the final drive from your 3.21 to one of Jimmy K's 3.70's. That way you wouldn't have to drop the
trans. Problem is, that 3.21 is a strong bullet proof unit. As I said before, the 3.50 sprocket set with the 3.21 FD gives you an
effective 3.70. IIRC price on the sprocket set is about the same as a 3.70, but IMO that 3.70 FD is a somewhat weaker unit than the
3.21. Some have said that the sprocket set puts more strain on the transmission, but I personally have not seen evidence to support
that. Most who have a 3.70 gear ratio...be it the combo 3.21 FD with 3.50 gear set, or the 3.70 FD have been very pleased with

performance and no change in gas mileage...even though the engine is spinning more rpm's per mile. Either way, towing through the

[Ken Henderson]

For what it's worth: When I first got the X-Birchaven in '98 I knew
NOTHING about GMC's, but the 3.50 chain sounded like a good idea, so,
having the engine out anyway, I had the transmission gone through and the
chain installed. I later swapped that whole front clip (front frame and
drive train) into a X-Palm Beach, which my son now owns. That drive train
probably has 85,000 miles on it -- without any problems. I discount the
proposition that the chain imposes too much load on the transmission, based
on the numerous applications where much higher torque engines are used.
And it's quieter than most final drives.

The only reason I didn't install a chain in the X-BIrchaven's current drive
train during one of it's several R&R's is that it came with JimK's 3.55,
which has been VERY satisfactory also.

JMHO,

Ken H.


On Thu, Dec 15, 2016 at 2:16 AM, Rob Mueller <robmu...@iinet.net.au>
wrote:

[Chris Tyler]

I dont think it would be worthwhile to do as an updrade unless you are pulling the transmission anyway.

I would consider it If I ever needed to replace the trans. I have had one vehicle that had one, it worked fine. Many were built, relatively few
problems from OEM that I know of. I think they were discontinued for economic reasons rather than reliability.

Recently learned that a TH400 SP core will not get you all the parts needed to change over a TH425, so if you do look at it you will need the right
core.
--
76 Glenbrook

[Scott Nutter]

It would be for a complete power train rebuild. Patterson 455, rebuilt 3.21 FD, and rebuilt tranny. And that's where the switch pitch tranny question
comes into play.

At present time I don't do much mountain travel, but who knows what the future holds.
I do like the option of having the ability to flip a switch and drop the rpm's back into the torque curve in hills if needed.

But at the same time the standard tranny has been a proven winner. And I have been happy with it the last 20 years.

I don't think any of these tranny's would be a bad choice, I'm just trying to make the best choice and I'm still on the fence.......

Any more suggestions? Scott
.

[Johnny Bridges via Gmclist]

My 26' coach with a 3.7 walked over the Rockies without complaint. If I try to jump off a light, it usually spins the front wheels, so I don't see
the value for me in a switch pitch. My 23' would probably benefit from the power drive chain mod, it isn't quick at startup. Even with the 3.07
though, it easily clears the two mountains I regularly see with a toad cliiped on the back at 40 - 45 per in second. I think a 3.5 would be optimum
for it in the Southeast.

--johnny
--
'76 23' transmode Norris upfit, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"The road goes on forever, and the party never ends" --Robert Earl Keen

[Emery Stora]

I think that you are looking at it wrong. I have an automatic controller for my switch pitch made by Bruce Roe. When I leave the switch in automatic, when I come to a full stop it is engaged in switch pitch so when I take off from a stop light it is less prone to spin the wheels because its in a “lower” gear due to the switch pitch. I have a Kanomata 3.55 final drive.

Emery Stora
77 Kingsley
Frederick, CO

[Rob Mueller]

Scott,

Here's my take on the "switch pitch" (SP) transmission vs the "standard"
(STD) transmission.

A STD Th-425 is the same basic transmission as the STD transmission, there
is a solenoid in the SP isn't in the STD transmission. When actuated, it
causes the vanes in the torque convertor to change angle and provide more
torque.

In the 66 & 67 Toronado the SP function was controlled by a switch actuated
by the throttle linkage. When you floored the gas pedal the solenoid in the
transmission would actuate, the torque convertor vanes changed angle, and
the car accelerated quicker. The switch had a timer that would only allow it
to stay in SP mode for a limited amount of time. No, I don't know how long
that was.

I have two TH-425 transmissions rebuilt by Manny to go into both my GMC's,
the one in the USA has the power drive feature as well so when with the 3.21
final drive I have an ratio of 3.6 to 1. The one here in Australia does not
have the power drive feature as I did not feel it was necessary as we ain't
got the Rocky Mountains here!

To me it boils down to - why not have the switch pitch feature as it can
help. HOWEVER, if you have a SP you need a controller built by Bruce Roe,
and Manny recommends an additional transmission cooler, and synthetic trans
fluid.

The rebuild will cost extra for the Power Drive and I think he charges a bit
more for the SP.

If you want more details on how the SP transmission works go to Bdub's
website and download the manual I sent him.

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Scott
Nutter
Sent: Friday, December 30, 2016 3:19 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Switch pitch transmissions. A want or a need?

[Emery Stora]

>
> If you want more details on how the SP transmission works go to Bdub's
> website and download the manual I sent him.
>
> Regards,
> Rob M.
> The Pedantic Mechanic

Rob
That information has also been on the GMCMI.com <http://gmcmi.com/> website since I submitted it back in 2009.

Emery Stora
77 Kingsley
Frederick, CO

[Scott Nutter]

Last questions:
If the solenoid fails, or the electrical supply to the solenoid fails, it will revert back to operate exactly like the TH425?

The only concern would be a potential overheat condition it not properly monitored while in switch pitch mode?

If "yes" to both questions, then I would think the switch pitch tranny would be very desirable to have......

[Ronald Pottol]

Also, I thought the stall speed in normal mode was a little lower, impling
that you can spin the motor a little slower before the torque converter
starts to lose efficiency.

[Rob Mueller]

The solenoid is normally closed shutting off the fluid path that changes the
torque convertor vane pitch. If it fails closed then the transmission can't
go into SP. If it fails open it won't come out of SP. I have absolutely no
data on the reliability of that solenoid.

Emery will have to respond to your second question as I am not familiar with
its operation.

I have two transmission oil coolers like this:

http://www.gmcmhphotos.com/photos/oil-cooler-engine-external/p60194-b-26amp-
3bm-70297-oil-cooler-out-of-box.html

I think the temp switch is set to have the fan turn on at 180° F.

Regards,
Rob M.
The Pedantic Mechanic

USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Scott
Nutter
Sent: Friday, December 30, 2016 12:37 PM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Switch pitch transmissions. A want or a need?

[Gary Kosier]

Scott,

There are two possible failure modes on that solenoid. An electrical
failure will leave it closed and a mechanical
failure could leave it open. Since you put power to it to get high stall,
then an electrical failure reverts to a normal
T-425. Also, the mechanical failure MIGHT not allow it to be completely in
high stall. I say this because I had a
failure of the solenoid several hundred miles from home and still got home.
I'm not sure if it was totally in high
stall or not. We called Manny and he said watch the engine temperature and
if it starts to heat up, pull over.
Aluminum radiators are a wonderful thing.

Gary Kosier
77PB w/500Cad
Newark, Ohio

--------------------------------------------------
From: "Scott Nutter" <winos...@gmail.com>
Sent: Thursday, December 29, 2016 8:37 PM

To: <gmc...@list.gmcnet.org>
Subject: Re: [GMCnet] Switch pitch transmissions. A want or a need?

[Scott Nutter]

I have been doing some research on the controller that Emory has recommended.

It is made by Bruce Roe, a toronado tranny tech. If I'm understanding his controller correctly, it sorta gives the switch pitch tranny a 6 speed feel
(maybe not the best description). Sounds like the controller gets most of its input from vacuum and brake peddle position, and the converter vanes
are constantly changing position during acceleration and deceleration and/or when the vacuum signal detects a heavy load.

My plan for a switch pitch tranny was to operate it as basically as possible. Via a toggle switch while running the mountains. I like manual!
But at the same Bruce Roe is only going to make another 100 controllers then retire his business. So I will be buying one just in case. And after a
year or so of experience with the switch pitch, maybe I'll install it.

[John Wright]

Bruce Roe’s contact email or phone # sent PM if you want.

J.R. Wright

[Scott Nutter]

The only contact info I have for Bruce Roe is his email. I think the controllers are a little under $150.
It is bcroe at juno dot com.

[Rob Mueller]

Scott,

I have two switch pitch tranny's and have ordered a couple of his
controllers. I will give him a call and have a chat to learn exactly how
they work when I get a chance.

Don't hold your breath waiting for me to do so, however, I have a list of
TTD's that is a mile long and this is way down on the list.

Regards,
Rob

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Scott
Nutter

Sent: Sunday, January 1, 2017 3:54 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Switch pitch transmissions. A want or a need?

[John Wright]

Rob,
If you have his phone number PM me online.
J.R.