[GMCnet] Here's one for the savvy....

[6cuda6--- via Gmclist]

So i was under the coach yesterday just poking around and looking at what i can do to shore up the black tank strap with the broken mounting bolt and
something caught my eye......the fuel vent line "T" by the tanks....it was a brass "T" with good clamps etc....no way they had zipties or stainless
clamps in the 70"s.....hmmmmmmm :roll:

So i got a quick look and it appears that someone has been there before but and here's the but....when we picked up the coach last year and i filled
it to capacity for my first time i had fuel running off the top of both tanks...now the RV was parked slightly on a slope so it was running off the
left corners of both tanks so i know its not the tanks seams. So to prevent that the rest of the trip home i just didnt fill it to max capacity.

So here's the question.....if they did at one point drop the tanks and they did replace the lines within the last 10 years or so...what could have
been leaking? Fuel sending unit gaskets? Could the vent lines be bad again? Would their be a particular marking on the "new type" fuel lines that i
could compare to whats there? Is there other fittings that both tanks have that are not used?

I suspect i'm going to have to drop the tanks either way but i just want to be somewhat prepared.......out of every job in a garage you could pick
dropping fuel tanks is the one i hate the most! :(
--
Rich Mondor,

Brockville, ON

77 Hughes 2600

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

[Matt Colie via Gmclist]

Rich,

I feel particularly qualified to answer this, not just because I had my tanks down five times, but that is part of it.

The fuel sending unit gaskets seem to seldom be the issue. But, when you get the tanks down they are easy to update.

No matter when the fuel lines were replaced, if the line material was not alcohol resistant, then there you go. I also made this mistake with an
early repair. I used rubber fuel line that I had kept in stock for a decade. Not only was it old already, but it only took about three years to go
bad again.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

[Jon Roche via Gmclist]

my experience on 2 coaches I have done myself, and helped with 4 others. is the 1st thing to leak is the ventline. that comes off at a little bit
of a angle, so that connection tends to 1. crack 1st if old. and #2 might leak if it is a new hose and a hose clamp is not tightened enough. (new
hoses will shrink just slighty, so you want to use really good clamps and tighten them well).


the chance of someone replacing part of the gas lines is very high. I have seen that a number of times, where they splice into hoses that they can
reach and replace what they can short of removing the tanks, saving the problem of the hoses above the tanks for someone down the road later.


Like Matt said- the only times i Have seen senders leaking is when someone is not careful installing them. There is a lock ring, and the wrong
mechanic pounding on that with a screw driver can mess that up. there is actually a tool for installing those lock rings, that allows even twist on
it. but a careful mechanic can install them without the tool. I have seen 2 that someone looked like they installed it with a air chisel.

I am going to knock on wood- my coach that sat for 10 years and had all sorts of fuel line rotted off. and my friend Ed's coach, that also sat for
10 years. both have functioning fuel senders/pickups, and only needed new hoses. others have got into the project and found holes in the tanks, and
bad senders, or worrse.




--
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/

[Jon Roche via Gmclist]

Rich,

the tank job is really not that terrible of a project, and really is nice once it is done. You know what you have after that.

the biggest thing is to get it at the right height, and jack it up. The other thing is getting the fuel out. I found using an electric pump drains
99% of the fuel out, if you just hook it up and suck the fuel out of the pickups. it takes at least 15 gallons of gas to pour back in, before it
will start priming and sucking gas again. last couple tanks we emptied that way, there was hardly any gas in the tank to slosh out and dump on
you when you go to pull the tanks down.

--
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/

[Richard H Staples via Gmclist]

Rich,
Being a bit of a fumble-finger myself, I'd make darn sure I had new sending unit O-rings on hand when dropping the tanks. I screwed mine up the first
time around and had exactly your symptoms. That said, as everyone pointed out, there are lots of potential leak points in there, including the
sending unit electrical terminal itself.

While in there the last time, I noticed that one of my pickup tubes sat about 2 inches off the bottom of the tank. (No way it should take 15 gallons
to start picking up fuel, IMHO.) So I carefully bent it down a bit.

BTW, if you can get the drain plugs loose, coat them with anti-sieze or some such to make sure they come out next time.

HTH
Rick Staples
--
Rick Staples, '75 Eleganza, Johnstown, CO

"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien

[Bruce Hart via Gmclist]

Replace the plugs with the external square head instead of the internal hex.

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class

[6cuda6--- via Gmclist]

Thanks for the info guys.....i did get 2 sending unit lock rings and seals the last time is was out to visit JimK country. I have replaced many a GM
fuel sending unit and yes that tool is awesome but careful use of a hammer and blunt screwdriver can get it done.

Here's hoping its simple.....lol. Now to make a list parts for this job as this virus stuff is cramping my ability to just simple get what i need
easily.

[Bruce Hislop via Gmclist]

Rich,
Here are some pic from when I last had my tanks down. Mine was leaking from the vapour port as was previously mentioned. The nipple seams to be
installed using a crimp method like a pop rivet and becomes loose and leaks. I replaced mine and sealed it with JB weld. About 5 years now and still
good.

http://www.gmcmhphotos.com/photos/g7006-fuel-tank-lines.html

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

[6cuda6--- via Gmclist]

Thanks Bruce...guess ill have to drop the tanks and deal with what is there....lol.

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

[James Hupy via Gmclist]

Most of my adult life, I have had a struggle with myself over starting a
procedure that I was unfamiliar with. Procrastination is the name of the
game. Not every time, but mostly my fears have been unfounded. Once I got
involved with the actual work, it usually went off well without all my
reservations coming up and biting me in the butt. Just Do It! is my new
mantra.
Jim Hupy
Salem, Oregon

On Tue, Apr 28, 2020, 6:46 PM 6cuda6--- via Gmclist <gmc...@list.gmcnet.org>
wrote:

[Ken Henderson via Gmclist]

Also pay particular attention to the electrical connection for the fuel
level sender -- the insulating feed-thru can deteriorate and create a
leak. I don't have a good fix for that -- I tried replacing the insulator
with a nylon one, which only lasted a year or two. I finally modified some
SS assemblies from eBay -- but didn't get very good level accuracy from
those.

Ken H.

[Johnny Bridges via Gmclist]

I trade on Matt and Ken's experience. Take the dam' things down once, and do ALL of it. ew seals, good electrical connections, proper barrier hoses,
use the genset feed if it was a trandmode with a tee, etc. If I had to take rust off the exterior, a couple rattle cans of Zinc - it.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell

[Larry via Gmclist]

FWIW, I change over to all steel lines.

http://www.gmcmhphotos.com/photos/dropping-the-fuel-tanks/p66041-rear-tank.html
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

[6cuda6--- via Gmclist]

Agreed Johnny...hence all the questions as they are only going out once if i can help it.

Johnny Bridges wrote on Wed, 29 April 2020 13:00

> I trade on Matt and Ken's experience. Take the dam' things down once, and do ALL of it. ew seals, good electrical connections, proper barrier
> hoses, use the genset feed if it was a trandmode with a tee, etc. If I had to take rust off the exterior, a couple rattle cans of Zinc - it.
>
> --johnny


--

Rich Mondor,

Brockville, ON

77 Hughes 2600

[6cuda6--- via Gmclist]

Thanks Larry, im thinking steel lines but not compression fittings ....but then again good hoses will outlast me probably.... ill have all the parts
on hand then make up my mind once i see the tanks on the ground.

Larry wrote on Wed, 29 April 2020 13:09

> FWIW, I change over to all steel lines.
>
> http://www.gmcmhphotos.com/photos/dropping-the-fuel-tanks/p66041-rear-tank.html
>

> http://www.gmcmhphotos.com/photos/dropping-the-fuel-tanks/p66043-front-tank.html

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

[Terry via Gmclist]

Check the hose barb for the vent on the tanks carefully. The one on my rear tank was loose in the tank due to rubbing on the floor. I could not
believe their was no top retention for these tanks except the floor! So I sealed the loose crimp connection with superglue, and then reinforced it
with JB weld type stuff, and then glued pads on top of the tanks to stop the fittings (hose barbs) from abrading against the floor. Could not come up
with quick and easy way to retain the tanks from the top down so I just improved GM's idea a little with the plastic pads from some CD-ROM packing. No
evidence of there ever being any pads up there.
After fixing that and replacing the distorted and broken Corvette vapor separator valve in the wheelwell, no more leaks!
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.

[6cuda6--- via Gmclist]

Thanks for the tip Terry! Ill get a look at that for sure.

Bullitthead wrote on Wed, 29 April 2020 23:43

> Check the hose barb for the vent on the tanks carefully. The one on my rear tank was loose in the tank due to rubbing on the floor. I could not
> believe their was no top retention for these tanks except the floor! So I sealed the loose crimp connection with superglue, and then reinforced it
> with JB weld type stuff, and then glued pads on top of the tanks to stop the fittings (hose barbs) from abrading against the floor. Could not come
> up with quick and easy way to retain the tanks from the top down so I just improved GM's idea a little with the plastic pads from some CD-ROM
> packing. No evidence of there ever being any pads up there.
> After fixing that and replacing the distorted and broken Corvette vapor separator valve in the wheelwell, no more leaks!


--

Rich Mondor,

Brockville, ON

77 Hughes 2600

[Jon Roche via Gmclist]

if you are having clearance issues to the floor, I would suspect your body pads are not in good shape. the tanks bolt to the frame, and there
should be some space between the tank and the floor. tank should float with the frame and not be attached to the floor. Opposite on a black sewer
tank, that rides with the body and is bolted to the floor, not the frame.

but Like I said, those vent nipples would be the first place I would look for a leak, both the hose, or the nipple into the tank.

--
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/

[6cuda6--- via Gmclist]

If i went with solid supply lines on the tank and solid vent lines on the tank.....does anyone remember how lone they needed for the remainder of the
rubber line?

I'm just trying to buy the correct length of lines...Gates Barracade is not cheap so if i don't need 25ft and only 15ft that's a hug difference $$$
wise.

[Jon Roche via Gmclist]

I know everything in canada is more expensive it seems. - but I would think anything is comparable.

I did not think it was too expensive, you want the carburation hose: GAtes #27315 for the 3/8" and gates #27314 for the 5/16

now if you are going with EFI, then that is a different story. the EFI hose is expensive. for my EFI, I have the pumps just forward of the tanks,
so I am using the low pressure hose from the tanks to the pumps, then I switched to hardline to the engine bay, where i switched back to expensive
EFI hose.


the proper brass comression fittings to work and deal with the hardline, and the cost of the hardline itself, I would think would be more money then
the low pressure fuel hose.

--
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/

[Terry via Gmclist]

I just replaced my supply and vent lines, and didn't need to do the section forward of the torsion bar cross member. Used over 25 feet of 3/8 hose and
25 feet of 5/16 for vent lines (not including the vent to the filler neck, that's 3/8). I did not replace some of the vent line going to the canister
because it was already done and passed all the tests I could throw at it. Seems like the dividing line between good and bad hose was the T-Bar cross
member. Reworked the fuel pump and added filter and fixed several areas of dislike and previous owners' modifications so my measurements will not be
the same as anybody else on the planet. Also, I could not use the last 4 feet on the reel of 3/8 hose because it was collapsed from being wound so
tight. Would have had to get another reel (25 ft)if I didn't already have some extra pieces.
Jim Bounds says there is 56 feet of fuel line to be replaced down there...

When I saw the leak at the vent port, I immediately went under there to check the body mount pads and look for evidence of missing tank pads on the
floor. No missing tank pads, and the body mount pads still had a 1/2>>5/8 inch gap to the frame, just the size of the vent line hose going to the
vapor separator. Same thickness everywhere.

This is a poor design with no retention straps on top of the tank. How did that ever get by SAE? I could winch those tanks right up against and even
raise the floor with them if I didn't pay attention carefully on installation. A floating/hanging fuel tank does not pass muster for me(unless you
plan to eject it sometime in flight), so I used pads glued to the tank to hold it FIRMLY in place. Still not the preferred retention from the top
down, but the best I came up with without welding and drilling holes in the frame.

This was all to no avail, as I still have the random loss of power that feels like running out of fuel... :(

--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.

[6cuda6--- via Gmclist]

Thanks for the info and lengths.

When it dies what happens when you check the accelerator pump function? Do you have fuel out the nozzels?

Bullitthead wrote on Fri, 01 May 2020 15:17

> I just replaced my supply and vent lines, and didn't need to do the section forward of the torsion bar cross member. Used over 25 feet of 3/8 hose
> and 25 feet of 5/16 for vent lines (not including the vent to the filler neck, that's 3/8). I did not replace some of the vent line going to the
> canister because it was already done and passed all the tests I could throw at it. Seems like the dividing line between good and bad hose was the
> T-Bar cross member. Reworked the fuel pump and added filter and fixed several areas of dislike and previous owners' modifications so my measurements
> will not be the same as anybody else on the planet. Also, I could not use the last 4 feet on the reel of 3/8 hose because it was collapsed from
> being wound so tight. Would have had to get another reel (25 ft)if I didn't already have some extra pieces.
> Jim Bounds says there is 56 feet of fuel line to be replaced down there...
>
> When I saw the leak at the vent port, I immediately went under there to check the body mount pads and look for evidence of missing tank pads on
> the floor. No missing tank pads, and the body mount pads still had a 1/2>>5/8 inch gap to the frame, just the size of the vent line hose going to
> the vapor separator. Same thickness everywhere.
>
> This is a poor design with no retention straps on top of the tank. How did that ever get by SAE? I could winch those tanks right up against and
> even raise the floor with them if I didn't pay attention carefully on installation. A floating/hanging fuel tank does not pass muster for me(unless
> you plan to eject it sometime in flight), so I used pads glued to the tank to hold it FIRMLY in place. Still not the preferred retention from the
> top down, but the best I came up with without welding and drilling holes in the frame.
>
> This was all to no avail, as I still have the random loss of power that feels like running out of fuel... :(


--

Rich Mondor,

Brockville, ON

77 Hughes 2600

[Terry via Gmclist]

It never dies, just won't get out of it's own way once in awhile. If I pull of to the side to check it out, it idles fine and the accelerator pump and
main metering circuit work just fine ( I mean it squirts AND will run high RPMs longer than just a few seconds on the side of the road when this
happens). Except for that, it feels like the carbs main fuel circuit runs out of fuel when climbing a mountain or sometimes just leaving a stoplight.
At one time, I figured it must be the Mallory ignition amp breaking down when hot, but disproved that in the winter.

--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.

[6cuda6--- via Gmclist]

Do you have a "battery voltage/amp gauge" on your dash or the stock dash? Have you checked charge current or your isolator recently? The reason i ask
is the same symptoms, happened to me on my way home from picking this coach up last year from the east coast. You'd be driving along and all of a
sudden it felt like you were running out of fuel even though i knew it wasnt.

Next time your out with the coach and that starts to happen switch the battery boost switch into the "boost" position momentarily and see if it cleans
it up...if so replace your isolator. You can test your isolator with a DVM as well instead if you would rather do that.....mine had a bad diode and
caused the mentioned condition and if left long enough when driving the coach would either die completely or overcharge the battery that it was
feeding all the current too.

Something to try as it seems you have gone down the fuel road already.....



Bullitthead wrote on Fri, 01 May 2020 23:41

> It never dies, just won't get out of it's own way once in awhile. If I pull of to the side to check it out, it idles fine and the accelerator pump
> and main metering circuit work just fine ( I mean it squirts AND will run high RPMs longer than just a few seconds on the side of the road when this
> happens). Except for that, it feels like the carbs main fuel circuit runs out of fuel when climbing a mountain or sometimes just leaving a
> stoplight. At one time, I figured it must be the Mallory ignition amp breaking down when hot, but disproved that in the winter.


--

Rich Mondor,

Brockville, ON

77 Hughes 2600

[Ken Henderson via Gmclist]

Excellent suggestion! Why? To understand what apparently happened, one
must understand the construction of the isolator: It's basically a piece
of aluminum with two metal-cased silicon diodes' cathodes (the "arrow" in a
diode symbol) welded to the piece of aluminum. There's a single stud
sticking up from the aluminum base plate and one on the anode (the "flat"
part of a diode symbol) of each diode -- the Alternator terminal, and the
two Battery terminals, respectively. Now that assembly is "potted" into
the finned aluminum heat sink/case with a thermally (but not electrically)
conductive plastic compound.

With the alternator connected to the two cathodes, when its output voltage
exceeds that of the connected batteries (by about 0.7 VDC), it sends
current to them. Conversely, when the diodes' anodes (connected to the
batteries) are more positive than the alternator terminal, no current
flows, therefore the two batteries are "isolated" from each other.

The most common failure mode for such an isolator, in my experience, is
that the continual thermal expansion and contraction of the potting
compound eventually breaks one of the diodes' weld to the base plate.
Since the chassis battery generally cycles more frequently through higher
current loads (from the starter depleting the battery) on the alternator,
that diode heats, cools, and therefore fails most frequently. When the
diode-base connection to the chassis battery is open, the alternator no
longer charges the chassis battery, but continues to monitor its voltage
and increases its output in attempting to do so. Meanwhile, the house
battery, with its diode still conducting, is absorbing that 18-25 VDC
maximum output from the alternator! By the time the chassis battery
voltage is too low to satisfactorily supply the ignition system, the house
battery may have been seriously damaged -- perhaps taking out a lot of
other electrical stuff too!

To complicate the troubleshooting, the chassis battery diode may only need
to cool down a couple of degrees to again make contact through the broken
weld. Intermittent connections like that can be extremely difficult to
identify.

Ken H.

[Matt Colie via Gmclist]

Bullitthead wrote on Fri, 01 May 2020 23:41

> It never dies, just won't get out of it's own way once in awhile. If I pull of to the side to check it out, it idles fine and the accelerator pump
> and main metering circuit work just fine ( I mean it squirts AND will run high RPMs longer than just a few seconds on the side of the road when this
> happens). Except for that, it feels like the carbs main fuel circuit runs out of fuel when climbing a mountain or sometimes just leaving a
> stoplight. At one time, I figured it must be the Mallory ignition amp breaking down when hot, but disproved that in the winter.

Terry,

I have a similar issue in hot places and finally tracked it down to the metal fuel line at the front cross member. That is the hottest place and the
lowest pressure in the system. I thought about verifying that with the IR gun, but since my hand said it was too hot, I just believed it. Crumpled
aluminum foil got us going reliably as a jury rig, and I keep looking for a simple and reliable solution. While the aluminum foil missed the last two
reassemblies, I am still considering:
Using the wrong fuel pump and sending the bleed back to the fill neck.
Or
Doing two low pressure (we are still carburetor) back at the tanks.

I have the wrong fuel pump on the shelf because that was all I could get one day.

We seldom go places that hot, and for sure won't this year. If Herr Governor ever releases us, there won't be much season left.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

[Terry via Gmclist]

Thanks for that info Matt, maybe today will be a good day for a GMC ride and I'll check that out with the pyrometer at my destination stop and
definitely right after a power loss if it happens. Pyrometer is now standard GMC and trailering tool for the toolboxes. Cheap enough now to warrant
multiple units and also allows you to cross check them occasionally.

--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.