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[GMCnet] Transmission Leaks [message #130852]

Sun, 19 June 2011 09:40

Ken Henderson

Messages: 8726
Registered: March 2004
Location: Americus, GA

Karma: 9

Senior Member

Y'All may remember that a couple of months back, Bill Bramlett visited
here for a few days and rebuilt some transmissions for us. The first
of those was for Stick Miller's coach.

Stick hasn't driven the coach much since then because it almost
immediately started leaking transmission fluid. We first thought the
leak was from the chain drive cover, but when we got it on my rack
last week, we discovered that everything forward of there was also
covered with red stuff. When we wiped everything down, we found a
couple of things: 1. There was a lot of black stuff on the bottom of
the final drive. 2. There was no dripping from the chain cover.

When we pulled the final drive cover to replace its gasket, we found
less than an ounce of gear lube in it. Then we discovered that the
ring gear would wobble side-to-side about 3/16". That didn't seem
like such a good thing, so we pulled his 3.42 FD and replaced it with
one of my spare 3.07's. We had a heck of a time finding the 3
necessary gaskets: The FD cover gasket wasn't too bad, the local NAPA
found one in a nearby town and their delivery truck was nearby; we got
the part that afternoon. I had a FD-Transmission flat gasket but
wanted to replace it -- I STILL want to replace it. No local store's
been able to find it -- Yeah, I know, Jim's got it, and I WILL be
ordering it, but I was THERE so I tried. :-)

The third "gasket" is the pair of face seals (known as the pinion
seal) in the final drive which prevent the transmission fluid and the
final drive gear lube from mingling. NAPA didn't have them, but "will
have them in the morning". "In the morning" turned out to be a week
later. When it became obvious that we wouldn't have the seals in time
to get Stick off my rack during the weekend, we decided that seal
looked good enough to use, so we reassembled his coach and sent him
happily on his way.

Friday, Stick and I decided to do one trivially simple repair that
he's been needing: Replace the 27" length of 1/2" hose which connects
the tanks' "burp" line to the fuel filler neck. As Stick pulled onto
the rack for that 15 minute job, my heart dropped -- red stuff was
just pouring from under the coach! Closer examination showed that the
leak was near the junction of the FD & transmission -- either the
flange gasket or the pinion seal. Another FD R&R :-( :-( ;-(

Since I'd been VERY careful with the flange gasket, I was reluctant to
believe it was the cause, so I dried everything up again and got Stick
to run the engine while shifting through all the gears several times.
I finally found that fluid was running off of the little "shelf" on
the transmission between the final drive and the engine. Baffled as
to where that could be coming from, I checked the coolant lines
connections at the transmission. Sure 'nuff, one of those lines was
leaking, forming a small puddle in the valley beneath them. But not
enough fluid was puddled to run over the flange that forms a dam at
the forward end of that valley, so that couldn't be the source of the
forward drip.

Or could it? Feeling the "dam" in Stick's coach, and in mine, which
is easier to reach with the Cad's iron manifolds in place, I could not
find any hole in the dams.

After disconnecting the leaking line and pulling the straight male to
inverted flare adapter, I found that the inverted flare seat was badly
damaged. My parts box didn't have a replacement, so I called JimK.
He offered to send me a couple via Priority Mail so we should have
them tomorrow. We also discussed the forward leak and came to the
conclusion that the pinion seal had to be the source: If the
transmission side seal leaks, fluid will flow past it, into the cavity
between the two seals, and out a small vent hole above the place where
our leak is visible. JIm agreed that the cooler line leak couldn't
reach that far forward. Another FD R&R :-( :-( ;-(

One last attempt to avoid "Another FD R&R :-( :-( ;-(": I filled a
bottle with water and tried to fill the "lake" below the cooler line
fittings -- I couldn't fill it!!! The water kept running out through
the bottom of the dam and cascading off the little "shelf" up front!
Cooling line leaks CAN reach the front of the transmission! I don't
know whether all 425's have a hole through that dam, but Stick's DOES.

Hallelujah! We went to the farm, where my spare engines &
transmissions are stored, and found some cooling line adapters. One
of those replacing the damaged one cured the visible leak, so we
knocked off for the day.

Yesterday Stick came over and installed a temporary replacement "burp"
hose (more in another posting). This morning he reported that there's
no transmission fluid puddle under the coach, so MAYBE we've cured it
and WON'T have Another FD R&R :-( :-( ;-(.

Sorry this is so long, but I wanted to emphasize to everyone the
importance of investigating all possibilities before jumping into any
repair. It's all too easy to get into the modern "replace things
until the problem goes away" paradigm. We were within an arm's reach
of picking up a wrench to start removing the FD.

I'll let Y'All know if this fix is NOT completed. (Or Stick will,
'cause I think I'll just shoot myself if not.)

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach