ATF Leak at Transmission Pan (or chain cover?)

[Fred Hudspeth]

I have isolated the source of the leak to the right rear corner of the pan
(as seated in the driver seat). 'Have "diapered" all case penetrations to
insure that no ATF is coming from them. 'Have tried many different pan
gaskets over the years (and gasket sealants) but none completely stops the
leak. The gasket that appears to work the best is a NAPA # 14525. Emery
Stora reports using this gasket with good success. I installed that gasket
during the last service about 6K miles ago.

The NAPA gasket controls the leakage to about 1/2 pint (measured from a drip
pan) over several months of non-use.

There is no leakage when traveling (as observed from no blow-back onto a
clean, oil-free underbody).

There does not appear to be a problem with the integrity of the
transmission case or pan at the leak location.

I have been unable to convincingly rule out the chain cover as the source of
(or contributor to) the leak. If mine is leaking, the source would be from
just above the pan/case interface location stated above.

Thoughts on proving(or disproving) the chain cover as the source of the
leak?

Also, thoughts on why the pan still leaks (if not from the chain cover)
despite my attempts with a variety of gaskets (and sealants applied to the
gaskets) to stop it.

 

[charles boyd]

Brake cleaner and wipe dry. Spray baby powder on suspected area. Start it up. Round the block maybe.

> I have isolated the source of the leak to the right rear corner of the pan
> (as seated in the driver seat). 'Have "diapered" all case penetrations to
> insure that no ATF is coming from them. 'Have tried many different pan
> gaskets over the years (and gasket sealants) but none completely stops the
> leak. The gasket that appears to work the best is a NAPA # 14525. Emery
> Stora reports using this gasket with good success. I installed that gasket
> during the last service about 6K miles ago.
>
> The NAPA gasket controls the leakage to about 1/2 pint (measured from a drip
> pan) over several months of non-use.
>
> There is no leakage when traveling (as observed from no blow-back onto a
> clean, oil-free underbody).
>
> There does not appear to be a problem with the integrity of the
> transmission case or pan at the leak location.
>
> I have been unable to convincingly rule out the chain cover as the source of
> (or contributor to) the leak. If mine is leaking, the source would be from
> just above the pan/case interface location stated above.
>
> Thoughts on proving(or disproving) the chain cover as the source of the
> leak?
>
> Also, thoughts on why the pan still leaks (if not from the chain cover)
> despite my attempts with a variety of gaskets (and sealants applied to the
> gaskets) to stop it.
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
C. Boyd
76 Crestmont
East Tennessee

 

[Fred Hudspeth]

Brake cleaner and wipe dry. Spray baby powder on suspected area. Start it
up. Round the block maybe.

> I have isolated the source of the leak to the right rear corner of the pan
> (as seated in the driver seat). 'Have "diapered" all case penetrations to
> insure that no ATF is coming from them. 'Have tried many different pan
> gaskets over the years (and gasket sealants) but none completely stops the
> leak. The gasket that appears to work the best is a NAPA # 14525. Emery
> Stora reports using this gasket with good success. I installed that gasket
> during the last service about 6K miles ago.
>
> The NAPA gasket controls the leakage to about 1/2 pint (measured from a
drip
> pan) over several months of non-use.
>
> There is no leakage when traveling (as observed from no blow-back onto a
> clean, oil-free underbody).
>
> There does not appear to be a problem with the integrity of the
> transmission case or pan at the leak location.
>
> I have been unable to convincingly rule out the chain cover as the source
of
> (or contributor to) the leak. If mine is leaking, the source would be from
> just above the pan/case interface location stated above.
>
> Thoughts on proving(or disproving) the chain cover as the source of the
> leak?
>
> Also, thoughts on why the pan still leaks (if not from the chain cover)
> despite my attempts with a variety of gaskets (and sealants applied to the
> gaskets) to stop it.
>

 

[LQQKatJon]

my memory from reading here, and what I believe my own coach suffers from:

torque converter leak down. from my understanding, When running, fluid is in torque converter, no leak. When you stop, and park it, the
converter leaks down and over fills the pan, causing some leaking out the pan gasket, cover or who knows??? Also why it is recommended to
check/deal with the fluid level after the coach is warm and has been driven, then you have the accurate "underway" level of transmission fluid in
the pan.

I have never seen mine drip a drop of ATF going down the road or running. But evidence of underside of transmission and the concrete where I park
the coach, it leaks when parked. I attribute it to the converter draining down. Not thinking if I change any gaskets it will really quit.

--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/

 

[jon payne]

Hi Jon, my experience is the same as yours. During the summer when the GMC is in operation, no leaks to speak of. As soon as it sits a while it
starts to leak, not a whole lot, just enough to stain the concrete a bit. I installed a Ragusa trans pan so I could add a trans temp sensor, have the
extra capacity and hopefully stop the leaks but I think the Ragusa pans leaks worse than the OEM pan! I did have better luck with the rubber trans
gasket from Napa over the cork one.

Jon
--
Jon Payne
76 Palm Beach
Westfield,IN

 

[a.]

> I have isolated the source of the leak to the right rear corner of the pan (as seated in the driver seat). 'Have "diapered" all case penetrations
> to insure that no ATF is coming from them. 'Have tried many different pan gaskets over the years (and gasket sealants) but none completely stops the
> leak. The gasket that appears to work the best is a NAPA # 14525. Emery Stora reports using this gasket with good success. I installed that gasket
> during the last service about 6K miles ago.
>
> The NAPA gasket controls the leakage to about 1/2 pint (measured from a drip pan) over several months of non-use.
>
> There is no leakage when traveling (as observed from no blow-back onto a clean, oil-free underbody).
>
> There does not appear to be a problem with the integrity of the transmission case or pan at the leak location.
>
> I have been unable to convincingly rule out the chain cover as the source of (or contributor to) the leak. If mine is leaking, the source would be
> from just above the pan/case interface location stated above.
>
> Thoughts on proving(or disproving) the chain cover as the source of the leak?
>
> Also, thoughts on why the pan still leaks (if not from the chain cover) despite my attempts with a variety of gaskets (and sealants applied to the
> gaskets) to stop it.
If you have an aluminum tranny pan, they can be porous and would need to be sealed from the inside. No matter what kind of pan you have, tranny fluid
gets past the threads of the bolts and drips. I can't find the thread on the forum where someone said to use O-rings on the bolts. I would think some
thread sealant would also do the trick.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."

 

[Carl Stouffer]

Last Fall, I changed from a Rockwell transmission pan to a Ragusa pan. Jim K sent me a gasket with the new pan, and I think it was a FelPro cork
gasket. I installed it dry and haven't had any leakage problems since. The gasket has nice tight holes for the bolts so it stays in place and seals
really well.

The reason I changed pans was that I could not get thew Rockwell to seal. I thought I had it, but about 300 miles into the next trip, it was leaking
badly from where the pan gasket had slid into the pan. I stopped at an O'Reilly's in Moab and got some brake cleaner to hose it down with, then
squeezed in some "friction additive resistant" Permatex RTV and it held until I got home and changed the whole mess out. Maybe if you t4ack the leak
down to the chain case, you could try that method of sealing it.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging

 

[Ken B]

> my memory from reading here, and what I believe my own coach suffers from:
>
> torque converter leak down. from my understanding, When running, fluid is in torque converter, no leak. When you stop, and park it, the
> converter leaks down and over fills the pan, causing some leaking out the pan gasket, cover or who knows??? Also why it is recommended to
> check/deal with the fluid level after the coach is warm and has been driven, then you have the accurate "underway" level of transmission fluid in
> the pan.
>
> I have never seen mine drip a drop of ATF going down the road or running. But evidence of underside of transmission and the concrete where I
> park the coach, it leaks when parked. I attribute it to the converter draining down. Not thinking if I change any gaskets it will really quit.

I have exactly the same problem on a Blazer that I own with 225,000 miles on it. If I park it for 2 or 3 days, no leak. If I park it a week or long
longer it starts to drip on the floor. Conventional wisdom says that it is a leaking converter. You can see it raise the level by simply checking
the dip stick every day without running the engine. I'm not going to pull the trans and 4wd drive unit on it to fix it. It is much simpler to put a
drip pan under it and add 1/2 a quart of fluid once a year.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[Jim Hupy]

They are just marking their territory. Leak down from the pump is a common
problem with many G.M. transmissions, but many never reveal it because
their gasket to sealing surfaces are intimate. Many can be encouraged
to not leak by massaging the sheet metal oil pan where the fasteners
penetrate the mating faces. I use a body hammer and dolly to flatten the
flanges where they have been distorted by overtorquing the fasteners. I use
button head internal hex head fasteners on my own stuff, with buna-n "O"
rings under the heads. They "usually" do not leak. When mounting the black
composition gasket that Manny T and also my tranny guy Sam recommend, I
spray both sides of it with "hi-tack" permatex gasket sealant and mount it
wet. Do not overtorque. 25 inch pounds works fine. Just what I do.
Jim Hupy
Salem, Or.
78 GMC ROYALE 403

> > my memory from reading here, and what I believe my own coach suffers
> from:
> >
> > torque converter leak down. from my understanding, When running,
> fluid is in torque converter, no leak. When you stop, and park it, the
> > converter leaks down and over fills the pan, causing some leaking out
> the pan gasket, cover or who knows??? Also why it is recommended to
> > check/deal with the fluid level after the coach is warm and has been
> driven, then you have the accurate "underway" level of transmission fluid
> in
> > the pan.
> >
> > I have never seen mine drip a drop of ATF going down the road or
> running. But evidence of underside of transmission and the concrete where
> I
> > park the coach, it leaks when parked. I attribute it to the converter
> draining down. Not thinking if I change any gaskets it will really quit.
>
>
>
> I have exactly the same problem on a Blazer that I own with 225,000 miles
> on it. If I park it for 2 or 3 days, no leak. If I park it a week or long
> longer it starts to drip on the floor. Conventional wisdom says that it
> is a leaking converter. You can see it raise the level by simply checking
> the dip stick every day without running the engine. I'm not going to pull
> the trans and 4wd drive unit on it to fix it. It is much simpler to put a
> drip pan under it and add 1/2 a quart of fluid once a year.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Ken H.]

Just the other day Manny pointed out one area on the pan flange where
there's only about 1/16"-3/32" of overlap between the pan and the housing.
That's where he finds most leaks. All he offered for a solution is use of
Aviation Permatex on the pan and a cork gasket. Sounds like your source
and solutions you've tried. Perhaps it's time to consider modifying the
pan in that area? I'll try to look at one here tomorrow to see if I can
visualize anything that might work.

Ken H.

>

> > I have isolated the source of the leak to the right rear corner of the
> pan
> > (as seated in the driver seat). 'Have "diapered" all case penetrations to
> > insure that no ATF is coming from them. 'Have tried many different pan
> > gaskets over the years (and gasket sealants) but none completely stops
> the
> > leak. The gasket that appears to work the best is a NAPA # 14525. Emery
> > Stora reports using this gasket with good success. I installed that
> gasket
> > during the last service about 6K miles ago.
> >
> > The NAPA gasket controls the leakage to about 1/2 pint (measured from a
> drip
> > pan) over several months of non-use.
> >
> > There is no leakage when traveling (as observed from no blow-back onto a
> > clean, oil-free underbody).
> >
> > There does not appear to be a problem with the integrity of the
> > transmission case or pan at the leak location.
> >
> > I have been unable to convincingly rule out the chain cover as the source
> of
> > (or contributor to) the leak. If mine is leaking, the source would be
> from
> > just above the pan/case interface location stated above.
> >
> > Thoughts on proving(or disproving) the chain cover as the source of the
> > leak?
> >
> > Also, thoughts on why the pan still leaks (if not from the chain cover)
> > despite my attempts with a variety of gaskets (and sealants applied to
> the
> > gaskets) to stop it.
>

 

[Fred Hudspeth]

> I have isolated the source of the leak to the right rear corner of the pan
(as seated in the driver seat). 'Have "diapered" all case penetrations
> to insure that no ATF is coming from them. 'Have tried many different pan
gaskets over the years (and gasket sealants) but none completely stops the
> leak. The gasket that appears to work the best is a NAPA # 14525. Emery
Stora reports using this gasket with good success. I installed that gasket
> during the last service about 6K miles ago.
>
> The NAPA gasket controls the leakage to about 1/2 pint (measured from a
drip pan) over several months of non-use.
>
> There is no leakage when traveling (as observed from no blow-back onto a
clean, oil-free underbody).
>
> There does not appear to be a problem with the integrity of the
transmission case or pan at the leak location.
>
> I have been unable to convincingly rule out the chain cover as the source
of (or contributor to) the leak. If mine is leaking, the source would be
> from just above the pan/case interface location stated above.
>
> Thoughts on proving(or disproving) the chain cover as the source of the
leak?
>
> Also, thoughts on why the pan still leaks (if not from the chain cover)
despite my attempts with a variety of gaskets (and sealants applied to the
> gaskets) to stop it.
If you have an aluminum tranny pan, they can be porous and would need to be
sealed from the inside. No matter what kind of pan you have, tranny fluid
gets past the threads of the bolts and drips. I can't find the thread on the
forum where someone said to use O-rings on the bolts. I would think some
thread sealant would also do the trick.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."

 

[emerystora]

Hi Fred
I had a small persistent drip from the right rear corner of mine.
I replaced the pan gasket and ran some sealant around the edge of the pan and around the lower half of the chain cover. But to no avail.
I mentioned this to Bill Bramlett one day and he crawled under and sprayed brake cleaner around and dried everyone with a cloth and after a while he crawled out and told me he thought it was leaking around the electrical spade where the kick down plug connected to the side of the transmission. I got a new pass through connector from Manny and installed it and put another new pan gasket on.
I torqued the pan bolts once to spec and ran the motorhome and NO MORE LEAKS!

We left this morning and are half way across Kansas and I just looked under and no drips.

It was about impossible to see a leak in the center of the electrical connector but that was indeed the problem.

Hope your problem is as simple as that.
In my case it leaked there and the airflow blew it back along the lip of the pan back to the chain cover. The tiny leak source was hidden by the rubber cover over the wires.

Emery Stora

>
> Thanks to all who have commented on this. I believe I have done all of the
> things recommended except replacing the stamped steel pan with a cast
> aluminum pan. And with the mixed results on the latter, I'm inclined to just
> stay with the OEM pan and makeup the ATF level occasionally as I have done
> for years.
>
> It is interesting that the THM 400 in the old Airstream I leave in Alaska
> does not leak. And I do nothing special to avoid leakage with it! Except for
> direction of rotation, the GMCMH THM 425 is reportedly the same as the
> THM400.
>
> 'Regards,
>
> Fred
>
>
> Fred Hudspeth
> 1978 Royale (TZE 368V101335) - Tyler, TX
> 1982 Airstream Excella (motorhome) - Cooper Landing, Alaska
>
>
>
> Message: 7
> Date: Mon, 12 Sep 2016 14:53:42 -0600
> From: A.
> To: gmclist
> Subject: Re: [GMCnet] ATF Leak at Transmission Pan (or chain cover?)
> Message-ID:
> Content-Type: text/plain; charset="utf-8"
>

>> I have isolated the source of the leak to the right rear corner of the pan
> (as seated in the driver seat). 'Have "diapered" all case penetrations
>> to insure that no ATF is coming from them. 'Have tried many different pan
> gaskets over the years (and gasket sealants) but none completely stops the
>> leak. The gasket that appears to work the best is a NAPA # 14525. Emery
> Stora reports using this gasket with good success. I installed that gasket
>> during the last service about 6K miles ago.
>>
>> The NAPA gasket controls the leakage to about 1/2 pint (measured from a
> drip pan) over several months of non-use.
>>
>> There is no leakage when traveling (as observed from no blow-back onto a
> clean, oil-free underbody).
>>
>> There does not appear to be a problem with the integrity of the
> transmission case or pan at the leak location.
>>
>> I have been unable to convincingly rule out the chain cover as the source
> of (or contributor to) the leak. If mine is leaking, the source would be
>> from just above the pan/case interface location stated above.
>>
>> Thoughts on proving(or disproving) the chain cover as the source of the
> leak?
>>
>> Also, thoughts on why the pan still leaks (if not from the chain cover)
> despite my attempts with a variety of gaskets (and sealants applied to the
>> gaskets) to stop it.
> If you have an aluminum tranny pan, they can be porous and would need to be
> sealed from the inside. No matter what kind of pan you have, tranny fluid
> gets past the threads of the bolts and drips. I can't find the thread on the
> forum where someone said to use O-rings on the bolts. I would think some
> thread sealant would also do the trick.
> --
> 73 23' Sequoia 4 Sale
> 73 23' CanyonLands Parts Unit 4 Sale
> Upper Alabama
> "Highest price does not guarantee highest quality."
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[Ken H.]

Fred, et al,

I've checked out that right rear corner of the transmission oil pan where
so many seem to have leaks. It really is a very narrow seating surface --
about 3/32" at most. Trouble is, I don't seen any simple improvement. It
might be feasible to braze the inside of the pan up enough to add 1/8" or
so of surface, but the pan and its flange might be warped enough to either
worsen, or not improve, the situation. One who REALLY trusts JB Weld or
similar epoxy putty might build up that area enough to help -- but I don't
know what the long term durability of epoxy is in ATF.

Sorry I can't really suggest anything useful.

Ken H.

On Mon, Sep 12, 2016 at 7:25 PM, Ken Henderson
wrote:

> Just the other day Manny pointed out one area on the pan flange where
> there's only about 1/16"-3/32" of overlap between the pan and the housing.
> That's where he finds most leaks. All he offered for a solution is use of
> Aviation Permatex on the pan and a cork gasket. Sounds like your source
> and solutions you've tried. Perhaps it's time to consider modifying the
> pan in that area? I'll try to look at one here tomorrow to see if I can
> visualize anything that might work.
>
> Ken H.
>
>>

>> > I have isolated the source of the leak to the right rear corner of the
>> pan
>> > (as seated in the driver seat). 'Have "diapered" all case penetrations
>> to
>> > insure that no ATF is coming from them. 'Have tried many different pan
>> > gaskets over the years (and gasket sealants) but none completely stops
>> the
>> > leak. The gasket that appears to work the best is a NAPA # 14525. Emery
>> > Stora reports using this gasket with good success. I installed that
>> gasket
>> > during the last service about 6K miles ago.
>> >
>> > The NAPA gasket controls the leakage to about 1/2 pint (measured from a
>> drip
>> > pan) over several months of non-use.
>> >
>> > There is no leakage when traveling (as observed from no blow-back onto a
>> > clean, oil-free underbody).
>> >
>> > There does not appear to be a problem with the integrity of the
>> > transmission case or pan at the leak location.
>> >
>> > I have been unable to convincingly rule out the chain cover as the
>> source
>> of
>> > (or contributor to) the leak. If mine is leaking, the source would be
>> from
>> > just above the pan/case interface location stated above.
>> >
>> > Thoughts on proving(or disproving) the chain cover as the source of the
>> > leak?
>> >
>> > Also, thoughts on why the pan still leaks (if not from the chain cover)
>> > despite my attempts with a variety of gaskets (and sealants applied to
>> the
>> > gaskets) to stop it.
>>
>

 

[Fred Hudspeth]

Fred, et al,

I've checked out that right rear corner of the transmission oil pan where so
many seem to have leaks. It really is a very narrow seating surface --
about 3/32" at most. Trouble is, I don't seen any simple improvement. It
might be feasible to braze the inside of the pan up enough to add 1/8" or so
of surface, but the pan and its flange might be warped enough to either
worsen, or not improve, the situation. One who REALLY trusts JB Weld or
similar epoxy putty might build up that area enough to help -- but I don't
know what the long term durability of epoxy is in ATF.

Sorry I can't really suggest anything useful.

Ken H.

On Mon, Sep 12, 2016 at 7:25 PM, Ken Henderson
wrote:

> Just the other day Manny pointed out one area on the pan flange where
> there's only about 1/16"-3/32" of overlap between the pan and the housing.
> That's where he finds most leaks. All he offered for a solution is
> use of Aviation Permatex on the pan and a cork gasket. Sounds like
> your source and solutions you've tried. Perhaps it's time to consider
> modifying the pan in that area? I'll try to look at one here tomorrow
> to see if I can visualize anything that might work.
>
> Ken H.
>
>>

>> > I have isolated the source of the leak to the right rear corner of
>> > the
>> pan
>> > (as seated in the driver seat). 'Have "diapered" all case
>> > penetrations
>> to
>> > insure that no ATF is coming from them. 'Have tried many different
>> > pan gaskets over the years (and gasket sealants) but none
>> > completely stops
>> the
>> > leak. The gasket that appears to work the best is a NAPA # 14525.
>> > Emery Stora reports using this gasket with good success. I
>> > installed that
>> gasket
>> > during the last service about 6K miles ago.
>> >
>> > The NAPA gasket controls the leakage to about 1/2 pint (measured
>> > from a
>> drip
>> > pan) over several months of non-use.
>> >
>> > There is no leakage when traveling (as observed from no blow-back
>> > onto a clean, oil-free underbody).
>> >
>> > There does not appear to be a problem with the integrity of the
>> > transmission case or pan at the leak location.
>> >
>> > I have been unable to convincingly rule out the chain cover as the
>> source
>> of
>> > (or contributor to) the leak. If mine is leaking, the source would
>> > be
>> from
>> > just above the pan/case interface location stated above.
>> >
>> > Thoughts on proving(or disproving) the chain cover as the source of
>> > the leak?
>> >
>> > Also, thoughts on why the pan still leaks (if not from the chain
>> > cover) despite my attempts with a variety of gaskets (and sealants
>> > applied to
>> the
>> > gaskets) to stop it.
>>
>

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