| [GMCnet] ATF Leak at Transmission Pan (or chain cover?) [message #307072] |
Mon, 12 September 2016 20:40  |
fbhtxak
Messages: 191
Registered: April 2006
Karma: 0
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Senior Member |
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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@list.gmcnet.org
Subject: Re: [GMCnet] ATF Leak at Transmission Pan (or chain cover?)
Message-ID:
Content-Type: text/plain; charset="utf-8"
fbhtxak wrote on Mon, 12 September 2016 13:14
> 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."
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| Re: [GMCnet] ATF Leak at Transmission Pan (or chain cover?) [message #307075 is a reply to message #307072] |
Mon, 12 September 2016 21:53  |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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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
> On Sep 12, 2016, at 8:40 PM, Fred Hudspeth wrote:
>
> 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@list.gmcnet.org
> Subject: Re: [GMCnet] ATF Leak at Transmission Pan (or chain cover?)
> Message-ID:
> Content-Type: text/plain; charset="utf-8"
>
> fbhtxak wrote on Mon, 12 September 2016 13:14
>> 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
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