Bad tranny leak! Seal with yoke/driveshaft? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

weever82 · 10-03-2013, 01:33 PM

Hey guys,

My TH400 has leaked since I bought it. and not a little bit, a pretty decent amount comes out where the transmission meets up to the driveshaft. I replaced the pan and governor seal when i first bought it and didnt help the problem at all.

Is there a seal between the driveshaft and yoke when I goes in the transmission that I can replace? It seems to be stemming from that location. If so, easy at all? I'm still half noob...

Any other thoughts would be great. Thanks!
Posted via Mobile Device

rcazwillis · 10-03-2013, 02:02 PM

Yes, the seal can be replaced by pulling out the drive shaft, prying out the seal in the end of the tail shaft, and installing a new seal. Hardest part is getting the old seal out. Buy a replacement seal and you will see how it installs.

Daddy'O · 10-03-2013, 02:10 PM

We had the same problem with our TH350 – after replacing the output shaft seal it still leaked. Turned out to be the yoke on the drive shaft – it had worn down enough over the last 40+ years so it wouldn’t seal properly.

Good luck!

Lee H · 10-03-2013, 04:01 PM

Yes, easy job. Clean the trans lip where the new seal goes very well and apply a "little" sealer to the metal lip of the seal before tapping in. Apply a assembly lube, cam lube or grease to the rubber part of the seal before installing yoke.

weever82 · 10-03-2013, 09:38 PM

Thanks for the heads up guys. auto zone by my house said there is two different sizes of seals when I asked if they had one in stock, will have to measure when I pull it out. When I unbolt the u joint by the axle, when I go to pull out the yoke... Is there a pin or anything I need to remove? Googling online I read about some pin to pull... Just double checking.

Thanks again!

JimKshortstep4x4 · 10-04-2013, 09:48 AM

The TH 400 has two different tailshafts which take different size yokes/bushings and seals. I am not sure when the changeover was made but up to 70 the transmission had the smaller yoke/seal. Spline size is the same but the yoke diameter where the seal/bushing fits is different. The larger yoke is 1.885 amd the smaller yoke is 1.685 approximately.

Check the fit of the bushing/yoke in case it is worn to the point where the seal won't work. If the yoke is loose then the bushing and/or yoke will need to be replaced.

Jim

10-03-2013, 01:33 PM	#1
weever82 Registered User Join Date: Sep 2012 Location: Queen Creek, AZ Posts: 551	Bad tranny leak! Seal with yoke/driveshaft? Hey guys, My TH400 has leaked since I bought it. and not a little bit, a pretty decent amount comes out where the transmission meets up to the driveshaft. I replaced the pan and governor seal when i first bought it and didnt help the problem at all. Is there a seal between the driveshaft and yoke when I goes in the transmission that I can replace? It seems to be stemming from that location. If so, easy at all? I'm still half noob... Any other thoughts would be great. Thanks! Posted via Mobile Device __________________ Weev- Life's tough...... It's even tougher when your stupid - John Wayne

10-03-2013, 02:02 PM	#2
rcazwillis Registered User Join Date: Aug 2013 Location: Fort Worth, TX Posts: 309	Re: Bad tranny leak! Seal with yoke/driveshaft? Yes, the seal can be replaced by pulling out the drive shaft, prying out the seal in the end of the tail shaft, and installing a new seal. Hardest part is getting the old seal out. Buy a replacement seal and you will see how it installs.

10-03-2013, 02:10 PM	#3
Daddy'O Registered User Join Date: Jan 2012 Location: Whitesboro, Texas Posts: 932	Re: Bad tranny leak! Seal with yoke/driveshaft? We had the same problem with our TH350 – after replacing the output shaft seal it still leaked. Turned out to be the yoke on the drive shaft – it had worn down enough over the last 40+ years so it wouldn’t seal properly. Good luck! __________________ Cheers - Wayne Our Shop Build - http://67-72chevytrucks.com/vboard/s...d.php?t=620966 '55 Wagon Build - http://67-72chevytrucks.com/vboard/s...d.php?t=689157 1971 Cheyenne Super Ochre/White LWB 350 Auto - my son's truck "Nancy" 1972 GMC K2500 Custom 4X4 Olive LWB 400 SB 4-speed -"Greenie" - Restoration to begin after the '55 Nothing sucks more than that moment during an argument when you realize you're wrong.

10-03-2013, 04:01 PM	#4
Lee H Registered User Join Date: Jun 2010 Location: Upland Ca Posts: 4,139	Re: Bad tranny leak! Seal with yoke/driveshaft? Yes, easy job. Clean the trans lip where the new seal goes very well and apply a "little" sealer to the metal lip of the seal before tapping in. Apply a assembly lube, cam lube or grease to the rubber part of the seal before installing yoke. __________________ 1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703

10-03-2013, 09:38 PM	#5
weever82 Registered User Join Date: Sep 2012 Location: Queen Creek, AZ Posts: 551	Re: Bad tranny leak! Seal with yoke/driveshaft? Thanks for the heads up guys. auto zone by my house said there is two different sizes of seals when I asked if they had one in stock, will have to measure when I pull it out. When I unbolt the u joint by the axle, when I go to pull out the yoke... Is there a pin or anything I need to remove? Googling online I read about some pin to pull... Just double checking. Thanks again! __________________ Weev- Life's tough...... It's even tougher when your stupid - John Wayne

10-04-2013, 09:48 AM	#6
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: Bad tranny leak! Seal with yoke/driveshaft? The TH 400 has two different tailshafts which take different size yokes/bushings and seals. I am not sure when the changeover was made but up to 70 the transmission had the smaller yoke/seal. Spline size is the same but the yoke diameter where the seal/bushing fits is different. The larger yoke is 1.885 amd the smaller yoke is 1.685 approximately. Check the fit of the bushing/yoke in case it is worn to the point where the seal won't work. If the yoke is loose then the bushing and/or yoke will need to be replaced. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC



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