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12-28-2020, 02:37 AM | #1 |
Senior Member
Join Date: Jan 2009
Location: Austin, TX
Posts: 1,079
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Th400 throwing oil out the rear seal?
I rebuilt this TH400 a few thousand miles ago. I'm for sure it's leaking out the rear seal. I can put it 1st gear up on jackstands and watch a bead of transmission oil work it's way out the seal. The entire underside of my truck is coated in trans fluid. Very minimal drips on garage floor.
The first thing I did was pull the extension housing and replace the bushing and seal with a spare that I had. Seemingly no change. I then put a dial indicator on the yoke to make sure it's not out of round and it has ~.020" of wiggle in the bushing/splines but almost zero out of round. This yoke is suspect. It's an ebay special and it lost the freeze plug out the back a few thousand miles ago so it got the grey silicone and washer freeze plug replacement. Though it's not leaking out the back of the yoke. I've found a really nice sonnax replacement yoke but I'm wondering if there is anything I should be checking before replacing the yoke?
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-- Josh Instagram: @americanmusc1e OLD SKOOL-- 1970 C10. 454/Th400/3.07 posi Build Thread FARM TRUCK----1949 Chevrolet 3800 Power Wagon Hauler Build Thread 1999 4wd OBS Tahoe - daily. DM me if you can't see photos i posted |
12-28-2020, 08:40 AM | #2 |
Registered User
Join Date: Oct 2013
Location: Maine
Posts: 2,358
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Re: Th400 throwing oil out the rear seal?
New bushing and new seal, gotta be the yoke. I haven't bought any new ones in years. I suppose if they are a couple thousandths too small it will leak. It would be interesting to measure a few yokes to see how close the tolerances are.
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12-28-2020, 11:11 AM | #3 |
Registered User
Join Date: Apr 2008
Location: Milton wi. 53563
Posts: 128
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Re: Th400 throwing oil out the rear seal?
do inside micrometer measurement of seal. i had same leak. i bought 2 seals 1 from major brand and another from across town. 1 was exact same size as shaft, the other was .oo1 smaller and does not leak. old money.
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12-28-2020, 02:36 PM | #4 |
Senior Member
Join Date: Jan 2009
Location: Austin, TX
Posts: 1,079
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Re: Th400 throwing oil out the rear seal?
I measured the current yoke as best as I could with my digital calipers. I'm getting 1.830"
This Sonnax yoke lists its journal diameter as 1.886" I measured a spare bushing and it's 1.892" so it's very possible that the yoke I have now is undersized. The seal that I have has a listed inner diameter of 1.829" which is probably why it's leaking. I was going to order that Sonnax yoke, but I found a Dana one for less money that will most likely still be an upgrade. Dana lists the diameter as 1.885" I ordered a Dana yoke and a new Spicer 1310 joint. We'll see what happens.
__________________
-- Josh Instagram: @americanmusc1e OLD SKOOL-- 1970 C10. 454/Th400/3.07 posi Build Thread FARM TRUCK----1949 Chevrolet 3800 Power Wagon Hauler Build Thread 1999 4wd OBS Tahoe - daily. DM me if you can't see photos i posted |
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