differential yoke causes rear trans seal leak?

[mole2000]

I recently had my transmission rebuilt (th400) and the shop said that my rear diff yoke was faulty and needed replacement. They were supposed to fix, but they never got to it. So a week or two later there was a leak so i took it in for them to look at. They said that as the yoke wasn't "correct" that couldn't do anything about the leak, which they said was coming from the rear trans seal.

"Okay, thanks for the help" and I went about my way.

So I got up under there today and pulled the drive shaft looking for something amiss. The rear u-joint fits snugly and securely in the yoke. There is no obvious damage to either the drive shaft or diff yoke. I have not been getting any vibrations while driving.

The truck is a 1970 with a swapped in 454 (unknown year but its HEI) with TH400. It originally came with a straight 6 and column 3 speed. I am presuming that the drive shaft is not original. The differential does appear to be original (based on matching grime/grease anyway)

Multiple questions: Are these 2 things are related? Is the rear diff yoke for a 6 cylinder a different size than for a same year 8 cylinder? Can I pull the rear diff yoke and take to a driveline shop and have the whole thing examined to make sure it matches? I have read that taking the yoke off removes the preload and the whole rear end will have to be set up again.

I'll post some pics in a sec.

Thanks!

[mole2000]

additional pics

[hugger6933]

If the diff yoke was bad enough to blow out the rear trans seal and tail housing bushing, [witch happens normally in pairs by the way] it would have knocked out the pinion seal long before the trans seal. Since there is no sign of that I am gonna call bunk on that one. I am Not however gonna thrash some ones elses shop or rep, this is just based on the info and the pics I have to go on here. I hope you do get this taken care of it sounds like an awesome combo, I have two of those planned my self. Jim

[geezer#99]

You can't remove the yoke on the rearend without disturbing the crush sleeve inside. If you do remove it to change the seal you need to reset the pinion clearances.
Besides no evidence of a leak I can see. If it were leaking you'd see a bunch of gear oil on the snout.
The yoke on the tranny however apears to be leaking around the seal in the tranny. You can clean up the yoke with some emery cloth (like fine sandpaper) and change out the seal.

[WIDESIDE72]

I am not an expert, but I see nothing wrong with the rear axle yoke. I would do as mentioned above and change the rear trans seal, clean the yoke with emery cloth and reinstall. I have never heard of a rear yoke affecting the front but not leaking its self.

[Bigdav160]

If you do remove it to change the seal you need to reset the pinion clearances.

Sorry, but that is totally false.

[68gmsee]

I agree, don't mess with the rear yoke asm if there's no sign of leaking there.

One thing that I don't like on that yoke is the sanding scratches. It should be glass smooth otherwise it will leak. I'd take the yoke off and take it to a driveline shop and have them either polish it or sleeve it.

[volksworld]

there should be a certain torque spec where the nut will tighten up and stay on without causing the crush sleeve to crush any further...however when I tried to research it I couldn't find the answer...closest answer I got was from a friend who builds rear ends....his quote was don't worry it takes a LOT to crush that sleeve...not a very definitive answer!

[geezer#99]

WE could get into a debate over the crush sleeve but that discussion is way over the OP head.

[bigmac73]

when i did my 400th swap back in the early 90's on another 72, the garage told me to go find a thick walled 400 yoke, maybe you have a thin walled yoke,
i would do some research on it , i think cars had a thinner walled yoke

i am still curious about the debate on removing the rear yoke and the crush sleeve issue, i would liek to upgrade my rear end yoke to a 1350 series joints and heavier yoke??????

[geezer#99]

THe yoke won't be different. Same outside diameter.
You want to debate the crush sleeve just start a new thread.

[bigmac73]

Originally Posted by geezer#99

THe yoke won't be different. Same outside diameter.
You want to debate the crush sleeve just start a new thread.

disagree on the outside diameter, if it is a thin walled yoke, then the outside diameter would be smaller

[geezer#99]

Originally Posted by bigmac73

disagree on the outside diameter, if it is a thin walled yoke, then the outside diameter would be smaller

THat might be true but do the thin wall or thick wall exist. I've only seen one type with the standard outside dimention.

[Fitz]

Originally Posted by mole2000

I recently had my transmission rebuilt (th400) and the shop said that my rear diff yoke was faulty and needed replacement. They were supposed to fix, but they never got to it. So a week or two later there was a leak so i took it in for them to look at. They said that as the yoke wasn't "correct" that couldn't do anything about the leak, which they said was coming from the rear trans seal.

I don't know what planet that shop is on but on our planet for the diff yoke to damage the trans seal it would already have pounded the bearings and the seal out of the diff and the vibration would have been REALLY noticeable. That diff yoke is fine. Your trans yoke looks like it might be the problem. It is scratched and has a half-moon shaped crater the size of Texas showing in your first pic which probably trashed the seal. A new 1330 yoke will set you back about $75.00, a 1350 about $90.00 and a new seal about $5.00.

You MIGHT be able to get a machine shop to polish your yoke or you could do it yourself with fine emery cloth and some kerosene. I would buy a new seal to replace the one that's leaking and some emery cloth to try polishing the yoke you have before buying an new one. Let us know how it works out. The OD and the spline count of every TH400 yoke is the same so that shouldn't worry you if you go to replace it. When you think you are finished polishing and your yoke does not look like the picture ....well...wax on wax off Daniel-san!

[clinebarger]

The Original TH400 '65-'67 used a yoke with a smaller outside diameter barrel, Ran across this several times.

[bigmac73]

Originally Posted by geezer#99

THat might be true but do the thin wall or thick wall exist. I've only seen one type with the standard outside dimention.

http://www.theturboforums.com/thread...the-difference

http://www.jalopyjournal.com/forum/a.../t-646060.html

http://www.jalopyjournal.com/forum/a.../t-646062.html


thin and thick walled th 400 yoke

[TBONE1964]

Two things:

Has anyone checked the tail shaft bushing? If it is wore, it will beat the seal up in no time at all. If you have ever had a bad u-joint, the tail shaft bushing has probably got a beating and needs replaced. A bad tail shaft housing bushing will cause the tail shaft seal to fail prematurely also.

Second, just to clear things up on the pinion crush sleeve, it is there to keep preload on the pinion bearings. Once it is crushed, it is not reusable. That is why when you buy a pinion bearing set, it comes with a new crush sleeve. To set pinion bearing preload, the carrier has to be removed. A dial type inch pound torque wrench is needed to check preload. If the procedure is not done correctly, you risk the chance of premature pinion bearing failure.

However, if you want to take your chances, just tightened the pinion nut down until the pinion nut stops moving and there is no play in the yoke and call it good. You will have no idea what the pinion bearing preload is.

[TBONE1964]

Originally Posted by clinebarger

The Original TH400 '65-'67 used a yoke with a smaller outside diameter barrel, Ran across this several times.

Absolutely true. Night and day different than the later thick wall. If you use a earlier version thin wall yoke in a later model thick wall style tail shaft, the transmission will dump fluid out like having a faucet open. It will not be a small drip.

[mole2000]

good discussion an all matters drive shaft.

Thanks to everyone for their input.

i have learned enough go back to my parts and along with assistance from Inland Truck Parts here in Austin, to see that indeed someone has messed with my rear yoke.

it should have a threaded yoke and someone has drilled out the threads and widened the ears, but left the tabs. So my caps were being held only by the ubolts (no clips). The cap sat on top pf the tabs. So looks like the rear yoke will be replaced (ahead of schedule with a locker rear end).

i'll post a final technical fix for all to review.

Thanks to all. Good Stuff!

[68 TT]

I have seen this a bunch of times. You have a 1330 U-joint on your driveshaft sitting in a 1310 pinion yoke on the rear end. Same cap diameters but different center section cross widths.

The tops of the U-joint caps should be inboard of the nibs with the 1310 U-joint pinion yoke like you have.

It seems like it works when you put it together but there is nothing to keep the U-joint centered in the yoke side to side. Just a few thousandths of an inch off center can cause a really bad vibration and damage to the trans like you are seeing.

You can put on a 1330 pinion yoke to use your driveshaft as is or put a cross over 1330 to 1310 U-joint into the driveshaft and leave the rear end alone.

I would get the 1330 pinion yoke so you can stay with the stronger U-joint and use much less expensive U-joints in the future. Cross over joints are typically quite a bit more money and not stocked at many of the parts stores. You usually have to pick one up from their in town depot store. Having the driveshaft modified to use 1310 U-joints is an option as well but you end up with a weaker U-joint out of the deal.