[robz]

Hi Guys.

My rear seal between U-joint and diff is leaking ever so slightly. I want to change it if it isn't too complicated. Problem is it is on my '69 GTO Conv but diff is a 3.31 Chevy Posi. What is the seal I should order (for a 3.31 chev or for a '69 GTO u-joint/driveshaft?) and what are the steps/difficulty to replace it?

Thanx in advance.

Robz

[bigborehunter]

It is likely a Chevrolet produced 12- bolt axle. The Pontiac versions have a slightly different cover, I believe it is notched on the sides. Check the casting number on the center unit and check with a GTO 12 bolt listing online. FWIW, my 72 is a Chevrolet 12 bolt posi just like a Chevelle unit.

[webfoot]

You'll want the chevy seal, 3.31 was for a 12-bolt, I think 3.36 was 10 chevy 10-bolt only. Count the bolts on the cover to be sure.

You would probably want to pull the whole unit and obviously remove the pinion yoke. May take a puller.

Also, inspect that your vent tube isn't plugged. When the fluid warms up it expands and can force it out of the seal if it can't push the air out.

[robz]

Hi Guys.

Just to clarify, yes it is a Chevy 12-bolt, my question was more if I have to order the seal, do I ask them for a Chevy 12-bolt, regardless of the driveshaft/u-joint that comes from a GTO?

The leak is right under where U-joint meets the front of diff, so not sure if I just remove driveshaft/u-joint and I have access to seal or is it necessary to take of diff cover and maybe diff completely to do?

Thanx again...

[webfoot]

Yes, the seal is the same regardless of the driveshaft/u-joint.

By u-joint do you mean the pinion yoke that holds the u-joint? I am assuming so. Getting the old one off will be harder than getting the new one on. You're probably going to have to wreck the old seal pretty good, but that doesn't matter.

When you have the seal off, check where the seal rides on the yoke for wear, if there is a groove worn in the yoke this may explain your leak if there aren't many miles on the seal.

[robz]

Originally Posted by webfoot

Yes, the seal is the same regardless of the driveshaft/u-joint.

By u-joint do you mean the pinion yoke that holds the u-joint? I am assuming so. Getting the old one off will be harder than getting the new one on. You're probably going to have to wreck the old seal pretty good, but that doesn't matter.

When you have the seal off, check where the seal rides on the yoke for wear, if there is a groove worn in the yoke this may explain your leak if there aren't many miles on the seal.

Thanx Jeremy...Yes I mean the pinion....Never worked on a diff/components b4, and the service manual is for Pontiac diffs so not sure if it's that diff't than a Chevy...You did mention earlier the vent tube...Is that located on top of diff? Do I just poke thru it to see if it's blocked? I only notice a small drop after I drive and it doesn't drip while parked, but I'd rather fix it now b4 it gets worse...That seal was replaced about 8 yrs ago, and have since put on about 4000 miles....If it requires special tools, I may just go to my tranny shop that did it back then, when I had a new clutch installed...I wanted to try as I have a lift now so work seems pretty straight forward, when car is up...

Let me know what you guys think...

Robert

[webfoot]

The vent tube is located on the top half of the pumpkin and is made of nylon. Just a tube with a little cap on top. Are you going to take the rear cover off? Just a puff of compressed air from inside should let you know if it is OK. You will either feel it or see the cap wiggle.

Only "special" tool would be a 2-jaw puller to get the yoke off. I bought mine for $40 from sears. You can probably rent one from AZ. The only other thing is after you remove the pinion nut you have removed all the preload off the pinion bearings and will probably have to have a new crush sleeve installed and reset the preload, I think it is 15-20 in/lbs but takes massive torque to achieve. (there's another special tool - in/lb tq wrench!)

When it is all said and done, probably easier to live with the small drop for now - just my .02.

[robz]

Thanx again...Yeah I have a torque wrench but have a 3 jaw puller I had bought many years ago but never used (was on sale..:-)) not sure if it will do...No not intending on removing cover as it doesn't leak and if I do got to refill with Posi lube too...so maybe better off bringing it in to shop as he said about 45 mins labour + $10 seal...so I'd say $100 with tax an all, from what you mention above seems a bit more work for me w/o all the tools...Just afraid to lose too much in the long run and burn my diff...I thought it was just a pull and replace type of job...Oh well, can't do everything myself...:-)

[robz]

UPDATE: I decided to it myself....I figured I have a lift and built my garage to do most of the work myself so I did...

Followed the advice from a few ppl/websites and so far removal was pretty easy..It took me about 15 mins to unbolt U-joint, and remove nut holding Yoke, as well as pull out yoke itself (a few small taps with hammer).

Below are pics of the parts so far. I did notice yoke was a bit rusty near edge so I used 600 Grit sandpaper and Fine steel wool..It feels smother but not sure how smooth I should make it...I didn't want to go coarser on the sandpaper as not to damage the yoke...is 600 enough? Where do I see if seal is damaged? Thanx....

[LPete]

You've gone this far -- replace the seal. I'd get the yoke as smooth as possible -- if you need coarser sandpaper, fine, but use finer paper to finish it.

Did you by any chance mark the pinion nut and pinion? That's what I do, and then tighten it very slightly tighter than it was before I took it apart. You can't measure turning torque of the pinion with the differential together -- there's way too much drag from the axles and differential. If you overtighten the nut the pinion bearings will go out in a very short time.

Check the housing seal bore to make sure it isn't damaged, and put a little sealer on the O.D. of the seal. I also put a small amount of sealer between the pinion flange and nut, and on the threads -- it keeps oil from wicking out around the pinion threads and the nut.

[robz]

Originally Posted by LPete

You've gone this far -- replace the seal. I'd get the yoke as smooth as possible -- if you need coarser sandpaper, fine, but use finer paper to finish it.

Did you by any chance mark the pinion nut and pinion? That's what I do, and then tighten it very slightly tighter than it was before I took it apart. You can't measure turning torque of the pinion with the differential together -- there's way too much drag from the axles and differential. If you overtighten the nut the pinion bearings will go out in a very short time.

Check the housing seal bore to make sure it isn't damaged, and put a little sealer on the O.D. of the seal. I also put a small amount of sealer between the pinion flange and nut, and on the threads -- it keeps oil from wicking out around the pinion threads and the nut.

Thanx, LPete...Yes I did mark the pinion nut and pinion (even though it already had a mark from the last time it was worked on)...I am going to change the seal but was just wondering how do u know it is damaged by looking at it (before removing it)?

As for RTV, I did read that ppl put some on the yoke splines but never around the seal itself (it's metallic, no?)...won't it make it hard to put back in (or did I misunderstand what u meant)?

[LPete]

You probably won't be able to tell if the seal is damaged unless it's really obvious, like torn or deformed. Taking it out will pretty much destroy it.

I always put sealer on the outside of the seal -- it doesn't make it harder to put in. It does, however, take care of nicks or dings in the housing bore, which happen all the time when the seal is removed carelessly.

I'm glad you marked the pinion. It's SO easy to overtighten the nut. I usually go just a tad past where the marks line up -- something like 1/16". The pinion should *just* get a little harder to turn when you're there.

You probably know that you can't loosen the nut once it's too tight -- you have to replace the crush sleeve.

[robz]

Thanx...Yes I did read about the extra 1/16" after the mark due to the stretching effect over the years...The only reason I'm afraid to use the coarser sandpaper is that it may remove too much metal (I wasn't going to go coarser than 480)...How smooth should we make it (OK if not perfectly polished?)?

[LPete]

I think the argument could be made that a slightly rough surface will help lubricate the seal. I wouldn't worry too much about it. They're not mirror-smooth when they're new.

[salem1912]

Before installing the seal, back pack the seal around the spring with some wheel bearing grease to prevent the spring from popping out when you tap it in.

[robz]

Thanx, Salem...will do....

BTW, guys I need your input on this. Since I removed the yoke/companion flange yesterday morning, it hasn't stop dripping until later this morning...In all I measured a bit over 1 Quart...I only have a '69 Service Manual so I don't know how much a 12 bolt holds, and I know the 10 bolt only holds 3 US Pints. When I removed the side drain bolt, the oil level is about 1 inch below it now. My question is if someone had overfilled it by as much as 1 Quart, could this have damaged the seal/gasket, as it would have if the engine may have been overfilled? Thanx...

[mike nixon]

If the diff was overfilled it'll leak.

Clean the splines with Brakleener and RTV between the splines and the yoke when you reassemble it.

Put a new seal in it unless you want to do it again.

[robz]

Originally Posted by mike nixon

If the diff was overfilled it'll leak.

Clean the splines with Brakleener and RTV between the splines and the yoke when you reassemble it.

Put a new seal in it unless you want to do it again.

Would it leak from anywhere in particular? Just wondering if this is what was causing the leak (but it was filled at least 8-9 years ago and it didn't leak until last year, so could it have started slowly to weaken the seal/gaskets)?

Yes Mike, I am changing the seal regardless...it's on order and will be in Monday...

[robz]

LATEST UPDATE: Finally got new seal, so removed old one using a 5 lb hammer and chisel, and compared the two. They look very similar but slightly different in shape of seal/contour...hopefully that small difference is negligible, as diameter of seal opening as well as outer structure is perfect. On the left is old crumpled seal after removal, and new one on right...

As far as damage on old seal causing it to leak: I couldn't find any great wear around rubber seal, but it may be so small that the naked eye cannot notice. Anyone have any experience to tell me why it would leak from the pics below (I know it may not be obvious since old one is a bit damaged)?

Also, cleaned around diff center and numbers a clearer now (date seems to be C161 , which equates to March 16, 1971, but diff number on right hard to make out..anyone knowledgeable with 12 bolts to guess what the casting numbers on right of center are)? Thanx in advance...

[salem1912]

I don't think you will be able to see why it was leaking. Most of the time the seal just gets hard.