At my wits end on the pinion seal: 64 GTO
 

Ever since we finished our 64 GTO about 8-10 years ago, we've had a hard time keeping a good pinion seal in the car. Each new one would last about 20-30 miles and then it would start leaking again. The last time we played with it I had it at a reputable shop who tried everything to diagnose the problem They even put it up in the air with the wheels raised, the car running and ran it through the gears while observing the axle and driveshaft. No problems were identified. They had a hard time locating an appropriate seal at that time so they replaced the entire yoke (A Chevy part if I remember) and found an appropriate seal for the size of the hole and the size of the pinion.

This is a BOP stock rear with 3.55 gears. It is leaking like mad again. I drove it maybe 5 miles today and the entire pumpkin is wet and dripping on the bottom and even the gas tank is covered in lube.

What can I do here? Internally is there a slinger the keeps oil mostly off the seal that perhaps could have been left out? I've replaced the seal a number of times and very reputable and experienced professionals have replaced it at least twice, and still the seals go bad in short order every time.

It could be leaking between the yoke and the pinion shaft splines. I've never dealt with that, but have heard about it happening. Also check to make sure your differential vent isn't clogged.

Diff vent is brand new. Issue is not there.

A spline leak is a few drips here and there, this thing is basically gushing, like an open artery. Besides, the splines were sealed every time it has been taken apart.

Did you check the vent even if new?
Maybe try it without the vent for a while. Or make a short piece of u shaped pipe and see if it helps.

Also make sure the oil level is not high.


Both can cause too much pressure build up.


:confused:

Ok. Makes sense about the splines. I would remove the vent and blow through it. Like johnta1 said, it could be new and bad. I've seen many gearboxes replaced mistakenly because of a missing or clogged vent. No seal in the world will hold it back if it isn't vented.

The vent is a simple tube of plastic with a loose cap. It is new and clean and clear inside.

Diff is not overfull, I've checked it off to make sure it isn't too low given all the leaking issues. Unless something in the entire assembly is blocking air flow from the axle tubes (where the vent is) to the pumpkin, I can't see how venting could be a problem. The axle housing was completely rebuilt during the restoration, there is no clog of grunge inside the housing.

You mention that "the seals go bad" - is there any actual damage to the seal? Or are you just assuming that based on the oil leakage?

Do you have any pictures of the leakage/aftermath and/or parts involved (seals, new/old yokes, etc.)?

What do the seals look like when removed? Like new? Wasted?

It may be that you need to purchase a slightly oversize outer diameter seal because the rear end metal has been wallowed out in the past, or is out of round

Since you have had so much trouble with this problem, I would go into an advanced diagnosis stage. I would take the car out and drive it and get the diff. hot. Then bring it in the shop and put on a rack. Use brake clean to hose down as much mess as possible. Remove the the diff lube with a suction tool, do not remove the rear cover to remove the lube. Get as much out as possible. Use duct tape to seal off the vent. Then fill the diff with smoke from a smoke machine. The leak will present itself pretty quickly. If it's the pinion seal, at least you will know for sure that's the leak point. You need to do this with the diff. hot. I suspect it might have a crack in the housing somewhere that is opening up when hot. I hope I am wrong.

Most pinion seal leaks are from the metal part of the seal to housing connection. Nobody has mentioned a check for this so far.

Have you (or your mechanics) been using sealer at this connection point? The outer perimeter of the seal itself.

The seals actually look ok when taken out other than dings inflicted in the removal process. The bore in the housing is smooth all around. Yoke is now almost new so also new/smooth. Pinion turns concentric to the housing hole. All bearings were new, diff professionally built. We haven't used sealer on the bore as the seals come with sealer already applied. Instructions say more sealer not needed. Buy maybe a film of RTV would help? Maybe pull the vent and apply compressed air to see if anything comes out the seal to see if vent is getting air to the pumpkin? Grasping at straws.

Maybe seals pressed in too deep or too shallow? This has been a problem on Chevy 12 bolts for years since most have stopped making the right seal and the ones listed as correct don't fit right. But even those don't leak like this.

I generally use a thin layer of permatex #2 when installing the seal - I've have heard of folks using some RTV on the end of the splined portion, but have never done that myself. Either way, I'd doubt that either would solve the deluge you are describing.

Once again, a smoke machine will find the exact source of the leak in 15-30 seconds 100% of the time. Although it's possible the pinion seal is the problem, it's unlikely so many seals have been incorrectly installed by professional builders. Not impossible, but not likely. IMO, a definitive test ends all speculation. If it is a seal again, then you know exactly what you have to deal with. At that point, I would buy the best seal available, make absolutely sure the garter spring stays in place when installing by using grease to pack it in place and use a light film of RTV on the OD of the seal. I am leaning toward a cracked housing or an issue between the the axle tubes and the housing. Pinion seals rarely leak huge volumes of lube without any visible damage, unless it's the wrong seal multiple times. Good luck with it and please report back so we can all learn something.

Will be a while before I can do much of anything, just had shoulder surgery yesterday.

Just putting this out there, it might help to post photos of the parts and the old seals which you say don't last long.

Maybe someone can see something in the used but new leaking seals? For it to leak that bad and so soon there might an oil deflector or something missing inside the housing, that or something was not put together the right way. There could be a chip or a burr on the inside that is tearing up the rubber inside edge.

One thing on any new lip seal is you need to apply several drops of clean oil around the inside of the rubber touch "edge" before you bolt-in the thing that spins inside of it. A bone dry; new rubber seal will not "seal."

Have you checked the lateral run out on the pinion itself?, also pinion preload?

All that was set when the rear was professionally built. But no, I haven't checked it. I believe the shop who installed the last two seals did check the runout, not sure about the preload.

Seems like a few things need to be verified.
1. Is the ID of the seal correct for the diameter of the pinion? I assume that when the pinion is inserted, it stretches or puts some pressure on the seal? How much is correct I do not know. It can't have a gap and has to have some pressure to prevent oil pushing past.
2. is the pinions the correct diameter? Is it round? An old pinion will have wear where the seal is. I've seen sleeves used to make up for that wear, but I don't love them because they will create a diameter larger than the original.
3. Is there any radial movement on the bearing allowing the pinion to move against one side of the seal?
4. Is the bore for the race round and concentric with the seal bore?

X2 on the smoke machine to get to the bottom of where the leak is. If the yoke is not damaged and there is no excessive lateral play, the seal should last for years and years. I suspect a mechanical issue with parts tolerance or as mentioned, a small crack somewhere. Smoke test it.