[Rich-Tripower]

The pinion seal on the GTO is leaking again. Or maybe I should say still. It doesn't leak when sitting but during a drive it leaks enough to get the axle housing and gas tank greasy. It drips lube after being parked after a drive, but if the grease is cleaned off it doesn't leak any more until the next drive.

The pinion seal itself has been replaced at least three times. The last time we installed a brand new yoke (that was hard to find) and a new seal to fit the yoke. It was dry for a while and started leaking again. The pinion threads were properly sealed, the case where the seal installs is sound, no cracks or gouges. I'm at wit's end as to why this thing is leaking so much with everything new. Also, when the axle/transmission shop who did the work last (new seal, yoke, etc.) worked on it they had it on the lift with it running and in gear and no wobbles or out of balance situations were observed (one bent wheel was discovered and that was replaced but not related). During the restoration the driveshaft was rebuilt and rebalanced and the shop that did the axle work verified the pinion is not wobbling. No weird drivetrain noises or vibrations are felt during a drive.

The only thing I can think of is that the vent on the top of the axle is plugged. I think I may have checked this before but worth checking again. Anyone know a way to verify the vent is open to the internals of the differential? Any other ideas what the issue could be with the seal? This last time around everything was installed by a very experienced shop so I assume everything was installed properly. Herb, the guy that did the work is a real (old) car guy, he probably knows the old stuff better than the new stuff and really, a pinion seal is a pretty basic component. He went above and beyond to find a new pinion yoke for me.

[JSchmitz]

My first thought was clogged vent. Also could be excessive play in pinion bearings? Does in make any noise? I would pull the vent hose off and blow air through it. Take the sight plug out and blow ait into it and feel the vent.

[rohrt]

New vents are cheap and there nothing to them really. Just pop the one you have off and blow through it.

Is this a 8.2 10 bolt?

[Chief of the 60's]

Clogged vent

Pit, burr or groove on companion flange

Bad pinion bearing

Bad U-joint

Chipping seal during install

["QUICK-SILVER"]

Originally Posted by JSchmitz

Also could be excessive play in pinion bearings? .

That was my first thought.

Feel for in/out up/down movement of the yoke. Any at all will wear out a new seal in no time.

Setting pinion bearing pre-load on a seal re-do can get tricky of you don't pull the carrier and replace the crush sleeve. My short cut was to use a shim between the front bearing and crush sleeve. That gives you a little more crush on the sleeve to get the pinion nut tight and not have the yoke tighten against the bearings themselves and be over loaded.

Clay

[JSchmitz]

Originally Posted by "QUICK-SILVER"

That was my first thought.

Feel for in/out up/down movement of the yoke. Any at all will wear out a new seal in no time.

Setting pinion bearing pre-load on a seal re-do can get tricky of you don't pull the carrier and replace the crush sleeve. My short cut was to use a shim between the front bearing and crush sleeve. That gives you a little more crush on the sleeve to get the pinion nut tight and not have the yoke tighten against the bearings themselves and be over loaded.

Clay

If it's just replacing the seal I make a scribe mark on across the nut and shaft. Then make sure it lines up EXACTLY when I reinstall it. Otherwise preload can get messed up.

[Rich-Tripower]

The entire rear end was rebuilt during the restoration. The rebuilt axle probably has less than 500-600 miles on it at this point. All new bearings, races, seals at that time. The only issue has been the pinion seal.

The pinion does not have movement, this has been checked by me and by the shop who did work on it last. The axle is quiet, as I mentioned above. The Safe-T-Track works well. Always used quality non-synthetic gear lube and quality parts.

I'll start again with the vent and see what that tells me.

[Scott65]

Leaking by the splines perhaps?

[Rich-Tripower]

Originally Posted by Scott65

Leaking by the splines perhaps?

No, the splines were cleaned and sealed each time. I've had that problem on my truck and that is just a slow leak, this is more than a slow leak.

[Scott65]

Stumbled across this while searching for a pinion spacer. Not saying it's true that the correct part is no longer available, but if so, its definitely worth checking.
https://youtu.be/eX-1MUTVnQ8

[turbo69bird]

I’d agree with putting some air pressure to it and seeing what happens. That would be my first move.

[Sirrotica]

In 50 years of working on cars, probably twice I have seen a bore for the seal not centered on the shaft protruding through it. It should never happen, but on a couple of rare occasions I have seen the bore off center. This allows one side of the seal to be too tight on the companion flange, and the other side to be not touching it and no matter how many seals you install, it still leaks.

You might try using a seal sleeve on the companion flange to enlarge the OD where the seal rides as there is no real repair to fix the housing if it's bored off center.

I may be completely wrong with this guess, but I have seen it before, something else to try because you' look like you covered all the bases already.

Good luck on your repairs.

[geeteeohguy]

Originally Posted by turbo69bird

I’d agree with putting some air pressure to it and seeing what happens. That would be my first move.

Have been using a smoke tester at work lately and it is unreal how good it is at pinpointing leaks that would otherwise be impossible to locate. Just a thought.

[mgarblik]

Originally Posted by geeteeohguy

Have been using a smoke tester at work lately and it is unreal how good it is at pinpointing leaks that would otherwise be impossible to locate. Just a thought.

Beat me to it. On a repeat failure, nothing better. Smoke it through the fill hole. That will verify the vent works and then plug the vent and the smoke will find the leak. Works every time.

[melemans]

I had a 12-bold that leaked like that. It turned out that the new seals fit too deep on the yolk. I made a spacer out of 1/8" rod to go between the seal lip and the housing and that fixed my leak issue. Luckily, I kept the original seal and I was able to compare it to the new seal to see the difference in depth.

[Rich-Tripower]

Originally Posted by melemans

I had a 12-bold that leaked like that. It turned out that the new seals fit too deep on the yolk. I made a spacer out of 1/8" rod to go between the seal lip and the housing and that fixed my leak issue. Luckily, I kept the original seal and I was able to compare it to the new seal to see the difference in depth.

Interesting.

[Scott65]

Yeah, the video I linked earlier shows this really well...

[Rich-Tripower]

Originally Posted by Scott65

Yeah, the video I linked earlier shows this really well...

I missed the link to the video, that was really informative. I'll just bet that's what is going on. So, now I have to pull the yoke and install a new seal but with a spacer this time. But since we changed the yoke to some kind of Chevy yoke (shop manager's idea last time it was worked on) I can't just order a Pontiac axle seal and that shop closed (guy retired) so I hope the seal part number is on the receipt!

[LATECH]

Did you install the oil slinger?

[Rich-Tripower]

Originally Posted by LATECH

Did you install the oil slinger?

Assuming that is inside. I didn't do the differential rebuild myself so I assume whatever was in there was reused other than bearings, races and seals.