[Rich-Tripower]

I have been round and round with a leaky pinion seal. The last round included an entirely new pinion and a seal to match. Was good for about 100 miles, now leaks like a screen door in a rain storm. After a short drive it leave a pancake sized spot on my driveway.

The other day, before taking it out I checked the fluid level to make sure the shop had topped it off and to make sure the leaks hadn't drained it too much . To my surprise, it was over full as lube came gushing out. I drained it until the fluid level was just at the lower bit of the fill hole but it was still trickling out. Could being overfull cause the pinion seal to leak?

The many times I have had it apart we have never seen a nick in the pinion seal mounting surface, no issues with the sealing surface on the pinion and the seal fits snug on the pinion shaft. The vent is in place and is clear. We have always cleaned the splines and threads and used a sealer on the threads. The pinion is not loose in the bearing (everything was new about 400 miles ago). I've no idea where to go with this PITA POS at this point. I can grudgingly tolerate a slow oil leak at the engine, but transmission and axle leaks are a never ending source of frustration.

AND, in checking the speedo against a GPS driven app on my phone, it looks like I need to change the speedo driven gear again. The last time I did that I ended up pulling the transmission and rebuilding it because first the driven gear fell off inside the tailshaft housing, then when we pulled the trans to pull the tailshaft housing to retrieve the gear we found that the countershaft was loose causing leaks and pending an entire transmission failure abused Muncie style. I don't wish to tempt fate again so I'll have to be more careful when pulling the driven gear bullet.

[Aaron65]

Is your axle vent clear? If the axle doesn't vent properly, that pressure will find a way out and take fluid with it.

[Rich-Tripower]

Originally Posted by Aaron65

Is your axle vent clear? If the axle doesn't vent properly, that pressure will find a way out and take fluid with it.

As I stated in my original post, the vent is clear.

[Cardo]

The over fill could cause it, but when the pinion nut was installed was a drop of rtv put under it? It's been a while, but i remember that you need to put drop of rtv either under the nut or washer somewhere to keep it from leaking through there.

[Chief of the 60's]

How are you checking the fluid level? Is the car level? Are you jacking it up by the rear end?

[Aaron65]

Originally Posted by Rich-Tripower

As I stated in my original post, the vent is clear.

Oops! Sorry, caught me skimming.

[Rich-Tripower]

Originally Posted by Chief of the 60's

How are you checking the fluid level? Is the car level? Are you jacking it up by the rear end?

The whole car is jacked up off the floor.

[Sirrotica]

FWIW, a few times during my years making a living as a mechanic, I have seen castings that have been machined off center. When this happens the seal will sit off to one side of the spinning shaft and only close examination will it be evident.

You might try removing the companion flange and pay close attention as you slide it into the seal to make sure it is centered. As I say, it's not a common problem, but when you have a job that won't seal up no matter what you do, it can sometimes be traced to an off center seal due to poor/defective machining.
I've seen it in a timing cover seal, and a transfer case seal both with this problem.

If you've had many Pontiacs you may have also come across rear mains that are problematic getting them to seal. The problem sometimes is the groove in the cap and block that the rear main seats in is poorly machined and off center.

[Rich-Tripower]

Bringing this one back from the dead. The pinion is still leaking. We've slowed it down, but still drips after every drive. It doesn't seem to leak when sitting still. That's about the only new info I have. New seals, new yoke, seal fits the yoke, nut and splines properly sealed. ARRGGHH!

[John V.]

Rich, no expert but I feel your pain so thought I'd give it a shot.

You've replaced the pinion along the way. Did you install a new crush sleeve and confident it was properly crushed?

I think it is possible to check runout of the flange. I think excessive runout can cause leakage.

I think this is essentially what Brad was suggesting. But rather than eyeball it, measuring runout might tell you for sure what is going on while the prop shaft is turning.

I think it can and should be checked in both the horizontal and vertical planes.

If the shaft is not turning centered and true, pretty sure the seal can't seal especially when spinning. At rest, might hold at least when pretty new so could explain why it doesn't leak when sitting.

[Rich-Tripower]

Well, the rear was built by a shop that had been around for 40-50 years. The guy who started the shop worked on this problem numerous times, we even had it on the lift, running, in gear to observe how things move and rotate. We could never find any issues.