vstypicals

While installing my new transmission, my mechanic said some oil dripped down/came out when he unbolted the drive shaft from the diff. Any ideas on what the issue could be?

I do have an aftermarket diff (Comptech housing with 4.57 final gear).

Leviisbigred

how much came out?

SpitfireS

As you can see here the prop shaft CV's end plates have little breather holes.
(end flange on the left, breather hole in the middle of it)

Grease = oil + thickener.
Over time some oil may separate from the grease and "leak" into the area between flanges.
What I mean is between the diff flange and the other end of the CV end plate (I hope I've explained it ok)

So if a small amount of oil leaked out when the flanges were separated it should not be a problem.
If it was a lot you may open up the CV, like in the picture, and re-fill with fresh CV grease.
Use some liquid gasket between the CV housing and end plate.
Btw.. when removing the prop shaft you do not see the insides of the CV.

It is a big difference if the pinion seal of the diff is leaking.
But that is leaking - IF it is leaking - with or without prop shaft bolted to the flange.

Did your mechanic have to change flanges because of the bolt size?
AP1 vs AP2 bolts?

Billman250

The leak is very likely coming from the dif. The oil is moving through the spline and out from under the nut and washer.

You are best not to touch it now...you would only disturb the dif pattern and ruin your dif.

The driveshaft will contain it. Let it ride.

S2KPUDDYDAD

I agree with Biltman on where the leak is coming from, I also agree with Biltman about not messing with if you do not have experience with a proper repair.
I respectfully disagree on not doing anything about it and letting it ride.

The leak is caused by a loose pinion nut or over crushed distance piece inside the rear. The 4.57 gears are probably the most incorrectly installed ratio of all. They require a thinner pinion shim than OEM gears and sometimes require back shimming in order to get a proper load on the pinion bearings. Most times an installer will reuse the OEM shim and also reuse the pinion nut, this is a cause for future issues such as, a leak and excessive gear whine. If they shim the pinion with to thin a shim the input flange will bottom out on the pinion spline. This bottoming out will also cause a leak as you have now, because the flange will not fully get tight before the pinion nut does.

If the gear whine has gotten any louder since you first got the rear installed then you have a real cause for concern.

Billman250

You're right, I should have been more thorough

IF the nut is tight, and hasnt moved, more damage can be done by disturbing the dif. I never recommend anyone mess with that dif nut.

IF you can get it to puddy then yes have him fix you up.

vstypicals

My mechanic said "not that much. It filled up that 'pouch'."

The new transmission had a broken drive shaft that was still attached to it. We transferred my old drive shaft to the new transmission. I guess he could have left the current drive shaft attached to the diff and just connected on the transmission end.

Is the oil leaking the same diff oil that we put in during regular diff maintenance or something else? I purchased this diff used so I wouldn't know what it was like when it was newly put together. Should I not drive the car anymore? What would happen if I left it as is and kept on driving?



THANKS FOR EVERYONE'S HELP BTW! <3

S2KPUDDYDAD

The oil that is leaking is the same gear oil inside the rear. If the pinion is loose it will continue to leak and get worse. You can /will also cause damage.

Here is a link to the last 4.57 I had to fix for the same issue you are having

https://www.s2ki.com/s2000/topic/911...ear-end-quiet/

SpitfireS

One would say "Don't mess with the DiffMaster" but I'm going to try
You open up diffs more often than most on this board so you have seen it all.
First of all I'm not going to argue about the conclusion Billman and you reached on where the oil came from.
But I do think your explanation needs some clarifiying.



You mention an overcrushed distance piece.
I mean, the distance between the bearings is as good as fixed.
Once you tighten the nut (and compress the distance piece) enough to get some preload on the bearings its unlikely the distance between the bearings is going to be much less then it is at that moment.
So I don't understand how one would overcrush a distance piece.
The bearings can not be compressed.
Is there really no "spring action" in the distance piece at all?
If the installer re-used the old one it could happen, no doubt.
He/she (its posible ) would then most likely also re-use the nut and that is asking for trouble.

What do you mean with backshimming?
Is that installing an extra shim between the small bearing (purple) and the flange (orange)?
There is a shim there originally.
You have a point that the flange should not bottom out to keep it all pressed together.
The OEM shim kit ranges from 3,08mm to 3.455mm, in my 4.57 setup I used a 2,90mm shim.
This is the shim needed between the pinion and main bearing (green)
Depending on the gear set, the diference between thinnest and thickest shim could be 0.6mm?
That is not much, is that allready enough to make the flange bottom out?


No argument here.

S2KPUDDYDAD

Dff master Your old install thread is such a great read I still read it from time to time
The installer could have over tighten the pinion nut that would over crush the distance piece. Even if the installer used a new distance piece and over crushed it then, backed it off to get a lighter load or, just used the old one....Either way there could have been pinion float causing the pinion nut to back off, that causing the leak.

There is some spring in the distance piece but not much.

I am with great certainty (99.9%) sure the leak is coming from the pinion spline, under the pinion washer.
As to back shimming….Some 4.57 gear sets require a very thin pinion shim. Using such a thin pinion shim will also require a heavier than stock back shim to prevent the flange from bottoming out.