LargeFarva

Does this look like an excessive amount of thrown grease? What with this and the ATF leak, the rear end of my car is looking quite messy! According to the PO (yes, i know what the FAQ's have to say about this phrase, lol!) the car was driven regularly, so I don't think the grease would have separated out, but it might be time to repack and seal.






If you guys concur then I might as well do all the rubber suspension bits back there at the same time, caliper rebuild, brake lines, differential fluid and seal... project creep is striking hard. But at least it distracts me from the rattle that i think is coming from the flexplate

zekgb

CV Axle grease typically leaves a racing stripe on the underbody as it gets flung out of the boots. This looks like differential fluid most likely from one of the seals behind the output flange. Do a search here, there's one that's really easy to get to and the other not so much.

Bigfoot928

that is an output shaft seal for sure.

Taguid

Agree that it doesn't look like grease from CV. There's a gap between CV and flange. Have you checked bolts for proper torque? I had a similar problem with leaking out of top vent due to splash guard misalignment attached to cover. I had also changed out the output shaft seals along with orings on the output shaft covers.

LargeFarva

928sg - it might be, but there is oil on the other side of the diff as well so the vent might be more likely. I'll be replacing the seals no matter what

Taguid - I found your thread, and there were some very useful pictures in there.

I need the lift right now for my wife's Focus but once all the parts come in for my rear end refurbishment I'll post back here with results. Really hoping it's a simple issue with the vent baffle out of place

Kevin in Atlanta

Looks like engine oil blown back on to the transmission. Oil pan is leaking?

LargeFarva

Kevin, I just had the belly pan off for an oil change and didn't notice any sort of leak up front but if new axle seals don't fix it, I'll put some dye in the diff oil and we'll know for sure.

Is this the flange seal part #? 928 332 215 02

(17) in the picture:

FredR

Not wishing to state the bleeding obvious but It might be prudent to check the oil level in your diff. Oil is a bit like blood- a little looks a lot- however assessing how much has leaked from physical appearance is impossible.

Overfilling also has a way of working itself out one way or another.

Taguid

Yes, change 17 and 14.

LargeFarva

Ok I've ordered a set of crush washers for the diff fluid change, and seals for one side. Also ordered a gallon of gear oil and the huge hex required for the drain and fill plugs. Dropped the exhaust for access and on closer inspection there is both gear oil coming out at the axle and oil from further up the car blowing onto the cross member, so good call on that Kevin

Edit: I don't know of any way to check the gear oil other than draining it and measuring how much comes out

Geza

Perhaps "top off" instead of "check" the gear oil is appropriate.

Kevin in Atlanta

I would consider a deep cleaning of all the areas and the wait and see where the oil is coming from.

LargeFarva

I've got the new seal in but the axle flange piece will not reinsert fully! I can feel the splines engage and it shoves in smooth until it just bottoms out against something. Shining a light in there doesn't reveal anything wrong with the splines in the diff, and there is nothing (visible) wrong with the splines on the flange either. I've tried taking it out, rotating it slightly and putting it back in, but it won't even go in to the point where the widened part would be touching the seal. Picture is as far in as I can get it. The central bolt that goes in it isn't even finding threads to bite if I try and put that in.

EDIT: The parking brake was on but I guess when i took the opposite wheel off it rotated something a small amount. I'll have to keep rotating the other hub and trying fitment, any quick way to do this or will it just be a lot of trial and error?
EDIT 2: It only took a handful of tries. Lesson learned not to mess with the hubs at all while doing this. Also, I guess I don't have an LSD? Since the direction of rotation was opposite that of the other wheel. I bought the car heavily modified, so I guess getting rid of the LSD was one of those modifications. Seller advertised it had LSD though

LargeFarva

As an update to this, new seal fixed the issue... on the drivers side. All dry there. The passenger side is now definitely leaking (even more than before). The sludge that I drained out of the diff was probably helping seal it up, and the new oil is so thin it's coming out faster.

Hopefully this teaches me the lesson of "why do one side when you can do two for twice the cost!"

dr bob

Your '90 S4 has PSD rather than a clutch-type LSD, so it's Ok to see the two flanges turn opposite directions. The fluid in the PSD needs to be changed every couple years. It's brake fluid, so nothing exotic, but the controller has a specific process for pump and solenoid activation that needs to be followed. Search Is Your Friend: look for "PSD Flush" in this forum.

The seals and sealing faces thrive on cleanliness. I usually invest in some detergent and elbow grease to get things really clean before opening a bearing or seal access. Old oil film attracts old dirt, which damages new seals. Clean also lets you identify any possible leaks when you are finished.

FIFY