C4 Front Diff Leak...

[Augurean]

Just got back from vacation and it's time to address this problem again
(started on this thread: Alarming Puddle of Oil After a Long Drive)

I've confirmed that my 1990 C4 is leaking fluid from the front diff. It only appeared to be from the rear earlier when I was parking on a hill because the fluid flowed down the skirts until it found an opening.

I've seen a few other posts here and on Rennlist (Any C4s with front differentiel leaks? - Rennlist Discussion Forums) of people with leaks from the front diff...does anybody have similar experience and can recommend which seals might need replacing, or other possible culprits? I'm hoping to replace them, change the fluid, and see if that solves the problem.

[GeorgeK]

If it leaks from the center cover, it is the imput shaft seal. A bear of a job to change. You basically have to drop the whole front axle, and disconnect the steering. Count with over 15 hours workshop time...

If it leaks on the driveshaft seals, it is much easier.

If you have to get the front diff out, take the time to change all 3 shaft seals.

[Augurean]

Thanks for the input.

Let's hope it's not the shaft seal then...thought I may have to replace all of them just for some piece of mind...

[alexjc4]

just done the input shaft seal myself, its no joke, the factory manual doesnt make it look too bad. dropping the front sub frames and disconnecting the drive shafts is the easy bit. the cap head bolts holding the diff onto the torque tube are 85 nm and the top two are near impossible to get to, try 3ft of extenders through the gear shifter hole. oh and then the diff is pretty heavy to manouver out amd will leak gear oil out the nose when you drop it.

its an odd design, the main seal actually seals against the outside of the clamping sleave which joins the centre drive to the diff input shaft, the splines themselves then offer a point of leakage and have to be sealed with a small washer and rubber ring screwed into the end of the centre drive shaft.

oh and dont scratch the oil seal surface on the clamping sleave when u slide it back its not cheap to replace and is special order from germany.

my 964 specialist mech advised to leave it and keep the diff topped up unless it got really bad. also advised that even when fixed it would probably start leaking again soon.

i did it anyway because i like a challenge and i'd just bought a lift.

[iamtheari]

Dredging up an old thread, but...

I am contemplating doing this job. My PPI found a slight input shaft leak on the front differential, 18 months ago when I bought the car. I changed fluid back in February with Royal Purple. Not sure how bad the leak is, as to be honest I have a much more significant leak from the steering rack. I'm going to replace the seals on that this winter, and removing it is part and parcel of getting the front differential out. So it's as good a time as any.

How nasty was it? Worth doing or don't bother? Do you happen to remember the part numbers for the output shaft seals? I only see the input shaft one side in the parts catalog, part number 999 113 347 40.

[viking66]

Hi,

Before you take it all apart check that the breather vent on top of the front diff is clear. Pressure created by heat expansion in the diff (if the breather is blocked) as you drive will result in oil being squeezed past the seals even if they are in good condition.

Hope it is as simple as this

[iamtheari]

I don't suppose there is any way to get to the breather vent without removing the differential from the car. Removing it sounds like the hard part. :-\

[viking66]

Unless memory fails me I think you can get to it (at least feel it) guess one could put a wee bit of air pressure in the diff to confirm the vent is clear.