Looks like mine has been leaking for some time now and Im told i need a new one...


Has anybody had experience with this problem and is there anyway I can get my old one recon'd rather than buying a new one?


Any help is appriciated...

 

I remember reading on here something about one of the possible causes was too great a difference on the tire size from the front to back and the tires needing to be within a certain rotation per min, that Match or are close With the combination of the diameter, on the 4 wheel p-cars

I'm sure someone else would know better then I

 

This is true!

So a previous owner must have used the wrong tyres on there!

 

Happened to mine as well. Car had only run 4000kms at that stage. Minor oil seal leakage was evident and further checking revealed excessive movement in the carrier race bearings. This movement was causing the flanges which slide in each side of the diff housing through the seals to have peripheral (upward/downward/fore and aft...not in and out) movement within the seals, removing the rubber seals normal ability to retain the oil inside the diff. There isn't much oil in the front diff anyway (only 1 litre or a bit more) so it doesn't take very much leakage at all to cause friction damage as well. The preload on the carrier race bearings isn't adjustable with threaded side plates therefore, the carrier race bearings require very precise shimming to maintain correct preload whilst achieving correct lapping position with the pinion gear, which I don't think the average P workshop has that training to do, so a new diff is always used. Needless to say there is always the strong likelihood friction damage from insufficient lubrication has occurred anyway so, i guess why waste time trying to recover the failed unit. Probably why PAG always specifies the issue of a new diff assembly.
In so far as the cause i believe it was just from faulty manufacture in the sense the carrier race bearing preload was insufficient. It can happen. Out of so many thousands made there will always be a few bad ones that slip through the net.

There has also been a train of thought expressed on this forum that excessive negative camber induced by shimming lower GT3 control arms (where fitted) can cause the seals to leak, damaging he diff. The theory is the velocity joint on the drive-shafts has only so much lateral slide movement before it begins pulling the actual shaft out of the diff, usually when the suspension is at full travel or steering lock, such as what can occur during track conditions etc. Therefore, once the driveshaft's sealing surface has been moved beyond the reach of the mating rubber seal's surface the oil will leak out of the diff seals, and also damage the seals in the process from the (alleged) abnormal in and outward movement through the seal.

However, the fundamental flaw with this particular theory is that the drive-shafts are totally separate units which bolt up to the diff's flanges on either side of the diff. These diff flanges however are in fact the actual components that slide into and through the seals on the diff housing and NOT the drive shafts as suggested, and these flanges are locked securely into position in the differential housing into the side gears inside the hemisphere, i.e. cannot slide in and out of the seals as inferred, as they are locked into position by way of circlips which are located on the internal (splined) end of each of these flange components, sitting inside the actual hemisphere of the diff. So the only way for these flanges to ever move or "slide" in and out of the diff housing would effectively mean the circlips must be firstly removed (unless somehow shattered/broken from extreme adverse tugging pressure against the flanges) so to allow the splined diff flanges to come free from their locked position so they can then be slid out of the seals and diff housing.

Incidentally i have GT3 LFCA's fitted and the level of shimming is minimal as i am only running @ 1.7 on the front, and the Porsche technicians examining my case thoroughly checked the movement in the velocity joints on full lock and, suspension travel (as i expressed my own concerns over the movement limits of the velocity joints after reading this particular theory), and all was found to be perfectly fine i.e.; no adverse pressure being placed upon the diff flanges from my neg camber settings...and the drive shaft velocity joints still having sufficient lateral movement etc, so there is no "tugging" against the fixed flanges as such. Porsche said that it's only where the LFCA's are shimmed to achieve neg camber of 3 -4 deg and more that other avenues should be taken (i.e. using top tarret plates etc) to achieve the required neg camber instead of excessively shimming the LFCA's as the driveshaft velocity joints can run out of lateral slide movement in those extreme cases, and then cause tugging onto the flanges, which (may possibly) result in breaking the inside circlips allowing free movement of he flanges in and out of the diff housing...to then cause seal leakage or damage. However, if that ever happened the circlips would get munched up in the planetary gears which is far more catastrophic than seals leaking IYKWIM. There were a lot of Porsche experts involved with my issue at the time and the general consensus after all the investigations had been completed was that the GT3 LFCA's and my camber settings had absolutely nothing to do with the seals leaking on my diff.

Using different diameter tires front to rear (or badly overly worn rears vs the fronts) can cause diff damage but I very much doubt if seals can be included on that scenario as the type of damage would be associated mainly to abnormal stresses being placed on the centre diff (or viscous coupling/clutch pack). As you may be aware the front diff incorporates a number of clutch plates in the centre diff which is a separate section of the front diff assembly. If the diameters are sufficiently different from front to rear there will be a "fighting "going on in this central area which regulates the drive between the front and rear diff more so than the actual diff centres themselves.

Incidentally when they replaced my front diff the first new diff was also found faulty....so faulty diffs do exist. Immediately after installation on test drive the car had a very noticeable vibration (chattering) at @ 80 to 90 kph after backing off from acceleration. A new diff was subsequently ordered and a month later after it arrived was fitted (there was none available ex germany unfortunately). Porsche said the problem again was unrelated to anything else on my car. Apparently when this first new diff had arrived the box was broken so there was a thought it had been dropped heavily as some of the oil had leaked out when they unpacked it. So another replacement new diff was ordered again. Anyway the next (2nd) new diff that was fitted has been perfectly fine and has been operating without fault or leakage thankfully. The faulty diff (the first new one with the bad vibration) that came out had lost all of its oil by that stage too so it was history. Both faulty diffs were returned to PAG. Hope this helps.

 

Speed21, thanks for your detailed write up, I finally feel like now I know someone who has had the same problem as Im having!!

Can I please ask what symptoms you have when you realised your diff was gone, you mentioned when that front wheels were knocking at full lock and Im finding generally the handling is now pants!


On a good note I have found a diff from a 997 turbo from a breaker, at a ok-ish price...

this is the part they have shown me,




Hopefully this is right?

Im still not sure as to which option would be better...

Put this (second hand but with warantee) diff on the car or find a specialist to recon this old unit for the similar sort of price...

 

Did they give any details regarding how many kms the car had travelled and whether it was stock or modified at all? Going by the photo that appears to be the correct diff assembly. I'd just make 100% sure that it is out of a 997turbo as I would imagine the ratios may be different to the C4/S being of lesser power. As you can see in the photo there is a flange on the side of the diff. Try as hard as you can to wobble each flange up and down and side to side. It should be very rigid with no movement. You may be able to move it in and out a tiny bit as the internal circlips are only there to retain the flanges from pulling out of the diff against the movement from the driveshaft velocity joints sliding in and out instead of the flanges falling out the side of the diff every time the suspension or steering angles dramatically change. As a general rule these diffs are very strong so even if the reported mileage is not that low or the car has had previous hp upgrades the diff should be fine, plus you have a warranty to rely upon to see if it all works perfectly once you've had it fitted. It's hard to say what requires replacement internally in your existing diff assembly without stripping the unit and examining all the parts. It may be as simple as replacing the bearings and re shimming the correct preload, it may not. If you have time on your side you could always have the unit removed and quoted by a gear and diff reconditioning specialist but that usually entails inspection charges for any labour used. Try to buy the unit outright and keep your old one. Let me know if you are close to Enfield (I will PM my Biz address there) and if you don't mind parting with the old diff i'll have my guys send the unit out to Aus in a shipment. I'd love to pull it down in our WS and see exactly what goes wrong with these things and whether it is viable to fix at all.

Edit. Sorry i forgot to post the symptoms. My original diff felt normal other than the car sounding like it had a bit of extra clatter in the prop shaft/driveline between the front and rear diffs when the car was being driven very slowly in first going lightly on and off the accelerator. It would feel like there was a level of slack there that shouldn't be there plus you would have a relatively pronounced clatter sound as the drive pressure changed between the front and rear diffs as you went on and off the throttle.
The second diff which was brand new was wild. You would drive the car normally and it all felt relatively fine but once you hit the throttle and accelerated, at @ 80 to 90kphs you would get this rumbling sensation come right throughout the car, you'd feel it through the pedals the steering wheel etc and the whole car felt really unstable....quite scary infact. It was a very high frequency vibration and a very un-nerving sensation particularly when the car gathered up speed under throttle. The car felt like it wanted to go its own way. The rumble would also become a bit more pronounced as you backed off the throttle.

 

Sounds good. I don't mind parting with it at all. It will be no good to me anyway! Getting it to Enfield will be no problems.


I will call the breaker yard in the morning and find out more details.

 

Hey all!


Got my diff today and putting into garage on monday!

Will keep you posted!

 

Good luck bro

 

Hey Usman .. Im having the same problem as urs right now and finally found a post about it. Hows ur car now? And im looking for the same part,front axle, if u know some one os willing to sell .. Cheers

 

I had mine rebuilt by http://californiamotorsports.net/ and they said the thrust bearings had worn out and became pitted. They replaced 4 thrust bearings and had the unit back in my hands the following week and works perfect now. Id give them a shout.
Good luck!

 

Thanks for ur reply, unfortunately i bought a new one and replaced it at the dealership's lol

 

No problem, Hey new is better than used from a scrap yard

 

Yeah of course but i ended up paying around $7000 while the used one with 50k kms on it was around $1750