996 4S Front Diff Rebuild

I noticed a small whine from the front diff a few weeks back and found it to be coming from the left front diff side bearing after a little inspection, time for a rebuild. I know i found a thread of someone attempting to rebuild the unit but only did the side bearings but since i decided to do the pinion shaft bearings as well i figured id post some pics of the rebuild for fun. Ended up replacing both side bearings, pinion shaft bearings and outer races, tail shaft bearings, pinion shaft nut, both side seals, some case o-ring seals, viscous clutch snap ring and washer, and spacing washers for setting pinion ring gear backlash. enjoy!

Nice work!

Outstanding! I replaced one side bearing, that was easy. You really dug into it.

Strong work. I had mine totally rebuilt last year.

Awesome pics and job. If you dont mind, what was the mileage? Was there a maintenance issue? Personally, I dont follow the longe fluid change interval recommended so I changed mine much sooner. With proper maintenance, the front dif should have lasted well over 100K before a rebuild. Anything unusual with this one?

wow intresting! i only get a Whine at a Certain speed with my Summer on, but not with the WInters.

I very occasionally get a bit of howl slowing down, but only on certain road surfaces. Might be harmonics?

Mine started to whine at highway speeds before it failed... it was very subtle. In the final stages of failure, there were two additional symptoms: 1. Leaking. It wasn't significant, but there were a few spots on the garage floor. 2. Noise. It sounded like a slipping belt coming from the front of the car, most noticeable when decelerating. A rebuild is a much, much cheaper option than a replacement. A dealer will typically replace the entire unit rather than rebuild it. The part alone is close to $7,000.

Any indication of failure whatsoever and mine goes into the metal recycle bin. Useless.

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thanks everyone. the diff had 70k on it, there was no maintenance issue i changed my fluid prematurely (30k) as well. nothing unusual found inside. i just rebuilt my friends front diff as well his side bearing completely failed, luckily leaving no damage to anything since the bearing cage blew apart. his front diff had only 60k on it.

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i would have done that but as a daily driver in WA and winter coming up i figured it to be somewhat useful to rebuild. Let me know if it starts to fail more than happy to help if you choose to rebuild it.

Interestingly the AWD system on the 996 wasn't designed for additional traction in slippery conditions or winter driving. It was designed for improved performance on dry pavement. Your best bet for winter traction is proper winter tires, not the AWD system. The viscous coupling only drives the front wheels if there is a speed differential between the front and rear wheels, such as when the rear wheels are slipping. The PSM system prevents the rear wheels from slipping. Therefore, the front wheels don't do much in winter conditions. On the track or when cornering on dry pavement, the speed differential between the front and rear wheels allows the front wheels to engage and help to pull the car through and out of the corner more aggressively than a RWD car.

The great thing is that you can remove the AWD components for repair and still drive the car =)

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Plus wintertime COLD conditions make the VC even less functional.

Well thats just fing great, bro. If we didnt have enough 996 bs problems, now us C4S owners can add this to the list of failures to fear.

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Relax.... It doesn't happen to all of them.

Hi, Appreciate this is an old thread but I replaced by diff side bearings and still have some noise (which disappears momentarily on lift off). I removed the cardan shaft and the noise completely disappeared on power but then was worse on lift off. I'm thinking it may be the pinion shaft bearings? I inspected the best I could without tearing apart but couldn't get enough torque to take the pinion nut off. I put it back together knowing at least it wasn't about to explode but I would like to get rid of the noise. Did you make up some sort of fixture to take the pinion shaft nut off which locks the output flanges? Any advice would be great! Thanks, Rich

I am interested to know if you have a parts list for this rebuild?

I'm in the process of tearing down my front diff. from a MY 03 996 TT in order to rebuild it. Can anyone comment on how the pinion nut was removed as well as a part list for rebuilding the unit? Any advice would be very much appreciated! Best Regards, Tim

Hi, I know, this is an old thread, but this includes my problem. Thus, I give a try and hope someone, who did the rebuild, reads this and can support me! I need to reassemble the side bearing cover and the housing (these two parts) My concern is to correctly push the bearing (foreground) into the housing (backgroung) without damaging the housing! Can I simply do this tightening the 8 screws connecting the cover with the housing or do I need a special "pressing" tool for this?? Any help is very welcome !! Thanks Marco

Hi, I know, this is an old thread, but this includes my problem. Thus, I give a try and hope someone, who did the rebuild, reads this and can support me! I need to reassemble the side bearing cover and the housing (these two parts) My concern is to correctly push the bearing (foreground) into the housing (background) without damaging the housing! Can I simply do this tightening the 8 screws connecting the cover and the housing or do I need a special "pressing" tool for this?? Any help is very welcome !! Thanks and greetings from Germany! Marco

Marco- If the same component is going back in the transmission that was taken out, there should be no issues. I assume you changed the bearing? There was most likely some very thin shims behind it to properly space it to the casing, but don't know for sure as it is a single row, deep groove ball bearing. The outside diameter of the bearing is a clearance fit to the inside diameter of the housing, and if it's the same component group that came out with exception of the bearing, it should be no issue. I would think there would be NO pre-load on that bearing, but an axial clearance to the housing. So just install and tighten away. If it binds up before the flange bottoms out, then something isn't right. Good luck! Ciao!

Hi, and thanks for the reply! You are right, the bearing was changed, but there were no shims! When I put the cover with the assembly back on the housing, there is a resistance between the bearing and the housing! That made me feel, that it needs to be pressed in somehow! I can not just push it in by hand!!

Use bolts of the housing to press it back in. But go evenly by tightening the bolts on opposite sides (like you would install a wheel.) Tighten them in stages; first time around half way, second 3/4, third seat, fourth torque to spec. This will press the housing back in evenly.

As with any press fit bearing, putting it in the freezer overnight before the install, will make it go in much easier

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That's a great idea and what should be done. Additionally, clean the housing where the bearing sits very well with some brake cleaner and scotch bright pad or something of the sort. This will polish it and remove any high spots. Clean it very well after this before installation.

Thank you for all the replies! I will put it in the freezer then and tighten it like @white out described! Cleaning of course is a must! Does anybody know the torques? Should I apply any sealant between cover and housing? Thanks again!

Sorry to push that up, but i�m prior to do the assembly and and support would help me! 1.) Is sealant required 2.) Torques of the bolts Thanks, Marco

Do yourself a favor and get this book: http://www.theknowledgegruppe.com/in...96-automobile/ You'll wind up using it every time you work on your car...

Nice book, but does it cover also the assembly of the front diff! The front diff is generally not available in parts... More important ist the question: Do I need any sealant?

Twinscroll, I was looking at an awesome post that you did about rebuilding/repairing a front differential for a 996 C4S some years back. Would you share where you got the Parts for your project, and the Specs to reassemble the differential? - if you even have part #/Bearing sizes that would be even better. Thank you for your consideration...

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Dennis thanks for this.I am sure many C4S noobs think they have a Subaru coupe for winter driving :-). Grateful to WWest for the comment that it is even worse in low temps. I wonder what % of C4 owners think they have the ultimate Porsche-ice/snow/rain machine . I confess I almost bought one with that in mind so thanks to both of you for the education. And here is a cost estimate for the record: https://californiamotorsports.net/co...t-diff-service

No problem. Don't get me wrong; my C4S was my daily driver in all conditions, including snow and ice. With proper tires, it did very well. Winter tires combined with the weight of the engine sitting over the primary drive wheels makes the car quite good in snow. Deep snow is the only real challenge.

So sand bags in the Frunk +Nokians for winter ski trips ?

A ski rack looks great on a 996 coupe, or you can fit a pair of skis in the cabin if you put the tails down on the floor in front of the passenger's seat and run them between the seats. Works like a charm!

Hi Guys, my front diff is leaking at the left drive shaft. Does anyone know the specs of the bearings? Many thanks!

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1 Post and I have to tell you to read the very Thread you have posted your question in ? Start at Post #1 in this thread and do use Search in future -you'll get much better responses.The theory is if you can't be bothered to Search ,it can't be much of a problem to you

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Hi Schnell Gelb, indeed I did read this thread as well as all other threads I could find on here regarding the 996 front diff. However, even now when re-reading the thread I couldn't find the specs for the bearings. Nevertheless it would be a great pleasure to hear back from you in case you are able to share them with us. I'm sure I won't be the only one who would very much appreciate that. Many thanks and kind regards!

LMGTFY https://www.google.com/search?q=996+...utf-8&oe=utf-8 or try the PET -seals? Seal - Differential Output, (40 X 60 X 9 mm) Part #: 999-113-454-41-OEM or 999.113.454.40 ?

Porsche doesn't sell components of the front diff individually as spare parts. From the PET I can only get the part numbers of the complete diff and the seals. Thus, I was asking if anybody happens to know the specs of the *** bearings shown in the very first post of this thread.

Please use the correct terminology.Do you really mean the specifications of the bearing or the part number or the Interchange .All are utterly different. You find these things by googling, posting your findings and then asking. We've had some epic threads based on this simple premise of doing some work up front ,sharing and then working together. And btw those of us in the biz usually buy bearings from a Bearing specialist.That is not the Porsche Dealer and that isn't what PET is used for.

Sorry for not being precise in my terminology. I plan to change the bearings and would like to get the parts before starting rather than getting the old ones out and then ordering new bearings based on the measurements of the old parts. Thus, the size of the bearings would be of great help. However, if you have part numbers of suitable bearings at hand this would be even better! And regarding your accusation that I haven't put much effort into finding suitable bearings I can assure you, that I have read quite a few threads regarding this topic on here as well as on other sites such as pistonheads, PFF etc. However, I didn't come across any part numbers or description of the bearing sizes. In case I missed it, I'm utterly sorry for spamming... Cheers

"I didn't come across any part numbers" The *** part number is clearly stamped on the edge of the outer race of the bearing - like most every other specialty bearing. You have to remove the diff to get the old bearing ....and then go to the local Bearing dealer with diff in hand.Since you live in Germany ,you probably would have some insights to share with us ? That is how a pro does it here usually YEMV. We get our hands dirty first. Replacing your leaking seal doesn't necessarily require a bearing replacement but I suspect we are still getting a cryptic ,piecemeal story so it is time to give up. And why not share with us the most helpful of the posts you found on the subject you researched?

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If you had used a fraction of the energy you've used replying in this thread to actually try to help this guy out it would have been nice. Instead, you've wasted a bunch of his time (and anyone else's who's read it thinking there might be some useful information here), and clearly yours as well - which can't be very valuable since you keep posting this useless drivel... Is this really how "We" pro's do it?

I told him where to find the bearing part number even though his problem is a leaking seal.I also gave the seal numbers. Contrary to what he claimed, the seals are available from Pelican and others.I did not want others who read this thread to be mislead. Even Amazon sell the seal ! This source may be of help and is on page 1 of the Google search for Americans: Amazon Amazon https://californiamotorsports.net/pr...t-diff-service . Since he lives close to the *** H.Q. in Germany (according to his avatar)he has more opportunity than most of us to share some bearing research with other Rennlisters.I am only able(as indicated) to take the part to a local specialist bearing house and ask their advice. Even if you get a part number off the Internet it is foolish to trust it from a single source.It is equally foolish to rely on dimesnions only. Read the related epic thread on gearbox repair to see specific(expensive) examples of such mistakes and huge amounts of research shared by Rennlisters. That is how we roll on Rennlist. Yes I was exasperated by the drip feed of vague info because it wastes time.The lack of any attempt to share links to diy info he found with others is very much against the spirit of sharing that makes Rennlist so useful to others who follow later.

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Agree- seemed like the question was simple and if I knew the answer I would have provided for the guy instead of these passive aggressive responses. To each his own though...

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Usually SG is pretty helpful - it just seemed like he had a hard on for this guy... I take his explanation at face value - except for the "that's the way we roll on reenlist"... whatever...

one more time 1. I gave him the part number for the seal to address his leak problem. Contrary to what the OP claimed it is easy to find the seal number and the part - Amazon & Pelican.I gave links. 2. I told him where to find the bearing part number.I told him where to find the replacement bearing and why.He already knew Porsche do not sell the bearing. Nobody else bothered to contribute anything to help the OP . Clearly I am wasting my time helping people. I have over 3000 posts on this and another site.I rarely ask a question.Most of my posts contain links and references to solving the problem for others.Not my problems, other peoples problems. And then I get style comments for trying to drag out from a rather evasive OP what he really needs or means. And he was sitting on some of the answers all the time and he failed to contribute any links from the many he claimed to have read to help others solve their problems.

Dear All, I know it is a quite old thread. I am just dismanteling the Diff and have now a problem to remove the pinion shaft nut (40) in order to remove the pinion shaft. Does somebody knew how to do this? What is the required torque for removing and for Setting up this nut later on. Thanks in advance for replying Best Regards Bemimue

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Your posts helped me quite a bit. Here I am four years later doing this same job. You made it easy for me. Thanks a ton.

Glad it helped and hopefully others will find the front differential info useful. Amusing to note I have never owned a 996 ,I was just being helpful.