Sniff

I posted this in the general 997 forum and received no responses. Perhaps someone here in the 997 Turbo forum can help me.

I'm getting ready to change the gearbox fluid in my '06 C4S and the owner's manual calls for changing the fluid in my front differential (final drive) at the same time. There is quite a bit of DIY info out there on changing the gearbox fluid, but extremely little on the front diffy.

For some reason the dealership wants $325.00 to do the fluid change in the front diffy which is almost $70 more than the gearbox (both jobs book at 1.5 hours and call for the same type of fluid). I asked the service manager why the difference and he said it was because of the different fluid amounts between the two. Not sure where these guys learned math . . . the gearbox contains around twice as much fluid as the front differential. Something doesn't add up so I am going to tackle the job myself.

Anyone have any good photos of the drain and fill plugs on a normally aspirated AWD 997 front differential? Any gotchas to share on changing the front diffy fluid? There really isn't much on this subject out there, so any information we can post should be able to help others. Much appreciated.

Sean

Macster

My info for the 996 front diff has the fill plug in the same general area. There is only one drain plug but the 997 front diff might have two. There looks to be two sumps.

The 997 front diff might require more fluid as it has a wet clutch system to transfer torque. (The 996 used a viscous coupling which uses its own special fluid.)

The front diff is probably well hidden and requires removal of one (or more) panels to access which can add to the cost of the fluid service.

Sniff

Macster,

Thanks for your comments. I found a great cross section photo of the 997 front differential. I believe I see the two sumps you are referring to.

Sean

Macster

After seeing the cut away I suspect there is only one fill plug. As you refill the unit, some of the fluid will run over the divider between the two sumps. As the car is driven I believe the ring gear slings oil and some of it makes its way into the other sump. This is intentional. As this fills then the fluid flows the other way back to the diff region where the gears are. I note the divider appears to have fins so this flow appears to be designed to take advantage of this to help keep the fluid cooler than it would be with just one sump.

'course you are at the unit, so you have to inspect it carefully for a second fill plug. For more confidence you are not overlooking something it might pay a visit to your local Porsche dealer and speak to someone in the service department who can tell you if there is another fill plug and where to look.

I've seen some of the newer cars on lifts but have never seen one with its front diff exposed. Even if I had come across this asking about the drain and fill holes would not have been on my mind.

Sniff

OK, I'll ask a technician. Yes I know, it's not worth taking the chance and screwing something up. However changing gearbox and differential fluid is as easy as it gets (provided you know where the correct drain and fill plugs are). I can't believe it's this hard to find someone who has changed front differential fluid on a 997 before.

Sean

Macster

997's are a bit new to have this service done even at a shop, let alone by an owner.

While the tranny/front diff fluids in my 03 996 Turbo have been changed twice I had this work done at the local dealer service department and I can't tell you where any of the drain plugs or fill plugs are.

The techs know how to do this in their sleep so there's no chance of me screwing something up by removing the wrong bolt mistaking it for a drain plug or to adding too much or not enough fluid. I forget how long it takes a tech maybe an hour or less and he gets to deal with the stinky transmission/diff fluid not me. (The smell nearly gags me. I've never changed my own transmission fluid even for cars for which I rebuilt the engine. I've always had this done at a shop.)

(The Boxster is even a better bargain. Shop time for a 5-speed tranny fluid service is 0.3 hours and the last time the shop gave me the fluid for $5/liter because it had some left over from some warranty work.)

Sniff

I just spoke with a tech at Auto Atlanta and he broke out the tech manuals. Here is what I found out. The front differential pictured above (with the two plugs on the bottom) is for a 997.1 Turbo. BOTH of those plugs are drain plugs. However there is only 1 fill plug on the normally aspirated AWD front differentials. To drain the old fluid in the turbo models, you need to open both drain plugs (make sure you can get the fill plug off first before draining any fluid!!). When you fill the diffy back up with new fluid, it fills the front sump up first then spills over into the rear sump (see cutaway photo). Continue to fill until the new fluid starts to run out the fill hole.

For the 997.1 C4 and C4S cars, there is only 1 drain plug and 1 fill plug. Same technique as far as refilling . . . pour the new fluid in until it just starts to pour out the fill hole.

As far as lubricating fluid, the front diff calls for the same oil used in the manual gearboxes (75W-90). The tech recommended I use Porsche OEM . . . it takes less than 2L so there is no reason to mess around with one of the alternative brands.

Sean

phillipj

I just talked to my tech about having this done.. He quoted me $425 for the diff's and the gearbox..

Kevin here on the site recommended changing these fluids at 50k miles. Well before what Porsche calls for. But Kevin is a Porsche tech and I respect his judgement. My car has 68k so I'm kind of in the middle.

I wouldn't tackle this myself either.. I might screw something up!

Good luck with your DIY!