Gweedo

I have a couple questions about doing fluid changes on my C4.

First, the brakes. Is there anything special that needs to be done when bleeding brakes on a C4?

Second, Tranny fluid. Can the transmission fluid be bled independent of the transfer case? Mobil 1 ATF is the fluid to use? How many quarts?

Third, Transfer Case fluid. Is there fluid? Just a seperate hydraulic system? Can it be done without a hammer?

Fourth, differential. Front and rear differential fluis changes are done like normal differentials? Suggested fluid?

Thanks guys!

993adam

Gweedo, no special stuff for the brake flush, just start at the farthest wheel from the master cylinder and work your way to the nearest. dont leave fluid on the caliper paint or get it on your paintjob The clutch flush may as well be done at same time; kind of a reach up under the car and out of sight. Same system. The tranny flush isn't big deal; just messy and something the shop barely charges much labor for; I would use Mobil 1 instead of Swepco since it is smoother and will shift bettter.

Robin 993DX

Yes, you don't have to change the transfer case oil together with the transmission. The transfer case is located up front which requires the removal of the under panel.

DO NOT USE ATF fluids! ATF is for automatic transmission!

Not sure if you are referring ATF for the front transfer case... The 996 shop manual calls for ATF fluid for the front transfer case, which was a typo! FWIW, The 996 front transfer case calls for the same type of fluid as the transmission.

Gweedo

Actually, I use ATF for my E36 M3 track car. It's the standard for those cars per BMW and why I asked if it was the same for the P car. I'm suprised folks use gear oil in the P-cars, that sounds like a bit much.

Is there a spot online where I can find procedures for these changes and the factory recommended fluids? I checked your site, but I only founf the tranny DIY.

Last question, for now. The tranny in the C2 is the same as the one in the C4, right? Or is it different because of the AWD?

Gweedo

Alright, I still have questions on this. I have changed the Tranny fluid (4 qts. 75W90 Mobil 1) and the front differential (1 qt. 75W90 Mobil 1). The tranny and read end fluids are combined in that on fill, right?

Are there any driveline fluids that I missed? Is there a seperate drain for the transfer case? How much fluid does it hold? Which fluid should I use?

Thanks!

RallyJon

The "transfer case" viscous coupling is sealed--no fluid change required or possible.

RallyJon

ATF is about 75 weight, right? And it's only ever GL-4, never GL-5, so you could never use it in a transmission with hypoid CWP gears like a Porsche. GL-5 gear oil is heavy stuff--75W90 or more--with ONE exception that I know of. Specialty Formulations MTL-P is 75W85 and GL-5 rated. I used it in the STI with great success. All the protection of a GL-5 and lets the synchros shift like butter! Maybe I'll try it in the 993...

Gweedo

Thanks!

Droops83

Actually, yes there IS a special procedure to change the brake fluid on the C4. The C4 uses a completely different brake booster than the C2. This has been gone over many times, will post a link to a thread where i posted the procedure here:

https://rennlist.com/forums/993-forum/295116-flushed-slave-cylinder-wow.html

Scroll down a bit its the long post by me.

---

Chris Andropoulos
Schneider Autohaus
Santa Barbara, CA

geolab

I would suggest two things also.
1st- Brake fluid highly absorbs humidity. Make sure you fill with newly opened can.
Tests have proved that a brake fluid exposed to air for 30 minutes, will absorb enough water that
will turn to bubbles in your calipers. Do not fill from a previously opened bottle. Never top up from an opened bottle.

2nd, if manually bleeding, clutch or brakes, do not push the pedal to the far end while pumping.
There is a great risk you will invert or crack the rubber seal inside the cylinder.
A good bleeding method is vacuum.
After you finish, start engine and brake several times before MOVING the car.

Garth S

If the C4 has the brake booster pump and accumulator in the trunk as does the C4S and Turbo ( which I think it does), read closely the procedure Chris linked above in post #9. You need to address the accumulator prior to bleeding the brakes and clutch.

ATF Dexron III is about a 10W oil - which is good in many BMW manuals, but not in any Porsche manual. It is used in the PS system, updated to Petrosin CHF 11S/CHF 202.

Monique

There are complete DIY descriptions on Robin's fabulous site.

www.p-car.com

Gweedo

Thanks! I had read the procedure in the manual, but that thread answered a few questions that I still had. Friday she gets the complete ATE SuperBlue Flush.

RallyJon

10W motor oil = 75W gear oil. Here's a chart showing the differing SAE standards: http://www.bobistheoilguy.com/visc.html

chris walrod

RallyJon is right. The single difference between conventional gbx's like that of the BMW and the 911 series cars is the integrated final drive (ring and pinion) called transaxle in the Porsche 911.

Its the extreme pressure created by the hypoid ring and pinion that requires the use of traditional gbx oil whereas conventional manual tranmissions can use ATF. Its really important to use the correct fluid as recommended.