MassGuy

The car I am buying is a C4. I am doing my research on how these cars work. Can they be switched into 4 anytime? On the fly? Dry pavement?

BIG-BRO

There's no "switch".......or any driver intervention to engage.... You should read up some more on the different version of the all-wheel-drive systems used in the different generations of 911's (i.e. the 964 system versus the 993 system, etc)

frankvan

awd is always on. Check out:

https://rennlist.com/forums/showthre...ght=awd+switch

BTW, welcome to Rennlist!

MassGuy

I wish I could post pics but I have not done enough posting so I am not allowed yet.
What is the switch on the center console above the shifter for?

I am doing my reading but I also wanted to post a thread to refer to.Thanks for your help.

Thanks for the link. Very helpful!!

sdycus10

My 91 C4 is always in all wheel drive (31% front axle and 69% rear axle). It also has a **** to put it into full four wheel drive (Porsche Dynamic Four-Wheel Drive) to lock the differentials. My manual says it can be used under 30 kilometers an hour and will disengage automatically at 40 km/h. It is not recomended on dry pavement. I have tried it in deep snow and it is very effective but noisy.

MassGuy

So let me be sure I have this right.

Its always in AWD.

If I put on the TC **** it will go into 4 weel drive.

The confusing part is....isnt it already in 4 wheel drive?

I need a better understanding because I am a little slow......

sdycus10

"All wheel drive" splits the power from the engine between the front and rear and changes that split if any slippage is detected. This is similar to Subaru Outbacks, etc. that drive around always with all wheel drive. "It delivers power to the wheels that slip" as the commercial goes.

"Four Wheel Drive", or the traction program as Porsche calls it, locks the differentials and all wheels get an equal amount of power from the engine. This is similar to a Jeep in four low. It is only useful when your Porsche is stuck in snow or sand according the manual. I always find myself on the beach.

MassGuy

ok I get it now. Thank you.

frankvan

sdycus10,

You find your self on the beach alot? In Denver?

How's your C4 in the snow there? Understand you are getting dumped on quite abit this year. Up here in the great white north (where we have snow all the time) the green light on the dash comes on quite a bit. Personal experience, the PDAS seems to do quite a good job of pulling out of the snow without engaging the 4x4 mode switch. In fact, I rarely if ever use the switch.
BTW, I'll be in WinterPark in a couple of weeks for a "conference" (and maybe a little bit of skiing!).

Adrian

This is NOT correct. There is NO full 4x4 switch or mode switch in the 964 C4. The C4 is permanently in AWD because the actual AWD system is 100% mechanical. Both the front and rear differentials are of the open type in normal operation.
The traction control system (PDAS) uses the AWD system to work through in order to provide traction when it is lost from one rear wheel, both rear wheels or both front wheels, but never from just one front wheel.
The **** in the centre console manually activates the traction control (PDAS) differential locks located in the transmission case. There are two locks. One which locks the rear wheels together and another that locks the rear driveshaft to the front driveshaft. The front wheels are NOT locked together and they continue to operate through an open front differential. When the centre lock is permanently activated by the traction control program **** it means that 50% of the drive is sent forward instead of the normal 31%, but it is not guaranteed to be equally distributed. You can still spin up a front wheel. In fact you can spin up both front wheels and then it makes a serious racket before it disengages when the left front wheel speed reaches approx 40kph (25mph).
I think somebody wrote some articles about this once.
It is very important to understand that the C4 AWD and Traction control system (PDAS) are two different systems and that if you lose PDAS you DO NOT lose the AWD system and the AWD cannot be switched on and off. and if you find yourself in 2WD you are in deep pooh pooh because parts of your transmission and drivetrain are now lying in the middle of the road.
Ciao,
Adrian.

sdycus10

Adrian,

So you are saying my '91 964 manual is incorrect? I am not sure that you and I said anything different. Yes, AWD is always on...I stated this. Yes, the **** locks the longitudinal and transverse differentials? Or, is this incorrect?

Sean

Adrian

Yes the American owners manual incorrectly titles the system and yes your understanding (via the owners manual) or how you have described the operation in your posts is partially incorrect. You say the AWD is always "on". No it's 100% mechanical. It is permanently mechanically engaged. There is an unbreakable (well hopefully) mechanical connection (called a power transfer unit or centre differential) creating the link between the engine, gearbox, rear wheels and the front wheels. To say it is "on" suggests it can be turned "off" or that something turns it "on". The AWD cannot be turned on or off.
The **** and the diff locks are part of the traction control system (PDAS) not part of the AWD system. The AWD is not capable of transferring drive when a wheel slips. Only through the traction control system diff locks can drive transfer be achieved.
Why is this important?
1/. People refer to the traction control program as a 4X4 switch and it is NOT, but people get the impression they are somehow controlling the AWD system and can turn it on and off.
2/. The PDAS or traction control system is an electronically controlled (speed wheel sensors and a computer) electro-hydraulic system (hydraulic pressure and differential locks) independent system and the AWD functions with or without it, which is very important to know when trying to troubleshoot and repair.
3/. The 964 C4 AWD system is purely mechanical and has no detection or automatic slippage control system. Drive is transferred via the clutch plated differential locks to lock the rear differential or by locking the front and rear driveshafts or both the rear diff and the driveshafts. All controlled by the PDAS electronics. Again very important when you are trying to troubleshoot and repair.
If you wish to learn exactly how the system works you can always purchase my book on it or read my articles on the subject or do a search on this forum because this has been discussed many times since 1998 when Rennlist was invented. People in the old days used to say that you could switch the AWD off and revert to 2WD or when the PDAS warning light came on you were in 2WD.
This is why it is very important to understand the correct explanation of how this system works if you own a C4. It will save you a lot of money.
Ciao,
Adrian.

PS: The PDAS system of the 964 C4 minus the longitudinal lock was also available as an option the 928GTS.

kusee pee

My New Year's Resolution is to win a technical argument with Adrian

Marc Shaw

Good luck!

Marc

C4Russ

You may wish to choose a different topic but whatever....best of luck