Russell Gardner

I want to disable the ABS on my '93 RS America for DE days. Can this be done? Is there a fuse I can pull, or need I install a switch?

DaveK

Hi,
It may not be exactly the same - but on my C4, fuse number 15 is the ABS (also affects the traction control).

Dave
90 C4

Adrian

Dear Russell,
You can do a couple of things. The first is to remove the connector from the ABS control unit or to remove relay R34. I do not recommend that you remove fuses. Just a personal thing. If you remove the fuse ensure you stick some gaffer tape of similar over the relay socket. Just a little safety issue.
Be advised though that the warn light will come on. Again you can cut a little square of black vinyl tape and stick on the indicator glass to cover it up.
Master warn cancel button deals with the rest.
Ciao,
Adrian
911C4

Roland Kunz

Hello

Cup cars had a switch for disabeling the ABS beside the clock. Those parts where sold from Porsche race department.
It was a typical small switch in Red with a bulb behind and a wireloom runing into the main circuit board.

Can´t say the electric hook up points for sure also CUP cars had a other main wireloom and simplier fuse/electric boards.

Grüsse

Adrian

Dear Roland,
This is why I did not mention this switch. The wiring is significantly different between a RS America and a Cup.I have never seen a hook up diagram for this switch for a standard 964 wiring loom. No point sending people on wild goose chases. For people in the USA who wish to investigate this switch further I suggest you contact a facility that prepares racing 964s or used to. Andial would be high on my list.
Ciao,
Adrian
911C4

Russell Gardner

Thank you all, and especially Adrian, for your helpful replies.
Russ

Roland Kunz

Hello

Just to clarify:

You are not interestet to switch off the ABS on Track events as you will not be competive in the class. ( With ABS your brakepoint is some 10-20% later virtually you brake trough the curve untill you hit the appex ). And as a Beginner runing without ABS is good for helping on learn how to brake ( and how things turn around if you aren´t on the spot ) but your tires will not love that.

And the Porsche ABS also works with sliks.

There are maybe a handfull people out there who can perform as good or better then the ABS but I think they wouldn´t ask on this board for assistance

The switch was used for the circumstance that you run off track and trough the gravel or over grass where ABS will not stop you like a set blocked wheels and for the circumstance that you made a 180° turn with your backtail and now skid backwards then the ABS bias made for optimized braking forward brakes only with the frontwheels.

Grüsse

John Boggiano

As someone who has experienced a 964 doing a 180 and going backwards at speed on wet grass , what effect (if any) will the ABS system be having in these circumstances?

(Just in case I should find myself there again!)

Cupcar

The wiring circuit for the RS/Cup ABS cut off switching is included in the normal shop manual wiring diagrams for the 964. I am not at my desk at home to indicate here which sheets the circuits are indicated on, but they are on the ABS pages and are labeled: "M001 version" I believe.

clubrcr

[quote]Originally posted by Russell Gardner:
<strong>I want to disable the ABS on my '93 RS America for DE days. Can this be done? Is there a fuse I can pull, or need I install a switch?</strong><hr></blockquote>

Russell:

Why would you want the ABS off? I understand that in a learning environment, you need to modulate your brake pressure, but if I were you I would think twice.

I have a Carrera Cup car with ABS. I race it with the ABS on. I have felt the ABS several times. The main reason I leave it on... several years ago David Murry was my instructor. I asked about the ABS. He made one statement that has stuck with me since.

" You can still steer the car with ABS ".

We can debate about in the grass or going off, but if you are learning, you need to be more careful not to be off.

Jim Newman
92 US Carrera Cup

Roland Kunz

Hello

OK the point is that you don´t race without ABS ( If it is allowed in the raceclass ) and there is no reason to switch the ABS off during the race.

And a DE is by no means anything close to a race.

As someone who has experienced a 964 doing a 180 and going backwards at speed on wet grass , what effect (if any) will the ABS system be having in these circumstances

Now if you fly off straight trough the gras or over the gravel you achive shorter brake distances with blocked tires. That is called "wedgeeffect", your tires just dig into the dirt using the "spoilereffect".

Now the desicion is on the driver at exact that moment. If he switches off the ABS he mostly skid straight on and ruins his tires but will not hit the wall ( or at lower speeds ) like rodeling over the grass/gravel/ice with ABS.
But if he keeps ABS working he can steer slight and his tires will survive to go back onto the track.
Normaly on race tracks with long run off zones ( Hockenheim ) you ride it out with ABS. On Tracks like Monaco or the Nürburgring you have no gravel or grass run off zones so you don´t need to disable ABS too. There are some tracks like Zolder, Le Mans, Salzburg, Monza or Spa with short run off zones at certain corners ( thanks to F1 races they got improved over the last years ) and stagered catch fences or the tire walls to fatal hiting from the walls. There you can decide on your own wich is the luckier draw then.

The general rule is drive as fast as you can stop but on the racetrack drivers tend to drive 101+% and you often see them fighting trough the corners, car bodys close enough to clamp a creditcard. If you get a slight hit curving at the limit you normaly loose the rear and the car usually makes a 180° with the heavy part moving on, that´s now the moment when you roll backwards.

With the ABS system your rear brakes force are limited to a certain balance based on the input from the frontbrakes. Said that the frontaxle is designed to block sooner and has more brake force then the rear axle.

If the car is braked now on a backwardmovement the frontaxle will block much sooner as the load force on the tire is much lower but your Bosch MK IV ABS is still thinking "forward" and loosens the brake force on the front to keep the tires rolling.

Now thats OK, but if you roll backward your rear end becomes the frontaxle and is capable for much higher brake forces the the front but the ABS is fixed to the forward sheme avoiding blocked rear tires under all circumstances so the result is if you brake backwards you need some 100% more way to halt.

If you rodel off backwards over grass you need to switch off the ABS to block all tires to stop the car effective. Exact thats the only moment when ABS works countereffective and you need to switch it off temporarly.

The switch is in the Cup cars to give the driver a choice for full control under such extrem situations but those people are not reacting like normal drivers. Normal drivers fly off and don´t know why. Skilled driver will feel they fly off before it happens. Expert drivers know they will fly off before it happens and think about what they want to do and what are the chances and then they react to achive the goal.

The point is ABS performs better on 99% from the circumstances on the road and on the racetrack as well and the 1% where ABS performs not as good you can just say that it still works better then 99% from the drivers.

If you are a Beginner on the racetrack and you fly off then you are not able to make correct desicions as your are not a expert.

The best desicion while flying off is to aim ( and hit ) into a free run off zone and if you see no clear way then try to hit something as frontal as possible using the full crash structure from your car. ( its just a car and you have to use the optimum to survive but don´t blame the car or the ABS system on a missperformance from the driver )

If you make a U turn and run backwards then you just impulse tilt the sterring while sometimes need to pull the emergencybrake then the car turns back again and you need a tilt back on the stering wheel to steer out the front movement and to straighten the direction. ( Schumacher or Villneuve do that on 180 mph with a formula 1 so it can´t be complicatet )

You can practice that mostly on wet skid plates beside the racetrack and before you are not able to make a 180° turn and bring your car back into the normal driving direction on the movment you are not skilled enough for doing anything more then rolling on the racetrack.

Now the fact is if you skid backwards and try to turn the car head on again you need more travel then just blocking the brakes to stop. The real benefit is you don´t loose to much time and stay in the field. But you need oversight and be under professionals who see/feel what you are doing.
if you get turned in the field you normaly try to get out from the dangerzone. If you try to flip back the chances that a following up car will cross your line and hit you sideways are damn high.
Just watch some Races and see what the drivers where doing in why they react sometimes "strange".
Then think about it and try to learn from the good reactions and try to learn from the bad reactions. And also recall you have a birdview and a clear field, if you are down there on the track then you need to imagen the actuall field like a blind chess board.

Remember always drive as fast as you can stop and if you overdoo then be prepared to pay for driving over your personal limit.

A DE is normaly not a "raceevent" and meant to give you a feeling for the limitations from the car and your own personal limit.

Now if you switch off the ABS on the DE what will you learn? ( How to ruin your tires faster or how to turn your backend often! ).
Later on the street you will have ABS disabled as well ?

Disabeling the ABS by pulling the fuse/relay or diconecting is just stupid and the only way to go is to incooperate a switch and have that switch on a place where you can reach it even while you spin off. This is what the factory did ( however the size and the spot from the switch are not the best choice, especially with driving gloves ).

Now a other important thing on a track event is maybe how to disable the Airbags ?

Sorry for the long post just try to clarify some things.

Grüsse

Cupcar#12

Cupcar(s)!
do either of you have the switch which kills the abs (causing the red brake warning light to light up on the dash) my car has the warning light but no way to activate the ABS kill switch. i must be missing something here.
Rob (92 carrera Cup USA) 19K smiles)

JC in NY

Here is a photo of the ABS kill switch from the 964 Carrera 2 Cup. It's right there near the clock.

Cupcar

The switch used by Porsche for the USA Carrera Cup cars (and Euro C-Cup too?) pictured above is a standard, Bosch switch available in Europe at parts stores. To connect the switch you need a harness that Porsche made that not only allowed the ABS switch to work but also activated the kill switch. I am not at my desk right now or I would be able to give you part numbers which I will post when I return home. I also have wiring diagram for the harness. <img src="graemlins/yltype.gif" border="0" alt="[typing]" />

Cupcar#12

Great thanks - i'll me looking forward to to and i have pictures of the cage (a recreation, mostly of the cage work Andial did - but in CrMo) up soon.