Pesty

My abs seems to come in too early. Granted its cold and a bit slippy around here this time of year and I havnt tested it on a warm dry day but Im sure its too early in its operation.

Are they all like that? 12 year old ABS systems are probably well old technology in this field or is it my car?

malc elliott

I think its the weather. Cold tyres, wet leaves, mud etc. There's not much weight over the front wheels remember, Very easy to get a chirp from the ABS.
I think the technology stands up very well compared with ABS of today.

Johan K

On a bumpy road my ABS is triggered very easily due to the stiff front end.

DaveK

Check your longditudinal accelerometer. I used to have a problem that my ABS was very poor (felt like it totally released the brakes, and for far too long) but it also cut in way too early. It took me 18 months and lots of money before the problem was found.

If you search you should find threads on it - the accelerometer looks like a relay and is in the transmission tunnel in front of the spoiler / diff lock switches. You can take it out, prise it apart and blow some air on it - make sure the pendulum moves freely.

When I had my brake problems many people told me it probably wasn't a fault. I'd say if it feels like it isn't working properly then it probably isn't.

Try pulling the AWD / ABS fuse and try some test runs on a quiet road. If you can stop much quicker (without locking the wheels) then you have a problem.

964RS

Can I disable the ABS by removing a fuse and then use the system as a non-ABS system?

/Anders

DaveK

Yes. On the C4 it also controls the AWD - I guess on a C2 / RS it will only be the ABS. You'll have to put up with the warning light though.

964RS

Terrific, thank's!

Pesty

Thanks for the info Davek,

when the ABS comes in it goes off in the normal manor(like all over cars Ive had) its just that IMO it comes in well before the wheels are locking. probably as malc says down to teh weather.

Accelerometer? damn these cars are complicated I imagine there are all sorts of things that could effect teh ABS. wheel sensors for example?

Pesty

Do you mean you can get to it from the inside of teh car by taking out the plastic where the switches are?

DaveK

Wheel sensors might also play a part - but I think failures there are usually picked up by the warning system. So are accelerometer failures - but not always as my car proved and several other people have had the same problem.

No - you can't get to it by taking the switches out. On the driver side of the transmission tunnel you should see a flap held on by two screws - in UK cars it has a switch on it. Take this out - and you can get to the accelerometers. It's not easy access but you can do it.

There are two - but I can't remember which is the longditudinal one.

It might be in Adrians book - I'll take a look.

DaveK

OK - Adrians book says the longditudinal accelerometer is behind the lateral one. The longditudinal one is aligned in the direction of the car (i.e. front to rear) - the lateral one is mounted at 90 degrees. This should make more sense when you take the panel off - if it doesn't, take them out one at a time and it will be obvious from the direction the pendulum moves.

One word of warning - once you've opened them, be careful. They are delicate and VERY expensive. If you break it, I think you can say goodbye to £500.

DarrylH

Definitely be careful - read this cautionary tale...
https://rennlist.com/forums/showthre...=accelerometer

Pesty

thanks davek. I have that litle switch on the transmision tunnel. £500 think ill leave it for now just in case. Im a lot better at breaking stuff than fixing it

Just working my way through adrians book at the moment and noticed that the wrong size rolling radious wheels may also effect the ABS making it come in earlier. Which is interesting as my car has 18 inch wheel fitted. perhaps this is why.

if I have understood him correctly

JW Hubbers

Assuming that the ABS is really activating too soon (in other words, you are not overestimating the amount of grip available) then no, they're not all like that. Mine isn't

I like the ABS on my 1991 C2 much better than the ABS on my 2001 Alfa 147. The 964 ABS allows me to lock up the front wheels quite noticable before it kicks in; just the way I like it. The new-fangled system in the 147 was probably setup with lawsuits and crappy drivers in mind: it kicks in very early, and gives absolute priority to steerability over stopping distance

Oh, and some hard data: I'm playing around with a data logger at the moment, and the maximum longitudinal decelleration I achieved in the 964 on a dry but cold surface (on summer tyres) was .976g
Not bad for a car that left the factory more than 13 years ago
During this kind of braking the ABS releases a tad of brake pressure once or twice, but usually not more than that.

If I get really bored I'll stick the logger in the 147 and see what the decelleration is with and without ABS, but I have more important things to do at the moment

Cheers,

JW

Marc Shaw

JW Hubbers: what type of data logger are you using?

Marc