the flyin' scotsman

Perhaps a naive question but here goes:

If the antilock fails whats the default? Full front brakes?

The reason I ask.............wore out a set of front pads since last August, Mintex Street............yes I drive hard...........yes the car's parked for the CDN winter.............they lasted for 10k kms max.

IcemanG17

Malcolm
The brakes work perfectly normal....until you hit them hard enough to engage the ABS.....if you did that....then they probably would just lock up and skid.....

the flyin' scotsman

ok...............tonight I proved that the front brakes are working well...............they locked and skidded with little feal for any rear brakes.

69gaugeman

Abs is a system that bypasses fluid pressure when the computer calls for it. There are valves that are open for normal braking and they close off and a pump takes over if ABS is required. The default condition is bypass the ABS and run like normal brakes.

Maybe you might want to look at the rear pressure regulators. They might not allow much rear braking. Most of the braking is done with the fronts.

Lots of trips up and down the crows nest pass? that'll kill your brakes. Cross drilled rotors? they tend to wear out pads faster too.

Imo000

Yes, that's right. When the ABS is deactivated it will work like regular breaks.

However,I don't know where but read it a while ago that a disabled ABS system does not perform as well as a car that doesn't have ABS at all.

69gaugeman

Actually, on smooth dry pavement, the ABS will take longer to stop. It is when one or more wheels are missing traction or there is cornering involved that ABS shines.

Disabling the ABS is just as if a pipe was in there. The fluid is allowed to free flow.

Unless there are recent changes that I am unaware of. There was talk of an analog system and brake by wire which could conceivably perform better on dry pavement.

the flyin' scotsman

The 'antilock' light comes on spardicaly.

I've owned the car for 6 years and have yet to see any wear on the rear pads. This will be my 4th set of fronts.

As I mentioned in the 1st post........the fronts are gone/ wore out.........10k kms.

Roger is sending PBR's tomorrow..........who else do you call with this type of concern at this time of day?

the flyin' scotsman

We live in the foothills of the Rockies and very close to the Crowsnest Pass...............funny you mention as it got to be a real concern following the team through the 'Road to the Sun'................steep gradients.

69gaugeman

jack up the back of the car and have someone press on the brakes. Although highly unlikely, it could be they are seized (abs would have moved them most likely).

The next thing would travel about 15 to 20 km/ hour with two wheels on the gravel and two on the pavement. Jam on the brakes and see if the rear wheel is locking up or not (gravel pattern after rear wheels)

Then check the other side. Also do you hear the ABS kicking in (pulsating)?

Changing the rear brake pressure regulators should be lowered only with careful thought. In panic braking having more rear brake will bring the *** end around real quick.

Alan

Rod - why would you assume it would be worse? I agree it wouldn't be better while you have full grip - but the ABS doesn't kick in and do its stuff until it detects one wheel slipping.

Its certainly possible to slip on dry pavement under heavy braking so in practice it will be better beyond that limit while no better in normal braking...

What am I missing?

Alan

69gaugeman

On dry pavement about 20% wheel spin is the maximum point of traction. ABS does not allow you to get to that point.

123quattro

While 20% slip is the peak of the mue slip curve, that is also a very unstable region and cannot be controlled. ABS typically controls to around 10% slip. The decel improvement from 10 to 20% is marginal. However, the gain from running 10% slip is that you can still turn the car. At 20% slip the car will not turn. 99.99% of the population cannot brake beater than an ABS system.

69gaugeman

I agree that most people cannot brake better than ABS. But someone who knows how to brake can stop straight faster in dry in a non ABS car.

Also newer ABS systems are better. The late 80's and early 90's controls had limitations that new systems don't.

I agree ABS is better.

123quattro

True. I should have referenced my comment that most people cannot brake better than a new system. Not one that is 20 years old.

Alan

I agree that many 20 year old ABS systems were quite basic - e.g. modulating all wheels together. I'm not sure that the Porsche system falls into that category - as a split 3 zone system it was rather more advanced (and $$). I'm sure there are still some further improvements on modern versions though.

I know Rich Andrade worked with Bosch on the electronics of their systems of the early 90's - maybe he can comment more.

What you say may still be true - but Porsche almost certainly had one of the very best systems available at the time. Virtually all drivers are better off with it virtually all of the time IMO.

I know I for one couldn't react as fast or modulate the brakes anything like so effectively. For those who think they can - good luck with it...!

Alan