ABS operation : slow?

Digitalchaos

Registered User
It seems when I engauge my brakes and the road surface is slippery enough to activate the ABS, the pedal will pulsate at about the rate of 1.5 times a second. It moves about 1/2 to 1" while doing this, and the wheels can be felt locking & unlocking.

The only other ABS system I have experienced was on a modern GM economy car, and seemed to work much faster.

Is this normal for this system? I always thought the system was suppose to be capable of "pumping" the brakes much faster than a human, yet I can go about twice the speed it seems to work at.

Thanks in advance..
 
Your accumulator may be on the way out. Mine did this just weeks b4 the Brake and Anti lock light would flash when I pressed the brake pedal.

Then after that I had a panic stop that made me pull the foam out of the seat with my cheeks, because I could hear the pump running and feel the pedal dropping as I came up on a stopped car. The breaks didn't do anything for about 20' then they locked. Very scary.

Jeff
 
This is normally what I would say but this car is a '93 with Teves Mark IV, and to my knowledge no accumulator.

I figure it must either be air in the system, or a bad brake booster?

Only problem is I am not sure and to guess either of these problems would run a couple hundred dollars.

What do you think?
 
I didn't even look at the year model, but I thought the change didn't come in until 94'. Since I have only really messed with early models and 94-95 models ignore me.

Jeff
 
I've got a 95 and it does the same thing (on ice anyway). I also thought it was odd. Other cars with ABS that I have driven (all newer- 2000+ rentals) seem to pump the brakes at what seems like 2-3X as fast as my SC. These experiences with the rentals where all on dry pavement, however. I just chalked it up to being a 10 year older design. But maybe there is a problem here.

I would hope that the self diagnostic would detect it if it were a real problem, but maybe this is just marginal enough not to trigger a code.

Here is my speculation on the situation based on my limited understanding of how ABS works and the physics:

Possibly it (SC) does this on ice only and on dry pavement the ABS would cycle faster.

My reasoning is that on ice if a wheel locks up on brakeing, the ABS detects this and releases the brake on that wheel. After the ABS releases the brake to allow the wheel to turn, the wheel would tend to come back up to speed more slowly then it would on dry pavement, because of the lack of traction / friction between the moving road surface and the non-rotationg tire. Until the wheel comes back up to speed, the ABS keeps the brake "off", lenghtening the period of the ABS cycle.

Once a tire has lost friction (either locking up on braking or breaking loose from a "burn out"), the coefficient of friction between the tire and road surface which applies to the situation switches from the "static coeficcent of friction" to the "dynamic coefficent of friction" (much lower). I may have the names for the coefficients wrong here, but you get the idea.

Hopefully we can get some more responses here from 94-94 owners, or a real brake expert.
 
I know on a '95 or so Cavalier I rented once the ABS brake operation on thick fluffy road snow was incredibly fast.. shook the pedal and the car stopped fast with almost no wheel pause.

I believe there are valves somwhere in this system which open and close for the ABS.. I bet they may start to wear if not maintained. Also I am going to check for locked or semi-locked calipers which maybe could also slow the system?

I agree, it would be informative to hear from others with the 93+ Mark 5 system.
 
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