C4 Brakes

My 93 did that some and I found out it was the beginning of the end of my master cylinder and booster. Check for vaccum leaks around the booster and flush the system and replace the fluid.

sounds like it may be your booster acting up..

What did the brake pedal feel like?

The first time I used the brakes in my C4 this morning, the ABS pump kicked in, the pedal pulsed, and there was no braking power at all. I backed off and tried again and it worked normally. This was in a sharp corner while slowing down for a red light, but not even close to the G's necessary for tire slippage.

Weird.

I have had a similiar problem with my 91. A couple of times when I've been parking the vette in front of the house, live on a small hill, and i'm creeping up to the neighbors car with my foot lightly on the brake, something triggers the ABS, it pulsates and pedel goes to the floor, along with car rolling forward. its happened a couple of times and so far i've been lucky in that I don't hit anything. now i slide the trans into neutral (automatic) and coast. I was figuring it was the ABS thinking I was skidding and trying to "pump" the brakes for me.

Now, do I have a problem in my ABS system?

Rev's problem might be a screwed up or intermittent lateral 'g' sensor. (Control unit doesn't know that the car is being cornered and thinks it's a straight line skid.) Might be worthwhile to see if this happens in both left and right cornering. Great Saturday morning workout on a big empty parking lot.

Not enough clues on Mike's issue: Could be a test sequence if the engine had just been started--a pedal pressure change is normal during test but the pedal going to the floor is wrong. Can't tell whether the problem is happening after the car had been driven above 8 mph (once it's gone through self-test and arming) or if this happens right after the car is started and first moved (ABS unarmed). Maybe too, this is a brake booster problem that's firming up the pedal making it feel like it's against the bottom stop. The human critter isn't much good at sensing control positions but is damn good at sensing force.

First off, make sure all three warning lights are working. Bleed the brakes. Check the wiring to each wheel sensor. Remove, inspect and re-connect the cable connectors to the control unit--mine are typical old-style Bosch connectors with unplated copper contacts--over the years, oxidation builds up on the contacts.

There are resistance checks for the lateral 'g' sensor and wheel sensors but each must be disconnected otherwise the juice from the ohmmeter will destroy the old-fashioned solid state stuff in the control unit. Better to find a good brake shop that has a Bosch ABS diagnostic unit. This ABS control was used on several makes of cars including Chryslers of late '80s vintage. You can find good service at other than the dealer.

HTH.... PJ

Mike wrote:

Understand the test sequence and don't believe its that. I see the ABS light come on and feel a short pulsing in the pedel (a second or two). No this is more of i'm creeping slowly forward in a downhill direction. haven't noticed it on level ground but suspect some gravity is working in there.

Not sure what you mean by all three warning lights. Can you point me to where the control unit might be? Have the manual but am at work so just curious.