Team,

Big problem here & I can't seem to figure it out.

Cavalier 99 2.4

Approx every 3 or 4th braking, my pedal will goto the floor with very little resistance. The car is slowing down, but I cannot press it down any more. I'm at the mercy of the system to slow me down.. Also, the car feels like its pulling left or right when its doing this.. I have also locked up the brakes a few times because I really had to stand on the pedal to try & slow down..

I have installed 2 new master cylinders & a whole new master cylinder assembly including the attached ABS module.

The master cylinder has been extensively bled up top & at all 4 wheels everytime.

Sometimes the brake pedal works great, other times, the pedal will sink. This can happen within 10 seconds of each other. Its totally random when it doesn't work.

When the car is off, the pedal is rock hard with no bleed down.

I have not had ABS on the car in several years, I recall there being an issue with one the wheel sensors & we never fixed it.

So- brake pedal sucks 40% of the time. 3 master cylinders later, issue still exists.

Any help is appreciated.
Thx

Have you checked for a leak? Like rear wheel cylinders? Other thing is that the abs module may need bled. Seen one at the.shop. you have to use a scanner to cycle it.

Got it figured out today...

Happened to be looking at the front wheel when I was putting it on the lift again. As soon as the wheel left the ground, it moved in some. This prompted me to shake the front wheel, it was moving a good 3/8" back & forth.

Turned out the wheel bearing/hub was bad. Not only was the bearing shot, the 3 T55 bolts holding it on had backed out like 1/16th. So it was loose & bad.

The car didn't make any noise when rolling to indicate a bad wheel bearing..

The loose wheel caused the rotor to wobble, which pushed the brake pads in, which compressed the caliper piston.

So, at random intervals, when the wheel would wobble, the right brake caliper would need 2-3 pumps to tighten the pads up. The other side was fine, so it would still slow down, however, all the pedal travel would goto the loose caliper, pedal feel was soft & the car would pull left & right when it occured..

Seems so obvious now & totally makes sense, but this thing was driving me nuts for weeks due to the randomness..

Both front wheel bearings for good measure, & a new set of pads.

This pig is stopping on a dime now !!!