I am still seeking to fix an ABS problem on my 87
The anti lock light comes on when i roll over 4mph.

I did all the resistance and voltage checks and they are in specs.
I replaced one wire that had resistance in it to the front left sensor.
The plug itself was shorting out and must of cracked internally. I installed new front sensors and light is still on.

Checking the rear sensors all the wires were ok including the plugs.
When spinning the rear wheels i notice a flucuation on the DVM.
Looking down the hole i see some of the teeth are shiny were it looks like it was rubbing. This is only on 4-5 teeth and only a little bit on the edges.

Could this be from the wheel bearings wearing out allowing it to touch?

Is it possible to shim the sensor up a few thousanths of an inch to increase the air gap?

There is no diags in the 86 and 87 making it hard to find the source of the problem.

I can't get it to the dealer because the brakes stick and lock up the wheels after a few miles. Not sure if it is the calipers sticking or the ABS making it stick. It says in the service manual in bold letters that "the brakes can't apply on their own" If i put the car in neutral it will slow to a stop without touching the brakes as if all four brakes are on. When i feel the rotors they are all warm or hot if i drive further. Makes it hard to test drive it for on the road tests.

One strange thing is when the car is on jack stands and in gear with only the rear tires spinning the anti lock light doesn't go on. When I hit the brake pedal the anti lock system activates and stops the wheels.

It is just like it does when it worked properly. Can this be used to diagnose the problem?

Anyone have any input on what to try next?

 

The jack stand test seems to point to one/both of the front wheel sensors being the culprit.

Jake

 

I tried unplugging the sensors in front for a test. As expected the light went on right away.

So I decided to try installing the NEW front sensors with the spacer and o-ring installed raising the sensor 1/8 inch. To my surprise the anti lock light did not go on at 4 MPH.



But when my foot is on the brake pedal while i roll to the 4 MPH secondary test it does not activate like it should. Normally you would feel a pulsing in the pedal.

I plan to find some sand to test it to see the motor will activate wen locked up on a slippery surface. This will confirm if the anti lock system is working or not.

Even thought the light is not on the brakes are still dragging after a few miles of driving. If I get the car going to 30 MPH and put it in neutral it will come to a stop faster than it normally should without pressing the brake pedal.

It could be the calipers sticking.
Or it could be the anti lock is not releasing the pressure
Anyone know if that is possible?

I been planning to rebuild the calipers and add SS hoses soon as I found the fault with the light.

Any help would be appreciatted.

You guys and gals have any ideas ?

 

You have brake calipers that are dragging on the rotors. The ABS only pulses the brake line pressure, it will not put out constant pressure and when the ABS is active you can hear the ABS pump run and the brake pedal vibrates. You need to find a GM dealer that has a C4 ABS tester which tests the ABS system and will indicate where the problem is. My ABS light stayed on after a longer than normal test on my 87 and I tried a new ABS computer, then looked at the waveform on an oscilloscope from each wheel sensor and found them to be all alike and normal. Finally, my mechanic brought home the ABS tester from the GM dealer he works for and we jacked up the car and spun each wheel and performed the tests asked for by the tester and it said the left rear sensor was defective. After replacement my ABS worked and has since then.