1986 ABS - modulator valve test and/or repair
03-28-2024, 10:29 AM
#1
Racer
Thread Starter
1986 ABS - modulator valve test and/or repair
Coming back to ABS issues on a 1986 coupe...
After this https://www.corvetteforum.com/forums...-light-on.html and this https://www.corvetteforum.com/forums...-test-run.html thread, I came back to tackle the issue again today.
Problem: no test cycle upon take-off, then warning light on
Normal brakes (ABS non-functional) work perfectly. Pls read above mentioned threads about what I have already done. In addition to swapping all relays I also swapped in another (used) controle module, didnīt help.
I recently performed all tests mentioned in the FSM (no tester, of course) once more: Test A, B and C table A and B check out, on table C I get no readings. Test D I get OL in both directions, but continuity only in one direction, so should be ok. Besides, if I understand correctly, the diode only switches on the warning light. Test E un-tilted is ok, I could not reach the switch to tilt yet. Test F and G table A and B ok, table C I get only 0,4-0,6 milli ohms with the relay on and OL and 0,9 ohms with the relay removed. Most of the above hints at a faulty modulator valve.
The modulator valve, if obtainable at all, is between 500 and 900 USD.
Before I shed out this much money, is there a test I could perform on the modulator valve to confirm itīs bad? Furthermore, is the modulator valve repairable? FWIW: I can get the pump running when I apply +12V directly to pin #9 on the valve body.
One more idea: althought the wheel sensors have the correct resistences and look ok upon visual inspection, is there a way to check if they deliver voltage and if those are in spec, with the vehicle NOT driving? Like jacking up one wheel at a time and have somebody spin it by hand?
After this https://www.corvetteforum.com/forums...-light-on.html and this https://www.corvetteforum.com/forums...-test-run.html thread, I came back to tackle the issue again today.
Problem: no test cycle upon take-off, then warning light on
Normal brakes (ABS non-functional) work perfectly. Pls read above mentioned threads about what I have already done. In addition to swapping all relays I also swapped in another (used) controle module, didnīt help.
I recently performed all tests mentioned in the FSM (no tester, of course) once more: Test A, B and C table A and B check out, on table C I get no readings. Test D I get OL in both directions, but continuity only in one direction, so should be ok. Besides, if I understand correctly, the diode only switches on the warning light. Test E un-tilted is ok, I could not reach the switch to tilt yet. Test F and G table A and B ok, table C I get only 0,4-0,6 milli ohms with the relay on and OL and 0,9 ohms with the relay removed. Most of the above hints at a faulty modulator valve.
The modulator valve, if obtainable at all, is between 500 and 900 USD.
Before I shed out this much money, is there a test I could perform on the modulator valve to confirm itīs bad? Furthermore, is the modulator valve repairable? FWIW: I can get the pump running when I apply +12V directly to pin #9 on the valve body.
One more idea: althought the wheel sensors have the correct resistences and look ok upon visual inspection, is there a way to check if they deliver voltage and if those are in spec, with the vehicle NOT driving? Like jacking up one wheel at a time and have somebody spin it by hand?
04-01-2024, 05:33 PM
#2
I sure wish you were near me in So Cal as I have the factory tester. Lift the vehicle to be able to spin the wheels and it makes short work of diagnosing. You can jump power (with a ground also) to the solenoids to check if they are pumping. If they were stuck closed you would have a dragging brake for that solenoid, or they could be stuck open even if pumping when jumped. As for rebuilding a solenoid there is a company that sys they can rebuild the whole ABS pump, but they are not cheap. I pulled mine apart and cleaned it and replaced the solenoids with another pumps. Sometimes you can find a used pump on here or ebay, or check the junkyards.