QuestionQUESTION: I’m having problems with the brakes on a 1992 Oldsmobile 98 with power brakes and ABS. I installed a rebuilt master cylinder. I bench bled the master cylinder. Then bled the master cylinder on the car and all four wheels numerous times. I do not get any air when bleeding. Now when the car is not running the brake pedal is nice and firm, but when the car is running the pedal goes clear to the floor. I disconnected the vacuum to the booster and drove the car around the block. The pedal had very little movement and was firm (not spongy), but of course it took a lot of foot pressure. Other than needing a lot of pressure the brakes worked well. Re-connected the vacuum to the booster and the pedal went all the way to the floor again. Any advice on fixing this problem would be greatly appreciated.
Vic
ANSWER: I need your VIN number to determine whether you have the Teves II or Teves IV ABS. I would try the bleed prociss once more. This time you should disconnect the sensor and bleed at the master cylinder for each brake, and start with the brake farthest from the master cylinder.
Also try: Without a scan tool, open the front bleeder screw at the modulator. There are two, so be sure you open the front one. Then bleed the modulator. Close the screw, then bleed both front brakes starting with the right one first. After checking for a firm pedal, drive the vehicle above three miles per hour. The controller will automatically reset the system by commanding the rear motor to run to the home position. Once this has occurred, you can stop the vehicle and bleed the rear brakes.
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QUESTION: I am sorry for the inconvenience of the follow up question. But in your first response you implied that you could give better (more accurate) information if you had the VIN of my car. So I sent it. Especially since you suggested bleeding the ABS modulator using the bleeder valves. But my modulator has no bleeder valves. Reference question 4894833 and 4894919.
Answersounds like you have a Tievs II ABS. To diagnose the system, a scan tool is required (DRB III or equivalent). Fault codes are displayed as messages on the tool. Each message will indicate a particular circuit or component. You must then refer to the appropriate diagnostic chart in a service manual to isolate the faulty component in the circuit or confirm the fault.
I have changed/serviced ABS many times and have not had this depth of problem. Autozone does the "loan-a-tool" program for a $20.00 deposit. I would not buy the scanner. Just rent it. These are very easy to use.
You need for help is no inconvenience. That is what I am here for.
