Master Cylinder

[curlybandit]

Hi all. Well, I think my master cylinder is acting up. My car is a 1991 Buick Regal GS Coupe, 3.8L with ABS. Actually, I think it is one of the ABS solenoids because the ABS light flashes on and off continuously, and the check guages light comes on occasionally too. When I depress the pedal, I get this funny buzzing sound and some pulsation in the pedal when it buzzes. The geniuses at GM assembled the master cylinder with the pump and the ABS solenoids in one unit, so basically, you if you have a problem with one of the sensors, you have to replace the whole unit. At least this is the news I'm getting from everyone I ask, and this thing is NOT cheap. Does anyone have any suggestions where I can purchase one without having to sell a kidney? Are there any sites I can check out, or used parts distributors? I've tried some local scarppers, but nobody has anything right now. Thanks.

[Ruley73]

The first thing I'd check would be your alternator. Believe it or not ,this can cause your ABS to operate irradically. The ABS requires ALOT of power to operate and is the first thing that the computer disables when the charging system is running low on power. This triggers the orange "ABS" light to come on in the dash to warn you that the ABS has been disabled. Your brakes should still operate properly, but they will lock up during a hard stop because of the ABS being disabled. It is still "safe" to drive your car with no ABS, just "not as safe" would be the best way to put it. This is simply because the ABS does decrease your stopping distance during an emergency stop. This may also cause your "Check Gauges" light might come on (i.e. check the Voltage gauge if equipped) because your brake lights also require a lot of power - on top of any other running accessories (i.e., headlights, A/C or heater, radio, rear defogger, etc.).

If the alternator is fine, I would take the car to a shop and have the ABS computer scanned. The ABS computer stores codes when the orange "ABS" light comes on the same way your engine computer does when the "Service Engine Soon" light comes on. This should help to diagnose the problem much quicker.

[curlybandit]

How would a failing alternator explain the buzzing sound when I depress the pedal, and the vibration in the pedal when it buzzes? If I press the pedal once breifly, it buzzes. If I hold the pedal for a while, like at a red light, it will buzz once every three or four seconds. The volt gauge holds steady above 12 volts when driving, so I'm pretty sure that's not it. I guess I can get the ABS comp scanned. Any other advice?

[Ruley73]

Yeah, you're right that's definitely not an alternator problem. Many times people overlook a bad alternator when the "ABS" light comes on. I just wanted to make sure that wasn't causing your problem before you replaced some costly parts for no reason. Unfortunately, I don't have anymore advice for you. I would just get the ABS computer scanned and go from there.

[curlybandit]

Ok. I will. Thanks for the help. We'll see what happens.

[curlybandit]

Ok. I tried to pull the ABS code using the tried and tested "paper clip" method. Well, not so much luck. My understanding is that my 1991 Regal has the OBD-1 system with the ALDL connector with 12 inputs. Such an input should look like this:
O O O O O O
O O O O O O

coded:

F E D C B A
G H. . . . M

Now I know that you can pull engine codes from connecting terminals A and B and then turning the key to the ON position. I had leaned that you can pull ABS codes by connecting A and H, unfortunately, my ALDL does not look like the above. It looks like this:
O O O O X X
O O X O O X
(where O is empty space and X has connector)

I tried to pull an ANY code using the conneectors that were there, but nothing happened. I guess I'll have to bite the $80.00 or so to get the "pros" to pull the code. Any suggesions?

[curlybandit]

Ok. I pulled the ABS code. It's code #62, "Low Accumulator Precharge". So... from what I'm told, there is a resevoir that stores pressurized air required for the ABS system to function. It appears that it's not holding the charge. There may be a leaky valve or something... At least this is what I've been told. Anyways, is this repairable, or am I looking at replacing the whole unit?