I am just getting to look at a brake problem on my just acquired 780. Driving it home the brakes felt weak with not a lot of power to stop the car. I did have my ABS light come on. After stopping the car for a short rest the light wnet off.

I know the first thing I need to do is inspect the entire brake system. I have rebuilt every part except power brake boosters on every model up to the 700 series. I have never done anything with ABS other than change rotors and pads. My question is, after you check out the "standard suspects" of the brake system, if the ABS is not working will you find a great difference in the feel of the brake pedal or do you rely on the dash light to let you know the condition of the ABS?
The question might sound strange, but I have never driven a car that had a ABS that needed attention. Any help would be greatly appreciated.

You can get system fault codes from the ABS - see the 700FAQ.

But a simpler piece of preventive maintenance you can do, is to clean the front wheel sensors. They're magnetic, and pick up all kinds of road debris and rust filings from the rotors. Use masking tape or something similar to clean them off, and reinstall.

This could cure any false activation of the ABS system and possibly the codes in the system. It won't increase stopping power or brake feel however, if there is a different problem.

You may need to bleed the system or you could have a stuck caliper or glazed pads. Inspect for even wear on the pads and see if anything looks out of the ordinary.

Pedal feel is soft, IMHO in all 700 cars. Bleeding the system can help but may not alleviate it completely.
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Rob Bareiss, New London CT ::: 87 244DL, 88 245DL, 90 745GL, 84 242DL project, 89 244 parts, 88 244DL to replace the 87

Thanks for your imput.

I found one frozen front slide and one ready seize. Cleaned up, re greased, should be good to go there. The rear rotors are polished like mirrors. Looks like time to replace.

Thanks for the tip on the sensors. Will do that and also power bleed the system for a fluid change.

Neal
98 S90, 89 780, 93 940, 80 244, 2-65 P1800 and a 60 PV544 (they keep following me home)

Good luck on getting fault codes on the earlier 700 series cars as they do not have the "blink box" under the hood and diagnosis on them is more of a trial and error thing and a matter of when the light came on.

The brake pedal should feel no different if the ABS light is on or off. The ABS system only functions when it is needed, i.e. panic stops etc, and the rest of the time it is passive and has no active part in normal braking sequences.

Depending upon when the ABS light comes on will dictate which area to look in. If you start the car and it never goes out then you have a hard fault in the system like a blown transient surge protector fuse or faulty control module. If you start the car and the light goes out and then comes right back on then you have to look for a hard wire fault like a broken wheel speed sensor harness or something. If your light goes out and then comes on above about 19mph then you need to look into dirty/faulty wheel speed sensors. The early cars did not have the capability to flash codes but they do have a series of tests and you need to know the sequence of the tests and what is being tested in each test to point you in the correct direction. Cleaning the front wheel sensors is your best bet. When they first came out with ABS we were running the diamond shaped Bosch sensors and never had a problem with them, the next year they went to a sandwich style of sensor made by VDO and they were pretty much garbage. If you have the sandwich style ones you may end up having to replace them, but regardless of their origin clean them up first and see what happens.

Mark

The light was caused by the pile of "crud" (good technical term) on the sensors. The poor pedal was the frozen slides, glazed rotors and pads. Had rear rotors turned to deglaze and the front since they are slotted a light glass bead knock off the glaze. Sanded the pads. This car now stops great everything working to perfection.
Just a note- The PO had put a disc behind the wheel to stop brake dust from getting on the wheels. I my opinion this was the cause of most of the glazing of the brakes. I have always looked for better ways to cool the brakes. Your wheels may stay clean, so you will look good as you wreck your car because you can not stop :-)

Thanks for all help provided by everyone.

Neal