Brake probs upon every initial startup

[metalsoul]

So when I bought my 90 325i the ABS light was on but the brakes functioned fine EXCEPT: Upon initial startup and the first couple of rounds of braking at slow speeds under 25 mph or so, the pedal would pump as I applied the brakes (much like ABS) stutter, then as I sped up and continued to drive it would go away and not return UNTIL the car was sitting again and upon initial startup the next time, and every initial startup for that matter.

I installed new rotors and pads, and inspected and cleaned the calipers, and bled and flushed the lines...but alas, the problem still exists.

Any input is appreciated, thanks!

[jlevie]

What you describe would be a problem with the ABS system, not the brake hydraulics or brakes. It could be as simple as a bad wheel speed sensor, or it could be a bad ABS module or pump. More diagnostic work will be required to figure out where the problem is.

If the ABS light comes on when you switch on the ignition, goes out when you start the engine, and then comes back on after the car is moving, it may be that one or more speed sensors are bad. A simple check of that is to disconnect all but one sensor and drive the car. If the light comes on while driving the ABS is getting a speed signal from that wheel and the ABS module faults because the other sensors aren't reporting speed. Meaning that sensor is good. Repeat the process with each other sensor connected and the others disconnected. If you find a sensor that doesn't tun the light on while driving, it isn't generating a speed signal and is bad.

If the light never goes off from the time you turn the ignition and through start of the engine, the ABS relay, ABS module, or ABS pump could be bad. Start by replacing the ABS relay or replacing its fuse (a search will turn up how to fix the fuse). If the relay is good the next part to swap out would be the ABS module.

[metalsoul]

That pretty much covers my options. I greatly appreciate the info and will test it out tomorrow and keep you posted on my results!

[metalsoul]

you guessed it...Front Right sensor! And I was happy to find that the replacement sensor is only a measly $142. LOL, whatever, at least it was only ONE that is bad! Thanks again jlevie!

[jlevie]

Although it can be a roll of the dice, a used part from a salvage yard is a lot cheaper than a new sensor.

[metalsoul]

Yessir, I got one from Levent being shipped out for $25!