Brake Question

#1

I have an 87 325i. I think it has ABS. It was made in May 1987. My right side tires seem to lock up prior to the left side. I have never felt any “ABS Pulsing” prior to lockup. Any ideas on what’s wrong? I have installed new Hawk HP PLUS pads all around - getting ready for DE’s. Rotors were not changed out but they were fairly new and unscored. Also installed the brass bushings on the front calipers and ATE Super Blue. Pedal feels good. Just wondering why the right side locks up.

#2

Sounds like you’ve got 2 issues…Right side getting more braking force then left, and no ABS.

If ABS light is not on, replace it’s bulb. The bulb has to work for the system to work.

How sure are you that it’s the right side locking up first? Has it happened many times under different circumstances? This sort of thing can fool you. Detecting lockup can be tricky, and detecting which tire locked up can be tricky.

'87 did come with ABS.

#3

I have never seen the light bulb come on so it must be burnt. I’ll replace this first and see what happens. Thanks!

#4

Replaced the bulb and it stays on. Braking seems linear - no premature lockup on either side. Any ideas on how to start hunting down the ABS problem? Scan tool gives an error code reading “speed sensor not functioning” or something like that. The speedometer works. Could it be an individual wheel sensor? How do i check that?

#5

RacerDan wrote:

If the ABS light goes on before the car moves, check the fusible link in the ABS relay above driver’s left knee. If the ABS light goes on only after the car starts moving, check the wheel sensors.

The fusible link can be repaired with some careful soldering, theoretically. I tried to do that, but ultimately just bought another relay.

#6

Will i be able to see the fusible link burned just by looking at the relay?

#7

RacerDan wrote:

Yes, but you’ll have to take the cap off of the relay. Then look for a thin 1cm long wire near one of the sides.

The purpose of the fusible link is to protect the ABS system from voltage spikes. It’s often blown by welding.

#8

Courtesy of R. Patton, a low tech way of diagnosing the wheel speed sensors is to disconnect all but one sensor. Then drive the car and watch for the ABS light to come on. If the sensor is good, the missing sensors will trigger the light. Repeat with each sensor to find out which won’t cause the light to come on.

#9

jlevie wrote:

I’d heard that before, but I didn’t really understand it. But this time I stared at it while and tried to figure out how the “disconnect 3 sensors” idea could work. Then it came to me.

A working connected sensor will tell the computer that the car is moving. Which is when the disconnected sensors trigger the ABS light.

But eventually you’ll have a non-working sensor that is the only one connected. And in that scenario, the car won’t realize that it’s moving. And therefore the disconnected sensors won’t trigger the light.

#10

Ranger wrote:

[quote]jlevie wrote:

I’d heard that before, but I didn’t really understand it. But this time I stared at it while and tried to figure out how the “disconnect 3 sensors” idea could work. Then it came to me.

A working connected sensor will tell the computer that the car is moving. Which is when the disconnected sensors trigger the ABS light.

But eventually you’ll have a non-working sensor that is the only one connected. And in that scenario, the car won’t realize that it’s moving. And therefore the disconnected sensors won’t trigger the light.[/quote]
We have a winner!