E60 ABS hydraulic unit

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jtlittle
Posts: 14
Joined: Sat Aug 09, 2008 12:35 pm

E60 ABS hydraulic unit

Post by jtlittle »

The hydraulic unit in my 5 series causes the left front brake to malfunction. Symptoms are:
1. Braking at highway speeds causes the car to veer to the right before straightening out almost immediately. The car stays in the lane but the problem is very noticeable.
2. If I bring the car to a stop at a red light and hold the car with the foot brake until the light turns green, the car resists movement.
3. If I stop on an incline and release the brake, the car does not roll freely initially. After more than a minute the car will very slowly begin to roll.

I have replaced the caliper myself and the dealer replaced it again under the parts warranty.

Based on the above, Im pretty sure the hydraulic unit is the problem. My guess is there is a "lazy valve" that responds slowly when pressure is added or released at the pedal.

The dealer price to replace the unit is prohibitive (>$4000 parts and labor).
The dealer says the hydraulic part and the electronic part of the unit are inseparable so replacement with a new unit requires reprogramming.
I'm looking for confirmation of my diagnosis or alternative opinions.
Also, does anyone know where I can have the unit rebuilt?

afadeev
Posts: 277
Joined: Mon Sep 28, 2009 9:02 pm

Re: E60 ABS hydraulic unit

Post by afadeev »

jtlittle wrote:The hydraulic unit in my 5 series causes the left front brake to malfunction. Symptoms are:
1. Braking at highway speeds causes the car to veer to the right before straightening out almost immediately. The car stays in the lane but the problem is very noticeable.
2. If I bring the car to a stop at a red light and hold the car with the foot brake until the light turns green, the car resists movement.
3. If I stop on an incline and release the brake, the car does not roll freely initially. After more than a minute the car will very slowly begin to roll.

I have replaced the caliper myself and the dealer replaced it again under the parts warranty.

Based on the above, Im pretty sure the hydraulic unit is the problem. My guess is there is a "lazy valve" that responds slowly when pressure is added or released at the pedal.

The dealer price to replace the unit is prohibitive (>$4000 parts and labor).
The dealer says the hydraulic part and the electronic part of the unit are inseparable so replacement with a new unit requires reprogramming.
I'm looking for confirmation of my diagnosis or alternative opinions.
Also, does anyone know where I can have the unit rebuilt?
I would have guessed sticking caliper as well, but you already replaced that. Did you rebuild or replace it altogether?
How do the caliper guide bolts look?
Have you tried bleeding the brake fluid a few times?

Do the right front pads wear significantly faster than the others?

If all of the above failed to improve the situation and the pads are not wearing differently than those on the left front corner, I would try to shop junk yards for used ABS pump. Should be significantly less expensive than new, and would be the next logical step in "throwing parts" at the problem approach.

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jtlittle
Posts: 14
Joined: Sat Aug 09, 2008 12:35 pm

Post by jtlittle »

Thank you for your response.

I totally replaced the caliper both times. I didnt't notice any unusual wear on or damage to the bolts but I can't say that I gave them much attention while I had them out.

When the dealer replaced the caliper, I had him bleed the brakes.

I haven't driven the car much lately and I replaced some fairly new pads when I replaced the first caliper so the pads are not worn enough to see a pattern. I do have the old pads. The left side pads do have a faint 'hot iron' smell.

You gave me a couple of good ideas.
I will recheck the bolts and look for uneven pad wear.
I'm not sure about the bleeding. Bentley says normal bleeding procedures don't work with this system.

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