[MP525i]

Hey Guys,

In a bit of a situation. So, I noticed a while back that my car started drifting to the right when I was braking. Nothing crazy, but I thought I'd check on it later. Life got in the way, and a couple months go by. The issue gets slightly worse and I find out my driver's side front brake is not engaging. I finally end up taking it to my mechanic.

He said that it was the Master Cylinder and it needs to be replaced... $1k. This is a local guy I use for basic stuff, European cars aren't his specialty. I bring it to a BMW mechanic (NOT the dealership). He takes the car out and says it's the ABS Hydraulic Unit is bad and needs to be replaced.... $4k. After I get my car back, I'm hanging out with local friends (and friend of friends).. One of which is a diesel mechanic. I tell him the story and he think's is the hose to the caliper and he's seen it multiple times (... on trucks mind you)....

I'm not sure what is broken. Brakes are working to the other wheels (brake dust is evident). The pedal is not spongy in any way. ABS kicks in when I brake hard (tested true multiple times). I'm not leaking ANY brake fluid. These are the signs of failure for the Master Cylinder and the ABS Unit.

I'm going to be taking off my wheels this weekend and putting on the winter wheels. While I have it up, I'm going to check the hose. I figure that's my lowest cost option right now, so I'll start small. Then I'll progress into the more expensive fixes if that doesn't do it.

Wanted to get any advice or feedback as to what you guys think it could be. 3 different mechanics, 3 different opinions...

Thanks for your input.

-Mike

[Unspec]

A good way to tell if it's the caliper or something upstream is to try to bleed the brakes at the front right caliper. If you pump the brakes and fluid comes out of the bleed nipple, then it's probably not an upstream device since fluid is clearly moving to the caliper, and it's likely a stuck caliper. If the fluid isn't moving, it's something upstream of the caliper.

[Blue Angel]

Originally Posted by Unspec

...it's likely a stuck caliper.

Have you ever seen a stuck caliper that won't engage? The only stuck calipers I've ever dealt with won't disengage.

The flex line to the caliper could be the culprit (torn reinforcing braids, bulging), but I would think that leads to a spongy pedal. If the pedal is indeed firm there must be something restricting the flow to the caliper. Something blocked in the ABS module certainly seems plausible. A faulty piston seal in the master cylinder would affect two wheels, not just one, and should also lead to a spongy pedal.

I'll keep an eye on this thread, for sure! Looking forward to finding out the cause.

[Unspec]

Originally Posted by Blue Angel

Have you ever seen a stuck caliper that won't engage? The only stuck calipers I've ever dealt with won't disengage.

The flex line to the caliper could be the culprit (torn reinforcing braids, bulging), but I would think that leads to a spongy pedal. If the pedal is indeed firm there must be something restricting the flow to the caliper. Something blocked in the ABS module certainly seems plausible. A faulty piston seal in the master cylinder would affect two wheels, not just one, and should also lead to a spongy pedal.

I'll keep an eye on this thread, for sure! Looking forward to finding out the cause.

Actually, yes. It's rare, but it happens

[ChiltiCoatl89]

Check brake pads, and check Rotors for wear and if it is uneven wear, as mentioned, check the brake lines and check for anything seized/corroded as I know NJ can have harsh winters, do you hear anything when you drive, do you hear like a whooshing sound or feel excess vibration? when driving normally not when applying brakes? You want to ensure it is not something simple and overlooked before you fork over some $mulaah$ for a new Brake Master Cylinder. Please give us updates! When was the last time you changed out the brakes? Have you ever replaced the Rotors? or done any Brake flushes/fluid replacement?

[MP525i]

Thanks for the input guys. I'm hoping to look at various points within the calipers, rotors, lines, etc., this weekend. *hoping to change out my wheels this weekend.

I'll try some of these fixes to help diagnose the problem and keep everybody posted! Might be delayed if I can't get to it this weekend.

Thanks again guys!

-Mike

[Blue Angel]

Definitely want to make sure you know what’s up before shooting it with the parts cannon!

[ChiltiCoatl89]

Please give us an update when you can!

[MP525i]

OK, update time.

Sorry it took so long guys - life got in the way and I just got around to swapping out my regular tires for my winter ones over the weekend.

So, there was zero wear on the rotor and pad (again, driver's side front). I kind of knew that because while the other wheels were getting dirty from brake dust, this wheel remained pretty clean. I took the brake line off - no fluid coming out whatsoever. Inspected the hose and it was clean and working properly.

I'm going to have to hook up my code reader to see if I can test the ABS system. So, doing more research, but the more I dive into this project, the more I'm almost convinced that it is, in fact, the ABS module (which sucks). I'd like to make absolutely sure though, so I'm going to test a few more things out.

I'll continue to keep everybody posted on my progress.

Thanks!

-Mike

[Blue Angel]

Ugh, not looking good! Hopefully you’re able to source used parts if it comes to that… a new module won’t be cheap.

[MP525i]

So, final update.

I pulled the trigger and replaced the ABS Module. Everything is back to working just fine. The job was not cheap (obviously), but the shop was top notch and I've had the car back for over 3 weeks without any issue.

Here's my thought process when making this decision. We're talking about my brakes here. While I'd like to think I (along with my close friends) are great at taking apart my car and putting it back together, I couldn't go messing around with the brakes (one of the components that could save my life). I didn't have all the right tools, and I didn't have the time. The Master Cylinder failure didn't make sense logically as I had stopping power with the front passenger side. And then there was this....

I did recall back to what could have caused this once I understood where this device is located (where the driver's side seat is) 2-3 years ago, I was coming off the main highway onto a local highway. As I was trying to merge (NOT looking forward), there was a ladder in the middle of the road. No big issue as I ran it over without too much hysteria. Looking back, probably jarred something with the ABS module.... FML.....

Anyway - car is all fixed and working perfectly again.

-Mike

[Blue Angel]

You can sleep soundly knowing it’s fixed properly. That’s all the justification you need.

Thanks for following up! Too many times threads are left open indefinitely.