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Discussion Starter · #1 · (Edited)
Hey guys,

Background:
My brake pedal has been squishy for a while, and I noticed my drivers side rear rotor was rusty. I assumed the caliper was seized open (I already rebuilt my front calipers after they began to stick). I bought a new rear caliper, and when I went to bleed the line, no fluid would come out. I opened the soft line going to the caliper, and it was not clogged.

After reading some posts with similar symptoms, I decided to crack open the "HL" line at the ABS module (the rear drivers line), and it was bone dry - no fluid would come out.

It appears I have a stuck valve in my ABS module (no ABS warning lights on the dash).

I've purchased the INPA cable from amazon - I read one post where someone "fixed" their stuck valve by simply cycling the ABS pump and valves with the software. I will try this.

Question:
If I can not free my stuck valve with the software, can the hydraulic ABS module be serviced at home similar to the vanos solenoids?
Or should I send the module away to be rebuilt by one of the eBay guys?

Thanks for the help!
 

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So, I’m going through the exact same thing with my M5 on the passenger rear. I’ve been fighting it for about a month now. Same exact thing as you. Noticed rusty rotor and thought it was a stuck caliper. Then when installing stainless brake lines I noticed no fluid coming out of the hard line at the rear right. I removed the line coming out of the hydraulic unit and didn’t find any brake fluid coming from there either. Tried cycling the valves using INPA with no luck. I purchased a known good hydraulic unit from Clemster and had it installed and bled. Didn’t fix my problem. My Indy believed it was due to a faulty abs module. I purchased a tested and rebuilt abs module, installed it and coded it and the problem persisted.

After chatting with another guru, he suggested it could be my master cylinder. I have an E65 master cylinder on the way although I have low expectations. The previous owner changed the master cylinder 2000 miles ago. Unless it was faulty out of the box I can’t imagine it’s the source of my problem. I guess we’ll find out.


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I removed the line coming out of the hydraulic unit and didn’t find any brake fluid coming from there either.
I assume you checked to see if fluid was coming from the input side of the hydro unit? If you aren't getting fluid from those lines, the blockage is not in the hydro unit. I had similar issues, took forever to get it sorted. A new hydro unit from BBA reman and rebuilding the calipers addressed my problems. Now its time to upgrade to an E65 MC.
 

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Discussion Starter · #4 · (Edited)
I solved my problem today.

I ended up buying a second-hand ABS module from eBay - it came with the hydraulic valve body, and the electronic module still bolted together.

I took my ABS module out of the car, and swapped my electronic module onto the second-hand valve body. By reusing my electronic module, I did not need to program the eBay unit with my vin.
950434


With my broken valve body on the bench, I used compressed air to verify the rear drivers side valve was stuck. When I blew air into the rear master cylinder input to the valve body, air only came out of the passenger side brake line port. No air would come out of the rear drivers side port. Since I no longer need my broken valve body, I used it as a sacrificial experiment to try and "un-stick" the valve. I was somewhat successful using denatured alcohol and compressed air to free up the valve. Its challenging, because you can not easily disassemble the valves like the vanos.

As you can see in the image below, the valves seem to be pressed into the valve body, and not easily serviceable.
950432


There are no moving parts exposed - those "bullets" do not move, so you can't manually free up the valves by wiggling them with your hands.
Anyway, I just kept pushing denatured alcohol through the ports, and they eventually freed up.
950433


Here is a video of my process - as you can see, the HL port (the plugged port), is starting to bubble and free up. It got better the more I did.
Attempting to clean an e39 M5 ABS valve body
(copy my process at your own risk - I did not use this valve body - I used my second-hand unit from ebay - screwing with your brakes is potentially dangerous - denatured alcohol seemed like the least bad solvent for this task).


I also wanted to write a brief description of the bleed process required after swapping out the ABS module.
Whenever you introduce air into the ABS valve body, a computer should be used to cycle the various ABS valves and pumps while bleeding the calipers to release any trapped air in the ABS valve body. Getting a computer setup to run the bleed procedure was arguably the hardest part of this project.

There are 3 pieces of software that can be used to cycle the various ABS valves and pumps:
1) INPA
2) ISTA+ (same thing as ISTA-D)
3) DIS

All three pieces of software require the same USB to ODB cable that can be purchased on amazon, or eBay, or by some guys on the forum. Just search for "K+CAN K+DCAN USB". It is critical you buy a cable that has a little toggle switch on the ODB port. This switch is required for e39 cars. If you buy a cable without the switch, it probably won't work. These cables are made in China and relatively poor quality. I needed to repair mine out of the box - one of the wires hooked to the switch came loose, and required some soldering to fix.

The INPA software is the easiest to get running on your laptop.
Follow this guys tutorial - he has a link to the software in the video description:
The EASIEST Setup Guide INPA and NCS EXPERT

However, the drawback with INPA is that it does not automate the bleed process. For e39 cars, INPA only allows you to toggle the ABS pumps and valves manually. I suspect this would work perfectly fine, but I do not know the exact procedure. I suspect you would just click and toggle the valves over and over while you bleed each caliper.

ISTA and DIS have an automated bleeding process with step-by-step instructions built into the software - I believe this is the process a dealer would use. However, the drawback to ISTA and DIS, is they require super technical computer skills to properly load them onto your laptop. You have to run software to run a "virtual" computer inside your computer, because DIS runs on Linux....all sorts of crazy complex stuff. I think it takes hours and hours to get them loaded.
Rather than waste my weekend trying to install ISTA or DIS, I purchased a hard-drive from eBay with all 3 software packages and Windows already installed. I literally plugged this hard-drive into my laptop, and 5 minutes later I had ISTA, DIS, and INPA running.

(I believe ISTA and DIS can also be used to code a second-hand electronic ABS module to your vin - this wasn't required for me, because my electronic module was not broken).

I used ISTA while I bled each wheel and simply followed the instructions shown on the computer screen. The procedure requires a "power bleeder" to force brake fluid through the system at ~20psi. I bought the "Motive Products - 0100 European Power Brake Bleeder Kit" from Amazon.

It worked great - brakes feel amazing for the first time in ages.
I'm very happy to have this problem solved.
Whenever I successfully tackle a project like this, I say to myself "not today car gods"
 

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Great work diagnosing the issue and thank you for posting the details. I'm experiencing the exact same issue, same wheel (left rear) and everything. Seems like my DSC hydro unit is at fault too.

Any idea if cleaning the hydro unit was successful? I know it was just an experiment and you installed the other/eBay unit, but wonder if a hydro unit can be salvaged by just cleaning it out.

Thanks again
 

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Discussion Starter · #6 ·
Great work diagnosing the issue and thank you for posting the details. I'm experiencing the exact same issue, same wheel (left rear) and everything. Seems like my DSC hydro unit is at fault too.

Any idea if cleaning the hydro unit was successful? I know it was just an experiment and you installed the other/eBay unit, but wonder if a hydro unit can be salvaged by just cleaning it out.

Thanks again
Hey Sweeney,
Glad I was able to help. I was able to somewhat unblock my hydro unit. When I first started to clean it, no air would flow. After spending 10-15 min cleaning it with compressed air and alcohol, the clogged port does flow air, just not quite as freely as the other ports. I would say give it a shot. Try cleaning it on the bench, and if your clogged port frees up, re-install. If your clogged port doesn't clear up, you'll probably have to buy a used replacement.

Overall, the project seemed daunting for me at first, but in hindsight, it wasn't very challenging. Getting the computer to run through the brake bleeding process was the hardest part to figure out.

Are you planning to get a computer setup to help bleed the ABS after you fix the clog?
 

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I'm going to try to clear HL this evening. If that doesn't work then I also have a used DSC assembly on the way from eBay.

My scan tool can cycle the DSC pumps and solenoids. That paired with a pressure bleeder should be sufficient to bleed the whole system.

Cant wait to have a firm pedal again....
 

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Discussion Starter · #8 ·
I'm going to try to clear HL this evening. If that doesn't work then I also have a used DSC assembly on the way from eBay.

My scan tool can cycle the DSC pumps and solenoids. That paired with a pressure bleeder should be sufficient to bleed the whole system.

Cant wait to have a firm pedal again....
Awesome! Sounds like a good plan. Good luck, and let me know if you have anymore questions.
My pedal feels 100x better after fixing the clogged hydro unit.
 

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is this why so many experience soft pedal and lacking initial grip at breaking?
 

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No luck cleaning HL on the DSC hydro unit. I'll swap it out when the used ebay DSC assembly arrives, fingers crossed that one works!

For some reason the brake pedal feels great now. I can't think of any good reasons why though.
 

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It was for me. I had multiple issues but replacing the hydro unit was the primary driver. Like IceMan said, like a 100x improvement.
I read about this here on the forum before. My braking performance gets worse as my speed increases. Meaning, if I’m traveling at 100mph and hit the pedal, it feels lots worse than from 40mph. Occasionally they are very sharp and immediately stop the car, sometimes there is no grip. I did have the DSC light while driving but it went away on its own. I will have to do what you did and clean the system buy disassembling the unit and flush solenoids?
Supposedly they are same as the vanos solenoids.

FYI. Isn’t there an online service that fixes these? I could swear I read it somewhere about it.
 

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BBA reman rebuilds them, others probably.

Occasionally they are very sharp and immediately stop the car, sometimes there is no grip
Not sure what you mean by grip. This could be your pads not being at sufficient temp to give you the same initial bite. Symptoms of a clogged ABS hydro unit are excessive pedal travel or fluid not going to one of the calipers.
 

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BBA reman rebuilds them, others probably.



Not sure what you mean by grip. This could be your pads not being at sufficient temp to give you the same initial bite. Symptoms of a clogged ABS hydro unit are excessive pedal travel or fluid not going to one of the calipers.
Brakes don’t have the same bite force and longer travel, I’m on oem Bmw pads btw.
 

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Unfortunately OP's cleaning technique didn't work for me, but replacing the hydraulic unit did the trick. Got a firm brake pedal and fluid at all 4 corners now. Finally
 

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Unfortunately OP's cleaning technique didn't work for me, but replacing the hydraulic unit did the trick. Got a firm brake pedal and fluid at all 4 corners now. Finally
Where did you source the replacement?
 
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