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soft brake pedal / hydraulic unit

16K views 30 replies 14 participants last post by  mr_g_bock 
#1 ·
Hello,

I think I've read just about all the threads (I think!) regarding brake system issues and based on some diagnosis I think I have narrowed down my issues to the ABS/hydraulic unit - and given I have no codes, I think the hydraulic end is creating the issue (issue is that front passenger corner is getting no pressure/fluid). I even PM'd Clemster who was very helpful on this topic. I have a couple quick follow-up questions which I couldn't quite decipher from the threads:

1. Is our ABS/hydraulic unit the same as found on the 7 series e38? Would such a unit be compatible with e39 m5 if coded to my specific car?
2. It seems any new or used unit, even off an e39 M5, would need to be coded to my car. Is "module masters" still the preferred group to send the unit to for coding to my car?
3. Has anyone actually taken apart the hydraulic part of the unit and refurbished it or "cleaned it out"? My brake line is clear and the brake components in front passenger corner all seem to be in good shape. Master cylinder seems to be in good shape. It seems something in the unit itself is not getting through or clogged.
4. Is there a part number that refers to the ABS (electronic portion), a separate part number for the hydraulic unit and then a part number for the combination? It's a little unclear on this page: http://www.realoem.com/bmw/enUS/showparts?id=DE93-USA-09-2001-E39-BMW-M5&diagId=34_1532. Also if you buy bmw part number 34522285051 on getbmwparts.com do you get the whole thing (ABS+hydralic part) or just the ABS module - electronic part? The prices on getbmwparts.com and real oem are very different, wondering if they are referring to two different things. Here is the getbmwparts page - I think item one is the unit... but not sure which end or if it's the whole thing. https://www.getbmwparts.com/parts/2...=&component=&searchText=&startRow=1&maxRow=10.
5. Finally, does anyone know the actual Bosch part number? I tried to look at the part in my car and I can't figure out what the heck the actual bosch part number is.

As you can tell I'm not a technician or car person - so sorry for my rudimentary questions and if I got anything wrong. My apologies if any of these were previously answered, I've tried to search and find the answers to these and didn't come across anything. If curious, 112k 2002 running great with many sensors / solenoids / thermostats replaced over the years.

H
 
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#2 ·
Ok first RealOEM looks to be hacked it redirects to some site in spanish.. So bare with me because I have no diagram to reference for you.

There are two parts
The Complete unit 34516769536 and then just the electronics /Control unit 34522285051.

It sounds like you're looking for just the electronics. Try FCP they have the Bosch version for 650ish while BMW wants 1200

https://www.fcpeuro.com/products/bmw-abs-control-module-1265950002
 
#3 ·
I would agree that if you have no codes and no dash lights (ABS, DCS, brake) that it may be mechanical, and with soft pedal maybe air in the lines. Have you done a recent brake bleed? You might start with opening the right front line and see if you have flow. (I recommend using a pressure bleeder for this.)
 
#4 · (Edited)
Some things to consider:

- Are you having more than wanted pedal travel BUT still retain good brake force?
- Does the it ever feel softer or firmer under unknown circumstances?

Only reason I ask is that I was in a similar situation. I always had poor pedal feedback even after changing my master cylinder with a new one.

Though for some reason I had good brake force, but I had too much pedal travel to achieve it compared to ALL the other bimmers I've had/driven. I bleed brakes, changed calipers, SS lines, Triggered ABS on dirt roads, nada no change. (ABS sure worked though).

I recently changed the sucking jet pump "Venturi Valve" that controls the vacuum from the intake to the brake booster and by god I think that fixed it. I would check into that, as it would be the cheapest part the check first.
I haven't had much time to drive it around since I cracked the original vacuum hose every so slightly. So I'm waiting for the post man to drop it off tomorrow.

As for a rebuild, Module Masters is still the go to place! And yes, another other ABS unit must be coded to car (I'm not 100% on interchangeability though)
 
#6 · (Edited)
Some things to consider:

- Are you having more than wanted pedal travel BUT still retain good brake force?
- Does the it ever feel softer or firmer under unknown circumstances?

I recently changed the sucking jet pump "Venturi Valve" that controls the vacuum from the intake to the brake booster and by god I think that fixed it.
I remember driving my sisters 3 series thinking how good and responsive the brakes were.

Would you mind sharing the part number or explaining which part this is exactly as I’m experiencing same sporadic symptoms. I drove two other m5 and indeed I do have a soft pedal. I replaced brake booster, master cylinder and bled the system 3x!

Thank you.

Edit: I searched real oem but found no such part.
 
#5 ·
All very helpful - thank you. Based on some diagnosis the line going to front right appears to be working and clear, but fluid will not come out of unit into the line. Part numbers super helpful. Regarding brake feel, all corners are firing except front right, which results in a tug to left under braking. ABS and DSC all working.
 
#8 ·
Problem is OP has two issues, soft pedal and car pulling left. Plus some kind of diagnostic showing right front not getting pressure. Vacuum issue would cause problem #1 but not #2. You might have air in the system plus enough air in the right front line to cause a complete lock. I would do or have done a complete system bleeding, preferably using DIS which activates the ABS unit in a way to vibrate loose air bubbles.
 
#9 ·
So why not just get the hydraulic half from Clemster and avoid the cost and the recoding. If you use the module you have then you should not need to code. It does sound like one of the solenoids is stuck but it is also possible the module is opening a noid even though it should not be, short or something. Maybe get the whole unit and do it in two steps hydraulics first module also if first fails.
 
#10 ·
I am the member Dking078 references. Here's my situation:

I have an S2 with Brembo brakes. My pedal was great for a few years but gradually the feel degraded. I was tracking the car regularly but ended a weekend early last year at Pocono as the brake pedal just sucked.

I have been fighting this problem for over a year.

I replaced the pads with two different compounds - no improvement.

I replaced the braided brake lines - no improvement.

I replaced the master cylinder twice - no improvement.

I replaced the brake booster although the one in the car was fairly new - no improvement.

I replaced the hydraulic DSC unit - no improvement.

I replaced the DSC electrical control unit - no improvement.

After every change I bled the brakes with a pressure bleeder on the MC and a vacuum bleeder at the calipers. I used Autologic to cycle the ABS pump 4 times at each nipple (2 per caliper).

I have run over 7 gallons of brake fluid through the system.

With the engine off, the brake pedal will easily "pump up" and the pedal will remain very hard. Start the engine and the pedal drops almost to the floor - and it's mushy.

The car has been to two shops that could not eliminate the problem. It is currently at a third shop and has been there for two weeks.

To the OP - I feel your pain!
 
#12 ·
We smoked the system thoroughly and while it was inconclusive, I replaced the booster anyway.

I've searched realoem for the sucking jet pump "Venturi Valve" but it appears there isn't one on the s62. I can find the one-way valve that holds vacuum when the engine is first turned off but I can't find anything that regulates or supplies additional vacuum to the booster as the sucking jet pump appears to do on other motors.

The line that supplies vacuum to the booster has a tee in it behind the engine but I can't see where the two lines that lead to the tee attach to the motor or intake to get their vacuum from.

Forgot to mention that of course every time we opened a bleeder, we tapped the caliper to release any air bubbles that might be trapped inside. Well, I started by tapping the calipers. After numerous attempts, the tapping may have become more like a beating. :smile
 
#15 ·
Please let me know if anyone finds out the fix for the soft break pedal. I changed my rotors and noticed that the rear caliper seals were shot. Before i tried to break in the rotors the pedals went to the ground, I didn't remove any break fluid so i don't understand what happened. I going to purchase new calipers and then flush the break fluid and see what happens.
 
#16 ·
Quick update here. Pressure bleed of brake system did not fix problem. I bought an E38 7 series hydraulic pump off eBay and Darien BMW was willing to put it on. It’s the same part. I got it for about 75 bucks before I realized clemster has like 50 of these things. Live and learn. Anyway this fixed the issue. Point is it’s the same Bosch part shared with e38. Given I never got any lights I can only guess that the existing pump had blockage. Correct that Given I simply kept the abs module in no coding was required. Re soft pedal, I have 112k miles and pedal is definitely soft compared to the wife’s new benz and probably when I bought the beast in 06. But if you press it the brakes still bite hard. Anyway this forum and my Peake reader continue to save me huge amounts of money every year - it’s amazing what you can learn on here even if you are not a car guy. Besides wear items and consumables I think I have now done a thermostat, this hydraulic unit, multiple cps, a Vanos solenoid multiple 02 sensors mafs... and probably a few other things I’m forgetting... and she’s still going strong.




Hello,

I think I've read just about all the threads (I think!) regarding brake system issues and based on some diagnosis I think I have narrowed down my issues to the ABS/hydraulic unit - and given I have no codes, I think the hydraulic end is creating the issue (issue is that front passenger corner is getting no pressure/fluid). I even PM'd Clemster who was very helpful on this topic. I have a couple quick follow-up questions which I couldn't quite decipher from the threads:

1. Is our ABS/hydraulic unit the same as found on the 7 series e38? Would such a unit be compatible with e39 m5 if coded to my specific car?
2. It seems any new or used unit, even off an e39 M5, would need to be coded to my car. Is "module masters" still the preferred group to send the unit to for coding to my car?
3. Has anyone actually taken apart the hydraulic part of the unit and refurbished it or "cleaned it out"? My brake line is clear and the brake components in front passenger corner all seem to be in good shape. Master cylinder seems to be in good shape. It seems something in the unit itself is not getting through or clogged.
4. Is there a part number that refers to the ABS (electronic portion), a separate part number for the hydraulic unit and then a part number for the combination? It's a little unclear on this page: http://www.realoem.com/bmw/enUS/showparts?id=DE93-USA-09-2001-E39-BMW-M5&diagId=34_1532. Also if you buy bmw part number 34522285051 on getbmwparts.com do you get the whole thing (ABS+hydralic part) or just the ABS module - electronic part? The prices on getbmwparts.com and real oem are very different, wondering if they are referring to two different things. Here is the getbmwparts page - I think item one is the unit... but not sure which end or if it's the whole thing. https://www.getbmwparts.com/parts/2...=&component=&searchText=&startRow=1&maxRow=10.
5. Finally, does anyone know the actual Bosch part number? I tried to look at the part in my car and I can't figure out what the heck the actual bosch part number is.

As you can tell I'm not a technician or car person - so sorry for my rudimentary questions and if I got anything wrong. My apologies if any of these were previously answered, I've tried to search and find the answers to these and didn't come across anything. If curious, 112k 2002 running great with many sensors / solenoids / thermostats replaced over the years.

H
 
#17 ·
Quick update here. Pressure bleed of brake system did not fix problem. I bought an E38 7 series hydraulic pump off eBay and Darien BMW was willing to put it on. It’s the same part. I got it for about 75 bucks before I realized clemster has like 50 of these things. Live and learn. Anyway this fixed the issue. Point is it’s the same Bosch part shared with e38. Given I never got any lights I can only guess that the existing pump had blockage. Correct that Given I simply kept the abs module in no coding was required. Re soft pedal, I have 112k miles and pedal is definitely soft compared to the wife’s new benz and probably when I bought the beast in 06. But if you press it the brakes still bite hard. Anyway this forum and my Peake reader continue to save me huge amounts of money every year - it’s amazing what you can learn on here even if you are not a car guy. Besides wear items and consumables I think I have now done a thermostat, this hydraulic unit, multiple cps, a Vanos solenoid multiple 02 sensors mafs... and probably a few other things I’m forgetting... and she’s still going strong.




Hello,

I think I've read just about all the threads (I think!) regarding brake system issues and based on some diagnosis I think I have narrowed down my issues to the ABS/hydraulic unit - and given I have no codes, I think the hydraulic end is creating the issue (issue is that front passenger corner is getting no pressure/fluid). I even PM'd Clemster who was very helpful on this topic. I have a couple quick follow-up questions which I couldn't quite decipher from the threads:

1. Is our ABS/hydraulic unit the same as found on the 7 series e38? Would such a unit be compatible with e39 m5 if coded to my specific car?
2. It seems any new or used unit, even off an e39 M5, would need to be coded to my car. Is "module masters" still the preferred group to send the unit to for coding to my car?
3. Has anyone actually taken apart the hydraulic part of the unit and refurbished it or "cleaned it out"? My brake line is clear and the brake components in front passenger corner all seem to be in good shape. Master cylinder seems to be in good shape. It seems something in the unit itself is not getting through or clogged.
4. Is there a part number that refers to the ABS (electronic portion), a separate part number for the hydraulic unit and then a part number for the combination? It's a little unclear on this page: http://www.realoem.com/bmw/enUS/showparts?id=DE93-USA-09-2001-E39-BMW-M5&diagId=34_1532. Also if you buy bmw part number 34522285051 on getbmwparts.com do you get the whole thing (ABS+hydralic part) or just the ABS module - electronic part? The prices on getbmwparts.com and real oem are very different, wondering if they are referring to two different things. Here is the getbmwparts page - I think item one is the unit... but not sure which end or if it's the whole thing. https://www.getbmwparts.com/parts/2...=&component=&searchText=&startRow=1&maxRow=10.
5. Finally, does anyone know the actual Bosch part number? I tried to look at the part in my car and I can't figure out what the heck the actual bosch part number is.

As you can tell I'm not a technician or car person - so sorry for my rudimentary questions and if I got anything wrong. My apologies if any of these were previously answered, I've tried to search and find the answers to these and didn't come across anything. If curious, 112k 2002 running great with many sensors / solenoids / thermostats replaced over the years.

H
Do you have part number please ?
 
#19 · (Edited)
MPBC - I’ll do you one better. I bought two e38 units on eBay. One worked that went in. I don’t know about the other one because we never tried it but I’ll send it to you for free. eBay seller says it is in full working condition and even offered free return. I can’t guarantee it’ll work tho. Just DM me your deets. If you google Bosch hydraulic unit e39 bmw you will find the Bosch part number. The bmw part number is already in this thread and Someone actually was able to get the bmw part number for hydraulic vs abs electronic already on this thread as well.
 
#21 ·
dannyboy223 - If you replace the ABC hydraulic unit and it fixes the problem, please post it. After my earlier post almost a year ago, I have since replaced all of the Brembo calipers with ones from my 20k mile S2, installed new Brembo slotted rotors, replaced the new slotted rotors with new Brembo drilled rotors, tried yet another brake pad compound and the pedal is still soft. I am convinced the problem has something to do with the car and not the brakes.
 
#25 · (Edited)
How about the ABS soft lines Danny? (the little 2).

My update is that after doing both an aftermarket (for diagnosing) and later OEM venturi pipe, the issue related to vacuum came back. Why... no clue.

I later blew one of the ABS soft lines and dam near drove with no fluid to the rears until the car yelled at me.

Replaced ABS lines Bled with Auto-logic 2x, pressure bled all corners, and dare I say it is better now.

Mine must have had a minor leak or something as the dam thing blew itself in half!
 
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