e34 540i M60 brake booster replacement???

**Trent54** · 07-06-2016, 09:17 PM

My local shop diagnosed the brake booster as having failed. They quoted me about $1500 parts and labor. I found a DIY video on youtube, but it is for the E39 which I understand has a different brake booster, and the brake booster is mounted on the firewall. On my care the brake booster is by the front left (USA driver's side) headlight. Can anyone give me some tips or a guide on how to replace this myself? I can't really afford to have the shop do it. They also want ~$850 for the part, I'm going to use a $270 part from O'Reilly's.

Much thanks,
Trent

**Layne** · 07-06-2016, 10:24 PM

I would buy a used one for like $50. They almost never fail. Actually I would confirm their diagnosis first, as it's highly probable they are wrong. As for the replacement, it's just a few nuts and bolts. You might need to remove the left headlight and grill for easy access. Be very careful with the brake lines where they go into the top of the master cylinder so you don't break them. If you can get the booster out without removing any brake lines you'll save a lot of time, but I'm not sure if it's possible. The fluid is probably old and needs changed anyway though.

**ross1** · 07-07-2016, 10:09 AM

Originally Posted by Layne

I would buy a used one for like $50. They almost never fail. Actually I would confirm their diagnosis first, as it's highly probable they are wrong. As for the replacement, it's just a few nuts and bolts. You might need to remove the left headlight and grill for easy access. Be very careful with the brake lines where they go into the top of the master cylinder so you don't break them. If you can get the booster out without removing any brake lines you'll save a lot of time, but I'm not sure if it's possible. The fluid is probably old and needs changed anyway though.

Agree with a second opinion on the diagnosis. Definitely remove the headlights for this job, the master is wedged in there pretty good. Not a difficult job but certainly a PITA one. These cars were never intended to have V-8s and this Mickey Mouse brake set up is proof of it.

**atl530i** · 07-07-2016, 12:16 PM

Originally Posted by ross1

Agree with a second opinion on the diagnosis. Definitely remove the headlights for this job, the master is wedged in there pretty good. Not a difficult job but certainly a PITA one. These cars were never intended to have V-8s and this Mickey Mouse brake set up is proof of it.

What he said. I don't think I've ever seen one of those fail before.

Agreed with the Mickey Mouse part

**Trent54** · 05-03-2020, 11:30 PM

Originally Posted by Layne

I would buy a used one for like $50. They almost never fail. Actually I would confirm their diagnosis first, as it's highly probable they are wrong. As for the replacement, it's just a few nuts and bolts. You might need to remove the left headlight and grill for easy access. Be very careful with the brake lines where they go into the top of the master cylinder so you don't break them. If you can get the booster out without removing any brake lines you'll save a lot of time, but I'm not sure if it's possible. The fluid is probably old and needs changed anyway though.

Do I drain the brake fluid through the calipers first? I built an air compressor attachment so I can attach an air compressor line to the fluid reservoir. And/or put shop towels down under the brake lines before I undo them from the master cylinder?

**moroza** · 05-04-2020, 12:52 AM

The booster can be removed without cracking open the brake lines. However, ten doubloons says your brake fluid is overdue for a change.

I once replaced the short PS hoses under the booster on an M60 car. The blend of incompatible hydraulic oils caused the original hoses to swell so much that they popped right off, despite crimp-style hoseclamps. Removed the booster, didn't have to touch the headlights. Don't remember the exact steps, but I do recall requiring an assistant to step on the brake just the right amount so that my socket extension could reach one of the booster bracket bolts on the bottom. IIRC I disconnected the pullrod, after marking its original position, and the assistant was necessary to get it to thread in again. Meanwhile the master cylinder just dangled out of the way behind the headlights.

**Trent54** · 05-05-2020, 07:04 PM

Originally Posted by Layne

They almost never fail.

Maybe this is the problem?Tear in Boot.jpg

Also, I can spin the black plastic ring above the top arrow.

Thanks!

**moroza** · 05-05-2020, 07:38 PM

I think those are just dust seals, not vacuum seals.

**Trent54** · 05-07-2020, 10:34 PM

Thanks for the help. If you don't mind, a few more questions before I tear in to it.

I'm trying to figure how it works in theory. I believe the E39 brake booster is connected to the engine though a vacuum line that has a one-way valve, which prevents air from the brake booster from being pumped back through the vacuum line. See part 14 here:

https://www.realoem.com/bmw/enUS/sho...diagId=34_0547

But the E34 doesn't have this. How does the E34 get away with not having this? I ask because, IIRC, I initially took the car in because I was failing emissions, and I was able to pass emissions after, among other things, plugging the vacuum lines, which had the side effect of disabling the brake booster. Does this make sense?

Originally Posted by moroza

I think those are just dust seals, not vacuum seals.

**moroza** · 05-08-2020, 12:06 AM

It should have a check valve, located on the booster, connected to the vacuum hose. It may have failed. It's not listed separately, but as part of item No.6 (note that the diagram incorrectly shows it further along the line. See attached photo of my 4/93 530iT).

Picture 190.jpg

**a777fan** · 05-08-2020, 01:36 AM

Wait. Original post was from 2016?!

OP, did you really wait 4 years to dig in here? If so, one hell of a bump!

**moroza** · 05-08-2020, 01:52 AM

Hah, I missed that. Still, the way I see it, it's extremely irritating to search for threads to answer a question, and find threads where there's no content except exhortations to the OP to search. Buck. Futter. Facepalm. Necro thread is usually bad form (this case is unusual), but regardless of form, I like to leave actual content and answers for the benefit of anyone searching in the future. Otherwise we should delete the thread so it doesn't clog up the internet and waste everyone's bandwidth or anyone's time.

**a777fan** · 05-08-2020, 10:28 AM

Originally Posted by moroza

Hah, I missed that. Still, the way I see it, it's extremely irritating to search for threads to answer a question, and find threads where there's no content except exhortations to the OP to search. Buck. Futter. Facepalm. Necro thread is usually bad form (this case is unusual), but regardless of form, I like to leave actual content and answers for the benefit of anyone searching in the future. Otherwise we should delete the thread so it doesn't clog up the internet and waste everyone's bandwidth or anyone's time.

Agree. Still, quite impressive OP!

**Trent54** · 05-08-2020, 11:52 PM

Thank you very much for clarifying this regarding the one-way valve. Given my understanding that there was no one-way valve on these cars, because of the parts diagram, I had assumed the booster had to be at fault. In light of what you've shown me, I think I should start by replacing part number 6!

And yes I have been procrastinating on this for a very long time. I didn't think there was any way to get it out without draining all the brake lines, and I have an aversion to brake fluid. Bleeding brakes really. I finally figured out how to do it though, so I decided to take a crack at this. Luckily I work from home but yes, I've been driving without power brakes since 2016. Maybe before that.

**a777fan** · 05-09-2020, 02:50 AM

Glad you are giving it a go!

Get yourself (or make yourself) a power bleeder. It will make the job a complete snap, and you’ll wonder why you’ve ever paid anyone else to do it.

**Trent54** · 05-09-2020, 03:43 AM

Check on the power bleeder! Last summer I had to replace the front rotors. I wound up McGyvering a master cylinder cap with an air line hookup for my compressor. It really helped. Still a PITA and a mess, because I didn't have a good understanding of how to bleed the brakes at the caliper. I recently had to do it to another vehicle, and I learned the trick of using a mostly sealed gatorade bottle (flush hole for surgical tubing, pin hole in cap), holding it level or above the caliper, and starting w/brake fluid in the bottle so no air gets sucked back in. I also almost dropped the car on my head at one point in the process, but that's another story. I tend to learn things the hard way. Trying to reform though. Thanks for all the help!

**moroza** · 05-09-2020, 06:56 AM

Originally Posted by Trent54

Thank you very much for clarifying this regarding the one-way valve. Given my understanding that there was no one-way valve on these cars, because of the parts diagram, I had assumed the booster had to be at fault. In light of what you've shown me, I think I should start by replacing part number 6!

You should start by inspecting it. See if you can blow air one way and not the other (specifically, out of the booster and not into it; some check valves are possible to mount backwards).

**Trent54** · 05-12-2020, 04:37 PM

I attempted to pull the line out of the booster yesterday, and it's in there pretty good. Do I just force pull/pry it out, or is there something I'm missing? I got to the point of putting a carbon scraper in between the boot and the brake booster and rocking it back and forth, but I decided to ask before I break something.

Originally Posted by moroza

You should start by inspecting it. See if you can blow air one way and not the other (specifically, out of the booster and not into it; some check valves are possible to mount backwards).

**moroza** · 05-12-2020, 06:03 PM

Patience, wiggling, and lube (dish soap works great for rubber).

**Trent54** · 05-12-2020, 07:42 PM

Thanks!

**a777fan** · 05-12-2020, 08:04 PM

Yep. Just be gentle and persistent and it will come out. Felt like it would break when I did mine, but it didn’t.

**Trent54** · 05-21-2020, 04:52 AM

I renewed 7 and both 8s tonight and carefully inspected 6. Basically I think I've confirmed it has to be the brake booster (you guys helping me seem like great mechanics--maybe skip to the last paragraph if my reasoning is tedious):

Air only sucks or blows one way. Also, having stretched some small, thin rubber o-rings around the groves on the nipple where 6 goes into the brake booster, it now fits very tightly, so I don't think there is any leak there.

Still no sense of having power brakes. The only delta (since I opened up the line to the brake booster a month or so ago) is that the car has a rough, low idle, and the check engine light has come on. I believe this means the brake booster has a vacuum leak.

Now, when I look at the brake booster from the driver's side of the car with my head just above 'level' with the brake booster, I can see that the mating surface between the master cylinder and the brake booster in not perfectly sealed - there is a .5mm gap at the bottom that goes about halfway up. The kind of gap you might expect if someone had grabbed the front of the master cylinder and pulled up pretty hard.

I note what appears to be a large o-ring between the master cylinder (part number 3 in the diagram above). Given what was said above about brake boosters seldom failing, could it be that this o-ring has failed? Does that seem likely, or am I jumping to conclusions?

**moroza** · 05-21-2020, 07:54 AM

Originally Posted by Trent54

Air only sucks or blows one way.

Which way?

I note what appears to be a large o-ring between the master cylinder (part number 3 in the diagram above). Given what was said above about brake boosters seldom failing, could it be that this o-ring has failed? Does that seem likely, or am I jumping to conclusions?

Could well be. You could try throwing an O-ring at the problem, or you could try testing for an air leak there. Propane and brake cleaner [EDIT: not fluid, derp] are less reliable. A smoke test is more reliable. A cheap smoke machine costs about as much as a used brake booster, and is a Divine Revelation of a diagnostic tool if you'ven't used one before (in other words, highly recommended).

**Trent54** · 05-22-2020, 12:43 AM

Since there's no way to blow air into the brake booster, because of the 1-way valve, I removed part 6 (see above) and rigged up some spare hose w/o-rings to seal in the rubber grommet in the front of the brake booster. When I blow in air through the hose into the brake booster, it clearly leaks out the back of the brake booster near the pushrod, i.e. brake pedal linkage.

If my understanding of how this is supposed to work is correct, this must mean the seal, inside the booster, between the vacuum chamber and the atmospheric chamber is shot, and the brake booster is pic related. Am I correct?totally fucked.png

**a777fan** · 05-22-2020, 02:50 AM

Originally Posted by Trent54

Since there's no way to blow air into the brake booster, because of the 1-way valve, I removed part 6 (see above) and rigged up some spare hose w/o-rings to seal in the rubber grommet in the front of the brake booster. When I blow in air through the hose into the brake booster, it clearly leaks out the back of the brake booster near the pushrod, i.e. brake pedal linkage.

If my understanding of how this is supposed to work is correct, this must mean the seal, inside the booster, between the vacuum chamber and the atmospheric chamber is shot, and the brake booster is pic related. Am I correct?totally fucked.png

Soooo....

The line to the brake booster provides vacuum, right? As such, during normal operation it would never be ‘blowing’ into the booster. What happens when you perform the same experiment, but suck, instead of blow...?

Great attachment btw...