Cheaper Brake Master Cylinder Replacement?

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Tom Ato
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Cheaper Brake Master Cylinder Replacement?

Post by Tom Ato »

I'm pretty sure my brake master cylinder needs replacing (after driving for awhile the brakes start to lock up, etc.), but e28 master cylinders are pretty expensive these days. I saw some posts about e32 master cylinders, and I'm just wondering if anyone could confirm about any cheaper (non-e28) options that should be drop in replacements in my 1987 535is?
Mike W.
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Mike W. »

If the bore is still good rebuild it. Rock auto has kits for $55. Expensive for a kit, but a lot cheaper than a new M/C.
Shawn D.
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Beamter
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Shawn D. »

Going to an E32 M/C will make your brakes noticeably firmer/harder. If you like the feel now, don't do it.
Tom Ato
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Tom Ato »

Is there a way for me to check if it's worth rebuilding before I go buy a kit? I saw an e32 one for $70
Mike W.
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Mike W. »

Tom Ato wrote:Is there a way for me to check if it's worth rebuilding before I go buy a kit? I saw an e32 one for $70
Sure, but you have to take it out and take it apart. Actually new seals even in a somewhat corroded bore will usually seal for a while.
Tom Ato
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Tom Ato »

Mike W. wrote:If the bore is still good rebuild it. Rock auto has kits for $55. Expensive for a kit, but a lot cheaper than a new M/C.
I just looked at Rock Auto's site and they are out of stock for the kit... :cry:
dsmith
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Re: Cheaper Brake Master Cylinder Replacement?

Post by dsmith »

I just buy the autozone rebuilds for $60. No issues and warranty.
Tom Ato
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Tom Ato »

dsmith wrote:I just buy the autozone rebuilds for $60. No issues and warranty.
I hadn't thought to look at Autozone for some reason...thanks for the tip!
tn535i
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Re: Cheaper Brake Master Cylinder Replacement?

Post by tn535i »

Tom Ato wrote:I'm pretty sure my brake master cylinder needs replacing (after driving for awhile the brakes start to lock up, etc.)
That (lock up) does NOT sound like a symptom of failing master cylinder. Sounds to me like calipers need to be rebuilt and brake lines replaced before needing the master.
dsmith
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Re: Cheaper Brake Master Cylinder Replacement?

Post by dsmith »

Tom Ato wrote:
dsmith wrote:I just buy the autozone rebuilds for $60. No issues and warranty.
I hadn't thought to look at Autozone for some reason...thanks for the tip!
Same price with core for calipers too, if you need those.

Before replacing anything, I would disconnect the rod from the brake pedal and make sure the pedal returns to rest on its own. Then shorten the rod 1/8th inch, reconnect and retest. If it still locks up, I would follow tn535i’s thoughts and replace calipers and soft lines first.
Tom Ato
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Tom Ato »

tn535i wrote:That (lock up) does NOT sound like a symptom of failing master cylinder. Sounds to me like calipers need to be rebuilt and brake lines replaced before needing the master.
Could you tell me a bit more? Bentley suggested cleaning the brakes or replacing the master cylinder. For calipers, it basically just says that if there is leaking fluid, replace the caliper, and similarly it just says to replace brake lines if they are leaking. I already visually inspected the caliper that I noticed most clearly binding/heating up, and I didn't see anything that looked like fluid. Is there a way to determine the probably cause before I go out and buy a master cylinder or new calipers or whatever?
dsmith wrote:Before replacing anything, I would disconnect the rod from the brake pedal and make sure the pedal returns to rest on its own. Then shorten the rod 1/8th inch, reconnect and retest. If it still locks up, I would follow tn535i’s thoughts and replace calipers and soft lines first.
I will try that, though what you are suggesting seems to imply it is always locking up (I could be wrong though). My issue only occurs if I have been driving for maybe 15-20 minutes. The brake pedal gets hard and only travels a very small amount in order to brake, plus the brake(s) bind. Does your suggestion still apply?
dsmith
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Re: Cheaper Brake Master Cylinder Replacement?

Post by dsmith »

Well, the Bentley is focused on newer parts that fail, so leaking fluid from a seal would be the main issue. These are now 30+ years old and all bets are off. Most likely you have 1 or more issues, some of the issues are difficult to diagnose and the issues you would have, not including the MC, will be close behind on the other calipers and brake lines. Brake lines degrade inside out and flaps of rubber can act as a one way valve, not letting a caliper release. Calipers can be corroded and you need remove each one to test pushing the pistons to make sure they move freely. Might as well replace at that point.

The best course is to replace calipers, rubber brake lines and MC and be confident in your brakes. Reuse your pads and rotors, if they are ok.

Yes driving for 15 mins, or a few miles, or a few brake applications and getting lock up can be caused by the brake rod engaging as little as 1/16" all of the time. If you then let the car cool for 10mins and it is ok and repeats, this could be a possible issue. So, my suggestion to shorten the rod and check return spring action is easy and free. If no change, I would shotgun the MC, calipers and lines.
Tom Ato
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Tom Ato »

dsmith wrote:These are now 30+ years old and all bets are off.
That is a good point haha
dsmith wrote:Yes driving for 15 mins, or a few miles, or a few brake applications and getting lock up can be caused by the brake rod engaging as little as 1/16" all of the time. If you then let the car cool for 10mins and it is ok and repeats, this could be a possible issue. So, my suggestion to shorten the rod and check return spring action is easy and free. If no change, I would shotgun the MC, calipers and lines.
That makes sense, I'll try the rod first and see how it goes. Thanks!
tn535i
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Re: Cheaper Brake Master Cylinder Replacement?

Post by tn535i »

And for anyone reading... Bleed your brakes at least every other year until clean fluid comes out. This will help keep moisture out and reduce corrosion which is what kills brake components from the inside out. Of course foul conditions can kill calipers from the outside in also. I think on all the BMW's I've owned I have only ever needed to rebuild calipers.

I think it's deplorable that most brake jobs don't include a proper flush of the old fluid. Not sure many shops even know how to do a proper flush/bleed. I know people who have had 'brake work' done and the fluid in the reservoir still looks like day old coffee. :roll:
HayekFan
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Re: Cheaper Brake Master Cylinder Replacement?

Post by HayekFan »

FWIW, I had the same symptoms in an old Toyota and a new master cylinder fixed it. Brakes normal for 10 or 20 minutes then start dragging and eventually lock up along with a high pedal. Let the car sit for a few hours and everything is back to normal. Had me pretty mindboggled so I did some googling and noticed a pattern of people reporting these same symptoms and fixing it by replacing the master cylinder. So I bought an Autozone cheapie to try out and sure enough that got it.
tn535i
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Re: Cheaper Brake Master Cylinder Replacement?

Post by tn535i »

The most common I've seen is water that corrodes the cylinder and then the roughness destroys the seal so it goes to the floor. However, I suppose or guess a check valve or port in the master might fail or clog then not allow pressure to drop once the pedal goes back up... or maybe simply the pedal is not returning all the way back up because something internal is torn up or something external won't let it? If that were to happen with either circuit maybe the brakes get harder and harder with each application. Plausible ??
JohnH
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Re: Cheaper Brake Master Cylinder Replacement?

Post by JohnH »

Tom Ato wrote: but e28 master cylinders are pretty expensive these days.
An alternative to fitting new parts is to get them re-sleeved. This is quite a popular procedure in Oz where the price of replacement parts has always been high. I got my 02tii twin vacuum servos with attached master cylinders re built and re-sleeved by Past Parts here in the UK http://www.pastparts.co.uk/index.php?ro ... ation_id=8
There are one or two US companies doing it as well, https://www.applehydraulicsonline.com/c ... s/sleeving $125 or so seems to be good value.
Alberto89
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Alberto89 »

Tom Ato wrote: Aug 27, 2019 10:40 PM I'm pretty sure my brake master cylinder needs replacing (after driving for awhile the brakes start to lock up, etc.), but e28 master cylinders are pretty expensive these days. I saw some posts about e32 master cylinders, and I'm just wondering if anyone could confirm about any cheaper (non-e28) options that should be drop in replacements in my 1987 535is?

Have you solved the problem? I have the same problem. I have replaced the brake hoses, and removed the calipers and overhauled them. Unfortunately, the problem still persists. I don't know where to start.
kojo96
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Re: Cheaper Brake Master Cylinder Replacement?

Post by kojo96 »

I had a very similar problem on na 83 533i. Car would drive / stop fine but sometimes it would feel like it was slowing down on it's own. It was strange in that it felt like the automatic transmission was binding up and at first I thought it was the clutches in the transmission but the car had a hard pedal. Usually it happened at a stop, or stop n go traffic and more so on hot days.
One day while on the highway, it randomly grabbed, and pulled the car to the right, knew them it was a brake issue.
Right front brake caliper was going bad, it was replaced and no issues since.
Alberto89
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Alberto89 »

Thanks for your reply. But this is a completely different problem. Here all brakes are locked. I also have a manual transmission.
Maaaate
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Re: Cheaper Brake Master Cylinder Replacement?

Post by Maaaate »

Posted the following in response to the 'Stuck Brakes M535i' post

Had the same problem when the car had fully warmed up - it was caused by the bush at the end of the master which deteriorates over time and swells when hot, gripping the rod and not letting it return, When the car cools down the problem disappears.
There's an excellent writeup on an E24 site - remove master, strip cylinder, slightly ease bush and reassemble, but removing the retaining circlip then extracting the rod and seals takes care - try to find the E24 post. Apologies I don't have the link still. Cost is entirely in your time plus fluids - might be worth emptying the steering/servo fluid first - mine drained itself onto the garage floor.
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