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M6 Brakes sticking

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Ethanh100
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M6 Brakes sticking

Post by Ethanh100 » Sun May 23, 2021 2:59 pm

I have noticed my brakes getting stuck on my M6 for a while now. I noticed the brakes were sticking because first of all there was a really bad shake at just over 40 when they were sticking. The power wouldn't feel as good, the car would come to a stop quicker than I thought, and I wouldn't roll back coming to a stop on slight inclines. It seems to suddenly just get stuck sometimes and then will eventually release after a while, sometimes only when I stop driving and let it all cool down, but sometimes even after cooling down it would be sticking. The brake pedal also feels stiff and different when this happens.

Last summer I replaced the calipers and rotors (kept the pads as they had lots of life and even wear) because I assumed the calipers were at fault especially after seeing how crusty and old they looked. The car is kept in storage every winter so Im wasn't surprised that the sitting caused the calipers to be getting stuck. However after replacing those parts I still had the problem. It seems like it is happening less frequently but still getting stuck and shaking bad.

So what do you think the problem is. My guess is the master cylinder however I dont quite understand what exactly would be the problem, is it just not releasing all the way? Is a rebuild an option if it is the MC, or does replacement just make more sense? All the brake hoses are nice braided lines that look in good shape, replaced a few years ago I think. Could it be the hard brake lines, or is less likely than the MC. Or even the brake booster? What are your thoughts?
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wattsmonkey
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Re: M6 Brakes sticking

Post by wattsmonkey » Sun May 23, 2021 6:59 pm

Is there a rotor that is hotter than the others? I had a sticky rear caliper that had just got gunked up and needed a clean and new seals - I knew it was that one as rotor too hot to touch on that side after drive with draggy feel to brakes in traffic.
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Ethanh100
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Re: M6 Brakes sticking

Post by Ethanh100 » Sun May 23, 2021 10:30 pm

wattsmonkey wrote:
Sun May 23, 2021 6:59 pm
Is there a rotor that is hotter than the others? I had a sticky rear caliper that had just got gunked up and needed a clean and new seals - I knew it was that one as rotor too hot to touch on that side after drive with draggy feel to brakes in traffic.
Both rear wheels feel equally hot after driving. The front driver is hotter than the rear which makes sense, and the front passenger is a lot hotter than the right but that also makes sense because the exhaust comes out on the passenger side so theres a ton more heat on that side. So I cant really say anything about the heat in the front because the exhaust makes it uneven, but the back does feel evenly hot so I dont think one of them is stuck and its effecting all of the wheels or only one of the fronts
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Jlc
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Re: M6 Brakes sticking

Post by Jlc » Mon May 24, 2021 2:22 pm

Is there excessive pad wear on one wheel? That could point to a sticky caliper. Had that happen on SIL's Toyota pickup. Wore pad to steel back on one side. Replaced rotor and caliper...
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Ethanh100
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Re: M6 Brakes sticking

Post by Ethanh100 » Mon May 24, 2021 2:49 pm

Jlc wrote:
Mon May 24, 2021 2:22 pm
Is there excessive pad wear on one wheel? That could point to a sticky caliper. Had that happen on SIL's Toyota pickup. Wore pad to steel back on one side. Replaced rotor and caliper...
All of them look pretty even and have a good even wear to them. Ive pretty much entirely ruled out an individual caliper being the problem because if ive replaced the front calipers there shouldn't be any issue with them sticking, however by the massive front end shake occurring clearly those front brakes are engaging still. So something upstream is causing them to have hydraulic pressure when they shouldn't
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bpoliakoff
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Re: M6 Brakes sticking

Post by bpoliakoff » Mon May 24, 2021 5:40 pm

Years ago, Brucie wrote a thread on the master cylinders, noting above all, the piston in the caliper is made from phenolic and can eventually bind up. Do a search here
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Re: M6 Brakes sticking

Post by plip1953 » Mon May 24, 2021 6:27 pm

Although you say you've replaced the original calipers, it's most likely that you have one or more sticking caliper pistons. Wattsmonkey has told you how to try to narrow down which corner(s) is or might be where the problem is, but your feedback from that doesn't seem overly revealing - although, btw, the relative proximity of the exhaust to one side at the front will have no bearing on hub temps.

Routinely checking that caliper pistons move freely within the calipers is part and parcel of a thorough service regime, although in practice it rarely get done unless someone reports the kind of issue you are having. Actually doing it isn't difficult, although care does need to be taken or you can end up with pistons popping out!!
Last edited by plip1953 on Tue May 25, 2021 7:26 am, edited 1 time in total.
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Re: M6 Brakes sticking

Post by Steve M6 » Mon May 24, 2021 6:57 pm

This is very likely the brake master cylinder. I had this problem on my car too.
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Ethanh100
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Re: M6 Brakes sticking

Post by Ethanh100 » Mon May 24, 2021 8:25 pm

Steve M6 wrote:
Mon May 24, 2021 6:57 pm
This is very likely the brake master cylinder. I had this problem on my car too.
Did you just opt to replace the whole master cylinder, or was there any rebuild option
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Re: M6 Brakes sticking

Post by Steve M6 » Tue May 25, 2021 4:20 am

Replaced with a new master cylinder. Happened away from home, so there was no other option.
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Ethanh100
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Re: M6 Brakes sticking

Post by Ethanh100 » Tue May 25, 2021 11:52 am

Steve M6 wrote:
Tue May 25, 2021 4:20 am
Replaced with a new master cylinder. Happened away from home, so there was no other option.
Got it. Ive seen people use the E32 MC instead of the E24 one due to price. Does anyone here have a reason to not use the one from the E32. I suspect the pedal will feel a little bit lighter as I am on an otherwise stock brake set up, but I wouldn't think it would be that noticeable would it?
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Re: M6 Brakes sticking

Post by plip1953 » Tue May 25, 2021 5:00 pm

Ethanh100 wrote:
Tue May 25, 2021 11:52 am
Steve M6 wrote:
Tue May 25, 2021 4:20 am
Replaced with a new master cylinder. Happened away from home, so there was no other option.
Got it. Ive seen people use the E32 MC instead of the E24 one due to price. Does anyone here have a reason to not use the one from the E32. I suspect the pedal will feel a little bit lighter as I am on an otherwise stock brake set up, but I wouldn't think it would be that noticeable would it?
At a quick glance of Real OEM it looks like the E32 MC maybe have a slightly smaller bore diameter than on an E24 and therefore you would expect to need a little less pedal effort, but pedal travel will be greater.

For reference, MC sizes that I found were E24 23.81mm and E32 22.2mm.
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wfwright2
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Re: M6 Brakes sticking

Post by wfwright2 » Wed May 26, 2021 8:54 pm

The recommendation is to use a MC for a 12 cyl e32, it has a larger bore than the e24/e28. It will reduce pedal throw, and depending on driver may make brake modulation a bit touchy. I did this on the 87 635CSi when I went with the 750 front brakes and found the e32 750 MC less expensive back about 10 years ago.
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Re: M6 Brakes sticking

Post by Atomic » Thu May 27, 2021 8:59 pm

bpoliakoff wrote:
Mon May 24, 2021 5:40 pm
Years ago, Brucie wrote a thread on the master cylinders, noting above all, the piston in the caliper is made from phenolic and can eventually bind up. Do a search here
Does it only stick when the car is warm? This is the exact issue I had on my M6 and Brucey's thread https://bigcoupe.com/phpBB3/viewtopic.php?t=16351 was invaluable. I picked up a new E32 MC (34311156643) and it completely solved the issue. The change in pedal feel wasn't noticeable to me.
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Ethanh100
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Re: M6 Brakes sticking

Post by Ethanh100 » Fri May 28, 2021 11:09 am

Atomic wrote:
Thu May 27, 2021 8:59 pm
bpoliakoff wrote:
Mon May 24, 2021 5:40 pm
Years ago, Brucie wrote a thread on the master cylinders, noting above all, the piston in the caliper is made from phenolic and can eventually bind up. Do a search here
Does it only stick when the car is warm? This is the exact issue I had on my M6 and Brucey's thread https://bigcoupe.com/phpBB3/viewtopic.php?t=16351 was invaluable. I picked up a new E32 MC (34311156643) and it completely solved the issue. The change in pedal feel wasn't noticeable to me.
Yep it seems like it. I will take it out for short runs to the coffee shop and it doesn't happen, but if I cruise around halfway through my drive it starts happening. Ill park it and it will usually be normal by the next time I take it out (at least 24hrs later). I also saw that thread which drives me towards the conclusion of the MC
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Re: M6 Brakes sticking

Post by ron » Fri May 28, 2021 1:12 pm

R/H drive cars suffer badly from this problem as the M/C is directly above the exhaust manifold.

I changed my Highline M/C to an E32 item and had to remake the pipes as the fitting was different.

I eventually had the same sticking problem with the E32 M/C. The cure was to ceramic coat the manifold.
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Re: M6 Brakes sticking

Post by smtguy » Sun May 30, 2021 3:15 pm

I had the identical problem on my '83. Replaced the master cylinder and all was well.
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Re: M6 Brakes sticking

Post by marc79euro645 » Fri Jun 04, 2021 11:57 pm

I had a caliper that kept sticking. After replacing the caliper it still would drag. It turned out to be the brake hose. They can rupture the inner hose, which pressurizes the outer hose causing it to collapse the inner hose. I don't know if you have a hose in common with all the wheels that are dragging on yours. I upgraded to ss hoses, and really like the firmer pedal feel.

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Re: M6 Brakes sticking

Post by GazM3 » Mon Jun 07, 2021 5:57 am

another one here with a sticky master cylinder replaced with the e32 750il one. Happened on the e23 as well
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Re: M6 Brakes sticking

Post by plip1953 » Mon Jun 07, 2021 8:19 am

Do we know what causes the MC piston(s) to stick? Simply deterioration of the seals? Is there a repair kit, or does the complete unit always have to be changed?
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bpoliakoff
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Re: M6 Brakes sticking

Post by bpoliakoff » Mon Jun 07, 2021 3:56 pm

To my way of thinking, it's not worth the aggravation to rebuild. Go new. Think how long your original lasted.
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