Binding brakes/faulty master cylinder; mystery solved???

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bpoliakoff
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by bpoliakoff »

Wow, if you look up "phenolic" you won't believe the total crap it is composed of. It has to be doomed to fail
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
sowhatsg
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Joined: Sun Jan 23, 2022 10:23 am
Location: France

Re: Binding brakes/faulty master cylinder; mystery solved???

Post by sowhatsg »

Also experienced binding brakes when used a lot, like in trafic jam and worse when weather is hot (i.e. not now in France...). Feeling you're driving with hand brake ON. Seems like all 4 wheels or 2 rear or 2 front as car does not drift. All OK after cooling, i.e. wait a few hours. Mechanic didn't find any problem, brake fluid was changed by BMW agent, I suppose they used the correct spec.
Looks like what Bruce is describing. BTW, excellent write-up. I don't feel like I'm competent to duplicate the work he did and will have to rely on local specialist, there are a few around. If it's coming from MC, I need to be sure before it's replaced.
KINGJOHN808
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Joined: Sat Feb 16, 2019 2:27 am
Location: Ewa Kai

Re: Binding brakes/faulty master cylinder; mystery solved???

Post by KINGJOHN808 »

Aloha all,

Just came across this thread. Experiencing the same issue, brakes are fine until I drive for a bit, when attempting to brake, pedal goes to the floor. If i slam my foot on the brakes, the car shoots to the left. The front left caliper is SUPER HOT. After I parked for a bit, the brakes are still binding slightly and the pedal came back to normal. After an extended park session (30 minutes or more) the caliper unlocks completely and the car drives and behaves normally. I actually had this happen a few years back, had to drive back home using the emergency brake...not fun at all. Took to a shop and they stated the they found a leak on the PS hose and had that replaced. Issue went away, then I put the car in storage, only driving it a few miles a month.

Have already replaced the mc to brake reservoir gaskets/seals (they were softswelling and leaking fluid). The calipers, brake pads and brake lines are all new (less than 10 miles on them) Since I'm already in the area, should I just replace the brake bomb too? Was also thinking about replacing both brake pressure switches on top of unit with the brake bomb. Pretty sure all the above listed parts are as original as everything else under the hood.

Since i'm still working on the issues with the AC system, decided to take a break from that system and focus on things more pressing...like the brakes! :o)

Part numbers found on REALOEM/FCP Euro for a 1984, 633CSi, automatic trans, build date 7/1984:

BMW Brake Pressure Switch, Ate logo- SKU: ATE-340028 (BMW Brake Pressure Switch - ATE 34351182270)
BMW Brake Pressure Switch, Ate logo- SKU: ATE-340029 (BMW Brake Pressure Switch - ATE 34331150922)
BMW Brake Pressure Accumulator, Ate logo- SKU: ATE-340024 (BMW Brake Pressure Accumulator - ATE 34331162054)
BMW Brake Master Cylinder, Ate logo- SKU: ATE-010193 (BMW Brake Master Cylinder - ATE 34311153919)
Ewa Kai, Hawai’i
1984 633CSi
1983 633CSi (wreckers)

“Aloha and have a great day!”
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JCS
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by JCS »

Replace the brake master cylinder,
Apparently, you did not read the blog
Jay
'88 M6, Red/Tan
My NEW Website https://www.jaysbmwparts.com/
KINGJOHN808
Posts: 127
Joined: Sat Feb 16, 2019 2:27 am
Location: Ewa Kai

Re: Binding brakes/faulty master cylinder; mystery solved???

Post by KINGJOHN808 »

JCS wrote: Fri Jun 10, 2022 2:53 am Replace the brake master cylinder,
Apparently, you did not read the blog
:roll: Apparently you can’t see my finger. Didn’t ask for you to be a smart ass.
Ewa Kai, Hawai’i
1984 633CSi
1983 633CSi (wreckers)

“Aloha and have a great day!”
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