Another brake problem, different than most

[wagons ho]

Brakes started dragging, and within a block, fully locked. Had been fine every day, till this event.
New hoses, full caliper rebuild, fluid flush. P.S. system flushed all leaks fixed, etc.
Several test drives, perfect!!
Made it 4 miles, brakes started dragging, took 12cyl power to get into parking lot.
Common problem? Any clues?
Over the years, one power booster unit, no other problems.

[cartoonz]

Brakes started dragging, and within a block, fully locked. Had been fine every day, till this event.
New hoses, full caliper rebuild, fluid flush. P.S. system flushed all leaks fixed, etc.
Several test drives, perfect!!
Made it 4 miles, brakes started dragging, took 12cyl power to get into parking lot.
Common problem? Any clues?
Over the years, one power booster unit, no other problems.

Master cylinder.

[hemi4me]

As cartoonz stated...It's a master cylinder issue. I had exactly the same problem, In my diagnosis I cleaned and lubricated all 4 calipers, flushed the brake fluid several times and still had 4 wheel drag until lockup. Ended up putting in a master cylinder from a 750 and all good. I can not tell any difference in pedal pressure or pedal feel. Car still stops very well. $100 from rock auto as opposed to $1200 from the dealer for one for an 850.....

[wagons ho]

I agree that the master is the likely suspect. I have just never had one fail this way.
I am going to take it apart tomorrow and inspect for piston sticking in bore.

[cartoonz]

I agree that the master is the likely suspect. I have just never had one fail this way.
I am going to take it apart tomorrow and inspect for piston sticking in bore.

Don't waste your time, just replace it. Shocked me the first time I saw it too, seemed counter intuitive that a master would lock the brakes rather than lose them... but this one does exactly that, and it is a very common failure.

[Diskovod]

Agreed, just got a new OEM one, though I was told that ATE from E32 would be almost identical.

[MHambrice]

What they said. I tried everything before replacing the MC that fixed it.

[Guts1200]

Can the 7 series mc be used in a 96 850?

[mbarrett635]

Can the 7 series mc be used in a 96 850?

RealOEM shows the same unit in all 8 series cars -- so, yes, you should be able to use it.

[JDP530]

I replaced the master cylinder and had the booster rebuilt a month or two ago. The E31 master is not available as far as I know so the popular replacement item is from the E32 735i and 750iL series #34311156643. This master is 1mm smaller bore than the E31 master but it fits correctly and works just fine even with the BBK I installed at the same time. I think I paid about $155 for a new ATE master.

I did not order a new reservoir because the 7 series is slightly different so I cleaned the one on the car very well letting it soak in brake fluid cleaner, etc, overnight. I also poured a bunch of BB gun BBs into reservoir and shook it around for quite a while till all of the crud was loose enough to rinse out. It came out very clean. The new master cyl will come with new rubber grommets.

'Decreasing MC bore size will decrease your pedal effort and increase your pedal travel. Conversely, a larger bore in your car's master cylinder will, all other components being consistent, increase your pedal effort and decrease your pedal travel.'

Since the difference in size is only 1mm I doubt there would be any notice difference in pedal feel but, my brakes were not working well when I put my car on the road for the first time earlier in the year so I don't know what the brakes should have felt like with a good OEM master. The brakes worked and stopped the car but the pedal almost went to the floor to stop the car. Then a couple of months later I noticed a very small puddle of fluid on floor of garage so I knew it was time to work on the brakes. Now the brake pedal is very firm to hard with less than an inch of travel.

[wagons ho]

Don't you hate it when the results are not confirmed?
Finally got the ate master. Ordered 34311156643, but got a 3212529023.
Bore size is reduced from 1.2" to 1.1 " Which is more than 1mm mentioned, so I question the superseded part, but brakes work well.
And because we all love pictures, the result of a lot time. Valve cover and intake refresh. Intakes were yellow, and v.c. leaking 20180626_180022.jpg

[rjbaren]

FYI, There are still two more rubber brake hoses that can be replaced. They are about 4 inches long and reside in the rear of the LHS wheel well. I do not think there is anyone making stainless replacements. I took what I could from REAL OEM for my 95 840Ci below. I am not saying this is your part or even the right part, but I just want all to be aware there are still two more rubber hoses that could be problematic after 20+ years.

The drawing for the
Brake pipe front ABS/ASC+T

09

Brake hose

2

09/1993

34321159891

$57.58

[Belgiumbarry]

was one off the first problems with my 850 last year , dragging brakes….to full lock. New master from BMW and all was fine.
(Forgot to see if it was the same part #.)

[Max Lumens]

If anyone wants to experiment, there is a master cylinder from an early 90s Mercedes van that is a very close match to the e31 MC. ATE part number is 03.2126-0511.3. It's virtually identical but it's made of cast iron and the ports are on the opposite side. Looks like you could either swap the internals or rig up some crossover pipes. I have a cylinder here if anyone wants it.

FWIW, lots of brake hardware is still called out in SAE units. E31 MCs are 1 1/16", e32s are 1", IIRC.

[shogun]

"Brakes started dragging, and within a block, fully locked." >>>>this is typical for a stuck master cylinder, when all brakes are stuck. There are 4 seals inside plus one bakelite ring, this ring swells over the years when it get's warm/hot and get's stuck. On the German 7-forum forum they have tested it and left the master cylinder in a oven at 65 degree C for 30 minutes and then it got stuck. After 10 minutes cooling down the cylinder got unstuck again as the power of the spring inside was then enough again. Some repair the bakelite ring by slightly smoothing it down with sand paper. Here a pic of the master cylinder internals from an E32 750iL
http://www.bimmerforums.com/forum/sh...aster-cylinder
there is also mentioned that a Merces W126 brake booster might fit.
Rockauto might als have reman units from A-1 Cardone.
Someone on the German E31 forum has replaced the bakelite ring with a self made PTFE ring made from a PTFE rod on a turning lathe

quote: @Shogun @Pusches
Danke für eure Hilfe und infos hab heute folgendes gemacht. Bin gefahren bis die Bremsen wieder fest waren. In meiner Werkstatt den HBZ im heißen Zustand ausgebaut und siehe da, konnte den HBZ mit doch größerem Kraftaufwand hineindrücken, aber raus ging er dann von alleine nicht mehr. Nach einer abkühlphase ging er dann wieder wie ihr beschrieben habt wieder raus. So nun wollt ich den HBZ zerlegen aber der Bakelit Ring ist so fest gesessen, dass ich ihn nicht rausbekommen habe. Nun hab ich ihn kurzer Hand zerbrochen und ihn so rausbekommen. Jetzt konnte ich ihn weiter zerlegen und ja die Dichtringe und Zylinderfläche waren ok. Hab alles gründlich gereinigt und mit ATE Bremsfett geschmiert und zusammengebaut. Den Bakelit Ring habe ich ersetzt durch einen aus PTFE (Stangenware)den ich auf der Drehbank angefertigt habe. Nun noch zusammengebaut und entlüftet danach raus auf die Piste und gefahren bis alles so richtig schön heiß war. Nach 1 Stunde Probefahrt war noch immer alles ok. Rein in die Werkstatt den 8er aufgehoben und alle 4 Räder waren schön frei. Somit kann ich nur ein großes Danke Lob und Respekt an eurem Fachwissen richten und mich wieder daran freuen mit einem der schönsten Coupes die BMW gebaut hat rumzufahren.

translated: Thanks for your help and info, did the following today. I drove until the brakes were stuck again. In my workshop, the master cylinder =HBZ expanded in the hot state, could push the HBZ with a lot of effort in but out he went then by itself no longer. After a cooling down phase it went out again. Then I wanted to disassemble the HBZ but the bakelite ring was so tight that I did not get it out. I broke it into pieces and got it out. Then I could disassemble it further and yes, the sealing rings and cylinder surface were ok. Everything thoroughly cleaned and lubricated with ATE brake grease and assembled. I replaced the bakelite ring with a PTFE (rod product) that I made on the lathe. assembled and vented, then out on the slopes and driven until everything was really nice and hot. After 1 hour test drive everything was still ok. Back into the workshop, lifted the 8 and all 4 wheels were nicely free. Thus, I can only say a big thank you, praise and respect to your expertise and I'm looking forward again with one of the nicest coupes BMW has built. Alex
-----
Be careful when DIY, this is a brake master cylinder, do it at your own risk.

[shogun]

@wagons ho

would be nice to get a feedback how the problem was solved finally.

[wagons ho]

Shogun, I too hate it when there is no confirmation of results. On 9/21 I posted that a new master solved the problem.
Now it's fuel pump(s) time. Always something.

[e31gixxxer]

And because we all love pictures, the result of a lot time. Valve cover and intake refresh. Intakes were yellow, and v.c. leaking

Yeah, yellow not doing it for me...

user1782_pic1325_1252748249.jpg