Brake binding

Hi all! I'm having a severe brake problem with my mini. It's a mk5 998 mayfair automatic. Sometimes the front right wheel remains strongly braked although no pressure is applied to the brake pedal. This happened 3 times so far, requiring 3 new disc and pad sets. I've replaced all master cyilinder and calipers seals and the front pipes with OE stuff, and the brake fluid is new. The last time the brake effect was so strong that when I suddenly stopped the car a lot of hot black smoke came out from the right brake assembly for about 1/2 hour!! What should I check? Calipers? Master cylinder? Pressure regulator? My mechanic has no idea, please help! Thanks in advance for your kind replies

Reply to
emilio
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You say you replaced the front pipes. Did this include the flexible hoses? If not, it is probably the flexible brake hose on the right side. This would have been my first guess even if you hadn't changed so many parts.

The inside of the flexible hose can break down and cause it to form a non-return valve inside the hose. On a brake line this leads to the pads dragging or locking on. On a clutch line it leads to the clutch slipping or releasing very slowly.

It is possible to damage flex hoses during installation. Check to see it has been installed in a twisted manner or if it appears to have been kinked.

Otherwise, you can break down the problem this way. Since only the right hand side is affected the fault must lie at or after the point where the front lines split from left to right.

You probably have a bit more work to do now than just fix the brakes. If you got things hot enough to smoke for half-an-hour then there is a good chance that you need to at least repack the right front bearings, you may also need to replace the seals. The heat could also have affected the caliper seals and possible the flexible hose.

Here is another possibility. What if the left-hand side flex hose is weak and balloons on braking. This would mean that when the brakes lock on the right would get more of the pressure. Both sides would get hot but the right might get hotter.

I have seen a case where the brake master cylinder pushrod was not returning far enough. This left one of the fluid reservoir holes in the cylinder covered. The result was that the brakes would pump up and never release. Very embarassing on a race course. Lots of smoke and very little speed. And very hard to figure out.

Cheers,

Kelley

Reply to
Kelley Mascher

Hi, I aghree fully with Kelly, I experienced this exact problem some years ago on a Fiat, and it turned out to be the brake hose.

Keith

Reply to
k

Yes the flexible hoses have been replaced

Right! I'll have a look

Sorry, what does "to balloon" exactly mean, technically speaking? My dictionary says it's "aerostato" in italian: you know, that big big ball with hot air inside with people flying in a small basket! ;)

thanks!

emilio

Reply to
emilio

"to balloon" is the verb form of the big, big ball with hot air inside, meaning "to expand from internal pressure." In American English and I suspect in others "balloon" can be a verb meaning to act like a balloon. Think of the rubber toy balloons that you blow up with your mouth.

In the case of the flexible hose, it may be expanding (espandere, si?) due to the brake fluid pressure and losing effectiveness.

Another thing to inspect is the linkage from the pedal to the master cylinder. It is possible that something is sticking somewhere or is misaligned.

Is it possible that someone put the wrong master cylinder pushrod in the Mini before you bought it? A BMC1300 series master cylinder might have a pushrod that is too long.

Did you drive this car very much before the brake problems started?

Cheers,

Kelley

Reply to
Kelley Mascher

si, "espandere" :)

I'll have a look: the radio-cd is very close to the brake pedal linkage. In the previous posts i've forgot to mention that the problem has always appeared when brakes were lightly hot (for example the last time i was downhilling(!) along a crooked road)

I don't think so, the car seems to be 100% original and here in italy BMC 1300 series are really hard to find (I've only seen one in Rome area about 15 years ago)

For about 20k Km

ciao! emilio

Reply to
emilio

hi i'm sure i saw a post similar to this ages ago ? it might be worth finding the archives and go through them.

Reply to
fragged

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