funny stuff, after brake bleed, rears locked up.......twice Options

[davep]

Remove one rear rubber line and see if you can blow through it. Since the system was working correctly before, there should be no restriction.

Can you return the prop valve to its original configuration? Does that help?

Was there any crap in the reservoir before beginning to bleed that may be restricting the MC operation or plugging the lines? I ALWAYS empty the reservoir and refill before bleeding.

If you have crappy old fluid in the system, then rust can form anywhere and cause problems. If the bore of the MC is rusted, then pushing the piston past the point of the rust (where you normally don't go) can cause damage to the seals, or possibly hang up a section of the piston.

[pete-stevers]

so how does one drain all this fluid? i am hoping this solution is the ticket....

[John]

I would NOT recomment draining all the fluid.

When I flush brakes each spring, I start out bleeding the passenger side rear.

I bleed the brakes until the reservoir to the rear is almost empty but not completely.

I then move to the passenger side front and drain the front portion of the reservoir almost empty.

I then fill the reservoir with fresh DOT4 fluid and move back to the passenger side rear. I fill and bleed this corner until I am sure that I have fresh fluid (a pint or so should be more than enough). This flushes all the old fluid out of the master cylinder back through the tunnel and to the proportioning valve and the passenger side lines and calipers.

I then move to the drivers side rear caliper and bleed that caliper (again about a pint should be good to flush it out. Your rear brake lines, proportioning valve, and calipers should now have fresh fluid in them.

Then move to the passenger side front caliper and bleed about a pint through there.

Finish up by bleeding about a pint through the drivers side front caliper.

You should now have completely flushed your brake lines (and used about 2 quarts of brake fluid).

That's how I do it.

While you are at it, please do disconnect and blow air through those rear rubber brake hoses and make sure they are not blocked. It would be a pain to do all this work and still have a problem.

Good luck to you.

[Root_Werks]

Pete, you still coming down Sunday? If you don't get this figured out by then, just drive on down and don't use the brakes. (IMG:style_emoticons/default/biggrin.gif) We'll take a look at those as well. (IMG:style_emoticons/default/driving.gif)

[pete-stevers]

dan i plan to be there.....!!!!!!!!
i will get this sorted tonight hopefully...

[pete-stevers]

well........
after much chin wagging and wondrering we decided to drain some brake fluid.....
and guesse what was found....two fluids in th e the line of two different colors and weights....they seperated in the container....
i figure it was a "gunk dot 3" and a mix of "pentosin dot 4"
those where only two fluids in th e shop.....
strange little coagulations inside the fluidn as well.....
which would explain the mc valve acting up...(hopefully)
we should get this completely sorted tonight..with a spare mc on hand jsut in case
the morale of the story...don't have cheap ass brake fluid in the shop!!!!
and if you do ...don' t mix it!!!!!!!!!!

[davep]

I've never seen fluids like that. Not unless one was a silicone fluid. There was a thread on those fluids not mixing recently, pictures included.

[kdfoust]

I think DOT 3 & 4 mix just fine. I believe DOT 5 doesn't mix with the other two.

If the brake are seizing after driving you are dealing with a heat induced problem.


There's no venting clearance to set on the rear BMW calipers is there? I don't think so. So you've got no e-brake, right?

I don't buy the proportioning valve theory. Assume the brakes worked before. How would proportioning valve cause the calipers to stick closed? I can't find the schematic of the prop valve but this seems like an unlikely failure mode.

I think that the MC operating rod is set incorrectly. Prior to you bleeding the brakes you said you had a spongy pedal. With a lot of air in the system you could probably drag one or more brake pads, due to a incorrectly set MC operatiing rod, and get away with it. With air in the system, it would manifest by feeling like progressively worse braking as the H2O in the brake fluid, due to air and old fluid began to boil. However, there was so much air and H2O in the system that it never generated enough pressure to clamp the calipers on to the extent you noticed. You could compensate by pumping the brakes as well. With bleeding the brakes you've taken enough of the compliance out of the system and now with dragging brake pads you actually expand the system, through heating, enough to clamp on the brakes.

I bet all four calipers are clamping down.
Check the free play in the brake pedal. It probably doesn't have enough. I wouldn't blame the fluid, other than to say it should have been changed at some point in time.. (IMG:style_emoticons/default/beer.gif)

If this isn't it I'll deny everything. (IMG:style_emoticons/default/burnout.gif)

Later,
Kevin