Re: [MV] M51 brake misbehavior

From: MV (MV@dc9.tzo.com)
Date: Mon Aug 29 2005 - 15:59:00 PDT


I have an M51 and it constantly uses brake fluid. Don't know where it
goes. I just make sure it is full before I take it out.

I have never had the problem you describe (pushing back), but I would
suspect the air booster. What else but air pressure could be pushing
back??

If your pedal is going further than it should and you have plenty of
fluid, I'd consider rebuilding or replacing the master cylinder. I once
had a 56 chevy truck that had an erratic brake pedal and non-power
brakes and the problem was the master cylinder. I rehoned the cylinder
and put in new seals and the problem went away.

Dave

Dave Sofio wrote:
> What does it mean when, with vehicle (M51) running and a full load of
> compressed air showing on the pressure gauge, my foot firmly on brake
> (say I'm about ready to cut engine, after parking on a slope...) the
> brake pedal decides to "fight back," as in trying to push up against my
> foot, while simultaneously losing a great deal of braking force, feeling
> almost as if not having the benefit of a booster? It's...a unique
> experience.
>
> Possibly-related item: The master cyl was...well, damned near empty
> when I checked it after buying truck. I augmented the stock filler
> setup (none) with a translucent reservoir I installed under the seat
> plus a vinyl hose down to the MC filler port, so now it's easy to check
> the fluid level. But filling it? To my great surprise, it took the
> better part of two14oz bottles of silicone fluid to bring the level up
> (air burping out the filler hose even now, after several miles), yet
> brakes had worked fine and there were no obvious fluid leaks apparent
> before or since. So there could be gobs of air in the lines for all I
> know... but then it's not the air-associated "spongy-pedal" problem I'm
> seeing, and in fact, the brakes are rock-solid, except when this
> moderately-terrifying new problem crops up, with the
> demonically-possessed brake-pedal trying to shove my foot off it!
> I also think there have been a couple of occasions when the pedal sank
> further than it should, such that the pedal arm scraped the slot in the
> sheetmetal floor.
>
> Anybody have experience with this?
>
> Dave S
> Honolulu
>
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