Re: [AMC-List] combination valve

[Tom Jennings <tomj@xxxxxxx>]

On Wed, 8 Nov 2006, Wayne E LaMothe wrote:

> I am trying to trace a problem in the brakes on my 83 Eagle.  I am
> getting premature (very) rear wheel lockup when braking.  EVERYTHING but
> the combo valve is new.  My questions are these:
> 
> 1.  Is this a bendix or kelsey hayes valve?

It's probably not a proportioning valve; it might only be
a combo valve that allows the brake-fail switch to see both
brake circuits.


> 2.  Is there a centering pin?  There seems to be but it does not move so
> I think it is sending all the braking to the rear wheels.

The switch, centering pin, etc have ZERO effect on brake
hydraulics.  The combo valve has a little shuttle (that tilts
the switch pin) between front and rear circuits that can only
move slightly one way or another; it can't block fluid in either
circuit, even if it fails.

If you recently worked on the rear brakes, it might be
leading/trailing shoes are swapped, adjusters setup wrong,
or other left-right/front-rear parts reversed.


TESTING:

Personally, I like to think up tests to generate symptoms that
give better hints.

Have you pulled a rear drum to take a peek? If a spring breaks,
a shoe could be jamming into the drum.

Do both rear wheels lock up identically at the same time?

The "parking brake" is a handy way to quick-check the rear
brakes; cruising at 20mph or so, pull the release lever and
press the parking brake; the rear brakes should behave like a
regular manual brake pedal, except weaker and "mushier" since
it's a cable that stretches a bit. If they grab badly you know
it's not a hydraulic problem.

If it's all still puzzling, back of the adjusters on both
rear brakes way off, then drive the car slowly; the fronts
ought to be capable of stopping the car without pulling. The
pedal will feel soft and very low because the rears will not
be working well.  If you have no pedal before you drive off,
with the back brakes backed off, it migt be that your fronts
are bad, but more likely a master cylinder problem.

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