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post #1 of (permalink) Old 12-15-2002, 04:46 PM
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Brakes problem

Working on My 71, and running into trouble with getting brakes to work right. I know that all four wheels are completely bled, and the rears are in correct adjustment. Brand new Master cylinder too. Problem is, the pedal still goes almost to the floor before i get brakes, and they aern't that good. My thought was the proportioning valve, but i dont know how to tell if this is bad, or what the effect would be if it was. Another thought was vacuum booster, but if this was bad I would think the pedal would just be harder to push down.Any ideas?
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post #2 of (permalink) Old 12-15-2002, 07:23 PM
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Re: Brakes problem

A couple of possibles.

The new master cylinder - nowdays many of the rebuilders no
longer understand how the m/c works. Maybe it's an English
problem - who knows.

They leave the check valve out of the side that goes to the
drum brakes. Ya gotta take it out of the old one.
When you try to talk to them about it - "No speakee Engli."

The drums need the check valve to keep a little residual
pressure in the line, else air gets in. No check valve for
discs.

And - it may still be the rear's adjustment. OK, you said
they are right, but did you follow correct procedure?

Adjust by tightening until the wheel no longer will move by
hand - make it tight - that centers the shoes.
Back off the adjuster 4 or 5 clicks, it will still feel tight
to turn the wheel.
Step on the brake pedal fairly hard, that centers them again.
You'll notice it's much looser than before you stepped on
the pedal.
If it still drags, back off 2 or 3 more clicks, then again
step on the pedal to center them.

If you don't constantly keep them centered by stepping on the
pedal you'll adjust them waaaaay too loose.
What happens is only one shoe moves back, the other keeps
dragging, making you think it's still too tight.

I rather doubt it's the hold-off valve - aka proportion valve.
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post #3 of (permalink) Old 12-17-2002, 05:54 AM
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Re: Brakes problem

Rrich-please explain this check valve to me. is it something i can take out of another master I have laying around? is there a positive way to tell if its there or not, wothout taking the master apart? thanks for the help so far.
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post #4 of (permalink) Old 12-17-2002, 11:16 AM
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Re: Brakes problem

The proportioning valve rarely goes bad. However, once in a while it does get set off. All it is inside is a piston that'll slide over and block off fluid to the front or rear brakes (whichever isn't building pressure) and then that little wire that comes off it will turn the brake light on.

I'm no brake expert, but it doesn't sound like the proportioning valve. In fact, you probably know more than me. I've never had problems with brakes. Are you getting adequate pressure to both ends? If you press on the pedal fast and hard, does the pedal stop moving and then slowly go to the floor?

If you're using rear calipers the bleeder needs to be pointed up or it won't get all the air out.

I, myself, am more inclined to think you got a lemon of a master cylinder. If you're using rear disk brakes it'd be a good idea to get a 1 ton master cylinder (moves more fluid).
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post #5 of (permalink) Old 12-18-2002, 12:42 AM
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Re: Brakes problem

The check valve is found right in the outlet of the master
cylinder. Look in the hole - if you can see the piston
inside it isn't there. Sometimes it's a spring loaded
ball in a brass keeper, or a rubber flapper.

The check valve keeps about 2-5 lbs pressure in the line
to the rear. Reason is the rear cups are tapered cups, if
no pressure is kept on the edge, the edge can let a tad of
air in. As you drive it keeps letting in a little more
air until you have enough bubble to cause trouble.

Discs use a square O ring, and the pads are always up against
the rotors. If you kept any pressure in that line - ie
check valve, they would constantly keep the brakes applied.

Rebuilders lately, especially the ones that supply the discount
stores like ZonedOut or Krappen take them out. If you adjust
the rear brakes excessivly tight it will work without the
valve -- and they get to sell you new shoes and drums long before
you should have needed them because they wear too fast too
tight.

Take the old valve out of an old MC.

And - the latest thing on shoes - they make the "lifetime"
linings - they make them out of super hard material so they
will last longer, but they don't stop very well.
They'll wear your drums out before anything - if they don't
kill you first.
Compare the expensive "lifetime" trash to the cheap stuff.
The cheap ones are much softer, and stop much better.

The valve/block that that has 4 lines on it - the differential
valve, is NOT the proportioning valve.
That one is used on dual master cylinders - ones where the
front to rear systems are isolated fluid wise. The intention
is in case of a massive master cylinder failure (low fluid etc,)
the little piston inside moves to the side because of the
pressure differential and lets fluid get to the end that
failed. It also usually has the switch to operate the
brake light to inform you there's a problem.

Sometimes that differential valve and the proportioning valve
are built into the same big block of brass, in that case it's
called a Combination Valve.

Many master cylinders that were intended to operate two types
of brakes, discs and drums, have different sized bores,
that gives the different pressures needed for the different
systems with the same pedal effort. Else you end up with
different braking efforts front to rear, creating a
"swapping ends time."
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post #6 of (permalink) Old 12-18-2002, 01:08 AM
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Re: Brakes problem

When I installed a D60 and rear disks, I had to bleed the crap out of it. It must of took 10 times before I started to get some good pressure. I had someone pump while I did the bleeders. The better way to bleed is to pressurize your system like the dealer does. Get more fluid and try to bleed them 5 more times and see what happens.
post #7 of (permalink) Old 12-18-2002, 08:06 AM
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Re: Brakes problem

Bleeding "procedure" can be the culprit too.

Either use a pressure bleeder or do it manually with 2 people.

DO NOT have your helper pump the pedal up and down fast, it
breaks the bubbles up into foam that's near impossible to
get out. The foam will eventually go back to just big bubbles,
but it could take up to 1/2 an hour.

It's important to bench bleed the MC if it has been disconnected
or drained. If you forgot, it still can be done in place.

Bleeding at the wheels:
You yell "push," he pushes the pedal down and holds it there
- no matter if it hits the floor or not - it's still pressurizing.
You open the bleeder, let whatever will come out.
Now close it.
It's imoportant that he holds the perdal down until you get
the bleeder completely closed, else air gets sucked in.
You yell "Up" - he lets the pedal up - and does nothing else.
You wait 4 or 5 seconds - important to let the MC fill completely
again - and it will purge bubbles in it too - just watch.
Now you yell "push" again, he pushes down again.

--- Never have him "pump" or "agitate" the pedal unless you \
want to leave some air in it. ----

Some folks only go through that sequence a few times, but often
leave air in it.
Depending on the system, routing of the lines, like whether
they have upward loops that can trap air, and how quick you
are between bleeding "pushes" it could take 20-30 "pushes"
to get all the air out.
Air gets stuck at the top of an upward loop - sometimes it
takes several "pushes" to get the bubble past that point.

I don't stop the process until I get clear running fluid at
least 8 times. Yes, it wastes a little more fluid, but the
brakes work.

By the way - the mess you make - brake fluid is hydro-scopic
- it will wash off nicely with a garden hose - if it hasn't
sat for long and penetrated the surface. Let it soak into
cement it will stain, then you need bleach.
If you try to remove it with solvents the solvents will causde
it to soak into the cement and cause the stain.

Let us know how it comes out.
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