disc brake help... on my impala

[bmfm64]

Not sure where to put this but you guys have been able to answer everything else I have so here we go.... I did a disc brake swap on my 64 impala on the front. The kit included a new master cylinder, booster, rotors,mounting brackets, calipers and new lines for the front. I installed everything and bled the whole system both with foot and with vacuum pump. I've verified that calipers are on correctly, and adjusted the rod between booster and mc. I can drive it just fine but the problem is all the braking is at the bottom of the peddle just before it hits the floor. It will lock up the brakes but just doesn't seem right.... Any ideas?
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[68gmsee]

If you pump the pedal does it seem to come up? If so there is still some air in the system.

Also, can you adjust the length of the rod more?

One thing to do is to couble check the rear drum brake adjustment again so that they barely rub on the drum when rotated by hand. If all the adjustments are correct it could be the master cylinder or the booster.

Master cylinders are cheaper so I'd go with that first. Even if it's new it may still be defective. I've had problems with them before. Be sure and bench bleed according to directions (very important).

[cdowns]

did you install the proper type of proportioning valve with the master cyl?

[406 Q-ship]

Check the rear drum adjustment to help with pedal travel. As for the lock up, is it the front or the rear that is locking up?


BTW there is a great site for Impalas, http://www.impalas.net/

[bmfm64]

Crap, sorry forgot some of the important info, yes I installed the prop valve that came with it, which was supposed to be a disc/drum one. And no the peddle doesnt pump up at all. I will check the rear adjustment and I'm not sure which end is locking up but the front dips pretty good as though the front is doing a lot of the braking. Also when I adjusted the rod between the mc and booster I was looking through the small holes in the bottom of the mc when I put it back on to make sure the rod inside the mc wasn't moving. It never moved but it seems like the rod is far enough out it should be pushing on it.
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[bmfm64]

Just got home from working on my junk, rear brakes are nice and tight. The push rod is adjusted to where it just touches the piston inside the mc. Still the same pedal!I did some research and found that some people say a residual valve in the rear line may help? I took a pair of flat vise-grips and pinch off a front line and still have the same pedal! I also tried to pinch off the rear, it was much stiffer and I didn't want to ruin it, so I'm not positive it was pinched off completely but still had the same pedal... Not sure what to do now, here's a couple pics of the mc/booster, maybe the bore of the mc is too small? The seller has sold tons of these and says the only thing he has ever had to do is adjust the rod between the mc and booster and that was only once? Could be BS but who knows... Any ideas?

[fastwillie 696969]

is there a adjustment to the brake pedal under the dash ? i know i had a old nova with a adjusting nut on the pedal

[bmfm64]

The pedal has a clevis attached to it and the peddle is adjusted all the way up to where the brake lights aren't on.... And there is plenty of swing.
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[68C15]

front and rear lines mixed on master?

[bmfm64]

Originally Posted by 68C15

front and rear lines mixed on master?

I don't think so... Here's how the lines are connected, the back one leaving the prop valve is the rear and the other 2 are the front....It's hard to see but there are 2 leaving the front, the one on top that you can see and one that leaves the bottom from the same area.

[bmfm64]

Anybody?
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[Boog]

I'm no brake techician but know a few things about em. The drum brakes require a residual valve to keep just a small bit of pressure on the lines as the springs on the drum shoes pushes some fluid back into the lines so when you mash the pedal you have a full pedal. Disc systems do not use a residual valve since there is no return springs on the pads. You can buy either a disc/disc or disc/drum master cylinder setup. Do you think this guy sent you the disc/disc setup in error or not? That could explain the excess pedal travel yet good braking. Compare your parts numbers. Just my thoughts on it.

[bmfm64]

I never knew the difference in the prop valves but the guy does sell both 4 and 2 wheels disc set ups, it's possible he sent the wrong one. I bought a 10 psi residual valve last night and will be headed out to install it after breakfast. I'll keep you guys posted.

[Richard H.]

Did you bench bleed the MC to force all the air out? Reset the valve? Are the rear brakes adjusted till they drag slightly?

[Richard H.]

Originally Posted by bmfm64

I never knew the difference in the prop valves but the guy does sell both 4 and 2 wheels disc set ups, it's possible he sent the wrong one. I bought a 10 psi residual valve last night and will be headed out to install it after breakfast. I'll keep you guys posted.

These are my valves , the one on the frame is the front ,2lbs.
Under the dash is a 10 lb; for the rear. Don,t know if the rear is in the pic or not. Ooops ,you gotta move the plastic to see it!

[bmfm64]

Grrr... installed the 10 psi residual valve on the rear, rebled whole system, checked all adjustments for the thousandth time.... Still the same.

[ETsC10]

You may have hit upon it a little earlier with the concept of the wrong bore on the MC.
Last time a similar situation happened here ('71 Pontiac), the kit came with a Corvette MC and never would stop.
After researching the bore sizes on NAPA's site, we hit on a MC for a '79 Chevelle and it worked like a dream.

Not saying this will work in your situation but it's worth a shot.

[bmfm64]

Originally Posted by ETsC10

You may have hit upon it a little earlier with the concept of the wrong bore on the MC.
Last time a similar situation happened here ('71 Pontiac), the kit came with a Corvette MC and never would stop.
After researching the bore sizes on NAPA's site, we hit on a MC for a '79 Chevelle and it worked like a dream.

Not saying this will work in your situation but it's worth a shot.

Thanks, I'll give it a shot, can't hurt... nothing else is working!

[Richard H.]

I looked at your pics and see nothing wrong,the valve I showed on my frame is the same purpose as your two front lines. Adding a 10 lb valve to what you have is redundit. You should only have about 1/2 " free travel in your pedal before it touches the piston in mc. If you can't get that then the rod is not right.

[bmfm64]

I've got the rod pretty close to where it doesn't push the push rod in the mc when bolted in and it doesn't take much movement on the pedal to see movement on the rod through the small holes in the bottom of the mc. I found a set of disc brakes instructions from CPP that explains how to test the prop valve and recenter it if necessary so I'm gonna try that tonight. Also take off the calipers and hold them straight up and down as the way they mount, the bleeder is at the top but I found a diagram that showed the way the holes are drilled in the caliper it is possible to trap a small pocket if not mounted straight up and down. I'll keep you guys posted. This is driving me NUTS!

[powerdriver 1958]

Just wondering is the larger reservoir in the master cylinder plumbed to the disc (front) brakes ?

[bmfm64]

Originally Posted by powerdriver 1958

Just wondering is the larger reservoir in the master cylinder plumbed to the disc (front) brakes ?

Yes the front (larger) reservoir is plumbed to the two front disc lines.
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