Need disc brake help
 

Well I have a 1970 that I converted over to Disc brakes in the front a few years back. My power brake booster and master came out of a 1982ish Chevy truck and I used 1972 parts for the brakes themselves. When I put the disc brakes on I could not remember if when I added power brakes a few years even prior to that time, if I had put the proportioning valve from the newer truck that would be disc/ drum or if it was the old drum/ drum. So I put it all together without knowing and everything worked great and has been for the last few years of daily driving.
I am now up grading to a nicer duel piston aluminum caliper (wilwood D52) on all four corners. I thought the fronts would be an easy switch out of the calipers and done. So I swapped them out last night. Only problem is that when I got them bleeded there is now too much preload on the pads and it is hard to move the rotors even without any pressure on the brake pedal. I thought where everything worked with the GM calipers that it would work just the same with the new Wilwoods. Everything is the same as before the only parts I changed out were the calipers and I switched to stainless steel brake hoses. The rotors and pads are the same ones I was running with my GM calipers.
Any advice would be appreciated as this is my daily driver. I had to borrow a friend’s car to go to work today and hope to get my truck fixed tonight.

Re: Need disc brake help
 

maybe the calipers are a little smaller, i have seen this before and the brake pads are actually rubbing the rotor , sand the pads downa little , or maybe the brackets have the caliper to far from the rotor and the front is dragging.

on the proportioning valve i dont run them, i throw them in the trash on all the race cars i build and just run the lines right out of the MC to the breaks, i have never had a problem with them, and i drive the race cars on the street also..

Re: Need disc brake help
 

I hope not. The pads I have on are already worn down quite abit from use. I oredered these specificaly for a 1972 setup.

Their tech line is telling me to bench bleed my master and bleed my lines again including my rears. Does that make sence?

Re: Need disc brake help
 

well you didnt change the MC did you? it should still be bled, i wouldnt see the need in bleeding the backs , you didnt do anything with them. have you drove the truck since you have put these on , try driving it a block or so and then check to see if it is any better. when the presure is released the pistons should go back in and the caliper it self should have a little play also they dont mount rigid.

Re: Need disc brake help
 

What actually causes the pads/caliper to retract when there's no pedal? Look at those parts and be sure they aren't subject to binding. Beyond that, look at the pedal ass'y and be sure that it isn't putting any pressure on the M/C push rod.

It's gotta be something simple....

Re: Need disc brake help
 

Your gonna have to change the prop valve to a four wheel disc valve. i used this one. http://cgi.ebay.com/ebaymotors/ws/eB...d=270639518160

you either have something not lined up right or the pressure is not releasing from the master, Are all four calipers stuck? Iv seen a bad brake hose hold a caliper, but not all four at the same time. if all four are stuck i would say its either the valve or the master. one of those two is not releasing the pressure.

Re: Need disc brake help
 

the Master clyinder

Re: Need disc brake help
 

Well I pryed gently on the barke pad tabs and backed off the presure just enough for the rotors to spin freely. I looked and nothing looked like it was binding. so I turned on the truck and pumped the pedal a few times shut her off and it is locked up just as tite as before. The pedal feels spungy, has more travel and I hear a air hiss coming from the booster evey time I push the brake in. I dont think I let the master run out of fluid when bleeding but it is possible as it was dark.

Could air in the master cause spongy pedal and locked up calipers?

Re: Need disc brake help
 

Get the brakes tight again. Then loosen the bolts that hold the master cylinder to the booster. Then see if the brakes release. If so, you might need make some clearance. Been there done that. The pin in the center of the brake booster is a bit too long. Pull it out and grind a bit off and repeat the process???

Re: Need disc brake help
 

air in the system would give you a spongy feel, however it wouldn't hold the brakes tight. you might check, the pin behind the M/C like cparman said that would hold pressure to the brakes, but not sure why it didn't do it before the caliper change.
one other thing. sometimes if you bottom out a M/C or go past its normal travel, while bleeding the brakes. if that happens it could tear one of the cups resulting in no pressure or break a piece of rust loose and get stuck in one of the fluid holes, resulting in the pressure not releasing.

Re: Need disc brake help
 

Well I threw the wheels back on and gave her a ride around the block. If I had not checked how hard it was to move the rotors by hand I would never have noticed I had a problem. Because it seemed to roll down the drive way on its own with gravity and didn’t seem to come to a rolling stop any faster than normal I thought that it was fixed. But I was sadly wrong, when I jacked up the front and turned the wheels by hand I could feel it still had the pressure and the passenger side was quite warm almost to where you could not hold your hand to it. I jacked up the back drive side and it did not seem to have a problem. This is really getting to me, thanks for the quick responses guys, I don’t know how I would stay motivated sometimes with out this forum.

Is there any way to bench test my master while it is still on the truck or backflush to remove debris?

Re: Need disc brake help
 

Let me know what you come up with, im having EXACT same problem NEW everything

are your soft lines new too? they collapse over time internally

Re: Need disc brake help
 

Lane, On those Wilwood calipers did you install the sleeves into the calipers that allows them to slide on the caliper mounting bolts? I have noticed that the Wilwood D52's that I have didn't have those installed. I'm thinking that if those sleeves aren' installed and you tightened the claiper bolts, the caliper can't move and may be the binding you feel. Does that make sense?

Re: Need disc brake help
 

oldblue1968chevy I have new stainless soft lines. they were the only other items I replaced besides the calipers.

Captainfab I put the little collar sleeves on the inside side of the caliper bolt hole before I bolted her down.

It is so weird, they are not stuck or grabbing. They work like normal except they do not release pressure all of the way off when the brake pedal is released. Where I have ran GM D52 calipers for the last few years with no problem this really has me stumped.

I am really bummed on this one. I want to get the d52's on the back as well but can’t get this front figured out. It seems like the simplest task are getting the best of me these days.

Re: Need disc brake help
 

It sounds like
1) you still have some air in the lines.
I would bench bleed the M/C on the truck. (just like you would in a vise,... but slowly move the pedal to remove all air in the M/C). Then hook up the lines and bleed them at the wheels.

2) Is there any chance that you got the wrong D52's?
They make 4 different ones.
2 fronts and 2 rears. (different width rotors and different piston sizes)
I wondered if by chance you got a set of D52's made for 1" rotors and they actually fit your 1.25" wide '72 rotors since your using your old worn brake pads?
Maybe they're not backing off enough when you release the pedal.

The worst part,... is when you decide to add your rear calipers,... you're going to have to change the proportioning valve and bleed everything again.

Re: Need disc brake help
 

I had a similar issue with my brakes. New M/C, lines and calipers. The front brakes would drag after applying them. It turned out that the prop valve button was not returning to an extended position. I replaced that with a wilwood adjustable valve and the front calipers would release properly. Just a thought....

Re: Need disc brake help
 

Ok, going to throw this in..

I never 'bench bled' the MC..I have the brakes bled now, the fronts slightly still hold?

And my aftermarket prop. valve AND my stock one, had a button on the front, whats this do? lol

Re: Need disc brake help
 

Well I installed a new wilwood adjustable proportioning valve and that did not solve my problem. I drove it to work and back 64 mikes to see if things would seat in but no luck. I opened my bleeder and that did not back off any pressure, so I think it is something mechanical with the calipers. So I pulled the caliper off again and found that my pads are digging into the willwoods because the point of the pad is the only thing in contact with the aluminum caliper. On my old GM setup it has a full 3/4" of flush surface that the pad and caliper engage. I think this might be what is holding up my brakes. What do you guys think? The first three shots are of the willwoods and the last two are the GM calipers. Look for the red arrows. The pad is flipped to better show the problem, not how I have them installed:lol:

Re: Need disc brake help
 

the one thing I notice is the anti rattle clip the factor caliper used one and i think it held the pad up off the caliper does the wilwood use them as well? if not they may be the problem. just a thought

Re: Need disc brake help
 

Here is an out line of my Brake pad and where they engage the calipers.

Re: Need disc brake help
 

ok. on these trucks 4 wheel drum system is the residual valve in the master ports or the proportioning valve..
if in the valve, there is your issue, as that valve (resilual) keeps 10-15psi on the system to keep the springs in a drum set up from backing off the shoes to far and cause'n a low petal..
used with disc it'll hold the calp on the rotor..