CPP power disc brake conversion, brakes dragging/locking up

[Blue Lepard]

Hi everyone. My wife and I just bought our first Chevy poject, a 1966 Chevt C10 short bed single cab. So getting right to it. I bought the CPP front power disc brake kit. I installed it. Everything was working nicely for about 20 min of driving when I noticed the truck felt slow. So when I had to do a quick stop, well she stopped fine. But when I let my foot off the brake. Nothing truck wouldn't go. Then I excelertated to make her go. The truck struggled but started. I could feel the brakes where still engaged. But after appoximately 5 seconds I could feel the brakes releasing a little. So I continued to drive. I hit the bakes again the truck stopped nice, the brakes didn't lock to a skid or anything. But when I took my foot off the brake. The truck did not go. I hit the gas and fought the brakes but after about 5 seconds I could feel the brakes releasing. Same thing all the way home. I did the usually,

1) checked the free play on the rod from the booster to the pedal, all good.
2) loosened the nuts off the master cylinder to the vacuum booster.
3) loosened the front brake master cylinder nut and let a little fluid out
4) loosened the front bake nut on the pro valve until a little fluid came out.
5) checked the calipers for missalignment
6) checked the rear brakes for brake shoes locking

NOTHING…!!!


While the truck was up on jacks, I hit the brakes (fluid still hot) and the front brakes locked up. Nothing I did would release them, except time. I waited about 5 minutes and walked over to them. Guess what they were free. So, with everyones experiance, what is going on.

[lumpy63]

Dumb question ….. did you try putting truck in reverse and backing up a couple of feet ? You have done all the correct diagnoses checks, I too have had brake locking issues with a cpp master cyl set up under panic braking situations only a couple of times . and I drive the crap out of my 56 60.000 mi. in last 4 yrs only happened maybe 4 times , found that stabbing the pedal a couple of times they would release. otherwise this truck stops on a dime even auto crossed it a few times at good guys events .

[Blue Lepard]

Well, I have backed it up several times. If I back it up fast then hit the brakes same issue. The brakes lock up for 3 seconds. Then the truck slowly starts to move. But forward, man…the truck just doesn't want to move.
Does going in reverse and hitting the brakes adjust or tighten the rear drum brakes? All the braking issues get worse when the truck is hot.

[lumpy63]

how close are the brake lines to the exhaust ?

[lumpy63]

if your rear brakes are self adjusting they will adjust by backing up and hitting the brakes , but I don't think thats your problem.

[scott657]

Lines crossed maybe? so the fronts are connected to the residual pressure valve for the rears? Just a thought. Or the m/c isn't retracting far enough due to defect or improper adjustment

[padresag]

are the front brake hoses new. if not is possible that you have one collapsing. does it appear to pull to one side after you let your foot of the brake pedal to go forward?
ron

[Blue Lepard]

Mornin guys, So the front rubber brake lines are brand new from CPP. I don't think the brake lines are crossed, only because CPP had already put the master/booster/and prop valve all together in one package. I also checked the instructions and everything looked right. I have 292 motors, so there is tons of room. The brakes lines aren't near any heat source. Pretty much stays locked up when it is cool for about 3 seconds before moving forward. I noticed last night that it doesn't appear to do it in reverse.

[padresag]

you still have a rear rubber brake hose. it has the symptoms of a brake hose. holds the brake on and the slowly releases. easy check. elevate the rear wheels and apply the brakes. if the rear wheels won't turn. if it happens on the front it is usually singular; one side

ron

[Blue Lepard]

Cool. The rear brakes are not locking up. Only the front. BUT, I did notice the rear rubber hose is the original or close to it. It is in pretty bad shape. So maybe that could be the problem.

[padresag]

brake hoses will only effect the wheels that they go to. I take it that you had drums on the front before. did you change master cyl and or add a proportioning valve?
ron

[Blue Lepard]

I bought the CPP kit that is an all in one kinda thing. The master/booster and prop valve all come together and hooked up. They do all the installation and clearances with the shaft that goes between the master and booster. So basically I bench bleed and throw it in. Yup disc brakes now.

[padresag]

if the fronts are locking and the rears are not that eliminates the rear. if they do that when the brakes are applied and not releasing it is something that is holding the fluid there and not allowing it to return to the master; hoses, prop valve or check vavle in the master. is it an adjustable prop valve?
you bled them l/rear, r/rear, r/front and then l/front?
or you got a hunk of crap in the front lines
ron

[61K10]

sounds like the push rod between the booster and the master cyl needs a little more clearance? I had to shorten mine some. my brakes weren't locking but draging some. (you couldn't push the tk by hand) Just a thought.

[Blue Lepard]

I went to CPP today. After speaking to a tech, he said that it was the prop valve and that they have been having a lot of them come back. He said there is a cylinder with a piston in it (Im guessing the residual valve) that is sticking, ie dragging and locking brakes. I took my prop valve off, took it down there. They gave me a new one. I installed it on my truck, and so far…well what a difference. But I have lost some faith in them…so I will drive it for the next couple of days and see if this prop valve continues to work.

[lumpy63]

Great news! Thinking that could be my problem too, thanks for the input

[doobiebro]

I bought the whole set up from CPP for my 60 too. New brakes, brake lines etc. Also had a leaking prop valve and they replaced it too. One day my truck was dragging driving down the road and it almost came to a complete stop with a brake burning smell and lots of smoke! I jumped outside and checked all wheels and the front rims where so hot to the touch. When I gave it time to cool off I drove it home. Next day I removed all wheels and checked the whole brake system. Found out it was the brake pedal return spring not allowing the pedal to return all the way back to the rubber pad stop (worn out). With a small pedal application the front brakes grab 1st and that's how the proportion valve works. To fix the problem I installed a new tighter spring..😀

[pvienneau]

Wow, just ordered a complete disc setup from cpp too (1949 3100). I will let you know how it goes.

[DLW]

Not sure if everyone is aware, but there is a tool your supposed to use in the combination valve when you bleed your brakes. It's purpose is to keep the pressure differential valve from moving to the front or rear when bleeding. Seems the issue some are having may be because this valve moved during bleeding and will not re-center on it's own, you have to manually do it.

A little video of the tool https://www.youtube.com/watch?v=osC7t3s3J7g

A nice video of how a combo valve works and also the tool https://www.youtube.com/watch?v=qPLaPv8DITE

Also some good troubleshooting guides from CPP http://www.classicperform.com/TechBo...t.htm#testprop

Another: http://www.mpbrakes.com/techtalk/how...ing-brake-drag

I don't think this one is a CPP issue or a bad combo valve (this same thing happened to me and it was the PDV had moved), but they should have known how to re-center the valve and offered proper bleeding instructions using the tool.

[Boatracer]

I'm having similar issues with the front brakes dragging. I spaced the master from the booster with a couple washers and that seemed to help, but I don't want to run it with them long term. I'm thinking the new booster is leaking also as the engine now surges like its got a vacuum leak.

[Boatracer]

Update on my problems if it can help others.
The combo/prop valve was the main issue with my front brakes sticking. After two replacements from CPP with the same problem and an added issue of them leaking fluid out of the front spring loaded bleeder port, I bought a new valve from summit racing that doesn't have that bleeder but is for my disc/disc setup and that solved most of the problems. I also had to adjust the pedal for another 1/8" of return and after driving a little bit the whole system is working great. The pedal returns all the way and the brakes are releasing as they should.