Break Man

[Bullzak_83]

I have a question any break guys/women out ther.
70 Chevy cst10 put a disk break conversion on the front, bought a drum to disk break portion valve for the master cylinder. The caliper on the passenger side is sticking, I can collapse the caliper with a c-clamp. My question is do I have the portioning valve hook up wrong?.

[dmjlambert]

How close to the header exhaust tube does that break tube get? In that picture it looks very close, but hard to tell from that angle.

[Bullzak_83]

The tubes are run outside the frame. The truck has barley been around the block. It is sticking as soon as you apply the break

[special-K]

I've read the thread and all I have to say is give me a "brake"!

[Getter-Done]

Did you replace the rubber hoses?

[Bullzak_83]

Originally Posted by Getter-Done

Did you replace the rubber hoses?

Yes everything is is new converted over from drum. I noticed when first installing that side seemed a little tighter against the rotor,than on the drivers side. But I pushed it away to all being new
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[HO455]

Start by having some operate the brakes while you carefully watch each caliper to see if there is a difference in how they operate. Make sure the caliper mounts are square and true and not flexing.

Then when it looks like the caliper has stuck and the brake pedal is up. Loosen the bleeder screw. If brake fluid squirts out of the bleeder then the hose is the likely culprit.

If fluid oozes from the bleeder the caliper is not stuck due to pressure but by a internal mechanical failure.

If you get a shot of fluid then pump the brakes and crack the fittings where the hose hooks to the hard lines. If no pressure then the hose is suspicious.

Since you are dealing with what seems to be a defective new hose I suggest swapping the hoses from side to side and see if the problem moves. It would be cheaper than just replacing the suspected hose.

A caliper has no return mechanism so once the brakes are released a piece of debris between the caliper piston and the body could cause it to stick.

[kwmech]

Pass side vs. drivers side out of the valve does not make a difference in performance. AND PUT A BRACKET TO HOLD THE VALVE!! Don't let it hang from the BRAKE lines like that. Constant vibration from the engine compartment will lead to a guaranteed failure. Are those copper out of the master?

[pjmoreland]

According to this document from CPP, you've got the lines hooked up correctly.

[68 P.O.S.]

Here's a great troubleshooting guide from CPP. See if it help at all. https://www.classicperform.com/TechB...oubleshoot.htm

[Bullzak_83]

Originally Posted by kwmech

Pass side vs. drivers side out of the valve does not make a difference in performance. AND PUT A BRACKET TO HOLD THE VALVE!! Don't let it hang from the BRAKE lines like that. Constant vibration from the engine compartment will lead to a guaranteed failure. Are those copper out of the master?

No they are steel, the front lines are steel.

[Bullzak_83]

No they are steel, and yes I agree I need to add a bracket. The truck is still a work in progress.

[firedemon]

Originally Posted by pjmoreland

According to this document from CPP, you've got the lines hooked up correctly.

on my truck the front brakes only have one line that comes out of the bottom of the proportioning valve then it tees off on the front crossmember on this diagram the one to the front right is capped off . is it possible one side of that prop valve is pushing more fluid

https://www.lmctruck.com/1967-72-che...brake-line-set

[jocko]

Originally Posted by firedemon

on my truck the front brakes only have one line that comes out of the bottom of the splitter then it tees off on the front crossmember on this diagram the one to the front right is capped off . is it possible one side of that splitter is pushing more fluid

Not quite following your statement. By "splitter" are you referring to the old in-line T-fitting that was left over from the drum brake system or are you referring to the proportioning valve itself (i.e. you said it comes out of the bottom of the splitter and then it tees off on the crossmember)? If you are saying that what you have labeled as Driver Side in post #1 goes to ONLY the driver side caliper rubber hose, but just happens to have the leftover T from the drum system with a capped circuit that used to go to the right wheel cylinder in the middle of the line - you should technically be ok. But, personally, I would would eliminate the old T and run a new line all the way from the proportioning valve to the driver side rubber hose. If this is how your lines are routed, I doubt it is related to your issue on the passenger side. If you are saying something else, can you clarify how your lines are routed?

You mentioned you did a "disk brake conversion on the front" and "bought a disk to drum proportioning valve for the master cylinder". Did you also install a disk/drum master cylinder? There is a difference between a drum/drum mc and a disk/drum mc. (you may have indeed done this, just wanted to confirm).

Brake problems are a pain...

[RichardJ]

Pull the Metering Valve pin OUT and hold it out while you bleed the front brake calipers. The pin is under the rubber cap.

[Accelo]

I would shorten the rod a little. The one between the pedal and the master cylinder. It can be just a hair too long and not no allow the piston plunger to uncover the bleed hole. I can't explain why this only evident on one side but I have seen this many times before and the rod adjustments fixes it.

I couldn't find where to source the bleeder tool. I found this on Amazon. It's not evident how it works compared to the factory tool.
A-Team Performance Brake Proportioning Valve Bleeder Tool, GM Style Combination Valves Compatible with DISC/DISC and DISC/DRUM PV2 & PV4 AC Delco 172-1353, 172-1371, Black

[firedemon]

Originally Posted by jocko

Not quite following your statement. By "splitter" are you referring to the old in-line T-fitting that was left over from the drum brake system or are you referring to the proportioning valve itself (i.e. you said it comes out of the bottom of the splitter and then it tees off on the crossmember)? If you are saying that what you have labeled as Driver Side in post #1 goes to ONLY the driver side caliper rubber hose, but just happens to have the leftover T from the drum system with a capped circuit that used to go to the right wheel cylinder in the middle of the line - you should technically be ok. But, personally, I would would eliminate the old T and run a new line all the way from the proportioning valve to the driver side rubber hose. If this is how your lines are routed, I doubt it is related to your issue on the passenger side. If you are saying something else, can you clarify how your lines are routed?

You mentioned you did a "disk brake conversion on the front" and "bought a disk to drum proportioning valve for the master cylinder". Did you also install a disk/drum master cylinder? There is a difference between a drum/drum mc and a disk/drum mc. (you may have indeed done this, just wanted to confirm).

Brake problems are a pain...

proportioning valve if you look at the lmc catalog i posted it shows how the factory 71-72 disk brake proportioning valve was with just 2 lines coming out of it one for the back and one for the front that split on the front cross member with a t fitting

[Bullzak_83]

Originally Posted by firedemon

on my truck the front brakes only have one line that comes out of the bottom of the proportioning valve then it tees off on the front crossmember on this diagram the one to the front right is capped off . is it possible one side of that prop valve is pushing more fluid

https://www.lmctruck.com/1967-72-che...brake-line-set

Hey FireDemon, I know what you are talking about. Mine also had the tee on the frame, splitting the two drums. That all went away when I installed the disk brakes

[Bullzak_83]

Originally Posted by Accelo

I would shorten the rod a little. The one between the pedal and the master cylinder. It can be just a hair too long and not no allow the piston plunger to uncover the bleed hole. I can't explain why this only evident on one side but I have seen this many times before and the rod adjustments fixes it.

I couldn't find where to source the bleeder tool. I found this on Amazon. It's not evident how it works compared to the factory tool.
A-Team Performance Brake Proportioning Valve Bleeder Tool, GM Style Combination Valves Compatible with DISC/DISC and DISC/DRUM PV2 & PV4 AC Delco 172-1353, 172-1371, Black

Accelo, thanks for the info, I will look into the rod length. Also the tool you show I bought one when I bleed the brakes to prevent the piston from sliding while bleeding the brakes.

[Bullzak_83]

Originally Posted by RichardJ

Pull the Metering Valve pin OUT and hold it out while you bleed the front brake calipers. The pin is under the rubber cap.

RichardJ, will the tool you insert into the proportioning valve not do the same thing. Just asking I am not familiar with this type of set up.

[Bullzak_83]

When I say tool I'm talking about the tool you insert into the brake light assembly to prevent the piston from sliding one way or the other

[pjmoreland]

One way you could test the rod length would be to get your passenger side brake into the state where it is locked up and then loosen the two nuts that attach the master cylinder to the booster. If moving the master cylinder forward causes the brake to unlock, then you know the rod is too far forward. If the rod is correctly adjusted, then you should have a small amount of initial free play when you push your brake pedal before the rod contacts the master cylinder piston. If there is no free play, then the rod might be preventing the piston from retracting all the way, as suggested by Accelo.

[Bullzak_83]

Originally Posted by pjmoreland

One way you could test the rod length would be to get your passenger side brake into the state where it is locked up and then loosen the two nuts that attach the master cylinder to the booster. If moving the master cylinder forward causes the brake to unlock, then you know the rod is too far forward. If the rod is correctly adjusted, then you should have a small amount of initial free play when you push your brake pedal before the rod contacts the master cylinder piston. If there is no free play, then the rod might be preventing the piston from retracting all the way, as suggested by Accelo.

Thanks for the info Ill give that a try

[RichardJ]

The Metering Valve is not physically connected to the Pressure Differential Warning Switch. They are two completely different animals.

The Combination Valve has three components. Metering Valve, Pressure Differential Warning Switch and the Proportioning Valve. These three components function completely independent of one another.

By combining these three components into a single unit it saves a bunch of plumbing. Some late '60s GM cars used all three as separate components. The Metering valve is the one with the rubber cap.

Some early Combination Valves had a Metering Valve with a pin that had to be pushed IN WHILE bleeding.

The last image is the actual Metering Valve. There is nothing there but a spring and a Valve seat. It does not connect to the Pressure Differential Warning Switch, PISTON.

It takes 40 - 60 psi to open the Metering Valve.

In the first post, you compressed the caliper and the piston would not come back OUT. With air in the new lines, the MC will compress the air and not generate enough pressure to open the Metering Valve to allow you to bleed the brakes.
By manually pulling the pin OUT, fluid will flow through the Metering Valve allowing a successful bleeding operation.

[RichardJ]

pjmoreland suggestion of loosening the MC nuts is a good way of checking to see if the booster pin is adjusted too far out. They sell a tool (pictured) for checking the actual adjustment. There are ways to to make the measurements without a special tool.