New Front Disc Brakes Drag

I'll pile on and bet a doughnut that it's a drum brake residual valve in the works. Second-most common issue after rod adjustment when converting. Propwash must have done this before!

The Horvaths said:

I'll pile on and bet a doughnut that it's a drum brake residual valve in the works. Second-most common issue after rod adjustment when converting. Propwash must have done this before!

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Naw man..............just stayed at a Holiday Inn Express last night. Hehehehehe s_dancing2:

Installed the new Pirate jack MC, the picture below shows how I have it hooked up (Switched from the current picture.) Currently when I have the brakes all bled down and close all bleeders, push the pedal down the front brakes are locked SOLID.

I have checked the booster rod by loosening the MC while the brakes are locked, if I move the MC back from the booster the brakes remain locked.

I am sure the proportioning valve is installed correctly.

Except for the master cylinder ports being wrong, I cannot think of what is the problem.

When the brakes are totally locked, if I open the bleeder at the wheel cylinder the disc's are then free again. Dang it!

Here is how I have the MC plumbed...

**UPDATED: I switched the master cylinder to proportioning valve lines and that cured the front discs locking up, now the rear drums are on all the time. Maybe I got a bad master cylinder residual valve? Anyone heard of that?

Boy John,

You've had one heck of a set of hurdles with your braking system. You're a patient man. I wouldn't guess it wouldn't be a bad residual valve in your new master. Those valves are only 10PSI. That is not enough pressure to overcome the return springs on your drum brakes. That being said, with the quality of stuff now days, anything is possible. If I was in your shoes, here's what I would check:

-Check to insure there is absolutely no preload on that piston into the master cylinder. Look down in the weep hole of the master (in the large chamber, your front brake chamber) to 100% positively insure the piston sits in the same position when free from the booster vs. bolted on. Installing the master you should not notice any sort of interaction of the piston of the master being in direct contact or preloaded with the rod from the booster

-Look/inspect the master cylinder rear drum port to see if something in that port is blocking the free flow of fluid back into the chamber. You can also remove the residual valve from that port, if you want to troubleshoot to see if the residual valve is bad

-Check to insure the rubber portion of your rear brake line is not collapsing in on itself. This is the line that runs from the mount on the rear floor pan, down to the rear end.

-Check to insure the rear drum hardware, springs & shoes are installed correctly.

-If you still have your old distribution block available, you could temporarily install it to see if is your proportioning valve (aka combination valve in your case) is failing.

-Id do not recognize that particular proportioning valve. I would check/review the specifications on that part to insure it did not also come with a residual valve built into it. It may be one part of a general or universal conversion kit, that does not have residual valves in the master, but uses it in the proportioning valve. Piggybacking residual valves can cause your issue.

I's start there and see where it takes you.

Confused. Lol, nothing new.

The way he has his master labeled, isn't it backwards? Pretty much same deal on my conversion, using a new disc/drum master. The larger (rear) bowl should go to the front disc brakes, since discs take more fluid movement.

Have to wonder if there's a restriction in the master's piston's movement. If so, that would give a brake 'on' signal, if the pistons were not moving fully back. One of the other guys had the same issue...probably wrong parts installed in the master. Pistons wouldn't return to the stop (snapring).
Or, could be a prob in the distributor block. Don't recall one like that either. Without knowing all the setup, could be a block somewhere else.

Well crap, that didn't take long. Pretty much 3 friggin days of lessons in confusion, frustration and then finally... understanding, happiness and brakes functioning correctly!

Through much anguish, cursing, surfing, posting, searching and calling (Propwash is the Man!), I finally narrowed it down to the damn rear drum residual valve in the master cylinder port.

After talking with Will, I ran across a The Ramman video and got up enough courage to tear the MC apart (doesn't it just piss you off to have to tear something brand new apart?)

Sure enough, the dang residual valve was full of crap, looked like paint.

Cleaned it all up, assembled it back, bled her down and brakes, glorious, wonderful brakes! YES! Brakes that don't lock, stick or bind!

Did I mention I have brakes? YES!

Thanks Will and The RamMan for all the help.

Here a vid of The RamMan working his magic...

[video=youtube;J3rIe5_2LoA]https://www.youtube.com/watch?v=J3rIe5_2LoA[/video]

That is awesome to hear!!! Congrat's John, I knew you would get it squared away man. It was a pleasure talking with you and I'm glad I could lend you my 2 cents...

Have fun! and try to keep this one under 150MPH Hehehehehe!

AMX364 said:

You are not the first nor the last to have this issue. I will even now bet that someone else is having the exact same issues.

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You are correct sir! We are having this very issue with our recently completed 67 GTX with a front disc conversion using factory parts. So thankful for this information!

Zancat

Propwash said:

Hey John, may be a silly question, but you didn't use the original drum/drum master for your disc upgrade did you? Sorry, I can't remember if you had your disc upgrade in your resto thread or not.

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i believe this is the problem i'm having. previous owner put 1970 front disc brakes on my 69 RR. had the dreaded front brake drag. proceeded with new calipers and flex line. bled brakes, and are worse. going to pull the m/c right now. my question is how in sams hell do you remove that upper right nut from inside the car? easy enough to get to the other 3. update: i got it out, just a pita though. bet mine has residual valve in both ports. i inserted a paper clip into each port and felt some kind of rubber in there. now to get a new m/c. well, this is one area of the car that i hadn't put money into till now.

miller said:

Confused. Lol, nothing new.

The way he has his master labeled, isn't it backwards? Pretty much same deal on my conversion, using a new disc/drum master. The larger (rear) bowl should go to the front disc brakes, since discs take more fluid movement.

Have to wonder if there's a restriction in the master's piston's movement. If so, that would give a brake 'on' signal, if the pistons were not moving fully back. One of the other guys had the same issue...probably wrong parts installed in the master. Pistons wouldn't return to the stop (snapring).
Or, could be a prob in the distributor block. Don't recall one like that either. Without knowing all the setup, could be a block somewhere else.

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That's my question too. Glad you have working brakes now but are they plumbed up wrong? That would work but the timing of not applying fronts first would be an issue.

69roadr said:

i believe this is the problem i'm having. previous owner put 1970 front disc brakes on my 69 RR. had the dreaded front brake drag. proceeded with new calipers and flex line. bled brakes, and are worse. going to pull the m/c right now. my question is how in sams hell do you remove that upper right nut from inside the car? easy enough to get to the other 3. update: i got it out, just a pita though. bet mine has residual valve in both ports. i inserted a paper clip into each port and felt some kind of rubber in there. now to get a new m/c. well, this is one area of the car that i hadn't put money into till now.

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I'd imagine you are having the same issue as John. Yeah, those nuts are no treat at all. I cannot think of a harder nut to get to on the car, than the right upper. Well, maybe the dash pad Pal nuts would rate right up there as well.

khryslerkid said:

That's my question too. Glad you have working brakes now but are they plumbed up wrong? That would work but the timing of not applying fronts first would be an issue.

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The picture is labeled wrong kid. The reservoir for the front brakes is the one located to the rear of the M/C, (closest to the firewall). Going through his last couple posts, he mentions that he did swap it back to the correct configuration.

Propwash said:

I'd imagine you are having the same issue as John. Yeah, those nuts are no treat at all. I cannot think of a harder nut to get to on the car, than the right upper. Well, maybe the dash pad Pal nuts would rate right up there as well.



The picture is labeled wrong kid. The reservoir for the front brakes is the one located to the rear of the M/C, (closest to the firewall). Going through his last couple posts, he mentions that he did swap it back to the correct configuration.

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Yes sir Will, picture is labeled wrong, but it is also plumbed wrong in the picture, the larger reservoir (front disc) needs to be plumbed to the front of the distribution block (left side) and same goes for the rear reservoir.

Are you talking about the master cylinder bolts? Haha, my hood is off and also my hood hinges, I can get right at them... no problemo? whats the big deal? hehe :frog:

Disc/drum master cylinder...yeah, there's differences internally between them, and drum/drum masters. Can't remember what year model (maybe 67, for my 64), but just make sure it is the right kind for the brakes type.