Dragging calipers on my '73 conversion

[Ross Wooldridge]

The 2nd pic is closer... generally the push rod should touch the master cup at about 1/16th of an inch out is the rule of thumb. Yours looks like a 1/4 which isn't too far off... you could try putting 1/16th inch thick washers or a piece of thick felt between the master and the booster to get it right...

If it's feeling better you're on the right track.

 

[traintech55]

I believe there is a spacer that goes between the master and booster. I will double check mine in the morning and let you know.

 

[Zymurgy]

I believe there is a spacer that goes between the master and booster. I will double check mine in the morning and let you know.

Thanks for checking for me. Never even thought that might be part of it too.

 

[cantflip]

Finally got in my shop late this afternoon. Saw I could only move the booster push rod about a 1/4, so bench bleed my new '68 master.

The good, fastest I have ever bench bleed a master and didn't seem to introduce any air in the system in the master switch.

Took it for a test drive within about 10 miles both calipers started closing. 3 miles from home at 6 1/2 miles cool down intervals.

I never touched the push rod so I turned it all the way in. The brake pedal now feels right to me, before it would brake immediately, now there he typically movement before the brakes are engaged.

I ran out of time for a test drive but did the test with the master cover off with a piece of plexy glass. No helper, but when I looked at it there was fluid dripping from it so I believe it passed

I included 2 pictures one to see if you think he push rod is the right length after the rebuild. The second show when I first started getting resistance when I was bolting the master back on.

View attachment 123263 View attachment 123264

The other guys with similar setups are your best source for info from here. The resistance bolting the master back on causes me hesitation. The "master cylinder test" with a partner to observe the action of the compensation ports still should be done to verify your suspicions. To get an idea of what you should see, you could bench bleed the other master and watch the turbulence carefully... BTW... the return springs of the rear shoes is the main cause of the more violent squirting action when releasing the pedal on the car... too much is supposed to indicate out of adjustment shoes, but there is always some there in my experience. Just mentioning so you have a greater understanding of what you are seeing during this test.

 

[Zymurgy]

The saga continues I took a master brake test with my phone. The video show me pushing the brake and then pushing the brake 5 times fast. Didn't seem like a geyser to me as the test suggested. Here is the test. I did this yesterday.



I then took it for a 3 miles test drive. The brakes are dragging just as bad as with the other master.

Jump to today I tried flat washers hoping this might cure my problem. I started feeling resistance at a 1/4" so I added equivalent to 3/16" giving it a suggested 1/16" of resistance. Failed test, no reaction. Added just a 1/8" same result, back to no washers, now hardly any fluid movement and was in the same position as the video.

BTY during these tests I had the front wheels off the ground and the wheels got hard to turn only spinning freely when I would crack the bleed valve on the he calipers

I am really at my wit's end. Could I have damaged other brake componores after last week's test drive where I really heated up the rotors?

 

[Ross Wooldridge]

Doubtful. If the hoses are not collapsing, and the metering (prop) valve is OK and connected properly, and the calipers are functioning and not seizing, and you've truly narrowed it down to the booster/master combo, then you really need to review stuff.

As far as I can see, all the major components are new or rebuilt by trusted rebuilders. That does not eliminate a faulty component, however. We've all experienced new faulty items, and sometimes, more than one of the same unit. I know I've gone through things like calipers where 3rd and 4th time's the charm.

Let's review:

Could the booster be the issue? After rereading all three pages, I don't see any attention being paid to the booster other than you said it was rebuilt by a highly acclaimed rebuilder. Could the booster still be bad? Could the booster hanging up for some reason? This would make any master cylinder look bad... hard to diagnose too. Call the rebuilder for guidance on how to diagnose if it is not releasing after warmup.

Try a THIRD master cylinder. Could be just your bad luck to get two shitty ones.

Double check the calipers, however, I think you've ruled them out because they release when you crack the bleeders...

I feel your frustration. Stick with it.

 

[pomonamissel]

sometimes the hoses deliver fluid but don't return it , hoses break down and close the through hole after the pressure stop coming from the master , should free up if you check off the bleeder valve . and was that proportioning valve replace for a disc/drum type , and the master cylinder does not have the same pressure check valves , disc uses a @2lbs , drums @8lbs . be sure of what you got .

 

[300rag]

Goldie likes giving you a hard time, I think. Wasn't there an issue last year or so that kept you rechecking your work?

 

[cantflip]

The saga continues I took a master brake test with my phone. The video show me pushing the brake and then pushing the brake 5 times fast. Didn't seem like a geyser to me as the test suggested. Here is the test. I did this yesterday.



I then took it for a 3 miles test drive. The brakes are dragging just as bad as with the other master.

Jump to today I tried flat washers hoping this might cure my problem. I started feeling resistance at a 1/4" so I added equivalent to 3/16" giving it a suggested 1/16" of resistance. Failed test, no reaction. Added just a 1/8" same result, back to no washers, now hardly any fluid movement and was in the same position as the video.

BTY during these tests I had the front wheels off the ground and the wheels got hard to turn only spinning freely when I would crack the bleed valve on the he calipers

I am really at my wit's end. Could I have damaged other brake componores after last week's test drive where I really heated up the rotors?

Try not to get frustrated. That never works out well. I would say you most likely have open compensating ports by that video... it is hard to tell for sure. I have switched to this manual to better match your components.
http://www.mymopar.com/downloads/servicemanuals/1968_Plymouth_Service_Manual.zip
and I am looking at page 5-68 and on...

Because you can get the system to hold pressure on the brakes while on your lift (I did mention you suck for that already)... this just got much easier to diagnose.

Pump the brakes until you have a firm pedal... if the front wheel is tight, open the line to the master cylinder... did fluid squirt out, or drip out? Is the wheel now free?
If that freed the wheel= master cylinder/booster issue.

If not, go to the steel line at the brake hose. Same preconditioning, pump until the wheel wont turn free, crack that line open... did fluid squirt out, or drip out? Is the wheel now free?
If that freed the wheel= buy a brake hose and retest.

If neither of these seems to work... time to get a closer look at your proportioning valve assembly... so many valves and combinations as the engineers tried to decide just how to tune the disc brake systems in those earlier days... you may have a valve holding the pressure on the front circuits... it may even be that it is still not correctly installed.

Try those tests, and let us know how they turn out.

 

[Zymurgy]

Thanks for walking me though all this. I am going to have a chance to swing by by shop tomorrow afternoon and give those tests a shot.

 

[cantflip]

Thanks for walking me though all this. I am going to have a chance to swing by by shop tomorrow afternoon and give those tests a shot.

You know it would be easier on me if you would just have bought a Formal... I have plenty
of resources for those

Of course then you already would have disc brakes

 

[Zymurgy]

Goldie likes giving you a hard time, I think. Wasn't there an issue last year or so that kept you rechecking your work?

Yes I had a couple of bad new, made in China, condensers. I have the original back on no problems since

 

[Zymurgy]

If the test show a fault in the master or booster I might try bench bleeding the master again. I bled it in 5 minutes and that has never happened that fast for me.

If I remove the master I might even try the old master with washers. I was getting several more miles with it before I was having issues.

I'll figure it out with you guys help and feel like a brake master when I'm done.

 

[cantflip]

I'll figure it out with you guys help and feel like a brake master when I'm done.

Believe it or not... you are well on your way. Lots of the guys doing this for a living wouldn't have any better clue than you have. And you could actually school many of them.

If you narrow down to something other than a hose... it is time to look harder and do something different. Bleeding isn't going to solve this...

 

[Ross Wooldridge]

Agreed - bleeding isn't the solution. I'm watching this very closely to see what comes of it.

 

[Zymurgy]

Ross I am going to take your suggestion of calling the company that rebuilt the booster. I would think they would be to give me some feed back too.

I still think that push rod is too far out. I made an exact measurement from the base of the booster. They at the very least should be able to tell me that spec. If that is wrong maybe something else is wrong in the rebuild.

 

[Ross Wooldridge]

At least you'll have answers and specs to go on.

Keep me posted

 

[70bigblockdodge]

Do the Cantflip test with cracking the steel lines upstream of the hoses that will eliminate the hoses or caliper entrance port, and point you directly at the master/booster

 

[mr. fix it]

I'm routing for you on this Mike
It's real strange what is happening here
I personally think it's a bad check valve in the MC or you have the plumbing crossed somewhere
Have you ever posted a pic of the distribution valve to the front brakes?

 

[Zymurgy]

I'm routing for you on this Mike
It's real strange what is happening here
I personally think it's a bad check valve in the MC or you have the plumbing crossed somewhere
Have you ever posted a pic of the distribution valve to the front brakes?

I did have it hooked up wrong. I removed it completely realized it was divided and hooked up the front brakes to the side with the 2 outputs and the rear to the side with one output. I blew through the box to confirm that this was correct.