Brakes dragging

[z8987]

Disagree, emphatically.  But, good luck.

I might agree with you. The information I found mostly on this site is how I came up with this.

It’s my understanding that the rear brakes require 10 psi of constant pressure, the front brakes do not. It’s also my understanding that the master cylinder is what maintains the 10 psi for the rear brakes but does not maintain constant pressure for the front brakes. If this is true and the brake lines are reversed, then a constant pressure of 10 psi will be on the front brakes and none on the back. The same thing was said in the referring pages I found above. At least that’s how I interpreted it. It doesn’t make sense to me that a manufacturer would label a product front (f) and rear ® if it doesn’t matter. I have very little experience with this, but I did run into this problem in the past. I’m not here to be right, I’m here to learn. If I’m wrong, that tells me to dig deeper. I don’t know what to look for next. Zedhead, what is wrong with analysis and conclusion? I’m honestly here to learn.


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[Captain Obvious]

Here's another link that talks some about the internals of the master cylinder and the possibility of switching the front and rear lines.

https://www.classiczcars.com/forums/topic/66168-brake-master-cylinder-identification/

[Zed Head]

The proportioning valve affects the parts after the valve.  The master cylinder creates equal pressure and flow in the lines before the valve.

It's difficult to follow this type of thread because the subject changes so often, plus many of the suggestions are not tried.  You started with a single sticking brake drum now you're apparently going to reassemble the hydraulics.  When you're done the drum will probably still be stuck, because it's most likely not a hydraulics problem.

If you're going to take it all apart you might as well remove the line to the wheel cylinder and see if the drum is still stuck.  That will relieve any pressure in the wheel cylinder.  If your premise is correct the drum will unstick.

When you're working on solutions ask yourself why one rear wheel would stick but the other not if the problem was caused by the hydraulics.

[Roberts280Z]

'When you're working on solutions ask yourself why one rear wheel would stick but the other not if the problem was caused by the hydraulics.'

That's exactly the situation I had.  The flex hose at the wheel cylinder was collapsed to the point that you could force fluid into the cylinder by standing on the brakes, but it couldn't flow back out.  This wasn't on a Z, but another vehicle that is 50 yrs old that had original lines and hoses.  This was isolated by disconnecting the hose first at the cylinder, and then at its other end further upstream.

[z8987]

The proportioning valve affects the parts after the valve.  The master cylinder creates equal pressure and flow in the lines before the valve.
It's difficult to follow this type of thread because the subject changes so often, plus many of the suggestions are not tried.  You started with a single sticking brake drum now you're apparently going to reassemble the hydraulics.  When you're done the drum will probably still be stuck, because it's most likely not a hydraulics problem.
If you're going to take it all apart you might as well remove the line to the wheel cylinder and see if the drum is still stuck.  That will relieve any pressure in the wheel cylinder.  If your premise is correct the drum will unstick.
When you're working on solutions ask yourself why one rear wheel would stick but the other not if the problem was caused by the hydraulics.

I’m sorry I’ve tied two issues to one thread. I tried what you suggested and there was no change. That was the first thing I did. I don’t think the m/c issue has anything to do with the brake locking up. I just came across it during my troubleshooting and brought it up.


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[Zed Head]

So that means the MC "issue" is just the fact there's an R where an F is expected.

One reasonable explanation for the F and the R is that it makes it easier for the people assembling the cars to put the big reservoir on the right spot.  The real discussion might be why they decided to switch the reservoirs.  Maybe a decision was made to switch the reservoirs and the switching of the lines followed, logically, but had nothing at all to do with how the stacked hydraulic pistons operated.

Anyway, if you're restoring it or you're going to be at car shows, then making it look right is probably worthwhile.  Otherwise you'll spend hours talking about F and R instead of the other cool things.

I only chimed in here because you implied that the previous owner did not know what they were doing, when they might have actually known exactly how things worked and decided it wasn't worth messing with.  

[z8987]

This is the image of the M/C sold on ZcarDepot . I contacted wilwood technical support to see what they have to say about master cylinders and disc/drum brakes.  His response was absolutely, f/r makes a difference. 

Page two of the master cylinder data sheet ds439.pdf explains the residual pressure valve and how it's necessary for the rear brakes and not for the front brakes.  I'm sold. I think I'll go with the Wilwood explanation.  

 

ds439.pdf

[Zed Head]

Probably right, for when you're climbing those really steep hills.  Good luck.

" If the master cylinder is mounted lower than the disc brake calipers, some fluid flowback to the master cylinder reservoir may occur, thus creating a vacuum effect that retracts the caliper pistons into the housing. This will cause the pedal to go to the floor on the first stroke until it has “pumped up” and has moved all the pistons out against the pad again. A Wilwood in-line two pound residual pressure valve, installed near the master cylinder will stop the fluid flowback and keep the pedal firm and responsive."

[Captain Obvious]

I took a quick look on the web and came up with this. Seemed to be the best detail of the situation(s):

https://www.jalopyjournal.com/forum/threads/tech-brakes-residual-pressure-valves.74978/

After reading through that, I'm not buying the "return springs" part of the theory, and I'm all in that the residual pressure is required only to prevent sucking air into the system at the wheel cylinders. But of course, I'm just a guy who read it on the internet. 

I've got a master cylinder here that I've taken completely apart, including the outlet valves. If I can find it, I'll see if I can determine any differences between the valves from F vs R. Of course, when I took them out, I didn't bother to mark which is which, so...

[z8987]

I took a quick look on the web and came up with this. Seemed to be the best detail of the situation(s):
https://www.jalopyjournal.com/forum/threads/tech-brakes-residual-pressure-valves.74978/
After reading through that, I'm not buying the "return springs" part of the theory, and I'm all in that the residual pressure is required only to prevent sucking air into the system at the wheel cylinders. But of course, I'm just a guy who read it on the internet. 
I've got a master cylinder here that I've taken completely apart, including the outlet valves. If I can find it, I'll see if I can determine any differences between the valves from F vs R. Of course, when I took them out, I didn't bother to mark which is which, so...

Did you read the wilwood data sheet above? Page 2 is pretty clear. My other z i removed the m/c and turned it around 180 degrees, then I connected the lines and slowly turned it back around and plugged it back into the booster.

Tonight I did the new z a different way. I loosened the m/c and removed both lines and reversed them. I had to spend some time on it getting them bent correctly and it’s a much better fit.

Another thing, before I disconnected my front brakes from the m/c, I jacked it up and I spun the tire, the brakes were rubbing. When I disconnected the m/c to the front brakes the brakes quit rubbing. Tomorrow I’ll bleed the brakes and see if the front brakes are still rubbing.

Another thing with the left rear drum, I pressurized the system to 15 psi, and turned the bleeder and I got fluid out of it. I’m a little confused about this, but I’ll dig back into it when I get my brakes bled.


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[Captain Obvious]

1 hour ago, z8987 said:

Did you read the wilwood data sheet above? Page 2 is pretty clear.

Haha! Yes, of course I did. And I found it completely lacking any explanatory detail whatsoever. In that data sheet there was one statement of fact with absolutely no explanation as to the WHY the situation exists. It said "This master cylinder contains internal residual pressure valves for drum brake use only which should be removed and not used in disc brake applications."

Well that's great, but so what? So Wilwood puts a valve into their aftermarket master cylinder. Got it.

But I want way more than that so I dug around to figure out the theory as to the WHY and I found (what I consider the best, most well explained and credible) info at that link I pasted above.

I'm just trying to provide some clarity as to the WHY they are in there because I believe understanding the issue might be the first step in coming up with alternatives.

So with that in mind... How about swapping the check valves between F and R instead of the hard lines? Wouldn't that fix any potential issues for the people who want a different solution other than bending the hard lines?   

[Zed Head]

Thanks for posting the jalopyjournal page, that was a good read.  I didn't actually absorb the whole of the page two of the Wilwood pdf.  It was kind of contradictory, with saying only use it for drums, remove it for discs, then put it back in for discs if the MC is lower than the discs.  ???

The jalopyjournal discussion is a lot like this one, with many different views, not all of which seem based in actual knowledge.  It does seem to show though that there is a reason for an R and an F, and they do differ due to pressure reasons.  So hydraulics do come in to play.  Seems like it would only be for pedal feel though.  Maybe balancing the contact times between shoes and pads, and/or reducing the pedal travel.  

So F and R do matter, for reasons not clear, therefore, also, importance is not clear.  But, since it is a hydraulic matter, if releasing the pressure at the cylinder of the sticking wheel doesn't unstick the shoes in the single drum, then F and R is not the cause of the sticking.

I learned something new.  It would be neat to put a pressure gauge at the ends of the lines just to see how much residual pressure is maintained.  And how long.