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Brakes dragging


z8987

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I doubt the engineers reversed the reservoir locations for no reason. Not totally sure what it was,  but it costs money to retool and redesign parts. It doesn't really happen for no reason

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9fcbed8bd6ab4d532591d2745cd7aca9.jpg
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Nothing comes out of the bleeder. Is this a rebuild or replace?

I don’t want to take things apart until I know where I’m going. Is this brake cylinder more current than a 1970?


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I've had that happen when the lines were plugged.  Usually happens at the ends of the flexible lines.  This would explain the dragging by maintaining some pressure in the slave cylinder.

Edited by Roberts280Z
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The wheel cylinder in your picture is the old series 1 style. The newer wheel cylinder isn't as tall and the brake line connects going straight in from the back rather than at an angle from the side. Check the thread I linked in post #5 of this thread for a visual comparison of the series 1 wheel cylinder and the newer cylinders.

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44 minutes ago, z8987 said:

Nothing comes out of the bleeder. Is this a rebuild or replace?

Did you press on the brake pedal?  Not clear what you're doing.  Nothing should come out until you apply pressure.

 

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I use a pressure tank at the master cylinder to simulate pressing the pedal, and yes.  That pressure bottle saved my marriage. LoL

 

The pressure differential switch has a line to each front brake and only has one line going to the back where it connects to a proportioning valve.  This makes me believe that master cylinders are marked for a reason.   All the lines are the same diameter, so that makes me think the back brakes may possibly require half the pressure?   

 

FYI - I learned that the "Differential Switch" is what the master cylinder is connected to in the engine compartment.   The proportioning valve is mounted in the back of the car and controls the the volume of brake fluid to the calipers.  

Edited by z8987
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Disconnect the line at the wheel cylinder.  Use your pressure device at the master cylinder and see if fluid comes through the line.  If it does then the bleeder valve or the wheel cylinder is clogged.  If it doesn't then there's a blockage before  the wheel cylinder.

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The last post in this thread by beermanpete explains how the master cylinder functions and why the lines from the master cylinder need to go to the proper area on the differential  switch in the engine compartment.  

 

 

 

The master cylinder for sale at zcardepot also explains what's going on. 

https://zcardepot.com/products/brake-master-cylinder-1-wilwood-240z-260z-280z

 

Edited by z8987
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2 minutes ago, Zed Head said:

Thought that you were working on a rear wheel cylinder and/or stuck rear brake (Brakes dragging.), one side only.  Not clear what the subject is.

1. My left rear drum was stuck. I found today that no fluids come out of the brake cylinder when it's pressurized and I open the bleeder. 

2.  I also discovered that my master cylinder is not connected to the differential switch as it should be. 

 

I started tracking all of this here.  For me at this point it's the same issue.  I have noticed the front brakes dragging which can be caused by #2 above.  

 

I believe getting my master cylinder / differential switch setup properly. 

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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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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.

image.png

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'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.

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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.
image.png.df4946a7179fe6c69e11ca0db2a295ef.png

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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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.  

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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.  

 

800-360_wilwood_master_1000x.jpeg

ds439.pdf

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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."

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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...

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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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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?   :geek:

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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.

 

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p.s. And, just because others, apparently, use a residual pressure valve on mixed drum and disc systems it doens't mean that Nissan did.  Despite the extensive descriptions that Nissan put in to the brake chapters, the only mention of a difference at the MC between front and back is about the reservoir.  The closest thing to an RPV is the check valve that they show.  But there is one on each side and they look the same.

image.png

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Yeah, since most of us here (including the OP) aren't running Wilwood stuff, then that datasheet is pretty much moot About the only thing that Wilwood data sheet did for me was confirm that "residual pressure valves" are really a thing, and (for me) raised the question of "Is Wilwood the only people who do this, or does everybody do it?"

And after some digging "on the internet", the answer appears to be "everybody does it and have been doing it for decades."

So my bottom line takeaways from all this are pretty much identical to yours...

Some sort of residual pressure valve is a good idea if you are running drum brakes with return springs*. And if you are running disk brakes and have your master cylinder mounted lower than the calipers, you should also use one, but it should be a lower pressure rating.

There could easily (probably?) be a difference between F and R outlets on the stock master cylinders and there could be issues if you don't account for that in some way.

I think we're all on the same page!

 

* I can get into my take about the "why" if anyone is interested, but not sure anyone wants to hear it at this point.   LOL

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