[Old Bird]

Sounds like a brake line that is sucking air and did not seal tight. Check any and all connections

[chipster]

"What would cause us to get a constant stream of bubbles when depressing the pedal, but no bubbles when using the pressure bleeder?"

There should be a residual pressure valve in the combination valve, in the fitting that the line to the rear brakes fits into. If this valve is missing or not working properly, It would allow the seals in the rear wheel cylinders to act as check valves, letting air into the system as the pedal is being released, but sealing up tight under any pressure so that no fluid could leak out. That is why you are getting bubbles with the 2-man method, and not with the pressure bleeder.

A drum/drum system has a residual pressure valve in each outlet port on the master
cylinder.

A disc/drum system has a residual pressure valve in the combination valve assembly, in the outlet to the rear only.

A disc/disc system has no residual pressure valve. Make sure that you are using the right combination valve and that it is connected properly.

I suppose, that depending what master cylinder and kit you are using, it might be possible that the residual pressure valve is in one of the outlet ports on the master cylinder. If that were the case, it would be critical to have the correct line going to the rear on the master cylinder.

[HWYSTR455]

If you keep getting air, then it's a leak, or a bad master. You bench-bled the master, right? Maybe the bleed screws aren't seated all the way, maybe take a look at that. As for a residual valve, regardless, you shouldn't get air. When you are bleeding the rears, (fronts too for that matter) you need to go back and forth between the sides. If your bleed tank holds enough fluid, open both backs at the same time.


.

[Jimbro727]

Thank you so much for the replies.

Originally Posted by chipster

"What would cause us to get a constant stream of bubbles when depressing the pedal, but no bubbles when using the pressure bleeder?"

There should be a residual pressure valve in the combination valve, in the fitting that the line to the rear brakes fits into. If this valve is missing or not working properly, It would allow the seals in the rear wheel cylinders to act as check valves, letting air into the system as the pedal is being released, but sealing up tight under any pressure so that no fluid could leak out. That is why you are getting bubbles with the 2-man method, and not with the pressure bleeder.

A drum/drum system has a residual pressure valve in each outlet port on the master
cylinder.

A disc/drum system has a residual pressure valve in the combination valve assembly, in the outlet to the rear only.

A disc/disc system has no residual pressure valve. Make sure that you are using the right combination valve and that it is connected properly.

I suppose, that depending what master cylinder and kit you are using, it might be possible that the residual pressure valve is in one of the outlet ports on the master cylinder. If that were the case, it would be critical to have the correct line going to the rear on the master cylinder.

The residual pressure valve makes a lot of sense, but if I'm understanding you correctly, wouldn't the symptoms occur on both sides of the rear brakes? I get solid fluid out of the passenger side, this is only occurring on the driver's side. Could it still be the residual pressure valve? It is a disc/drum setup by the way.

Originally Posted by HWYSTR455

If you keep getting air, then it's a leak, or a bad master. You bench-bled the master, right? Maybe the bleed screws aren't seated all the way, maybe take a look at that. As for a residual valve, regardless, you shouldn't get air. When you are bleeding the rears, (fronts too for that matter) you need to go back and forth between the sides. If your bleed tank holds enough fluid, open both backs at the same time.


.

I did bench bleed the master, several times. We were wondering if that could be the issue, if somehow I didn't bleed it correctly, or we let more air in accidentally (we don't think we did). We were dreading taking it off again, but it's worth a shot. Would air in the master cause so many bubbles? The fluid looks like soda using the two man method. Opening both sides is interesting, we can give that a shot.



I'd also like to mention that the bubbles happen instantly after switching from the pressure bleeder to the two man method. If there was air somewhere being forced into the system due to the two man system (combination valve, leak, M/C), wouldn't we get solid fluid for at least a few pumps, and then some bubbles? The bubbles happen instantly, which makes no sense. Taking this into account, the only possibility would be that the bleeder is letting air in, but only under the amount of pressure created by the 2-man method, and not by the 10psi or so created by the pressure bleeder. Does that logic make sense?

[chipster]

Originally Posted by Jimbro727

Thank you so much for the replies.



The residual pressure valve makes a lot of sense, but if I'm understanding you correctly, wouldn't the symptoms occur on both sides of the rear brakes? I get solid fluid out of the passenger side, this is only occurring on the driver's side. Could it still be the residual pressure valve? It is a disc/drum setup by the way.



I'd also like to mention that the bubbles happen instantly after switching from the pressure bleeder to the two man method. If there was air somewhere being forced into the system due to the two man system (combination valve, leak, M/C), wouldn't we get solid fluid for at least a few pumps, and then some bubbles? The bubbles happen instantly, which makes no sense. Taking this into account, the only possibility would be that the bleeder is letting air in, but only under the amount of pressure created by the 2-man method, and not by the 10psi or so created by the pressure bleeder. Does that logic make sense?

It is very possible that one wheel cylinder is sealing better than the other. I would be willing to bet that that's how all that air is getting in. And that is why you are only getting the bubbles on one side, instantly. If the leak were somewhere else, the bubbles would take longer to appear. I think at this point I would replace the cylinder on the side with lots of bubbles with a good one from NAPA. And yes, I think a lack of a residual pressure valve could still be a factor too.

What is happening is you are sucking air through your driver's side wheel cylinder. There is no doubt about that from what you have described. It is either being caused by a faulty wheel cylinder, lack of a functioning residual pressure valve, or both. As I said before, the first thing I would try would be a new wheel cylinder on the driver's side. If the problem remains, add a 10lb residual pressure valve to the line to the rear. I would NOT use the 2-man method to bleed the brakes, because you risk damaging the seals in the master cylinder, and it is just a major PITA. Power bleed or gravity only. I only use gravity.

[Shiny]

What exactly was happening with these bad cylinders? Is it just that they're sucking air in through those seals?

What I read somewhere was air can be sucked past the cups inside the bore. Apparently there are different designs for the cups, with later designs adding expanders to reduce this. This has nothing to do with the boots you see on the outside, but something about the piston cups inside.

Maybe some day when I get to work on my car again and replace those rears, I'll see if I can suck air by pulling a vacuum on the port. It might bring closure for me before I launch them as far as I can throw them.

I share your pain.

My combo valve is from inline tube, so I'll call them and confirm if it does or does not contain a residual pressure valve.

Mine too, along with my master. I trust the company and they provide great quality products and support. One of their techs told me it had the resid pressure valve, another said no. Gotta believe that thousands have been sold and used with success, with or without the resid valve.

If I were doing it again, I would not think about the resid pressure valve until replacing the rear cylinders. Adding the valve is a pain because you have to break the line, chase fittings, flare the tubing, etc. and when you are done, it looks wrong and you've added more connections.

if I crack a rear bleeder open, shouldn't fluid stream out since it's under 10lb. of pressure from the residual pressure valve?

I don't think you would notice. There is nothing pushing on the system, so there won't be enough displacement when you crack the bleeder to see much fluid. It would take a lot of residual spring stretch or other source of displacement to cause a steady stream. 10 psi is not enough to push the shoes against the springs, so at rest, the springs will retract the shoes and push the pistons back, then end up with just that little bit of pressure (10 psi) left. Without the valve, the springs would push back the same, just wouldn't leave the 10psi residual.

Good luck with this.

Mike

[Jimbro727]

Thank you VERY much for the responses, guys. It sounds like everyone's in agreement that I need to ditch these wheel cylinders in favor of some NAPA units. I'm going to order two, replace the passenger side, see if that helps, and if it does, replace the driver's side as well for peace of mind. I'm also considering buying a M/C from NAPA - does anyone think that the M/C could be causing some of these issues? After some googling, I've found a lot of people questioning the quality of parts from some of the chain parts stores (autozone, advance, pep boys, etc.). If my problems aren't solved by replacing the wheel cylinder, then I'll probably want to try bleeding the master again, in case I let some air in during all of this. If I do that, though, I think I'll just pick up a new one from NAPA (again for peace of mind), since it's the same amount of work as bleeding my existing one.

Originally Posted by chipster

I would NOT use the 2-man method to bleed the brakes, because you risk damaging the seals in the master cylinder, and it is just a major PITA. Power bleed or gravity only. I only use gravity.

That's fine, the 2-man method is annoying anyway, my only concern is that when you use alternative methods, you gloss over potential issues (like this one we're discussing here), since you're not using the brake system (really just the M/C) in the same way it is used when you're actually braking. Had I only used my pressure bleeder, I wouldn't have discovered this wheel cylinder problem.


Again, I can't thank you guys enough! I'll try to get to those cylinders this week/end and report back!

[Shiny]

Jimbro-

Sucks about the knee. Good to hear you are recovering enough to tackle your brakes again.

Mine are working well enough to tell me chipster probably has the diagnosis nailed, but I suggest replacing the rear cylinders before anything else. You said you tried that, but check the picture from Walt in this other thread and tell us which style rear cylinders you have ( I put it here too). So far, what I call the "evil cylinders" are proving to be a big part of this problem for at least me and another victim (Walt) who figured it out.

http://forums.maxperformanceinc.com/...d.php?t=598515

I had installed new or rebuilt rear cylinders when I first started working on my car. At the time, I had drums in the front. The drum master has a residual pressure valve built into it. The brakes bled fine and worked fine. I started having trouble when I went to discs in the front and replaced the master. Like you, I installed an aftermarket combo valve. When I started having trouble, the rear cylinders were the last thing on my mind. I wasted hours and money replacing everything else.

I ended up adding a residual pressure valve, which was a major pain, so go down that path as a last result. For me, it just confirmed the problem was sucking air through the rear cylinders when the pedal was released. When I am next united with my car, I plan to replace the rear cylinders with the NAPA style for peace of mind.

I was never convinced the aftermarket combo valves have any residual pressure function. I got 5 different opinions from 5 people. I know that mine does not have a check-valve at the rear port (the type valve used in the drum master). The disc master cylinder definitely does not have this function on the rear line. Most people must get away without it. I don't know for a fact, but I think your odds will improve if you use the NAPA style rear cylinders. I do know for a fact it is a cheap and easy thing to try before swapping everything else in the system.

Let us know which style rear cylinders you have....

Left is Walt's NAPA replacement, right is the style I have

[Jimbro727]

Update: Operating under the assumption that we made some sort of progress, since the pedal did seem stiffer, we bled the front brakes to ensure no air was there (and there wasn't any), started her up, and tested the brakes. They still feel spongey and too soft, BUT they do stop the car. Pushing the pedal to the floor (which is very easy to do), stops the car on a dime (I didn't take it on the road, but brought it up to 10MPH or so in my driveway. The car can now be stopped normally without putting the pedal to the floor - at about halfway down, I can bring the car to a normal controlled stop. BUT, the brakes still do not feel right. And I probably shouldn't have to put the pedal to the floor to stop the car quickly going 10MPH, I should be able to stop quickly from that speed before the pedal is anywhere near the floor (right?).

Thoughts?

Originally Posted by Shiny

Jimbro-

Sucks about the knee. Good to hear you are recovering enough to tackle your brakes again.

Mine are working well enough to tell me chipster probably has the diagnosis nailed, but I suggest replacing the rear cylinders before anything else. You said you tried that, but check the picture from Walt in this other thread and tell us which style rear cylinders you have ( I put it here too). So far, what I call the "evil cylinders" are proving to be a big part of this problem for at least me and another victim (Walt) who figured it out.

http://forums.maxperformanceinc.com/...d.php?t=598515

I had installed new or rebuilt rear cylinders when I first started working on my car. At the time, I had drums in the front. The drum master has a residual pressure valve built into it. The brakes bled fine and worked fine. I started having trouble when I went to discs in the front and replaced the master. Like you, I installed an aftermarket combo valve. When I started having trouble, the rear cylinders were the last thing on my mind. I wasted hours and money replacing everything else.

I ended up adding a residual pressure valve, which was a major pain, so go down that path as a last result. For me, it just confirmed the problem was sucking air through the rear cylinders when the pedal was released. When I am next united with my car, I plan to replace the rear cylinders with the NAPA style for peace of mind.

I was never convinced the aftermarket combo valves have any residual pressure function. I got 5 different opinions from 5 people. I know that mine does not have a check-valve at the rear port (the type valve used in the drum master). The disc master cylinder definitely does not have this function on the rear line. Most people must get away without it. I don't know for a fact, but I think your odds will improve if you use the NAPA style rear cylinders. I do know for a fact it is a cheap and easy thing to try before swapping everything else in the system.

Let us know which style rear cylinders you have....

Left is Walt's NAPA replacement, right is the style I have

Thanks!

My combo valve is from inline tube, so I'll call them and confirm if it does or does not contain a residual pressure valve. I actually did come across that thread after posting to this one. It looks like I have one of the "evil" cylinders, with the rubber on the outside. Did you find issues with many of these? Replacing that one cylinder (which was also an "evil" one), seemed to help, but I'm still having issues. What exactly was happening with these bad cylinders? Is it just that they're sucking air in through those seals? I don't get any air out of the passenger side rear, so maybe that one is OK and the driver's side is not? If I pump the brakes a few times and then pressure bleed the driver's side rear, I should be able to test for this, right? If I get solid fluid, then it's not sucking in air, if I get bubbles, it is.

And I almost went to NAPA to replace the driver's side cylinder on Saturday. DAMMIT!

EDIT: I just did some quick research on residual pressure valves, and it sounds like this could be my problem as well. Given my symptoms, what do you guys think? Inline Tube is closed right now, but if I'm understanding what the valve does correctly, if I crack a rear bleeder open, shouldn't fluid stream out since it's under 10lb. of pressure from the residual pressure valve?

[Jimbro727]

UPDATE: I replaced both sides with NAPA wheel cylinders. After replacing the driver's side (where I was getting constant bubbles), it was a night and day difference. The brakes still weren't where I'd expect them to be, BUT it wasn't like having NO brakes. I then replaced the passenger side, and the pedal was either the same or a little worse. It's tough to gauge that sort of thing.

We then decided to start fresh and bench bleed the master. We got some bubbles. We then pressure bled the entire system, got some bubbles out of all four corners (expected). Pedal is still funky. The pedal isn't as firm as I'd expect, and no real braking power comes until the end of the pedal's travel. It just doesn't feel right.

While we had the master off, we decided to measure the booster rod. I'm not sure what we were supposed to be measuring, we pressed the pedal and measured how far it comes out, and it comes out just under 2". The rod coming out of the booster consists of a metal rod running through the middle of a larger cylinder. Both pieces move out and in as an assembly, but the smaller rod can be removed from the cylinder very easily. Is that how it is supposed to work?

Another note: I noticed that the pedal STOPS (reaches the end of its travel) a few inches from the floor. I can measure it exactly if needed. Is the pedal supposed to stop that early, or is it supposed to go down near the floor? With the M/C off, it drops down much more.


Any ideas? It's beautiful out and I need brakes!!

[PontGuy]

Sounds like some progress, but you still have air somewhere. After bleeding are you getting any bubbles from the rear with the new cylinders? With mine I always got small bubbles, almost milky, until I replaced the cylinders. Then with the new cylinders it stayed perfectly clear after just a few minutes of bleeding.

There should be just a little gap between the booster rod and the M/C, enough to ensure that the master retracts all the way. You can't feel this play with the pedal. I discovered that mine was too tight by watching the rear port inside the M/C through the fluid while tightening the mounting bolts. I put a couple of thin washers between the master and the booster and it solved my problem with that.

I think the pedal travel is limited by the travel allowed by the M/C and booster so the pedal may not actually reach the floor.

Also I would double check the fittings at the front to make sure they are not leaking. Getting the air out of the back may have increased the line pressure enough to create a leak somewhere else.

Walt

[67 LeMans 326]

I appoligize for not reading through this entire thread, but, did you install a new porportioning/distribution valve during this install? If so, are you aware that during the bleeding process if one of the resevores in the master cylinder happens to go dry, you will need to "reset" the valve? I found this out during my 4 wheel disc brake conversion. I could not get rear brakes at all, another friend could get rear but no fronts etc. In both cases we had installed new distribution blocks and they had to be reset.

In these new all in one combo valves that are on the market now, they have a safety backup built in, if one of the resovores in the MC goes low or empty, the valve shuts that resevore off and puts all the stopping power to either the fronts or rears whichever of the two did not go dry. Then, what you have to do is remove the sensor on top of the valve, push something thin down into the hole and it moves the internal saftey mechanism back to it's "home" position. I was told to use a straightened paper clip and beleive it or not, this solved all of my issues and bang, everything worked perfectly. Incredibly, this proceedure was NOT in the troubleshooting guide or instructions with my kit, I was given this info from the tech support line...

[Shiny]

Good info 67 Lemans 326...

Don't give up Jimbro !! Sounds like you are almost there...

I was told if the imbalance thing happened to loosen the front bleeders and push the pedal to try and "reverse" the pressure imbalance that tripped the switch the first time. This seems to assume the problem was pressure in front and not in the rear, which is a safe bet if the rears weren't working right.

My combo valve has a switch driven off the "imbalance piston", so if either system loses pressure, the brake light in the dash will come on. If the switch is there, you can put a meter or continuity light on it and see if it is making contact while the brake is pressed. This might be a good way to diagnose if the non-centered plunger is causing the problem. I think Walt had this problem and I don't know if he ever fixed it?

Walt - you still have your switch off-center? Maybe this will help? Also, didn't you have a tool (expensive paper clip?) to center the switch?

Also, there may be a pin protruding from the combo valve. My original manual said to hold it pushed in when bleeding. The support tech at Inline Tube, where I bought my valve, said this is not usually needed, but it may be another thing to try?

[PontGuy]

Yes, mine is still stuck but it is not affecting operation of my brakes. I have the '69 Inline Tube distribution block, not the later combo valve- I am not sure if that makes a difference or not. They look identical on the outside so maybe this "reset procedure" would work for me too.

How do you remove the sensor- does it just screw into the block?

With the original 69 block the switch would trip when you stepped on the pedal and the dash lamp would light, and then automatically reset when you released the brake pedal so the dash lamp would go off. My lamp does not go off. I have tried resetting the switch using a variety of methods without success. Since my brakes work perfectly my theory is that the switch is just stuck from all the messing around I did. But again, my brakes are working perfectly and I still have a long list of debugging work to do so the light hasn't risen to the top of the list yet. Trans pan leak, exhaust leak, that sort of stuff.

Jimbro, is your light stuck on? To be honest I am not sure why this would cause a low pedal but maybe another piece of the puzzle.

Walt

[goatsheadsoup]

I chased a sloppy brake pedal for years. I too replaced and double checked everything. I could bleed brakes with 3 or 4 different methods in my sleep. I changed master cylinders and wheel cylinders. I changed the brake lines. I adjusted and readjusted the brakes all over a 4 or 5 year period. I finally took a original brake booster and compared the rod length to the reproduction. The rod length was shorter and I machined a correct length rod on my grinder. The goat now stops on a dime with a firm pedal. The first time ( the last time) my wife drove it I saw the 68 going sideways when the brakes locked up. I pump them to avoid that. Even with silicone fluid it stops as good as the 2000 trans am (almost). I am so confident I would not even consider upgrading to disk brakes even with the 428, they are that good.

[Shiny]

walt - I replaced my aftermarket switch with an original.. been a while, but I think it had something to do with the connector. It is a threaded part, just unscrew to get access to the switch piston. I put a meter on my switch, and it never made contact, so I can't comment with any experience.

I would think the switch piston motion could be a matter of degree, though - maybe it can come on with the pedal pressed and then re-center as you described... but I think if there was a bigger differential, maybe it would get stuck like yours ??

I attached the combo valve diagram I pulled off the web again in case it might help.

I also added a picture looking down into the master through the fluid to show what Walt is saying about looking for the rod too long. If you look down into the drilled hole, you can see the piston in the master. If you watch this piston when you unbolt the master from the firewall, it will move (retract) if the rod is too long and has been preventing the piston from returning all the way when the pedal is released. It is an easy thing to check for, seems worth a shot ??

ghs - what do you mean by "sloppy pedal" you mean it went to the floor and you never had brakes? I think that is a new possibility that hasn't been given much thought in all of this. Any way to tell if the rod length is short if you don't have an original for comparison? Maybe looking in the master at the piston again, how much pedal travel before the piston moves??

[goatsheadsoup]

Interesting thread...By sloppy I mean pedal travel was too far, almost to the floor. I could not adjust it at the booster by turning the rod at the brake pedal enough to make much of a difference. You could experiment by rounding off a similar diameter bolt to the booster rod and taking off the master cylinder its only two bolts and would take a couple of minutes. Grind the bolt down to the length that makes your brake pedal travel satisfactory. I will use this method in the future to put the pedal firmness where I want it. I would of course make sure everything is correct first this is the brake system, we can't forget that but from now on I will check this as a regular brake item. These cars have been worked on for 40 years and different parts from different vendors and countries can make restoration a challenge.

[Jimbro727]

Thank you so much for the replies!

It sounds like we've got a few potential issues here:

Combination valve: I do not have my switch hooked up right now, if I remember correctly, I broke the end of it off taking off the combination valve at some point, so I need to replace it. I recall reading that when it's cutting one of the systems off, it grounds the pin - is that correct? I have a multimeter with a continuity tester, so I'd clip one probe to the pin on the combo valve and the other one to a good ground point somewhere (a bolt or something). That's how I was testing if the safety system was activating, and it never did. Can anyone confirm that that is the proper way to test it without the light hooked up?

M/C resetting: This is a simple one, and I'll look into it to make sure it's returning fully. (Thanks for both pictures Shiny!)

Booster rod length: This sounds like it could be an issue. Does anyone know where I can find what the proper length is supposed to be for my car? I don't have access to another booster, so my only recourse would be to replace the booster again and hope that one had the correct rod. goatsheadsoup, would you say your pedal felt like mine? Did it feel like the brakes were actuating, just not very well, and you'd have to floor the pedal to get the stopping power you should be getting pretty early on in the pedal's travel?

[MikeR64]

I tried to see if this had been addressed yet, and from what I can see it hasn't. You said the brakes had never been right since you bought the car. Way back when, the spazzoids in the shop where I worked would occasionally put the front calipers on the wrong sides. This would give the exact same symptoms you have; pedal really low, brakes kind of work, and if you bleed them about ten thousand times, you eventually get to the point where no more air comes out. The problem is, the air is still there in the top of the caliper and this makes the pedal spongy and kind of like yours is now.

They were famous for doing that on GM cars and this was back in the 70's. I don't even know if you can put the calipers on backwards any more, but you may want to check that out.

[PontGuy]

I still have my original '69 distribution block. It is really beat up but it always worked fine- it would light the dash lamp when I stepped on the brakes with one side of the system out, and then reset when I released the pedal. I guess I should remove the old brake lines and figure out how it is put together. The new one will just not reset.

Jimbro, yes you can use a meter to check the switch for continuity as you describe.

GHS, by booster rod length are you talking about the rod that attaches with the clevis to the brake pedal? I could see that being a problem if it is way off. But since the pedal stops before reaching the floor but the brakes are soft then its probably not Jimbro's issue.

MikeR, I don't think the caliper possibility has come up. But in the other post we did discuss mixing up the left and right drum adjusters on the rear brakes. That creates a problem since they will loosen as the brakes are cycled instead of tightening. I've seen that one done before.

Walt