[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

[PontGuy]

I'll jump in here too..

I don't know if it is a design problem or a quality problem, but the pair of NAPA cylinders I bought was the solution for me. I have about 600 miles on my car now and the brakes are still working perfectly, with no additional bleeding! The only problem I have is that the switch is still stuck. I have been hoping that it would "magically" pop free, but it doesn't look like that is going to happen.

My car definitely does not have a residual valve, and I am convinced that it never did. I still have the original distribution block and there is no valve in it (the car came with factory disc brakes.) So the design really relies on the cylinder seals to prevent air from getting sucked back into the system.

I know its a real PITA to replace them, but I suggest that you try a pair of the NAPA-style wheel cylinders before doing anything else. Chances are that it will fix your problem.

Walt

[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!

[PontGuy]

Just to be clear- I am not a Napa salesman! I just know that they carried the style wheel cylinders that worked for me while the other chain stores I checked here carried the ones that didn't work.

I would be willing to bet that your M/C is fine. But you are right that brake parts from the local discount stores can't really be trusted. If you read all the way through the other thread, you may remember that my rod was too long between the M/C and booster even though I bought them as a matched and assembled set. I figured that one out pretty quickly, but it took a while to chase down the wheel cylinder problem.

Whatever bleeding method you use, your pedal should firm up right away if the wheel cylinders are the fix. After bleeding what seemed like gallons through my brakes it only took a few minutes to get the system clear of bubbles after replacing the cylinders.

Walt