[Shiny]

Guess this means you have not figured it out?

Me either.

Interesting you have the combo valve up at the booster. Me too, even though mine's a LeMans... I don't think it matters, since lots of aftermarket brackets move the valve up top.

Your comment about the bubbles at the master and air rising in the lines even under pressure is also something I chased. Does your master have bleed screws? My new one does, and I noticed I was sucking air back into the master when I bled using a "one-man" bleeder bottle, so I sealed the bleed screw threads and it eliminated that symptom. After that, I have not seen any more bubbles from those bleeders, so I don't think air is trapped between the valve and the master on mine. My test with the master ports plugged supports my conclusion that air in the master is not my problem, even though I keep getting told that.

My last attempt at bleeding, I saw no bubbles at master or any wheel, and I got a firm pedal with engine not running (no booster). So I got cocky and drove around the block. Within about 5 braking attempts, the pedal dropped back to near the floor before stopping the car.

I now believe the fault may well be the master cylinder not returning as mentioned in the post below. I have not looked at mine again, as I now have a much bigger problem to deal with... but I plan to loosen the adjuster between my pedal and the booster and see if it helps. This is my last hope for a fix.

It might make sense if, as described by ericwy/sts, the "refill" port is being blocked by the piston not fully returning, then it might effectively pull a vacuum on the rear system and either pull in air or more probably, pull the rear cylinders away from the shoes. If this happened, I would think it might act like the rear shoes were adjusted way too loose. If this is true, then the pressure build-up in the rear system would be way late, delaying pressure build in front. Just speculating, but it makes some sense... and I need an explanation that makes sense to keep from going crazy.

Along the same line, is there any chance the booster is "boosting" without me pressing the pedal? If so, could this be another explanation for why the master is not returning correctly?

[Jimbro727]

Originally Posted by Shiny

Guess this means you have not figured it out?

Me either.

Interesting you have the combo valve up at the booster. Me too, even though mine's a LeMans... I don't think it matters, since lots of aftermarket brackets move the valve up top.

Your comment about the bubbles at the master and air rising in the lines even under pressure is also something I chased. Does your master have bleed screws? My new one does, and I noticed I was sucking air back into the master when I bled using a "one-man" bleeder bottle, so I sealed the bleed screw threads and it eliminated that symptom. After that, I have not seen any more bubbles from those bleeders, so I don't think air is trapped between the valve and the master on mine. My test with the master ports plugged supports my conclusion that air in the master is not my problem, even though I keep getting told that.

My last attempt at bleeding, I saw no bubbles at master or any wheel, and I got a firm pedal with engine not running (no booster). So I got cocky and drove around the block. Within about 5 braking attempts, the pedal dropped back to near the floor before stopping the car.

I now believe the fault may well be the master cylinder not returning as mentioned in the post below. I have not looked at mine again, as I now have a much bigger problem to deal with... but I plan to loosen the adjuster between my pedal and the booster and see if it helps. This is my last hope for a fix.

It might make sense if, as described by ericwy/sts, the "refill" port is being blocked by the piston not fully returning, then it might effectively pull a vacuum on the rear system and either pull in air or more probably, pull the rear cylinders away from the shoes. If this happened, I would think it might act like the rear shoes were adjusted way too loose. If this is true, then the pressure build-up in the rear system would be way late, delaying pressure build in front. Just speculating, but it makes some sense... and I need an explanation that makes sense to keep from going crazy.

Along the same line, is there any chance the booster is "boosting" without me pressing the pedal? If so, could this be another explanation for why the master is not returning correctly?

Sorry for the delay - I wanted to work on this a bit more before responding.

My master doesn't have bleed screws, I've never seen one like that - where did you get it?

I don't believe that my problem is the m/c not fully returning, because I can feel in the pedal when the booster is engaging the M/C. I suppose this could be something else that I'm feeling...

I just spent the past few days bleeding. First I bench bled my master again, and got some air out. I then hooked up my pressure bleeder, and left it connected for a few days. Two days last week and once again today, I spent an hour or so and bled each corner. I took around 40oz or more out of each corner each day. The first day I got bubbles everywhere. Second day I think I got some bubbles out of one of the rear brakes and nothing out of the front. Today I got no bubbles out of the rear, nothing out of the passenger side front, and a ton of bubbles out of the driver's side front. I waited until I thought there were no more bubbles up there, then decided to test it. I've literally made no progress. The pedal feels firm without boost, and goes right to the floor with little resistance with boost.

I did notice something interesting, though. With the M/C cover off and the engine off (no boost), the M/C will shoot fluid out of the reservoir with a light tap on the pedal. With the engine running (boost), that same tap yields no shot of fluid. In fact, mashing on the pedal doesn't even shoot fluid out.

My pressure readings at the driver's side front caliper show that I still get virtually no pressure until very very late in the pedal's travel (almost on the floor). Without boost, I get around 100PSI with the pedal as far as I can push it (I believe it's as far as it goes). With boost, I get around 200-225PSI with the pedal on the floor if I press it quickly.

It is possible that more air needs to settle, so I'll continue bleeding. But my gut tells me that there's something else wrong here. People drive around with air in their lines, I think I'd only see something like this if my lines were FULL of air.

Any thoughts?

As to your question about the booster boosting without you pressing the pedal, I don't think that's possible. I've looked over diagrams of how these boosters work, and I don't see how it could do that. I'm by no means an expert, however, so take that with a grain of salt.

[Shiny]

Hey Jimbro,

I haven't got back to mine yet, so no news. Sorry to hear yours is still acting the same, especially after all that bleeding again... 40 oz per corner !! yikes

I got my master from Inline Tube. It is a new repro, with a rectangular body. Looks good, but did not fix my brakes. I also bought my combo valve from Inline.

Good luck and post any updates.

[KEN CROCIE]

You mentioned several times about low pres. on the dr. side calp. Is the pres. the same on the pass. side calp.? If not, find out why not.

[Shiny]

I hope you can clarify. I understood you had solid pedal with the booster off, including to the front calipers. Then, with the booster, it changed and ended up with low pressure at the calipers??

I want to make sure, because that is how mine acts and I am hoping you will figure this out. When I bleed it, with no booster, I can literally see and hear the front calipers squeeze hard and the pedal is good. I do not have a pressure gauge. Then, when I drive it and operate a few times with the booster working, the pedal goes to floor, and ends up with no brakes until the pedal is near bottom, but never completely goes to zero. I think this is the same for yours, right ??

I was trying to understand the way the combo valve worked, and thought I understood the front would not pressurize until the rear system had pressure. Based on this, I have been assuming my rear system is somehow losing pressure, and the combo valve keeps the front from pressurizing. If this is way off, somebody please explain how the metering and proportioning functions may or may not play a role in these symptoms ??

Thanks again.

[Jimbro727]

Originally Posted by KEN CROCIE

You mentioned several times about low pres. on the dr. side calp. Is the pres. the same on the pass. side calp.? If not, find out why not.

I didn't check it this time around, but the previous times I had checked it, and it was low, too. Same symptoms :-\

Originally Posted by Shiny

I hope you can clarify. I understood you had solid pedal with the booster off, including to the front calipers. Then, with the booster, it changed and ended up with low pressure at the calipers??

Sort of. My pedal is hard with the booster off, but I don't know if it's as hard as it should be with the booster off. It's hard - hard enough that I can't press it to the floor (well, not so much that I can't, but don't want to because I'd have to press so hard that I'm afraid of bending the pedal arm or something). It doesn't quite feel as hard as a newer car does without the engine running (no boost). Pressure appears to be the same with or without the booster, the only thing that changes is how hard it is to press the pedal. This makes sense, because with or without boost, each point in the pedal's travel should create the same amount of pressure. The booster should just make it easier to apply this pressure.

Originally Posted by Shiny

I want to make sure, because that is how mine acts and I am hoping you will figure this out. When I bleed it, with no booster, I can literally see and hear the front calipers squeeze hard and the pedal is good. I do not have a pressure gauge. Then, when I drive it and operate a few times with the booster working, the pedal goes to floor, and ends up with no brakes until the pedal is near bottom, but never completely goes to zero. I think this is the same for yours, right ??

Without the booster, does the pedal feel good, as in how it should feel with the booster, or good as in how it should feel without the booster? Without the booster, my pedal feels a little bit harder than it should with the booster. Have you tried braking without the booster? Maybe back it out of the garage with the vacuum unhooked and see if the brakes are good. Mine aren't without the booster, in fact, it makes things more difficult, because the pedal is harder, and I have to press it almost to the floor to get it to stop from a roll.

Originally Posted by Shiny

I was trying to understand the way the combo valve worked, and thought I understood the front would not pressurize until the rear system had pressure. Based on this, I have been assuming my rear system is somehow losing pressure, and the combo valve keeps the front from pressurizing. If this is way off, somebody please explain how the metering and proportioning functions may or may not play a role in these symptoms ??

Thanks again.

From what I understand, this is sort of true. The metering valve doesn't allow pressure to the discs until a certain pressure has been reached in the rear system. This allows the shoes to contact the drums before applying pressure to the discs so that everything brakes at the same time (since the pads are always in contact with the discs, but shoes are usually not in contact with the drums, and require a bit more pressure to begin braking). The proportioning valve sends more pressure to the front brakes than the rear brakes because most of the braking is done at the front (due to weight distribution among other things).

Following along with your logic (and it makes a lot of sense), perhaps the rear system isn't reaching the "threshold pressure" so the metering valve isn't allowing pressure to the front system until very late in the pedal's travel when the rear system finally reaches that pressure. That would explain the sudden jump in pressure towards the end of my pedal. It wouldn't explain why that pressure is so low - if the metering valve were to finally allow pressure through to the front system, shouldn't the pressure spike to whatever it should be so late in the pedal's travel - over 1,000PSI?

If this is what's happening, then one of two things are causing it: Either the rear system really isn't reaching the threshold pressure until very late in the pedal's travel for some reason (it's losing pressure, a cylinder is bad, the M/C is bad, etc.), or the metering valve is just broken.

Here's a great article on combination valves: http://auto.howstuffworks.com/auto-p...ter-brake2.htm

[Shiny]

Jimbro - sorry I did not see your reply. I am going to try to figure this out again and appreciate your thoughts...

Originally Posted by Jimbro727

Without the booster, does the pedal feel good, as in how it should feel with the booster, or good as in how it should feel without the booster? Without the booster, my pedal feels a little bit harder than it should with the booster. Have you tried braking without the booster? Maybe back it out of the garage with the vacuum unhooked and see if the brakes are good. Mine aren't without the booster, in fact, it makes things more difficult, because the pedal is harder, and I have to press it almost to the floor to get it to stop from a roll.

On mine, I bleed the brakes, and with no booster, the pedal feels like I would expect. The pedal travels maybe a half inch, then firms up pretty solid. I have not tried driving this way, but expect it will stop with a lot of pressure. Your observation that it won't stop with no booster, yet feels firm, seems odd???

On mine, with no booster and a firm pedal, the front calipers are getting squeezed hard, as I can literally see the brackets move and hear some strain. But I'm not sure about the back, as it has a new posi and is a little stiff to rotate the rear axle and check.

Then, when I start the car and drive, it is obvious the booster works, reducing the pedal pressure required, and making the pedal travel a little farther, but it still stops and feels pretty solid - maybe an inch of pedal travel, but still pretty solid. Then, after repeated stops, the pedal gradually drops to near the floor before I get significant braking. After shutting the engine off, the pedal does not "recover"... it now goes nearly to the floor with no booster and acts the same with the engine back on and booster boosting. But it is definitely worse.

So on mine, something changes after I get it bled, but there is NO fluid leak that I have detected.

I will try the following next:

- bleed again and see if I get bubbles indicating air has leaked back in
- then verify my rear shoes are actuating and seem to have pressure against the drums
- look harder for signs of leaking
- I will try your suggestion and drive with no booster

So what can I conclude based on behavior with no booster? If it stays the same, then what? If it still deteriorates, then what?

I have a related question. In my repair book, it shows a gauge to verify the rod between booster and master is "correct" to allow full return of the master and avoid blocking some internal port. Do you know what the depth of the rod should be? I checked the pedal side, and there is definitely a little clearance before it "hits", so I think the pedal is OK. I am still not confident my master is fully returning with the booster "on", so how do I verify that? I am guessing the depth gauge effectively assures that, but is it possible I have a bad booster that is "always" boosting or something similar??

[the-rookie]

My son had the exact same problem on his 1st car/truck 69 C10, pedal almost went to the floor and could hardly stop the truck at all when he bought it . The problem, the lines to the proprotioning valve were switched around. What seemed to be correct was not.

[Shiny]

Thanks for the idea. That came up earlier, and pics were posted. We never heard if they were connected backwards, but I suspect not or it would have been obvious to somebody... take a look and let us know, though.

I also hope someone can answer the question about the rod depth on the booster. There is a gauge shown in the repair book to confirm clearance between booster and m/c. Anyone know what the limits are? I have the short rod, but not sure if this alone assures a correct assembly. I think I remember reading where someone put washers between the booster and m/c to add clearance and had a good outcome. Anyone familiar with this?

[Jimbro727]

It's been a while since I last posted, I had some knee surgery and couldn't work on the car for a while, but just got back out there with a buddy this evening, and made some kind of progress, which just raised more questions. Here's what's happening:

• Replaced driver side wheel cylinder with new one from AutoZone, we thought it was a little funky when we installed it the first time.
• Began bleeding the brakes using the classic two person method (one person presses the pedal, the other opens the valve, closes it, first person releases pedal, repeat).
• Starting at the passenger side rear brake, we pulled some bubbles, then solid fluid.
• Driver's side rear, we pull out constant bubbles. The size and frequency of the bubbles changed, but we kept pulling out a fairly constant to very constant stream of bubbles. We did this for about an hour...
• The pedal firmed up during this. Now it feels pretty solid after being depressed about half way, which is a huge improvement, since it went straight to the floor when we started. But after an hour of bleeding, we were at a stand still.
• We then moved to my pressure bleeder. We pumped 10psi and opened the driver's side rear bleeder, and got a few bubbles (nothing like we were getting with the other method), then NO BUBBLES, just a constant, solid stream of fluid.
• We then went back to the original bleeding method, and got the same stream of bubbles.

It's probably worth mentioning that when we used the two person bleeding method, we left the M/C cover on sealed (we'd constantly open it to fill the fluid). We read later that you're supposed to leave the cover on loose. Does this matter?

We stopped there, figuring we'd post and see if anyone had any ideas. What would cause us to get a constant stream of bubbles when depressing the pedal, but no bubbles when using the pressure bleeder?

WTF, this is extremely frustrating - help PLEASE

Shiny - Did you ever solve your problems?

[Old Bird]

Don't forget your ebrake will stop in the car in an emergency since it is a cable. In a pinch it is always there to get you stopped before you hit something.

[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?

[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?

[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