[HWYSTR455]

The more I think of this, the more I think you should ditch the combo valve.

Try running a 'T' for the fronts and block the backs, as a test at least, and see how the pedal feels. That would eliminate one variable, and you could isolate it to the booster or master at that point.



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[Shiny]

Jimbro. Thanks for the update, sorry to hear you are still fighting this, but glad you are back at it because that means the less pleasant priorities are behind you.

When I went down a similar diagnostic path, I concluded I could not break a line without letting air in and needing to bleed.

If you opened any fittings and did not bleed again, I wouldn't trust any conclusion.

I started by plugging the front system by pluggng the front outlet on the M/C. That caused the pedal to be rock solid. So I figured the issue is not in the rear system (valid assumption?)

I'm confused by this. What do you mean by "plugging the front system"? How would that eliminate the rear system? Seems it would indicate rear system ??

And I'm not sure about the air in the master. If you plug only one outlet, I'm not sure you should expect a firm pedal. If you plug both, yes, but I am ignorant about the scenario you describe. I did plug both outlets in my master and pedal was solid, so I concluded my master was bled and not "bypassing" as some had suggested. I don't recall pluggin only one, so I just can't comment. I reconnected both outlets and bled again after that.

Walt says "start over" and I think he is giving you good advice. I think it is unlikely you sucked air into the master, but plugging it up is probably the only way to confirm. I suggest plugging both outlets on the master at once to start. This will give you confidence in the master before you move on.

But after verifying the m/c I recommend bleeding again before doing anything else.

I think there may also be diagnostic guages available, maybe you could rent one from the parts store ?? It may be a pain, but you could possibly get a direct measure at each wheel and reduce some confusion without breaking fittings at the combo valve ??

[chrisp]

Had a similar issue , no signs of leakage anywhere , turned out after i peeled the dust caps back from the wheel cylinders 1 was wet , remember no sign of any leakage . Was such a small leak pushing fluid out and then drawing it back in along with air upon pedal release . Inline tube asian wheel cylinders , got a set from Napa , made in US . wasted 3 days on and off . Been doing breaks for 25 years , 99% of the time when something is leaking you can see it .

[Jimbro727]

Thanks for the replies! This one is kind of long because I responded to each individual comment/question individually (I thought it'd be a bit clearer that way)

Originally Posted by PontGuy

I think that the danger of pulling and plugging lines at the combo valve is that if you get air in the system it could give you false readings. My suggestion- hook it all back up, bleed the system and then repeat your test- plug the front of the master and see if you get a hard pedal. But then if you do get a good pedal, reconnect the front and plug the back and see what happens.

I agree, that's my concern as well. The only test I know I can trust is my first one, which was plugging the front port on the M/C (since the system was bled before then, so I know there was no air anywhere). After then, it's a crapshoot, because I exposed the front system to air.

Originally Posted by PontGuy

Also check for continuity at the switch while you do this. If it does not trip the switch then something is wrong there, because you will only be putting pressure on one side of the system.

I did check continuity throughout my tests, and got no continuity between ground and the brake light switch (post) on the combination valve - something is wrong there, right? With one side of the front plugged and the other not, the unequal pressure should have tripped it, right?

Originally Posted by HWYSTR455

The more I think of this, the more I think you should ditch the combo valve.

I've had a bad feeling about this as well. This one is from inline, before this one, I had one from YearOne. Is there any way that I can verify there's something wrong with this valve? Where can I pick up a good one?

Originally Posted by HWYSTR455

Try running a 'T' for the fronts and block the backs, as a test at least, and see how the pedal feels. That would eliminate one variable, and you could isolate it to the booster or master at that point.

I like that idea - where can I get an appropriate T? This is a pretty simple test, and it removes the combo valve, so I can verify everything else works.

Originally Posted by Shiny

Jimbro. Thanks for the update, sorry to hear you are still fighting this, but glad you are back at it because that means the less pleasant priorities are behind you.

Absolutely!

Originally Posted by Shiny

When I went down a similar diagnostic path, I concluded I could not break a line without letting air in and needing to bleed.

If you opened any fittings and did not bleed again, I wouldn't trust any conclusion.

I agree. But then how do I diagnose using this method? Should I bleed between each test?

Originally Posted by Shiny

I'm confused by this. What do you mean by "plugging the front system"? How would that eliminate the rear system? Seems it would indicate rear system ??

I plugged the port on the M/C for the front system, leaving only the rear hooked up. Since I got a rock solid pedal, my thought process was that the rears were not the issue, since removing the front system entirely from the equation produced the desired result (solid pedal).

Originally Posted by Shiny

And I'm not sure about the air in the master. If you plug only one outlet, I'm not sure you should expect a firm pedal. If you plug both, yes, but I am ignorant about the scenario you describe. I did plug both outlets in my master and pedal was solid, so I concluded my master was bled and not "bypassing" as some had suggested. I don't recall pluggin only one, so I just can't comment. I reconnected both outlets and bled again after that.

My thought process was that the pedal in a power brake system with no issues should feel the same with the engine off and everything hooked up as it does with the M/C plugged. By plugging one half of the system (at the M/C) and leaving the other connected, I'm removing an entire system (front or rear) from the equation to try and deduce where the issue is. If I had some magical way of plugging the brake system that didn't introduce air, I should logically be able to plug the front, see the pedal is solid, hook it back up, see it's soft, then work my way down the brake system from the M/C until it's hard again to try and determine where the issue lies.

Originally Posted by Shiny

I think there may also be diagnostic guages available, maybe you could rent one from the parts store ?? It may be a pain, but you could possibly get a direct measure at each wheel and reduce some confusion without breaking fittings at the combo valve ??

I had one for a while, it showed very little pressure at the front wheels. It didn't come with the proper fitting to check the rears. Then I stripped the fitting

Originally Posted by chrisp

Had a similar issue , no signs of leakage anywhere , turned out after i peeled the dust caps back from the wheel cylinders 1 was wet , remember no sign of any leakage . Was such a small leak pushing fluid out and then drawing it back in along with air upon pedal release . Inline tube asian wheel cylinders , got a set from Napa , made in US . wasted 3 days on and off . Been doing breaks for 25 years , 99% of the time when something is leaking you can see it .

Yes I heard about these! I actually replaced my wheel cylinders a few months ago with NAPA units. There was a definite improvement, but not enough, so perhaps it was one of a few issues.

[Shiny]

Jimbro,

I agree. But then how do I diagnose using this method? Should I bleed between each test?

that's what I did.. I think I went through 2 quarts of fluid

....By plugging one half of the system (at the M/C) and leaving the other connected, I'm removing an entire system (front or rear) from the equation to try and deduce where the issue is. If I had some magical way of plugging the brake system that didn't introduce air, I should logically be able to plug the front, see the pedal is solid, hook it back up, see it's soft, then work my way down the brake system from the M/C until it's hard again to try and determine where the issue lies.

I wish I knew more, but somehow the m/c pistons must be independent for front and rear systems. If the front system was solid, and the back was all air, how would you ever feel the back soft effect if the two m/c pistons were tied together rigidly? The front would build pressure, the back would not, but you would only feel the solid front? Make any sense? This is why I am not sure plugging a single port at a time on the m/c is a good test. Maybe somebody with knowledge can clear this up?

Yes I heard about these! I actually replaced my wheel cylinders a few months ago with NAPA units. There was a definite improvement, but not enough, so perhaps it was one of a few issues.

I'll go with this one. I replaced my m/c, didn't fix. Then I found a leak at a fitting, fixed it, but still not right. I can believe you may also have more than one issue.

I still think you should block both ports on the m/c to eliminate it, then bleed, then sit overnight, bleed again, bleed some more...then put pressure on the system and look for leaks. If you don't see any, but the system is still soft, then you either aren't bleeding well or something is leaking. I am totally in agreement with chrisp that the leak could be fluid going out OR air getting sucked back in.

Here's my thought:

after bleeding, push and hold the pedal

if fluid is leaking fluid out, I think the pedal will slowly go to the floor

if it stays firm without moving, then pump it repeatedly

if this makes the pedal go to the floor, and you see no leaks, you are sucking air in somewhere. this is much more likely in the rear system than in the front as the calipers don't move much and the rear shoes can move a lot if no residual pressure is in the line

My combo valve is also from Inline, and I am pretty sure it does not have a check valve for the rear. I say this because:

1. I stuck a paper clip into the port and there was nothing there
2. I added a residual pressure valve to the rear and it made a big improvement.

Someday I will have a reunion with my car and replace the rear cylinders with the NAPAs.

I also never saw my switch trip when I had an imbalance. I am not convinced it works at all.

Good luck

[PontGuy]

I went through more than 2 quarts last year when debugging my brakes. I bled them completely between everything I tried. And I never blocked off ports as part of the debugging process.

I think that Shiny is right about that the pedal should be hard if you block off one of the ports of the M/C even if the other port is wide open, never thought of that.

At the end of the day if the M/C is good and the system is bleeding properly then there just has to be a leak or air in the system somewhere. The reason the the bad rear wheel cylinders are hard to debug is that air can get sucked into them without an apparent leak (unless you have a residual valve in the system.) But I can't think of anywhere else that this can happen.

Interesting that neither of you guys have seen the switch trip as part of the debugging process because it seems to me that it should have. Mine has always been stuck closed and yours is stuck open. Starting to make me think about the quality of the piston assembly in the Inline Tube blocks.

[Ed Fitzgerald]

[QUOTE=Shiny;4070462]Jimbro,



that's what I did.. I think I went through 2 quarts of fluid



I wish I knew more, but somehow the m/c pistons must be independent for front and rear systems. If the front system was solid, and the back was all air, how would you ever feel the back soft effect if the two m/c pistons were tied together rigidly? The front would build pressure, the back would not, but you would only feel the solid front? Make any sense? This is why I am not sure plugging a single port at a time on the m/c is a good test. Maybe somebody with knowledge can clear this up?



The top half of the pedal is for the rear brakes and the bottom half is for the front brakes. Had a company truck (84 Ford Ranger) that I let one of my guys drive and he told me he was having problems with the brakes. Pulled the back drums and sure enough wheel cylinder blown. MC reservoirs (front full of brake fluid ---rear empty). Top half of brake pedal non existent, bottom half would skid front tires on hard application. Replaced wheel cylinder,drum and shoe. Bled system and bled system and bled system to get air out and finally brakes worked good as new.

[stucky2947]

I read most of this thread and didn't see anything about the rod that goes in between the power booster and the master cylinder. I had the same problem with the brakes on my '62.

Take the master cylinder off and look at the power booster. There will be a rod (the one that goes thru the firewall and attaches to the clevis pin that is attached to the brake pedal). That rod pushes on the master cylinder piston. There shouldn't be much play in the end of the rod and the master cylinder piston. That was the problem I had. I wouldn't get any brakes until the pedal was almost to the floor. I had replace the ENTIRE brake system, like you did, and couldn't figure for the life of me why I didn't have brakes.

That rod length is important. Consider where the fulcrum point on the brake pedal is and you can see that a small difference in rod length will translate into a large amount of pedal travel. There should be very little 'play' between the power booster rod and the master cylinder piston. Mine had a rod between the two and apparently during re-assembly it didn't get put back. I ended up making one. Measure from the face of the power booster to the rod in it (the one coming from the brake pedal). Then measure from the face of the master cylinder to the end on the master cylinder piston. The rod that was missing from mine was the one that took up this gap (add the two measurement together). I made a rod this long and then added a dimple in the end that contacted the power booster rod. (the rod from my master cylinder had a radius on the end).

I attached a sketch, hopefully it helps.