[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.