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Soft brake peddle cause

XJ-ARNIE said:
Well the valve can move based on a pressure differential between the front and rear half of the system. They do this so if there is a leak in the rear you still have some front brake actuation and vice versa,
Click to expand...

The way I see it, unless there is an issue with the master cylinder running dry on one side only (that causes a paddle to go to the floor and not activate the other side of the brakes?), all the combo valve does in case one side leaks, is keep that line from running dry?

Which is it? Or is it both? :)
 
Digger87xj said:
If the valve is off center enough to impede bleeding, the red brake light will be (or should be) on.
Click to expand...

I suspect my brake light switch is bad, or the Combo valve is not moving during bleeding on mine. The brake light went off once right before I started this brake job again about 4 months ago, then went out. I had lost some fluid to the rears, but then the leak stopped. Later found one rear wheel cylinder leaking air in but no fluid out. It was one of the parts I replaced.
 
XJ-ARNIE said:
There you go. Now, do you guys see why this valve has to be centered before and during the bleed process?

Please keep me posted and let me know if this solves your spongy pedal.
Click to expand...

Just dawned on me that it might be possible for air to get into the lines through the brake switch port. I may try a brass plug there or the tool I ordered last night (thanks for the help on that), and fill it with brake fluid to push air out and then bleed for fun. Already had one bad wheel cylinder leaking air in but no liquid leak out.
 
Slow leakage will not turn on the light, nor will normal bleeding. There has to be a major pressure differential (450psi was mentioned above) to get the valve to switch.

If you've ever been bleeding the brakes and pressed hard with a bleeder open and felt/heard a click and the pedal drops slightly, and if the key is on, the light will pop on. that is the valve moving.
You will also get a resulting click once the system is bled and closed and press hard on the pedal, it will, or should reset to center, turning out the light.
 
Thanks.

I just answered my other question about why the valve is designed to shut off flow....as the peddle goes all the way to the floor (no brakes) when bleeding just one wheel. Just had to think it through and do some memory jogging.
 
Ecomike said:
The way I see it, unless there is an issue with the master cylinder running dry on one side only (that causes a paddle to go to the floor and not activate the other side of the brakes?), all the combo valve does in case one side leaks, is keep that line from running dry?

Which is it? Or is it both? :)
Click to expand...
The point of the two chambered master is to prevent loss of all fluid in case of catastrophic failure of one circuit.

The combo valve, as explained, does 2 things.
1. proportions pressure on a disc/drum system so there is ~ 70/30 pressure split so the rear brakes don't lock on light to moderate braking.
2. close off a circuit (and turn on the light) in case of catastrophic failure so the loss of fluid is minimized, and, so the other half of the braking system will still function and stop the vehicle.
 
Bingo time! I went to the store in the cold rain last night (not fun for someone with severe RA), and the brake light went off!! Brake pedal starting going to the floor. Still had brakes, even today.

This morning the MC was still full on both sides. Determinded that the bleed fitting on the front of the combo valve was a little loose (obvious when pressing the pedal). But after tightening, I could still get a wet spot on my finger under the seal area pumping the brakes for a bit.

The brake switch is an odd critter. Thought it was shorted out, but it works. I could see no difference on a VOM meter (looked shorted over the entire stroke of the pin) but the live test showed it worked.

Then my helper broke the threaded part off in the Combo valve. Such fun. So now it is broke :(

So I may have found the source of air now that the gremlin cloaking device failed. Will update more as this saga continues
 
Well I bought one of them but it does not fit the 87 jeep combo valve. The tool is 1/4 pipe thread (NPT) from the looks of it (the one for the GM combo valves), and the Jeep valve is 1/8" pipe thread (NPT) from the looks of it. Any ideas where to get one for 1/8"

XJ-ARNIE said:
ok folks, heres the scoop.

The jeep combo valve is a GM part. I was thinking early Chrysler, forgetting about AMC. Its a common one, just the procedure is a little bit different.

The problem with the OP's jeep (any many others from the sound of things) is that any air trapped in the combo valve will result in a failure to bleed the lines. The valve will off center, making the bleeding process ineffective. The valve must be re centered and held in its center position. this tool will be screwed in where the idiot light sensor goes and will hold the tiny valve for you.

This valve makes the test with the pinch off pliers inconclusive. It was however a fantastic thought, but the valve that has the capability of moving without your input, therefore making any blockage of the lines in the name of testing inaccurate.

I think this is the one you are after, however I would double check your measurements.

http://www.summitracing.com/parts/c...W1nV6uFIxQjEWEhZmomOciNEsYuFOCsDGIaAmTG8P8HAQ

Next, I would advise the combo valve be disassembled and cleaned out with brake cleaner, and thoroughly inspected with a magnifying glass. Any deep scoring, broken springs, or cuts in seals means its junk.

I would be willing to bet this tool can be acquired at the parts house, I will check and get back to you guys.
Click to expand...
 
I just flipped through tooltopia trying to find one, and I spent $950.....thanks ecomike.

Anyway, if you cannot find one that screws in, there is another one that looks like a clamp, and has a rubber nipple connected to the screw. You just clamp that bastard in there, and off you go.
 
XJ-ARNIE said:
I just flipped through tooltopia trying to find one, and I spent $950.....thanks ecomike.

Anyway, if you cannot find one that screws in, there is another one that looks like a clamp, and has a rubber nipple connected to the screw. You just clamp that bastard in there, and off you go.
Click to expand...

LOL, your welcome my friend!!!!

I might just take an old BL switch and fill the inside with steel filled epoxy so the pin can not move up?

In the mean time I think just found a NEW leak on the top side front inlet to the Combo valve from the MC :) . Loose connector? Will report back.
 
Ecomike said:
Sorry but yes, that is the one. We might be able to use a thread die and tap it down to 1/8 NPT(?) and use them. We need to verify the 1/8" NPT thread on the jeeps first. I have pretty good eye for pipe threads...but I could be wrong on the exact thread.
Click to expand...


Yes, it is too big.
I came home just after midnight feeling very determined, So I rounded off a nail with a similar size as the tip of the tool with a bench grinder. I then gave the nail 2-90 degree bends with my vise and hammer so it wrapped around the prop valve. Taped it in place with electrical tape so it would hold the metering valve, once centered. Then, after bleeding the system, I pulled a great amount of air from the front calipers.
Now I have brakes!!!! Finally!!!
Thanks for your support Mike, and I hope this helps you, or anyone else chasing this problem.
And a big thanks to XJ-Arny for your expertise and steering us in the right direction! I am SO grateful
After this ordeal, I don't think I can be stumped again!

:clap::new::idea:
 
Last edited:
Awesome idea, glad it worked. I may just find a 1/8" brass nipple and epoxy a nail inside, after hearing what you did!!!! Thanks to all the posters on this thread for the great ideas!!!!

I found a T-shirt for sale on Facebook last night that says "Never underestimate a man that drives a JEEP". LOL:roflmao:
 
davesdetail said:
Yes, it is too big.
I came home just after midnight feeling very determined, So I rounded off a nail with a similar size as the tip of the tool with a bench grinder. I then gave the nail 2-90 degree bends with my vise and hammer so it wrapped around the prop valve. Taped it in place with electrical tape so it would hold the metering valve, once centered. Then, after bleeding the system, I pulled a great amount of air from the front calipers.
Now I have brakes!!!! Finally!!!
Thanks for your support Mike, and I hope this helps you, or anyone else chasing this problem.
And a big thanks to XJ-Arny for your expertise and steering us in the right direction! I am SO grateful
After this ordeal, I don't think I can be stumped again!

:clap::new::idea:
Click to expand...

No problem bud. I'm glad you have brakes...they are sort of important lol.
 
This, I'd never heard of.
I suspect I've been battling a similar issue with my other heep. Glad you found it & posted up! Thanks!
 
Ecomike said:
Awesome idea, glad it worked. I may just find a 1/8" brass nipple and epoxy a nail inside, after hearing what you did!!!! Thanks to all the posters on this thread for the great ideas!!!!

I found a T-shirt for sale on Facebook last night that says "Never underestimate a man that drives a JEEP". LOL:roflmao:
Click to expand...

I like Your idea too! The way I did it may or may not work for everyone.
If you want to make a brass tool, the thread is a M10x1.0
I want that T-shirt! Lol
 
davesdetail said:
I like Your idea too! The way I did it may or may not work for everyone.
If you want to make a brass tool, the thread is a M10x1.0
I want that T-shirt! Lol
Click to expand...

Hmm, so much a pre-made 1/8" brass pipe nipple. Maybe a brass bolt M10x1.0, and drill a small hole through it to push a steel wire coat hanger sized wire through, and grind the tip to a point.

Thanks for the measurement!!!!
 
Ecomike said:
Hmm, so much a pre-made 1/8" brass pipe nipple. Maybe a brass bolt M10x1.0, and drill a small hole through it to push a steel wire coat hanger sized wire through, and grind the tip to a point.

Thanks for the measurement!!!!
Click to expand...


Great idea! I'm also thinking that your idea of taking a old brake light switch and using epoxy to hold the pin in place would work. Or, we could cut the top off, remove the spring and force a small bolt or screw through the top to hold the pin in place, then screw the switch in. It should work since the switch is plastic.
 
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