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Soft brake peddle cause

XJ-ARNIE said:
I read this entire thread this morning, if your rear brakes are adjusted properly, and installed correctly, the only culprit is air in the system.

Based on what I've read, I would imagaine that the rear brakes are adjusted correctly, and installed correctly.

So, my professional opinion (with out my own eyes on it, and my own tools turning the bolts in my own shop, on my own rack) I'm going to draw the conclusion that you have air in the system. This air is located in the rear, and the only way it's coming out is by using the special tool to bleed the proportioning/metering valve. (technically called a combination valve) It's job is to delay fluid flow to the rear so the drums don't lock up instantly, and then meter the pressure during braking with waaayyy less to the drums, if it wasn't there, the drums would just self energize and lock up at every light.

All of that being said, there is a special tool to bleed that bastard, and I'm pretty sure it will solve your dillema. I've got a few different style in box at my facility, and I do not need them to often, but I have solved this issue on jeeps, trucks, SUVs, cars, station wagons, vans, anything with a disk front, drum rear with one if the aforementioned tools on many occasions.

WWW.tooltopia.com

Www.thetoolwarehouse.net

You can find the one you need at one of these vendors. If you were in Illinois by me (where brake lines rust, and brake repair about covers my overhead every month) Id tell you to stop by, and we'd get her done together. Let me know If i can help.
Click to expand...

What tool do you recommend?
 
Here's a dumb question: what would happen if you temporarily bypassed the combination valve and then tried to bleed the system? The result should give you the definitive answer to whether that valve is the problem.
 
There's one that that screws into the end of the valve, and depresses the forward and rearward springs, bypassing the valve altogether, notvtge one that clamps on. It depends on which prop valve the Jeep in question has. Hard to definitely say because there are many different thread pitches and sizes. Measurement is needed.
 
Matthew Currie said:
Here's a dumb question: what would happen if you temporarily bypassed the combination valve and then tried to bleed the system? The result should give you the definitive answer to whether that valve is the problem.
Click to expand...

The rear brakes would activate to quickly, and with too much pressure, but one could do this as a test and spend the money on the fittings, and the fluid. (Probably equal to the cost of a new combo valve)
 
Thanks for great feedback and offer.

Two issues, you may have missed.

"This air is located in the rear"

One, I tried the rubber brake hose clamp test one hose at a time and I did not get a hard peddle after closing off the rear hose at the rear axle to body location.

On two separate occasions I did get a hard peddle by closing off one of the front brake hoses Telling me the rears were not the problem). One time it was the passenger, the other the drivers side, 2 weeks apart.

There were parts changed and the system opened in between the 2 front hose clamp tests on the front only.

With all parts recently new (except the combo valve, and the calipers are both brand new-rebuilt ones, no new ones available), I got a soft peddle after replacing the driver side caliper. That was when we discovered AZ sold me a front mount caliper when I needed rear mount (No way to bleed it with the bleeder on the bottom). That was replaced, but we did not get the expected hard peddle after that.

We did get an air free bleed, bled both sides and the Combo valve twice, got a very tiny amount of air the second time after a hard brake usage drive test, but no change in the peddle feel. So since the front and rear fluids do not ever make contact(?), I see no way the rears could be the problem anymore due to the two times I got a hard peddle by clamping off one front hose? The rears were one of the problems before earlier in this thread!!!! One rear wheel cylinder(s) was letting air in but not leaking fluid. And one brand new AZ wheel cylinder pissed all over the driveway in the first bleed attempt, which was when I switch brands.

Thanks for the combo bleed advise and links, I WILL check them out for sure.


XJ-ARNIE said:
I read this entire thread this morning, if your rear brakes are adjusted properly, and installed correctly, the only culprit is air in the system.

Based on what I've read, I would imagine that the rear brakes are adjusted correctly, and installed correctly.

So, my professional opinion (with out my own eyes on it, and my own tools turning the bolts in my own shop, on my own rack) I'm going to draw the conclusion that you have air in the system. This air is located in the rear, and the only way it's coming out is by using the special tool to bleed the proportioning/metering valve. (technically called a combination valve) It's job is to delay fluid flow to the rear so the drums don't lock up instantly, and then meter the pressure during braking with waaayyy less to the drums, if it wasn't there, the drums would just self energize and lock up at every light.

All of that being said, there is a special tool to bleed that bastard, and I'm pretty sure it will solve your dillema. I've got a few different style in box at my facility, and I do not need them to often, but I have solved this issue on jeeps, trucks, SUVs, cars, station wagons, vans, anything with a disk front, drum rear with one if the aforementioned tools on many occasions.

WWW.tooltopia.com

Www.thetoolwarehouse.net

You can find the one you need at one of these vendors. If you were in Illinois by me (where brake lines rust, and brake repair about covers my overhead every month) Id tell you to stop by, and we'd get her done together. Let me know If i can help.
Click to expand...
 
Last edited:
XJ-ARNIE said:
There's one that that screws into the end of the valve, and depresses the forward and rearward springs, bypassing the valve altogether, notvtge one that clamps on. It depends on which prop valve the Jeep in question has. Hard to definitely say because there are many different thread pitches and sizes. Measurement is needed.
Click to expand...

Can you elaborate?

"depresses the forward and rearward springs, bypassing the valve altogether"

How does it bypass the valve?

How do you remove the tool with out letting air back in?
 
XJ-ARNIE said:
There's one that that screws into the end of the valve, and depresses the forward and rearward springs, bypassing the valve altogether, notvtge one that clamps on. It depends on which prop valve the Jeep in question has. Hard to definitely say because there are many different thread pitches and sizes. Measurement is needed.
Click to expand...

This was all I could find on either web site. Not even close. Can you find the actual tool for the 87 Renix XJs?

http://www.thetoolwarehouse.net/otc-tools-equipment-7853-P28269.aspx
 
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.
 
the tool that looks like a little clamp is for RWAL trucks. I do not believe old jeeps were equipped with this system.
 
Update on my '89 xj; I changed out the proportioning valve, bled the system again, and I still have almost zero brakes. This is the first I've heard of this tool for centering the valve, so thank you for the info.
 
I hope it works out for you. It isn't always needed, but when it is usually these are your symptoms. Of course, all of this is assuming that all of the brakes are adjusted properly, and all of the other components are free of air.
 
XJ-ARNIE said:
I hope it works out for you. It isn't always needed, but when it is usually these are your symptoms. Of course, all of this is assuming that all of the brakes are adjusted properly, and all of the other components are free of air.
Click to expand...


I hope it does too. Your assumption is correct. Every part in this system is new. I've adjusted the rear and e brakes so many times I dream about it.
By the way, how do I know if the valve is centered before installing this tool? And, once it's installed, will the air that's trapped in the valve go out the front and rear, or do I need to bleed lines at the master? Thanks again.
 
XJ-ARNIE said:
I hope it works out for you. It isn't always needed, but when it is usually these are your symptoms. Of course, all of this is assuming that all of the brakes are adjusted properly, and all of the other components are free of air.
Click to expand...

I am not disagreeing with you, I really appreciate the help and new ideas and your credentials and experience, but explain to me how a brake hose test that gives me a hard peddle can not confirm that the rest of the brake system is sound, and or how air could be in the combo valve when I am getting a solid brake peddle? Or am I miss understanding the cause? I am having a wee bit of trouble visualizing but I think I am close? And if the air is in the side that the hose clamp test is saying is good, how is that possible? Is the combo valve getting fluid from the hose I clamped and suddenly sealing off one side of the brakes that has the air giving the misleading data?
 
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, that being said, if there is a problem in the system like trapped air, and you pinch off a line, the valve will move, or not move, making the test innacurate.

The tool should center the valve as you install it, it doesn't need to be forced or torqued to a million foot pounds, just needs to be gently screwed in and snugged up.

If you Google image search for brake combination valve, and look at an exploded view, it will make a lot more sense if you are a visual learner.
 
Great write up here:

http://www.autozone.com/repairguide...SYSTEM/Combination-Valve/_/P-0900c152800a8604

The standard combination valve is located in the engine compartment, directly under the master cylinder. It consists of 3 sections: the metering valve, the warning switch and the proportioning valve.
The metering section limits the pressure to the front disc brakes until a predetermined front input pressure is reached, enough to overcome the rear shoe retractor springs. Under 3 psi, there is no restriction of the inlet pressures; the pressures are allowed to equalize during the no brake period.
The proportioning section controls the outlet pressure to the rear brakes after a predetermined rear input pressure has been reached; this feature is provided for vehicles with light loads, to prevent rear wheel lock-up. The By-pass feature of this valve assures full system pressure to the rear brakes in the event of a front brake system malfunction. Also, full front pressure is retained if the rear system malfunctions.
The pressure differential warning switch is designed to constantly compare the front and the rear brake pressures; if one should malfunction, the warning light (on the dash) will turn On. The valve and switch are designed to lock On the warning position once the malfunction has occurred. The only way the light can be turned OFF is to repair the malfunction and apply a brake line force of 450 psi.
 
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.
 
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