Proportional control valve problems

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Swamp Squatch

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Hey guys, first time posting, please let me know if this goes in a different area of the site.

The e-brake light on my 06 LJ is stuck on while the e-brake isn't in use. My(limited) research has led me to believe this happens when the pressure between the front and back brake lines are out of wack. In an attempt to trouble shoot yesterday I attempted to bleed the back right brake lines and nothing came out. The sun was going down and I decided to take it to the local mechanic the next day and see what he has to say. They called and said "The Proportional control valve has internal short to ground". They quoted me $600 in parts and $400 in labor. I'm new to jeeps but I'm not an idiot, I think he's trying to fleece me. I'm going to get my jeep tomorrow and try to fix this problem. My question then becomes, what's the best way to troubleshoot this? The brakes are spongy when pressed, and when stopped at red light will slowly bleed(as in the petal will slowly go to the floor, then I have to pull off and re-apply the brakes). When the jeep is off the brake petal can be depressed a few times then they lock up. Any help would be apricated, and thanks in advance.
 
Sounds like air in the brake lines. Attempting to bleed and nothing comes out needs to be investigated. If this is a new to you rig you should thoroughly inspect the entire brake system. Flush the brake fluid and bleed properly. There’s a thread on here explaining how to get the proportional valve back into whack.

Your first post should go to the new member section. The admin might move it.
 
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Swamp Squatch said:
Hey guys, first time posting, please let me know if this goes in a different area of the site.

The e-brake light on my 06 LJ is stuck on while the e-brake isn't in use. My(limited) research has led me to believe this happens when the pressure between the front and back brake lines are out of wack. In an attempt to trouble shoot yesterday I attempted to bleed the back right brake lines and nothing came out. The sun was going down and I decided to take it to the local mechanic the next day and see what he has to say. They called and said "The Proportional control valve has internal short to ground". They quoted me $600 in parts and $400 in labor. I'm new to jeeps but I'm not an idiot, I think he's trying to fleece me. I'm going to get my jeep tomorrow and try to fix this problem. My question then becomes, what's the best way to troubleshoot this? The brakes are spongy when pressed, and when stopped at red light will slowly bleed(as in the petal will slowly go to the floor, then I have to pull off and re-apply the brakes). When the jeep is off the brake petal can be depressed a few times then they lock up. Any help would be apricated, and thanks in advance.
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Your mechanic is an idiot. Find the leak. In the meantime, try stomping the pedal to turn the light off and equalize the pressure.

The reason your mechanic is an idiot is there is no wiring or circuit sensing on the proportional control side. There is a shuttle safety valve right behind the switch in the combination valve that senses high differential pressure by shifting to one side. When it does that, it moves the plunger on the switch out of the detent and completes the circuit to ground which then trips the dash brake light. That is the normal function and you can't probe the switch connector because both pins are connected when it is on the switch. It is a series circuit with a couple of places that close the circuit to ground.

If after careful examination of the corners and brake related bits and you don't see a leak or signs of one, then you will need to pull the master and see if there is fluid in the booster. If so, then you need a new master and a new booster. If you don't see any in the booster and no evidence of fluid at the rear of the master, then it is possible the master is bypassing internally. That is very low on the list of possibilities though and I suspect you have a small leak somewhere you haven't found.
 
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Richard49 said:
Sounds like air in the brake lines. Attempting to bleed and nothing comes out needs to be investigated. If this is a new to you rig you should thoroughly inspect the entire brake system. Flush the brake fluid and bleed properly. There’s a thread on here explaining how to get the proportional valve back into whack.

Your first post should go to the new member section. The admin might move it.
Click to expand...
I think I've seen that method when I was originally googling, I was hoping to avoid it but I think I'm going to have to flush the brake system anyways. Ill put any future post in the new member section, thanks.
mrblaine said:
Your mechanic is an idiot. Find the leak. In the meantime, try stomping the pedal to turn the light off and equalize the pressure.

The reason your mechanic is an idiot is there is no wiring or circuit sensing on the proportional control side. There is a shuttle safety valve right behind the switch in the combination valve that senses high differential pressure by shifting to one side. When it does that, it moves the plunger on the switch out of the detent and completes the circuit to ground which then trips the dash brake light. That is the normal function and you can't probe the switch connector because both pins are connected when it is on the switch. It is a series circuit with a couple of places that close the circuit to ground.

If after careful examination of the corners and brake related bits and you don't see a leak or signs of one, then you will need to pull the master and see if there is fluid in the booster. If so, then you need a new master and a new booster. If you don't see any in the booster and no evidence of fluid at the rear of the master, then it is possible the master is bypassing internally. That is very low on the list of possibilities though and I suspect you have a small leak somewhere you haven't found.
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I thought the mechanic sounded funny, but I'm not an expert. You gave me a great starting point for tomorrow though. I really appreciate it!
 
Only the first post should go in new member section. The admin will move this if necessary. You’re ok. stay here and keep us updated.
I should have mentioned the possibility of a leak but I didn’t want to go into too much detail not knowing your situation.
Anyway, mrblaine answered your query with an eloquence I can only aspire too.

BTW is this your first TJ? How long have you owned it?
 
Richard49 said:
Only the first post should go in new member section. The admin will move this if necessary. You’re ok. stay here and keep us updated.
I should have mentioned the possibility of a leak but I didn’t want to go into too much detail not knowing your situation.
Anyway, mrblaine answered your query with an eloquence I can only aspire too.

BTW is this your first TJ? How long have you owned it?
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First jeep, owned it for a few months but I just recently turned it into my daily driver due to a (girl)friend in need that is using my truck. I work from home so it made sense to let her use the better vehicle.

I checked for leaks, didn't see any, that's not to say their not there, I just couldn't find any. With the vehicle on the brakes hold, even before starting this job they would only give out occasionally when stopped at a red light.

So update. I slammed on the brake and the e-brake light went out. I attempted to bleed the back half of the brake lines and nothing came out. I cleaned out the bleed screws just to be sure, but still nothing. The front half was also bled, it had a lot of air in the lines. I had a friend pump the brakes 6-7 times while bleeding(he would press down, I would crack the bleed screw, fluid would come out, I would shut the bleed screw, he would pull up on the brake, repeat process) and I was still getting little tiny bubbles in the brake line under the master. There was a lot of air in the two front lines and the brakes already feel better after bleeding, but the fact that I cant get any fluid to the back half of the vehicle seems weird.

Side note, the booster, master and brake lines all look new compared to the rest of the vehicle. Not sure if it matters but figured it was worth mentioning.
 
There is a trick to bleeding with that shuttle valve which is often required, and requires a special tool as I understand it. I’ve not had to do it, so not an expert there. I’m sure Blaine or someone else will chime in with the procedure though. Good luck, and welcome to the forum.
 
Swamp Squatch said:
First jeep, owned it for a few months but I just recently turned it into my daily driver due to a (girl)friend in need that is using my truck. I work from home so it made sense to let her use the better vehicle.

I checked for leaks, didn't see any, that's not to say their not there, I just couldn't find any. With the vehicle on the brakes hold, even before starting this job they would only give out occasionally when stopped at a red light.

So update. I slammed on the brake and the e-brake light went out. I attempted to bleed the back half of the brake lines and nothing came out. I cleaned out the bleed screws just to be sure, but still nothing. The front half was also bled, it had a lot of air in the lines. I had a friend pump the brakes 6-7 times while bleeding(he would press down, I would crack the bleed screw, fluid would come out, I would shut the bleed screw, he would pull up on the brake, repeat process) and I was still getting little tiny bubbles in the brake line under the master. There was a lot of air in the two front lines and the brakes already feel better after bleeding, but the fact that I cant get any fluid to the back half of the vehicle seems weird.

Side note, the booster, master and brake lines all look new compared to the rest of the vehicle. Not sure if it matters but figured it was worth mentioning.
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Follow the no fluid problem one connection at a time and see where you are losing it. Engine off, reservoir full, start at the master. Loosen the line, see if fluid runs out. Repeat at combo block and the next connection in line until you find the problem.
 
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I think I found the problem, its getting fluid from the master so I think its the internals of the prop valve. Is this something that should be replaced or can i remove/clean/re-install?

IMG_1452.jpg
 
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Swamp Squatch said:
I think I found the problem, its getting fluid from the master so I think its the internals of the prop valve. Is this something that should be replaced or can i remove/clean/re-install?

View attachment 300413
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You need to pull the switch and see if the detent is visible in the hole. Fluid will be restricted to one of the output ports if the shuttle valve is shifted. The plunger is spring loaded and that is what holds the shuttle valve in place.
 
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mrblaine said:
You need to pull the switch and see if the detent is visible in the hole. Fluid will be restricted to one of the output ports if the shuttle valve is shifted. The plunger is spring loaded and that is what holds the shuttle valve in place.
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Pulled it and cleaned it. There was blockage in the little hole between the prop valve and the line heading to the back brakes. Re-bled all lines starting with the RR and ending with the LF. Thanks for the help everyone(especially mrblain)!
 
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