Brake Bleeding

[Eagle]

Pete - how do you center the proportioning valve so the light on the dash will go out, after bleeding the brakes for the second time around? - meaning with the front bleeder open so the shuttle the valve will travel to one side, while rebleeding the rears. :help:

Not Pete, but ... stomp on the brake peddle HARD. That should reset the shuttle.

 

Did I mention HARD?

[Wildman]

 

It takes approximately 250 pounds of force to re-shuttle the distribution block, to turn the brake light off.

[RLCollins]

Thanks Eagle and wildman for the informaion - I shall try it in the morning. :chillin:

Sorry Eagle the reason I said pete, was the picture at the top of this thread with the MJ valve cut in half, sure would like to see an XJ cut in half. The XJ has a spring in the end of it. It would be nice to see the difference between to two :chillin:

[Eagle]

I had one from an XJ cut in half to go along with the MJ one -- it disappeared in the mess before I got to take the photos. How the XJ valve works is a mystery to me. Best I can figure out is that it does the opposite of what it needs to do. What you want is to limit the maximum force in a panic stop so the back end doesn't try to get down the road faster than the front end. What the XJ valve seems to do is not allow ANY brake fluid (force) to the rear wheels until the brakes have been stomped on pretty hard. Which seems logical -- how many people with XJs have had to replace the front pads three or four times before touching the rear shoes? :waving:

[Wakerider933]

now that i have removed the height sensing valve what flex line should i use with a 4 inch lift?

[Eagle]

I used a '94 Wrangler hose. I think Pete used a '95 Dakota.

[Wakerider933]

thanks eagle for all the help

[JACKED88]

Yeah, the rear proportioning valve DOES require a special procedure. First, bleed all four wheels normally. After that, the FSM says to do the following:

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

 

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

 

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

 

After re-bleeding the rear brake cylinders the entire system must be bled again.

 

Bleed the brake calipers and cylinders in the following sequence:

 

1st -- Right rear

 

2nd -- Left rear

 

3rd -- Right front

 

4th -- Left front

Sorry to have to drag up an old subject but I've got a problem with the above bleeding procedure.

 

Did everything like it says but when I open the front bleeder to "shuttle the by-pass differential valve" the brake warning light does not come on. Yes, I had tha key turned on. I pushed tha peddle to tha floor numerous times but no light. Even tried opening both front bleeders but still no light.

 

Would the arm on the height sensing valve being disconnected effect my bleeding procedure? Tha pre-owner never hooked it up after doing the SOA. The arm is currently tied up at about a 45* angle.

 

Speaking of which, with the height sensing valve arm being fixed in an upward 45* position, wouldnt that mimic a load being on the truck and therefore allow more pressure to the rear brakes?

 

One more thing ...... I've been reading all the brake threads I could find and have come to the conclusion that I'm totally confused on weather the rear brakes have both a proportioning and a height sensing valve. Some people are talking about the height sensing valve where others are talking about a proportioning valve. :hmm: So which is it or do we have both?

I know we have a valve and or distribution block below the master cylinder. Which is it? A proportioning valve or a distribution block?

If its a distribution block, where is our proportioning valve? Or, does the height sensing valve serve as a proportioning valve?

If the height sensing valve serves as a proportioning valve, that might explain why everybody calls tha same part by two different names) :dunno:

Either way nobody seems to like the stock system and either wants to re-route lines and remove the height sensing / proportioning valve completely or replace it with one from an XJ.

 

Here's what I'm thinkin. We don't actually have a proportioning valve like found on most vehicles. We have a Load Sensing Proportioning Valve that controls how much rear brake pressure is applied pending how much weight is on the rear axle. The body mounted load sensing valve is mechanically controlled via an arm thats connected to the differential. As weight is increased in the rear of the truck, the mechanical arm moves upwards opening the valve allowing more brake pressure to be applied to the rear brakes.

Somebody on here claims the load sensing valve doesnt open or close anything. I disagree. If that were true, it wouldnt serve any purpose at all. How else would it be able to control how much braking pressure to apply to the rear brakes? A valve by any name is a devise used to control the movement of gases or liquids. On a vehicle, weather its a mechanically controlled Load Sensing Proportioning Valve or a spring loaded pressure sensitive proportioning valve the end result is the same. Its still a valve that opens and closes controlling the amount of pressure applied to the brakes.

 

Assuming I'm correct on how the system works, I'm gonna leave my rear Valve in place but disconnected from the dif. I'll set it in a fixed position as if the truck has a light load in it or with the amount of rear braking I feel is sufficient for normal driving conditions. If the front brakes have to work a little harder due to a heavier load .... so be it. Pads are cheap and easy to replace.

 

I would however like a better explanation on how the emergency braking system works. Talkin about tha system that kicks in if you loose front brake pressure. Is that what yall are talking about bypassing by re-routing the rear lines in the distribution block? Or is the re-routing part of removing the load sensing valve?

Either way I wanna dump the emergency system. Couldnt I re-route tha rear line at tha distribution block but in my case still run tha line through the load sensing valve so I can control my rear braking?

[Eagle]

Speaking of which, with the height sensing valve arm being fixed in an upward 45* position, wouldnt that mimic a load being on the truck and therefore allow more pressure to the rear brakes?

I think that would be correct.

 

I know we have a valve and or distribution block below the master cylinder. Which is it? A proportioning valve or a distribution block?

If its a distribution block, where is our proportioning valve? Or, does the height sensing valve serve as a proportioning valve?

The thingie in the front on the XJ is a proportioning valve. The thingie in the front of the MJ performs no proportioning. It is a distribution block, AND an emergency bypass valve in the case of losing the front brakes.

 

Assuming I'm correct on how the system works, I'm gonna leave my rear Valve in place but disconnected from the dif. I'll set it in a fixed position as if the truck has a light load in it or with the amount of rear braking I feel is sufficient for normal driving conditions. If the front brakes have to work a little harder due to a heavier load .... so be it. Pads are cheap and easy to replace.

What I see as the flaw in your thinking is that your "solution" retains all the disadvantages of having the rear height-sensing valve but eliminates the one advantage it offers. You will still have two hard lines, doubling the length of steel tube exposed to rusting out. And you still have a 20+ year old time bomb that could explode (like mine did) in a panic stop. The better way to accomplish having constant rear brakes set for light loading is to use a single line with a Wilwood adjustable proportioning valve. Or run a single line and run smaller wheel cylinders in the rear brakes.

 

I would however like a better explanation on how the emergency braking system works. Talkin about tha system that kicks in if you loose front brake pressure. Is that what yall are talking about bypassing by re-routing the rear lines in the distribution block? Or is the re-routing part of removing the load sensing valve?

Back up in this thread and look at the cut-away photo of the MJ front metering block. There are TWO outlets that feed to the rear. The outlet that comes out of the "nose" of the metering block is the outlet that normally feeds to the rear axle. The line from that outlet always has full pressure. It goes into the rear height-sensing valve, where the valve proportions how much of the pressure is allowed to go to the brakes. The outlet on the front bottom is the emergency bypass. Normally, it is blocked by the sliding shuttle valve that runs horizontally across the top. If you lose the front brakes, the pressure differential causes that shuttle valve to slide, opening up the bypass port. (NOTE: As was commented when I first posted the photo, the unit in the photo is DEFECTIVE! The factory did not finish boring the hole for the bypass circuit, so it looks like that outlet has no fluid supply.) That outlet has a hard line that tees into the rear circuit AFTER the height sensing valve, so when in bypass mode you always get full pressure to the rear brakes.

 

Either way I wanna dump the emergency system. Couldnt I re-route tha rear line at tha distribution block but in my case still run tha line through the load sensing valve so I can control my rear braking?

Yes, you could simply block the front/bottom out let on the metering block and block off the tee fitting after the height sensing valve to eliminate the bypass circuit. That, IMHO, would be a very poor approach. You will still have a 20+ year old height sensing valve that may explode in a panic stop. At least if you leave the height sensing valve connected to the actuator rod you would be offsetting the risk by having a functional height sensing valve. If you are just going to fix the arm in one position, why risk driving ab=round with a time bomb when you can eliminate that and use a device that's MADE for the purpose -- the Wilwood manually adjustable proportioning valve?

[JACKED88]

OK, so lets say I leave the system in its factory configuration other than setting the load sensing valve in a fixed position. What have I defeated other than the progressive braking of load sensing valve?

 

BTW, I don't have a rust or corrosion problem. All of the lines look great as does the rest of the under carriage. Knowing I don't have a rust problem and the lines are in good condition, I'm not worried about having an extra line exposed to the elements or having one explode due to rust or corrosion.

 

Back to my problem of the brake light not coming on when I try to shuttle the emergency valve. Like in most vehicles that light is supposed to come on momentarily while your cranking the engine and then turn off once it starts. And, although on a different circuit, it should also come on whenever you have the e-brake set. In both of those functions the light is coming on. So why won't it come on when I try to shuttle tha valve?

I'm gonna try it again. Maybe for whatever reason we missed seeing the light due to the bright @$$ lighting in my nephews shop building.

As it is, my peddle goes about half way to the floor before it starts getting hard to push. It'll go even further pending how much pressure I apply. Thats actually an improvement since it'll no longer go all tha way to the floor.

 

I'm old school. We didnt have all this new fangled safety crap in tha vehicles we learned to drive in. If I had my way, I'd have one line coming out of the master cylinder T'd off and going straight to tha front brakes and another coming out for tha rears like they used to be without all this other crap. Even then I never though tha rear brakes worked as good as tha fronts. Can't say I remember tha front catchin up with tha rear to often either. (unless we did it purposely with tha e-brake)

 

I don't have a problem leaving the brakes in their factory configuration so long as they actually work without having to stand on um. Out of all tha XJ's we've owned through tha years, I've never though tha brakes were worth a crap in none of um. Same goes for this MJ.

[victorgallas]

 

Yeah, the rear proportioning valve DOES require a special procedure. First, bleed all four wheels normally. After that, the FSM says to do the following:

 

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

 

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

 

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

 

After re-bleeding the rear brake cylinders the entire system must be bled again.

 

Bleed the brake calipers and cylinders in the following sequence:

 

1st -- Right rear

 

2nd -- Left rear

 

3rd -- Right front

 

4th -- Left front

 

 

 

Quick question, 

If we leave one of the front calipers open while we do the rear in order o bleed the line of the proportioning valve, following this special procedure, arent we introducing air into the front brake lines?

Is this procedure above correct for those of use that have a working load sensing valve at the rear of the truck?.

 

I just ask this because using the pedal to pump the fluid will surely suck air into the open front caliper in between pumps. Or would you say to leave the front caliper open, then bleed the rears using a vaccuum pump/?

[Eagle]

 

 

Yeah, the rear proportioning valve DOES require a special procedure. First, bleed all four wheels normally. After that, the FSM says to do the following:

 

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

 

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

 

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

 

After re-bleeding the rear brake cylinders the entire system must be bled again.

 

Bleed the brake calipers and cylinders in the following sequence:

 

1st -- Right rear

 

2nd -- Left rear

 

3rd -- Right front

 

4th -- Left front

 

 

 

Quick question, 

If we leave one of the front calipers open while we do the rear in order o bleed the line of the proportioning valve, following this special procedure, arent we introducing air into the front brake lines?

Is this procedure above correct for those of use that have a working load sensing valve at the rear of the truck?.

 

I just ask this because using the pedal to pump the fluid will surely suck air into the open front caliper in between pumps. Or would you say to leave the front caliper open, then bleed the rears using a vaccuum pump/?

 

 

This procedure was quoted directly from the factory service manual (FSM). Yes, it allows air into the front circuit. That's why it says "After re-bleeding the rear brake cylinders the entire system must be bled again." The procedure is for vehicles with a functional rear height sensing valve. The purpose of this procedure is to ensure that the emergency bypass circuit is properly bled.

[rylee144]

I am bleeding my brakes and hit a snag. No fluid comes out the front right. Pulled the bleeder in case it was plugged, nothing. Pulled soft line still nothing. 

[88towmanche]

19 hours ago, rylee144 said:

I am bleeding my brakes and hit a snag. No fluid comes out the front right. Pulled the bleeder in case it was plugged, nothing. Pulled soft line still nothing. 

Plugged line?

 

My brothers & I used to resurrect old chevy's and flip them for cash - from the mid '80's to early '90's you could still pick up decent '65-'69 Chevelles for cheap (even back then, 1st gen camaro's were expensive and Novas were usually trashed) go through them to get road worthy and shoot fresh paint - we'd flip 4 or 5 cars a year make $10-$15k for the effort.  

 

Anyway, one of the problem we'd run into with the brakes were plugged lines - don't know what crap gets in there, but sometimes those blockages are why we couldn't get the fluid to flow.

 

 

[rylee144]

Could they be blown out with an air compressor?

[rylee144]

Still no luck. Some say stomp the brakes to get the proportioning valve to move. One guy told me don't do that I'll ruin my brake booster, specifically the diaphragms inside. Another says just keep bleeding them. I still can't get anything out of front passenger side even with the brake line off. So it's either the proportioning valve or a blocked line right? 

 

Is there one more likely? Getting the brake line off the proportioning valve to blow it out is a real b. I'd rather not do that until it's my last option. 

[Pete M]

I would eyeball the entire length of the tube and check for any kinks or damage.

[rylee144]

That was done. Everything worked great before the axle swap. 

[Pete M]

I would try disconnecting the length of tube at both ends and back flush with compressed air.  this will be messy so be prepared for that. 

[Eagle]

11 hours ago, rylee144 said:

Still no luck. Some say stomp the brakes to get the proportioning valve to move. One guy told me don't do that I'll ruin my brake booster, specifically the diaphragms inside. Another says just keep bleeding them. I still can't get anything out of front passenger side even with the brake line off. So it's either the proportioning valve or a blocked line right? 

 

Is there one more likely? Getting the brake line off the proportioning valve to blow it out is a real b. I'd rather not do that until it's my last option. 

 

This is for an MJ? The proportioning valve is above the rear axle and does not affect the front brakes. That thingie beneath the master cylinder on the MJ is a distribution block, not a proportioning valve.

[rylee144]

Ah yes distribution block. And yes mj.