Brakes and proportioning valve questions.

[JACKED88]

I'm about to do a 4 wheel brake job and while I'm at it would like to do what I can to improve my trucks braking. Short of installing disc brakes on tha rear .... What is it you guys are doing to improve braking?

I've heard about using a "double booster" but don't know what booster your talking about. I've heard about using a different master cylinder but don't know which one works on our trucks. I've heard about using larger rear wheel cylinders but again don't know which ones to use. And then there's tha rear proportioning valve. I don't know what the hell yall are doing with that. Some say to dump tha rear valve and re-route the front lines giving you full 4 wheel braking.

 

Replacing tha booster and master cylinder are simple enough but if the rear valve is removed, what do you put in its place to connect tha now disconnected brake lines together?

 

Beep, Beep, back up a minute. ..... Is removing that rear valve a good idea on a daily driver? I don't want tha rear catching up with tha front every time I try to stop on a wet street. :eek: I often pull a trailer in which obviously increases my stopping load. Doesnt that valve have something to do with load sincing and how much rear braking to apply? Once removed, whats it gonna do without it?

 

If I leave tha rear valve operational, whats all this b/s ya gotta do to properly bleed tha system? If tha brakes will work properly without it ..... I'm all about removing it.

Instead of removing tha valve and having to deal with reconnecting tha lines, whats this about removing its piston and or its spring essentially disabling its operation?

[kastein]

Booster/MC swap - you want one out of a WJ (99-04 Grand Cherokee iirc.) I just put one in, MUCH better.

 

I kept my height sensing valve. I decided I wanted to be able to put a thousand pounds of junk in the back and just drive off without fiddling with a brake pressure adjuster in the cab, since I do that on a fairly regular basis. I've also been picking up spare HSVs at the junkyard every time I see them, since they just don't make them anymore.

 

For the WJ booster swap, here is the thread I used: http://www.naxja.org/forum/showthread.php?t=924285

 

I actually bled my master outside of the vehicle because it wasn't bleeding well while in the vehicle. Unbolted it from the booster, filled the reservoir up, put the lid on, shook the hell out of it, dumped all the fluid out (to get rid of the gunk all over the inside of the reservoir) then bled it.

 

I used 4 or 5 (forget) 1/4" flat washers on each booster mounting stud as spacers to make the pushrod hole to mounting surface distance the same as the original booster - if you don't do this, your pedal will be MUCH higher after the swap.

 

I'm not sure if you'll get lucky but I did on my 91. I measured and discovered I did not have to drill the hole in the pushrod out at all, and the distance from the hole to the brake switch actuator flat was only about 1/16" different so I just adjusted where the brake light switch was. Still got some kinks to iron out with that though, my cruise control deactivates when I go over potholes on the highway.

 

Proper brake line routing to keep the HSV - viewtopic.php?f=9&t=17968&p=238880#p238880

 

Bleeding - http://comancheclub.com/forums/viewtopic.php?f=2&t=4917 (I actually haven't done the extra stuff yet, works fine but probably won't work in emergency situations! Gotta get on that this weekend)

 

Clear as mud? :dunno:

[-600JeepMJ]

:typing: more help full info on the booster

 

http://www.madxj.com/MADXJ/technical/te ... pgrade.htm

 

 

http://www.4x4wire.com/jeep/tech/brakes ... 3/booster/

 

http://www.cardomain.com/ride/325707/15

[Eagle]

I'm about to do a 4 wheel brake job and while I'm at it would like to do what I can to improve my trucks braking. Short of installing disc brakes on tha rear .... What is it you guys are doing to improve braking?

Removing the rear height sensing valve ... that thing you're so worried about.

 

I've heard about using a "double booster" but don't know what booster your talking about.

Not "double booster." "Double diaphragm" booster. Typically from a late model Cherokee, although I would probably go with one from an older AMC car that still uses the old style master cylinder. Don't trust plastic.

 

And then there's tha rear proportioning valve. I don't know what the hell yall are doing with that. Some say to dump tha rear valve and re-route the front lines giving you full 4 wheel braking.

I am one of those who recommend that.

 

Replacing tha booster and master cylinder are simple enough but if the rear valve is removed, what do you put in its place to connect tha now disconnected brake lines together?

Nothing. One of the lines serves no purpose and should be removed. That leaves you with only one line to worry about, and no special bleeding procedure.

 

Beep, Beep, back up a minute. ..... Is removing that rear valve a good idea on a daily driver? I don't want tha rear catching up with tha front every time I try to stop on a wet street. :eek: I often pull a trailer in which obviously increases my stopping load. Doesnt that valve have something to do with load sincing and how much rear braking to apply? Once removed, whats it gonna do without it?

The rear valve allows more braking force when the rear is loaded. If yours is working correctly (which it may or may not be ... most of them aren't), you'll have more brakes when towing. With the rear valve removed, you will have maximum braking when towing. No problem there. Is there a possibility of premature rear wheel lock in slippery conditions when NOT loaded? Yes. If that's a problem for you, put a Wilwood manually adjustable proportioning valve in the line to the rear where it exits the front distribution block, and use that to dial back the rear brakes when you run empty.

 

If I leave tha rear valve operational, whats all this b/s ya gotta do to properly bleed tha system?

It isn't BS. The procedure is spelled out in the factory service manual, and if not followed you may have NO rear brakes.

 

Instead of removing tha valve and having to deal with reconnecting tha lines, whats this about removing its piston and or its spring essentially disabling its operation?

That's for Cherokees, and it's in the front proportioning valve. The front metering block in the MJ is not a proportioning valve and does not have the spring and O-ring you can remove.

[JACKED88]

Worried??? I aint worried. I just wanted to know how the brakes react without it before I take it out. Sounds to me they'll work about tha same as we had on our older 60's/70's cars/trucks.

 

Thanks for correcting me on tha "Double diaphragm" and for the info on where to look for one.

 

OK, maybe I shouldnt have refered to that bleeding procedure as b/s. But you gotta admit it sounds like a royal pain in tha @$$. One well worth eliminating so long as your brakes still work properly.

 

 

Back to that valve I'm not worried about :roll: With an upgraded booster, master cylinder and wheel cylinders, and making sure the valve is working properly, wouldnt your braking be considerably improved even if you leave tha valve operational?

How does that valve work anyway? I understand its purpose but we didnt have um on our older trucks and tha brakes worked just fine. No, not as good as these new anti-locks but they kept us from running over everything in our path.

[Eagle]

Back to that valve I'm not worried about :roll: With an upgraded booster, master cylinder and wheel cylinders, and making sure the valve is working properly, wouldnt your braking be considerably improved even if you leave tha valve operational?

No.

 

What the height sensing valve does is severely reduce the amount of braking force to the rear wheels when the truck is running unloaded. I don't know how much it reduces it, but I'd guess between 75% and 100% (meaning NO rear brakes at all when empty). If you upgrade the booster (I don't see how changing the master cylinder can in any way "improve" the braking, unless you swap in a master with a very different piston diameter), you improve the braking pressure in the system. That means the front brakes work better/harder. If the rear proportioning valve eliminates most of the pressure going to the rear brakes, then by definition it eliminates 75% to 100% of any improvements you make to the system.

 

IMHO the single biggest and easiest improvement you can make to MJ brakes is to eliminate the height sensing valve.

[kastein]

I haven't had the opportunity to try out mine with a functioning/in-circuit height sensing valve completely unloaded yet, but I can tell you that braking is worlds better with my rear brakes working again, a functioning height sensing valve, and a full load (spare d30, 2.5L engine, ~150-200lbs of metal stock, jackstands, spare tire, a few toolboxes) in the bed.

 

In a week or two I'll know more. Personally I intend to keep my valve unless it turns out it isn't functioning, which I would be surprised by, as it is in amazingly good condition compared to the rest of the undercarriage.

[JACKED88]

When the previous owner did the SOA, and installed an XJ axle, he didnt re-install the rod that goes from the axle to tha valve arm. He just tied the arm up so it wasnt just hanging there. In theory, having that arm tied in an upward position, wouldnt that make the valve think there's a load in the bed and allow the rear brakes to be applied?

 

Found this write up and pix. Since mine isnt operational I've never looked at one that is. Its tha pic I was mostly interested in however his adjustable rod looks is good idea. viewtopic.php?f=9&t=17968&start=0

 

Looking at the above pic with everything installed and if I understand how it works, the further up that rod pushes the valve arm the more rear braking pressure is applied. So if you were to a-fix that arm in an upward position then the valve would be in a closed position allowing rear brake pressure to be applied. While in the down or level position, the valve is open allowing the braking pressure to bypass the rear brakes and be diverted to the front brakes.

With my valves arm in its fixed upward position I'm pretty certain my rear brakes are working. That may not be tha best way to bypass the system but its apparently working.

Now, to bleed my system couldnt I first bleed tha rear by moving the valve arm up to the closed position and then bleed the front by moving the arm down to the open position?

[Eagle]

When the previous owner did the SOA, and installed an XJ axle, he didnt re-install the rod that goes from the axle to tha valve arm. He just tied the arm up so it wasnt just hanging there. In theory, having that arm tied in an upward position, wouldnt that make the valve think there's a load in the bed and allow the rear brakes to be applied?

 

Found this write up and pix. Since mine isnt operational I've never looked at one that is. Its tha pic I was mostly interested in however his adjustable rod looks is good idea. viewtopic.php?f=9&t=17968&start=0

 

Looking at the above pic with everything installed and if I understand how it works, the further up that rod pushes the valve arm the more rear braking pressure is applied. So if you were to a-fix that arm in an upward position then the valve would be in a closed position allowing rear brake pressure to be applied. While in the down or level position, the valve is open allowing the braking pressure to bypass the rear brakes and be diverted to the front brakes.

With my valves arm in its fixed upward position I'm pretty certain my rear brakes are working. That may not be tha best way to bypass the system but its apparently working.

Now, to bleed my system couldnt I first bleed tha rear by moving the valve arm up to the closed position and then bleed the front by moving the arm down to the open position?

Bypass to the front brakes?

 

The front brakes are completely independent of the rear brakes. Moving the arm up does not "close" anything, and moving the arm down does not bypass anything to the front brakes. Wherever you found that explanation of how the valve works, it is incorrect. You either bleed the rear brakes the way the FSM says to bleed them, or it isn't done right.

[JACKED88]

When the previous owner did the SOA, and installed an XJ axle, he didnt re-install the rod that goes from the axle to tha valve arm. He just tied the arm up so it wasnt just hanging there. In theory, having that arm tied in an upward position, wouldnt that make the valve think there's a load in the bed and allow the rear brakes to be applied?

 

Found this write up and pix. Since mine isnt operational I've never looked at one that is. Its tha pic I was mostly interested in however his adjustable rod looks is good idea. viewtopic.php?f=9&t=17968&start=0

 

Looking at the above pic with everything installed and if I understand how it works, the further up that rod pushes the valve arm the more rear braking pressure is applied. So if you were to a-fix that arm in an upward position then the valve would be in a closed position allowing rear brake pressure to be applied. While in the down or level position, the valve is open allowing the braking pressure to bypass the rear brakes and be diverted to the front brakes.

With my valves arm in its fixed upward position I'm pretty certain my rear brakes are working. That may not be tha best way to bypass the system but its apparently working.

Now, to bleed my system couldnt I first bleed tha rear by moving the valve arm up to the closed position and then bleed the front by moving the arm down to the open position?

Bypass to the front brakes?

 

The front brakes are completely independent of the rear brakes. Moving the arm up does not "close" anything, and moving the arm down does not bypass anything to the front brakes. Wherever you found that explanation of how the valve works, it is incorrect. You either bleed the rear brakes the way the FSM says to bleed them, or it isn't done right.

:thwak:

My bad. Thanks for trying to set me straight. I've done my homework since then and know how it works now. I should have just taken your word for it in the beginning but I wanted to know exactly how this system works and I wasnt gonna quit till I did. Now, thanks to you I know how it works and what to do to improve my braking without sacrificing safety.

Without going into detail I'm thinking about making sure mine works and then make it adjustable. Doing it that way I'll also retain the intended function of the front valves emergency rear braking in which is activated upon front pressure failure. Hence the purpose of that third line.

 

Thanks for your help.