MJ Load Sensing Valve Delete Procedure

[cruiser54]

[HOrnbrod]

^^^  Not worried about that. If unsat, I'll pop in the disk/disk ZJ prop valve.

[MeanLemons]

Don, where are you located? I MAYYYYYYYY be interested in the skid plate

[HOrnbrod]

North Alabama near Huntsville.

[MeanLemons]

North Alabama near Huntsville.

ah. Shipping probably would be a b*@$£ then.

[HOrnbrod]

 

North Alabama near Huntsville.

ah. Shipping probably would be a b*@$£ then.

 

Si.

[cruiser54]

Well, how ya gonna do it?

 

Gotta $#!&can the dristo valve and go one of three ways since the distro valve has .050" orifices for the front brakes.

 

Use a ZJ prop valve or an XJ valve with ZJ prop valve guts since the distro  valve has .050" passages versus XJ prop valve .100" passages for the front brakes. 

 

Or use  a T to give the front brakes full power and use an adjustable prop valve for the rear. 

 

I wasn't making this $#!& up. Been there, done that, got the T-shirt. 

 

I just verified the orifice size on an 89 XJ I'm parting out.  Every orifice is .100" on the prop valve. 

 

Confirmation of my initial  findings. 

[Eagle]

So, on to plan B. I will now plug off the block snout port and use the existing lower front port for the rear brake feed line as it is now used. According to Eagle's cutaway, both ports are on the same internal block channel so the output pressures are the same for both ports. Also plugging the snout port will be much easier to get to than plugging the one on the bottom.

 

Don, you can't use the lower forward outlet from the distribution block. That port doesn't get any brake pressure unless the front brakes fail and the shuttle valve moves to open the inlet to that circuit. That lower port is strictly an emergency bypass. That's why in our back-channel communication I told you you might have to buy a longer flex hose.

 

You have to feed the rear brakes from the "snout" outlet.

 

The other option would be to use an XJ or ZJ proportioning valve, which doesn't have a "snout" outlet and will connect the regular line to the rear to the lower front outlet.

 

MJ Distribution block:

 

[HOrnbrod]

Yes, I can see that there is no path for pressure out of the lower front port the way the shuttle valve sits during normal operation. I also can't see how the shuttle valve can move at all unless it's a 2-piece sliding unit. Is it? Some guys here are using the lower front port as the rear feed and report they are locking up the rears?    :hmm:

 

AAARG, this is confusing and starting to kick my azz. I prefer complicated electricals over brake line valves and lines. Easier to see how they work for me.

 

I have a ZJ disk/disk prop valve in hand - I guess I'll just use that and see what happens. Thanks for your help Eagle.

[Eagle]

Yes, the shuttle valve is two pieces. In the photo, just to the right of the plunger for the brake warning light switch there's a shoulder, and the last O-ring is just to the right of the shoulder. The basic body ends at that shoulder, and the slider portion is the part to the left, incorporating the recess that the switch plunger rides in. If the front circuit fails, the pressure in the rear circuit pushes the sliding plunger to the right. This pushes up the switch plunger, activating the brake warning light, and it also moves the left-most O-ring to the right to open up the by-pass circuit for full pressure to the rear brakes.

 

Since you have a ZJ proportioning valve, I'd say try it. If you're not getting enough force to the rear brakes, open it up, remove the rubber cup washer and spring inside, and slide the internal plunger all the way toward the nose, then reassemble.

 

Before you install it, open up the big fitting at the nose, and clean out the interior very well. Be sure the rubber cup washer is soft and pliable, and that the plunger can plunge. The XJs have a known issue of eventually losing rear brakes because the proportioning valve clogs up and stops allowing any fluid pressure to the rear. The accepted "fix" in the early days of NAXJA was to remove the cup washer and spring, slide the plunger fully forward, and reassemble. What that did was to eliminate the proportioning function and let the rear brakes have 100% force at all times.

[HOrnbrod]

Thanks - understand how the damn thing works now. It appears the best option will be to junk the MJ distribution valve and replace it with the ZJ disk/disk valve. See how the braking is, them pop out and modify the plunger as needed.

[cruiser54]

Thanks - understand how the damn thing works now. It appears the best option will be to junk the MJ distribution valve and replace it with the ZJ disk/disk valve. See how the braking is, them pop out and modify the plunger as needed.

You likely will be just fine. My wife's 88 is that way except for an XJ prop valve with ZJ guts in it. 

 

And you will also realize better overall braking with the larger ports in the ZJ valve. .100" vs .050".

[HOrnbrod]

 

Thanks - understand how the damn thing works now. It appears the best option will be to junk the MJ distribution valve and replace it with the ZJ disk/disk valve. See how the braking is, them pop out and modify the plunger as needed.

You likely will be just fine. My wife's 88 is that way except for an XJ prop valve with ZJ guts in it. 

 

And you will also realize better overall braking with the larger ports in the ZJ valve. .100" vs .050".

 

 

The ZJ valve has .078 (5/64") ports - just measured. Better than .050" anyhow. Assume the port assignments for the ZJ valve are as follows:

 

[Eagle]

That looks pretty ratty, Don. Aren't you going to have it chrome plated before you install it?

[HOrnbrod]

That looks pretty ratty, Don. Aren't you going to have it chrome plated before you install it?

 

Nope. It's pretty on the inside - that's all that matters.  :yes:

[cruiser54]

You guys will never realize optimum braking performance by leaving the distro valve in the system.

[HOrnbrod]

I NOW HAVE GREAT REAR BRAKES!

 

Today I broke out the FSM and re-read the load sensing valve (LSV) adjustment procedure - again. Referring to the diagram below, rear brake bias is optimal when the LSV shaft flat (shown by the red line; flat is actually on the splined portion of the shaft) points down at the 6.00 o'clock position while looking at the LSV from the front. The factory adjustment procedure used a wonky 85* adjustment fixture to do the procedure; naturally they are now unobtanium. But in reading the procedure I could see exactly what was happening and how it worked. I pulled the LSV lever partially off the LSV so I could see the shaft flat, and it was pointing at 3:00 o'clock! WTF? I then pulled the lever completely off, and rotated the shaft clockwise 360*. You could feel the pull in the shaft as the LSV internal rotary piston passed across the inlet and outlet fluid ports, then after it passed over the ports, it turned freely with no pull. This is how it regulates the rear brake bias depending on the vehicle load, and if the lever isn't in the correct orientation, the ports are blocked, thus there's no opening for the fluid to pass. Which of course causes weak or no rear braking.

I then rotated the valve shaft so it faced at about the 8:00 o'clock position, which simulated a fully loaded MJ and maximum rear braking. Then while keeping the shaft from rotating, slid the lever back on the splined shaft, pressed it on, and tightened it all down. Went for a test drive and slammed on the brakes, and the rears locked right up. Yay! Then I fooled with different lever positions on the splined valve shaft, and the best braking ended up to be when the shaft flat was facing right at the 7:00 o'clock position.

Now in a panic stop, the fronts lock up just before the rears - perfect. After about four full pedal stops, all four disks were hotter than the hinges of hell. Whereas before, just the front disks got real hot. I'm happy now - no ZJ proportioning valve and re-routing of the brake lines is now required. :)  At least for now.

Does this make sense to y'all? Unfortunately, the 91-92 LSV's are different than the older ones as there's no flat on the splined arm of the 90 and below LSV's. And the older LSV's use a completely different adjustment procedure and adjustment fixture, even wonkier than the HO's do.

 

[jerpderp]

H0rnbrod, when I first saw this thread, I thought hell froze over since you always seemed dedicated to the LSV. I am glad all is now right in the world. I do have 1 question though: with your new adjustment, do you think braking will be affected by a load? I'm curious if the valve will turn out of the happy, full braking zone.

 

 

Sent from my iPhone using Tapatalk

[HOrnbrod]

I think not. With the MT rear springs the rear end doesn't drop nearly as much as it did before with the stock springs. But we'll see what happens on the next  REALLY HEAVY load.   :yes:

[Minuit]

I suspect that since discs need more fluid pressure than drums, this would give too much rear braking on a factory drum setup?

[Pete M]

wait-wait-wait...  so you're not going to chrome the skidplate and reinstall?!  :dunno:  I'm so confused...

[HOrnbrod]

I suspect that since discs need more fluid pressure than drums, this would give too much rear braking on a factory drum setup?

 

I don't know. It definitely increased my disks. Try it and see. It only takes a few minutes and you can always go back to the same lever/spline position you started with.

 

wait-wait-wait...  so you're not going to chrome the skidplate and reinstall?!  :dunno:  I'm so confused...

 

Hmmmm. Never thought of that Pete. Brilliant!

[SBpunk]

Throw a moose in the back to test those M/T springs hahaha. My buddy's 2500HD was almost scraping the ground at the bed. Looked like one of those "cool" kids that can't afford the rear part of their lift.

[Keyav8r]

If you are considering eliminating your load sensing valve (as I was), do Don's check and adjustment procedure (below) first and see if it improves your braking. I took the arm off mine this morning and found the flat was at about the 4:30 - 5:00 position. After turning the flat to about 7:00 - 7:30 and re-installing the arm, I took my truck out for a test run. Braking action greatly improved from poor to good. The whole job, including getting and putting away tools, jack and stands took about 30.- 45 minutes and was well worth the time. I'm still planning on doing the '96 XJ double diaphragm booster upgrade but the priority has dropped a few spaces down on the to do list.
Kudos to Don for this MJ Tech jewel.
 

I NOW HAVE GREAT REAR BRAKES!
 
Today I broke out the FSM and re-read the load sensing valve (LSV) adjustment procedure - again. Referring to the diagram below, rear brake bias is optimal when the LSV shaft flat (shown by the red line; flat is actually on the splined portion of the shaft) points down at the 6.00 o'clock position while looking at the LSV from the front. The factory adjustment procedure used a wonky 85* adjustment fixture to do the procedure; naturally they are now unobtanium. But in reading the procedure I could see exactly what was happening and how it worked. I pulled the LSV lever partially off the LSV so I could see the shaft flat, and it was pointing at 3:00 o'clock! WTF? I then pulled the lever completely off, and rotated the shaft clockwise 360*. You could feel the pull in the shaft as the LSV internal rotary piston passed across the inlet and outlet fluid ports, then after it passed over the ports, it turned freely with no pull. This is how it regulates the rear brake bias depending on the vehicle load, and if the lever isn't in the correct orientation, the ports are blocked, thus there's no opening for the fluid to pass. Which of course causes weak or no rear braking.
I then rotated the valve shaft so it faced at about the 8:00 o'clock position, which simulated a fully loaded MJ and maximum rear braking. Then while keeping the shaft from rotating, slid the lever back on the splined shaft, pressed it on, and tightened it all down. Went for a test drive and slammed on the brakes, and the rears locked right up. Yay! Then I fooled with different lever positions on the splined valve shaft, and the best braking ended up to be when the shaft flat was facing right at the 7:00 o'clock position.
Now in a panic stop, the fronts lock up just before the rears - perfect. After about four full pedal stops, all four disks were hotter than the hinges of hell. Whereas before, just the front disks got real hot. I'm happy now - no ZJ proportioning valve and re-routing of the brake lines is now required. :)  At least for now.
Does this make sense to y'all? Unfortunately, the 91-92 LSV's are different than the older ones as there's no flat on the splined arm of the 90 and below LSV's. And the older LSV's use a completely different adjustment procedure and adjustment fixture, even wonkier than the HO's do.
 

[HOrnbrod]

If you are considering eliminating your load sensing valve (as I was), do Don's check and adjustment procedure (below) first and see if it improves your braking. I took the arm off mine this morning and found the flat was at about the 4:30 - 5:00 position. After turning the flat to about 7:00 - 7:30 and re-installing the arm, I took my truck out for a test run. Braking action greatly improved from poor to good. The whole job, including getting and putting away tools, jack and stands took about 30.- 45 minutes and was well worth the time. I'm still planning on doing the '96 XJ double diaphragm booster upgrade but the priority has dropped a few spaces down on the to do list.

Kudos to Don for this MJ Tech jewel.

Good to hear Fred. Thanks for trying this.