HOrnbrod Posted June 16, 2017 Share Posted June 16, 2017 Anyone know where the picture that was posted of the MJ distribution block with the ports labeled is? Can't find it anywhere.............. Link to comment Share on other sites More sharing options...
Jeep Driver Posted June 16, 2017 Share Posted June 16, 2017 Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 16, 2017 Author Share Posted June 16, 2017 Gracias! Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 16, 2017 Author Share Posted June 16, 2017 I'm going to bypass my rear load sensing valve (think it's clogged up and finally died) and replace my existing MJ distribution block with a ZJ proportioning valve (they are set up for front & rear disks) since I have rear disk brakes installed. The picture below is of a 96 booster and proportioning valve. Does the 96-98 ZJ disk/disk proportioning valve have the same port assignments and threads as the pictured XJ proportioning valve? I @$$ume it does, but want to be sure. Â Link to comment Share on other sites More sharing options...
Jeep Driver Posted June 16, 2017 Share Posted June 16, 2017 You really should try it with the MJ block first.  The plug will cost  you about a $buck. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 16, 2017 Author Share Posted June 16, 2017 You really should try it with the MJ block first.  The plug will cost  you about a $buck.  True, but you know what happens to your brakes when a line breaks w/o a proportioning valve. They disappear... Link to comment Share on other sites More sharing options...
Eagle Posted June 17, 2017 Share Posted June 17, 2017  You really should try it with the MJ block first.  The plug will cost  you about a $buck.  True, but you know what happens to your brakes when a line breaks w/o a proportioning valve. They disappear...   :???:  No, they don't.  Both the XJ/ZJ proportioning valve and the MJ distribution block have completely separate circuits for the front and rear brakes. If a front line or hose breaks, you will still have rear brakes. With the MJ unit, you'll have 100% rear brakes, with the XJ/ZJ unit you'll theoretically have 100% rear brakes but more likely you'll have proportioned rear brakes. If a rear line or hose breaks, you'll have 100% front brakes (which you always have, anyway). Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 17, 2017 Author Share Posted June 17, 2017 Crap - you're right. Completely forgot about your MJ block cutaway and the segregated circuits. What size was that block front port plug again? 1/2x20? Link to comment Share on other sites More sharing options...
Eagle Posted June 17, 2017 Share Posted June 17, 2017 10-4 ... 1/2x20 Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 17, 2017 Author Share Posted June 17, 2017 The simple way to eliminate the rear height sensing valve is to disconnect the rear axle flex hose from it, run a new hard line from the "nose" of the front distribution block directly to the rear flex hose, and to plug the forward/lower output on the distribution block. That's it -- done.  Eagle, I know eliminating the height sensing valve doing the above with the stock drums will work fine, but what's your take on how it will bias my Explorer rear disk brakes? I've searched to see if anyone had rear disks and eliminated the load sensing valve but didn't find anything. Would I be better off throwing in a ZJ disk/disk proportioning valve? I'd much rather do it as quoted above if it will bias the rears okay since I'm a lazy bastid nowadays........... Link to comment Share on other sites More sharing options...
Pete M Posted June 17, 2017 Share Posted June 17, 2017 there's no single answer for that one. Â far as I can tell every iteration has been tried and both works and didn't work for different people (stock with drums, stock with disks, XJ with drums, XJ with disks, etc) Â I figure the best bet for success is the aftermarket adjustable prop for the rear line. Â :yes: Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 17, 2017 Author Share Posted June 17, 2017 Yeah Pete, this question has been beat to death. The only given I have now is that I had great rear disk brakes by tuning the adjustable load sensing rod I've had for years; now there are basically zero rear brakes. Bled the crap out of them, and got NO air from the rear calipers. Even bought a Motive pressure bleeder and had the same results as the pedal pump method. I can only assume the load sensing valve is now a no-op clogged fluid flow blocker.  I guess the best course course of action is to bypass the load sensing valve by using the existing rear brake line from the front distro block port (instead of running a new one since my brake lines are in great shape) to the rear flex junction, then plug the lower distro block front port, and see if that restores the rear brakes. Then if needed for proper biasing I'll plumb in a Wilwood prop valve on the rear supply line. AAARG - this isn't fun anymore.. Link to comment Share on other sites More sharing options...
Eagle Posted June 17, 2017 Share Posted June 17, 2017 Here's my understanding on the XJ vs. ZJ proportioning valve issue: Â XJ rear brakes are drums. All modern (since about 1930, I think) drum brakes are what used to be referred to as "servo-assisted" brakes. This was so well-known that they stopped using the term long before drum brakes were phased out in favor of disc brakes, but AMC still used the term in their factory service manuals back in the 1960s. What the term means is that the geometry of the shoes and hold-down hardware is such that when the brakes are applied when the vehicle is rolling forward, the rotation of the drums tends to grab the shoes and rotate them against a cam block or pin of some kind to wedge the shoe tighter against the drum, thereby increasing the braking force with no increase in peddle pressure. This is why with drum brakes the parking brake always holds better when the vehicle is pointing downhill (forward) than when it's facing uphill (when the tendency is to roll backward). Â The reason for a proportioning valve in a front disc/rear drum setup is to limit the braking to the rear wheels in order to compensate for the fact that disc brakes don't (can't) have any servo-assist function. Some vehicles have more of a problem in this regard than others. I've commented previously that the 1968 - 1970 Javelins were front disc/drum rear and did not have a proportioning valve. The 1968-1970 2-seat AMX, which was the exact same car but a foot shorter, DID use a rear proportioning valve. The reason was that the shorter wheelbase made the AMX easier to spin out if the rear brakes locked prematurely. Â I don't know of any way to document it, but I have read that the ZJ proportioning valve provides LESS proportioning (i.e. more braking) to the rear wheels than the XJ unit. This is because the ZJ has 4-wheel disc brakes and doesn't have any "servo-assist" at the rear wheels. Staying with the MJ unit is just taking it a step farther by not having ANY proportioning. That said, I assume there is already some "proportioning" built into the system, based on the relative sizes of the front and rear rotors and the size of the pads and caliper pistons. I drove my '88 MJ with rear drums and no proportioning for several years before it took itself off the road. Except for one incident that was a result of a combination of circumstances, it was not a problem. I can't know, but I don't think it would have been any different with disc brakes in the rear. Â And, of course, if it becomes a problem it's relatively easy to plumb in a Wilwood adjustable proportioning valve and fine tune the system. Â Related reading assignment for the day: https://www.quora.com/Which-one-is-best-drum-brake-or-disc-brake Link to comment Share on other sites More sharing options...
cruiser54 Posted June 17, 2017 Share Posted June 17, 2017 I used an adjustable prop valve for the rear circuit for both drum and disc brakes on 2 of my MJs.  Join the front lines and pressure tube from the master. Install the adjustable prop valve in the line to the rear. $#!&can the extra line. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 17, 2017 Author Share Posted June 17, 2017 I used an adjustable prop valve for the rear circuit for both drum and disc brakes on 2 of my MJs.  Join the front lines and pressure tube from the master. Install the adjustable prop valve in the line to the rear. $#!&can the extra line.  :hmm: Link to comment Share on other sites More sharing options...
cruiser54 Posted June 17, 2017 Share Posted June 17, 2017  I used an adjustable prop valve for the rear circuit for both drum and disc brakes on 2 of my MJs.  Join the front lines and pressure tube from the master. Install the adjustable prop valve in the line to the rear. $#!&can the extra line.  :hmm:  And bypass the rear height sensing valve. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 17, 2017 Author Share Posted June 17, 2017 Join the front lines and pressure tube from the master. Â Need a little more detail on this statement - I'm listening......... Link to comment Share on other sites More sharing options...
cruiser54 Posted June 17, 2017 Share Posted June 17, 2017 Eliminate the factory prop valve. Using a T, join the pressure line from the master to the 2 front brake tubes.  From the master cylinders pressure tube to the rear brakes, install an adjustable prop valve.  At the rear, remove the height sensing valve and use a union to connect the lines together.  Condemn the line that runs up to the engine bay to the old prop valve. Link to comment Share on other sites More sharing options...
Jeep Driver Posted June 17, 2017 Share Posted June 17, 2017 Remove sensing valve.......trash can.  Cut and flare rear brake hardline at frame. Attach soft line to axle.  Cut and remove/discard sensor line.  Install plug at front of block.  Bleed.  Enjoy.      It's that simple, really. Link to comment Share on other sites More sharing options...
cruiser54 Posted June 17, 2017 Share Posted June 17, 2017 I did that initially.  Rear brakes locked up early.  What I found was the MJ prop valve has an opening in it for the front brakes that is quite a bit smaller than the brake tubing size. Eliminated it completely and had much better overall braking performance.  Hence, my newer method for eliminating the factory crap. Link to comment Share on other sites More sharing options...
Jeep Driver Posted June 17, 2017 Share Posted June 17, 2017 My rears have never locked.  We are dealing with rear discs here. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 17, 2017 Author Share Posted June 17, 2017 Remove sensing valve.......trash can.  Cut and flare rear brake hardline at frame. Attach soft line to axle.  Cut and remove/discard sensor line.  Install plug at front of block.  Bleed.  Enjoy.  It's that simple, really.  Yes, this is the plan. Don't know about the "enjoy" part........  Will use a 1/2x20 plug with Teflon tape to seal the distribution block front/lower port; I see no need for hacking off a bolt. IF the rear disks lock too early, then I'll plumb in an adjustable prop valve. Less plumbing and fittings this way. Rear drum and disk configurations are all different and require different amounts of biasing, or maybe none at all. Hoping for the latter........  Thanks guys for all the comments. Link to comment Share on other sites More sharing options...
cruiser54 Posted June 17, 2017 Share Posted June 17, 2017 My rears have never locked.  We are dealing with rear discs here. I understand that. I've done this on 2 MJs. One with rear shoes and one with rear discs.  That doesn't change the fact that the prop valve has small orifices to the front brakes..... Link to comment Share on other sites More sharing options...
cruiser54 Posted June 17, 2017 Share Posted June 17, 2017  Remove sensing valve.......trash can.  Cut and flare rear brake hardline at frame. Attach soft line to axle.  Cut and remove/discard sensor line.  Install plug at front of block.  Bleed.  Enjoy.  It's that simple, really.  Yes, this is the plan. Don't know about the "enjoy" part........  Will use a 1/2x20 plug with Teflon tape to seal the distribution block front/lower port; I see no need for hacking off a bolt. IF the rear disks lock too early, then I'll plumb in an adjustable prop valve. Rear drum and disk configurations are all different and require different amounts of biasing, or maybe none at all. Hoping for the latter........    You will most likely have early rear lock up. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 17, 2017 Author Share Posted June 17, 2017 It's not a prop valve, it's a distribution block. I've got a ZJ prop valve, but won't use it unless I have to...... Link to comment Share on other sites More sharing options...
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