eliminating the MJ proportioning valve?

[BrettM]

I'm nearly done with the 3 link, and one of the small things left is the brakes, and I'd like to just get rid of the load-sensing proportioning valve. I want to do this the easy way by keeping the 2 lines running to the rear so I don't have to mess with stuff all the way up to the master cylinder.

Here is what the factory setup is; can I just plug or reroute a line or two?

http://img472.imageshack.us/img472/4799/untitled0ek.jpg (http://imageshack.us)


and while we're on the topic of brake lines, does anybody know a source for some good little tabs for attaching brake hard lines to a bare axle?

[davidt]

bumpity bump, I want to know this as well.

[summitlt]

Just run the main line (with pressure}) to your rubber line. Thats what I did, the old line is still there, just not connected to anything.

[rsalemi]

I replaced the MJ prop valve and removed the extra line on the Drag MJ. But the previous poster says that you can just disconnect, so that works also. For brackets for the hard line; I used the threaded holes on top of the right side and just made a small luminum bracket. The left side is short and stays in place if bent properly

[Jeff in VA]

Just run the main line (with pressure}) to your rubber line. Thats what I did, the old line is still there, just not connected to anything.

Did the same as well, then later went back and removed the second line completely and capped the port on the prop valve under the MC (3/16" IIRC)
Jeff
http://img.photobucket.com/albums/v220/mjeff87/propvalvebypass.jpg

[Andy in Pa.]

I am about to do this as well, which line is the MAIN line? Can't you just tee both of those lines together (from the prop. valve) and run that to the rubber line?

Andy

[Jeff in VA]

I suppose you could.....the second line is actually a "safety" line that pressurizes in the event of a front brake circuit failure and sends full braking to the rears. It is normally not pressurized. It is the line that runs out of the bottom of the prop valve (the one toward the front, not the rear). The main line that supplies the rear comes out of the nose of the prop valve. Do a quick search on this topic or on user Pete M....he posted a nicely labeled pic of his prop valve on here a little while ago.
Jeff

edit: Here's the thread...
http://www.naxja.org/forum/showthread.php?t=60086

[red91]

I donated one to Eagle to disect.....hopefully the results will be in soon as to...

1.) how it works....
2.) what would make a suitable replacement...
3.) can you bypass it safely without loosing all braking ability ?

Stay tuned....:D

[Lawn Cher']

I replaced the load sensing valve with a tee on my '87... now I can lock up the rear wheels. Whether that is good or not is your call.

[summitlt]

I dont understand how the second line was for emergencys, the bottom line had no fluid in it when I pulled it, so that wouldnt help at all.

It can be removed, I did it, stops fine.

[NHscrambler]

I just replaced the manifold at the master cylinder with one from an XJ and removed the prop. valve all together.
Done.
The XJ only has one line going to the rear axle.

[Kaczman]

and while we're on the topic of brake lines, does anybody know a source for some good little tabs for attaching brake hard lines to a bare axle?
www.aa-mfg.com has the brake tabs for $.84 each.
http://www.aa-mfg.com/pdshop/images/aa-100-a.jpg

-Jon

[tealcherokee]

i just finished my brakes on my xj, i have 3/4 ton brakes front and rear, i run one line to the rear, and one line to a "t" for the fronts, no valve, all 4 lock up at the same time

[Eagle]

I dont understand how the second line was for emergencys, the bottom line had no fluid in it when I pulled it, so that wouldnt help at all.

It can be removed, I did it, stops fine.
Be careful.

The MJ FSM says that the second line is (as someone pointed out) a safety line. In the event of loss of the front brakes, rear braking is shifted to that second line and bypasses the load-sensing proportioning valve. As well as I can determine, if you block off that second port leading to the rear, in the event of losing the front brakes I believe you will have NO brakes.

Two solutions, both eliminating the rear load-sensing proportioning valve:

(1) As some have done, run both lines into a tee fitting somewhere downstream from the front combo valve, then run a single line from the tee to the rear axle flex hose; or

(2) Remove the MJ combo valve and replace with an XJ combo/proportioning valve, and run a single line from that the the rear flex hose.

I strongly advise against running with that second port blocked off.

[BrettM]

Be careful.

The MJ FSM says that the second line is (as someone pointed out) a safety line. In the event of loss of the front brakes, rear braking is shifted to that second line and bypasses the load-sensing proportioning valve. As well as I can determine, if you block off that second port leading to the rear, in the event of losing the front brakes I believe you will have NO brakes.

Two solutions, both eliminating the rear load-sensing proportioning valve:

(1) As some have done, run both lines into a tee fitting somewhere downstream from the front combo valve, then run a single line from the tee to the rear axle flex hose; or

(2) Remove the MJ combo valve and replace with an XJ combo/proportioning valve, and run a single line from that the the rear flex hose.

I strongly advise against running with that second port blocked off.
thank you, considering I've lost front brakelines twice in the last 18 months (once on the street, once on the trail) I will not block off the second port.

[BrettM]

Be careful.

The MJ FSM says that the second line is (as someone pointed out) a safety line. In the event of loss of the front brakes, rear braking is shifted to that second line and bypasses the load-sensing proportioning valve. As well as I can determine, if you block off that second port leading to the rear, in the event of losing the front brakes I believe you will have NO brakes.

Two solutions, both eliminating the rear load-sensing proportioning valve:

(1) As some have done, run both lines into a tee fitting somewhere downstream from the front combo valve, then run a single line from the tee to the rear axle flex hose; or

(2) Remove the MJ combo valve and replace with an XJ combo/proportioning valve, and run a single line from that the the rear flex hose.

I strongly advise against running with that second port blocked off.
just to clarify, your option 1 is this, correct:

http://img475.imageshack.us/img475/5379/untitled1fr.jpg (http://imageshack.us)

[Eagle]

Running both lines into a tee will mean you'll always have rear brakes, but as Lawn Cher notes -- the rear will be prone to locking up because an empty PU has very little weight over the rear axle. IMHO swapping in an XJ combo valve is a better solution, but the best would be to eliminate both the combo valve and the proportioning valve, and run a single line right from the master cylinder to the rear axle flex hose with a Wilwood adjustable proportioning valve in it. That way you can dial in the braking so it won't lock up, and still adjust for more bracking if you're going to tow or carry a heavy load.

But ... you would lose the brake system failure warning light switch, and that might not be legal. I assume most of us are sensitive enough to know instantly if we've lost half our brakes, but I wouldn't sell a vehicle with that feature disabled.

[Eagle]

just to clarify, your option 1 is this, correct:

http://img475.imageshack.us/img475/5379/untitled1fr.jpg (http://imageshack.us)
Correct.

[bj-666]

On the xj they have a brake light that is pluged into the prop valve. Will that work with the mj if so you could put in an xj prop valve and run a single hard line back and eliminate all the double lines and t-fittings. simple = Better.
As Eagle state front's directly off the master rears to a wilwood style prop valve back to rear axle is my preferance too

[bj-666]

Hijacked

I'm nearly done with the 3 link, and one of the small things left is the brakes

Well, if it's nearly done, WHAT THE HECK IS TAKING YOU SO LONG TO GET SOME PICS UP.

ha, saw a lot of good ideas in the design phase just want to see how they turned out for ya.

Hijack over

[OT]

Oops.
I thought this was a thread about eliminating the MJ.
Nevermind......
Sorry.......

[Bounty Hunter]

On the xj they have a brake light that is pluged into the prop valve. Will that work with the mj if so you could put in an xj prop valve and run a single hard line back and eliminate all the double lines and t-fittings. simple = Better.
As Eagle state front's directly off the master rears to a wilwood style prop valve back to rear axle is my preferance too
The XJ Prop. valve goes right in, no problems. KISS is the route I took, using the XJ prop. valve and losing the bias valve at the rear. Then a Dakota soft brake line for the SOA lift.

[MJlogan]

Correct.


thats what i'm running. it does give the rear quite a bit of bias. With 3/4ton discs in the rear the brakes are like a lightswitch. Wasnt so bad with the 44 with drums, though.

[Pete M]

When I replumbed my system, I originally plugged the wrong rear port at the front combo valve and I had absolutely no pressure at the rear brakes. That's why I thought that it was a "return" line. Maybe the "safety" plunger doohicky simply cuts off the return line, resulting in full pressure to the rear brakes? What does the "return line" do in the meantime? I find it hard to believe that it simply waits around for a front brake failure. But if that second line is a return line that bleeds off pressure to the rear brakes, where does that extra pressure go?
Someone needs to cut open a combination valve and then a height sensing valve and see what's really going on in there.
Jeep on!
--Pete

[Pete M]

Wait, I think I've got it! Maybe there's a connection inside the front combo valve between the return line and the front brake lines that allows the excess pressure to go into the front brakes? That would certainly cause a need for the combo valve to block off that connection so all your fluid doesn't just squirt out the front if it were to spring a leak. Anyone got a spare combo valve and a bandsaw?
Jeep on!
--Pete

[Eagle]

When I replumbed my system, I originally plugged the wrong rear port at the front combo valve and I had absolutely no pressure at the rear brakes. That's why I thought that it was a "return" line. Maybe the "safety" plunger doohicky simply cuts off the return line, resulting in full pressure to the rear brakes? What does the "return line" do in the meantime? I find it hard to believe that it simply waits around for a front brake failure. But if that second line is a return line that bleeds off pressure to the rear brakes, where does that extra pressure go?
Someone needs to cut open a combination valve and then a height sensing valve and see what's really going on in there.
Jeep on!
--Pete
That's why RedXJ in Washington sent me a surplus MJ combo valve. I haven't found a mchine shop that'll split it for me for free, but I talked to a guy today who says he'll do it -- for some $$$. This has gone unanswered for long enough that I'll pony up and have it done. I'll do a rough cut over the weekend with a hacksaw and drop it off Monday to have him clean it up.

According to the MJ FSM, yes that second line does indeed just sit around waiting for the front brakes to fail. If that happens, it bypasses the rear proportioning valve and diverts full pressure to the rear brakes. That's what the book says, and since plugging the wrong line gives you NO brakes in the rear, I'm inclined to believe it. All my dissection experiment is going to do (hopefully) is show us how that is accomplished.

I think the simplest route is to swap in an XJ combo valve. That's the route I'm going to go. But my rear proportioning valve blew up, so it's not like I have a lot of choices.

[Eagle]

thats what i'm running. it does give the rear quite a bit of bias. With 3/4ton discs in the rear the brakes are like a lightswitch. Wasnt so bad with the 44 with drums, though.
Summit Racing ==> Wilwood adjustable proportioning valve, in the rear circuit only.

[BrettM]

That's why RedXJ in Washington sent me a surplus MJ combo valve. I haven't found a mchine shop that'll split it for me for free, but I talked to a guy today who says he'll do it -- for some $$$. This has gone unanswered for long enough that I'll pony up and have it done. I'll do a rough cut over the weekend with a hacksaw and drop it off Monday to have him clean it up.

According to the MJ FSM, yes that second line does indeed just sit around waiting for the front brakes to fail. If that happens, it bypasses the rear proportioning valve and diverts full pressure to the rear brakes. That's what the book says, and since plugging the wrong line gives you NO brakes in the rear, I'm inclined to believe it. All my dissection experiment is going to do (hopefully) is show us how that is accomplished.

I think the simplest route is to swap in an XJ combo valve. That's the route I'm going to go. But my rear proportioning valve blew up, so it's not like I have a lot of choices.
I'll have mine out soon, unless someone else has a cleaner method, I'll take some cutting wheels and the sawzall to it.

[jpnjim]

I think the simplest route is to swap in an XJ combo valve. That's the route I'm going to go.

That's what I did.
Swapped a 2001 MC, booster & p-valve.

Even used the XJ's brake lines (rear line extended a foot, or so), to replace the rusty ones that were in the MJ.

Works well, even with 11"x2.5" rear drums instead of the 2001's 9"x2.5"s

[Eagle]

I'll have mine out soon, unless someone else has a cleaner method, I'll take some cutting wheels and the sawzall to it.
Save your cutting wheels. I did a rough cut on my spare this evening, with a hacksaw. The machine shop is open on Saturday until noon, so if possible I'll drop it off in the morning. If not, I'll get there Monday. He'll mount it up in a Bridgeport milling machine and plane it down right to the centerline and we'll see exactly where the passages are and how it works. I'm pretty sure from what I can see that the by-pass theory is correct, but it's not taken down far enough yet to photograph.

[Eagle]

Rather than drop $65 at a machine shop for an hour of his time, I spent a couple of hours with a file and got it down fairly neatly. After I clean up the parts I'll get photos for posting, but for now -- I was shocked at what I found, and so was my friend the retired Jeep service manager.

BIG surprise!

The good news -- the bypass does not work as I had expected. Pressure and fluid flow to the line coming out of the "nose" of the front combo valve are not stopped when the combo valve goes into bypass mode, so if you block off the bottom line to the rear you will NOT lose all brakes if the front circuit blows. So my concern in that regard was unfounded.

Now for the bad news: The way the thing works is actually quite simple. From where the rear line goes into the combo valve from the master cylinder, a hole goes straight down to the longitudinal bore in which the plunger for the brake warning switch rides. This hole continues straight through as far down as the centerline of the "nose" fitting. A hole is bored in from the "nose" to intersect that hole. This is the normal path for brake fluid to the rear circuit - an 'L' shaped path within the combo valve.

There is another hole drilled straight up from the other rear circuit line on the bottom of the combo valve, into the bore for the warning switch plunger. Normally this hole is blocked by an O-ring on the plunger. If the front brakes fail, the plunger is pushed out of the way, allowing fluid for the rear circuit to flow through this other hole. Nothing blocks off the 'L' shaped hole, but with the second hole open fluid can now flow directly to the tee fitting downstream of the rear proportioning valve, thus bypassing it.

EXCEPT -- that in the valve I cut apart, the hole for the bypass circuit wasn't drilled all the way into the upper bore. It stopped about 1/16 of an inch short. Which means if the vehicle this came out of had experienced a loss of front brakes, it would not have had any bypass. The rear brakes would have worked, but they would still have been reduced in power by the rear proportioning valve.

Summary: I know agree that there's no real problem with just blocking that bottom outlet and running a single line from the "nose" of the combo valve to the rear flex hose. The combo valve will still act as a brake system warning light if you lose either front or rear brakes. But you will have full braking to the rear wheels, not proportioned. As Lawn Cher commented, this may result in a tendency for the rear wheels to lock prematurely. I guess all I can suggest is -- try it. If there's too much rear wheel lockup, then either swap in a Cherokee combo valve or add a Wilwood adjustable proportioning valve in the rear circuit.

I hope this settles the issue.

Now I need to cut open an XJ combo valve and figure out how it provides proportioning ...

[Bounty Hunter]

http://www.mpbrakes.com/combocutaway3.jpg
Some good brake info here: www.mpbrakes.com/mpfaqvalving.htm

[BrettM]

just to clarify, your option 1 is this, correct:

http://img475.imageshack.us/img475/5379/untitled1fr.jpg (http://imageshack.us)
okay, so I did this and I have NO braking in the rear. When I bleed them it all seems perfect, but with the axle on jackstands and the motor idleing in gear the brakes don't even stop the tires.


:wierd: ??

[Jeff in VA]

You might be "backfeeding" that second line with fluid...instead of pressure pushing on the wheel cylinders it's pushing back toward the prop valve :dunno: Maybe try cracking that line at the prop valve and bleeding it from there....

Jeff

[Lawn Cher']

Oops.
I thought this was a thread about eliminating the MJ.
Nevermind......
Sorry.......

I have a MJ Eliminator.

[BrettM]

So I capped the one line that is totally dry, and I still have NO pressure at the rear. The other line is running straight to the flex hose, and has fluid, but no pressure. When I open the rear bleeders fluid just dribbles out whether you're holding the brakes, pumping the brakes, or off the brakes.

I'm thouroughly confused. I know the easy answer is to get the XJ valve, but I'm not sure I'll get a chance to get to a junkyard before I'm supposed to leave for Johnson Valley on thursday night.

any ideas what's going on? any idea of how to fix it without the XJ valve?

[Pete M]

Just to be sure, you are using this port, yes?
Jeep on!
--Pete


http://pic5.picturetrail.com/VOL91/512063/1637926/39161025.jpg

[BrettM]

yep, that's the one

[Ramsey]

I have a MJ Eliminator.
no one cares

[Pete M]

Maybe the line got pinched or there's some contamination inside blocking it?
Jeep on!
--Pete

ComancheClub.com

[Jeff 98XJ WI]

Do you now have the front port run directly to the rear rubber line with the "return" or more correctly "Safety bypass" line on the bottom plugged? If so, you should be getting full braking pressure to the rear axle. One thing you could do is to crack the plugged line and bleed that port at the manifold. You could also crack the line at the rubber line and bleed there. Finally try cracking the lines at the wheel cylinders and bleed there. Jeff

[stupidfast]

seems here that the question hasnt been answered yet. any new info in the last 2 months??

[87manche]

I eliminated my rear proportioning valve, since it didn't work right anyway. I'll snap some pictures. The one drawback is that it will lck the rears before the front. It's reliable though, so managable. When I redo the brake lines in the spring I'll probably put in an adjustable valve, so I can manually adjust the brakes in the back in relation to a load in the bed, or trailer tongue wieght

[ZPD]

I have a question... I eliminated the prop valve as well and plumbed it with a T like Brett's diagram and I have the same problem as Brett had. I have bled the brakes and there is no air in them and they still don't hold at all. I haven't tried bleeding the second line up at the front manifold yet though.
Brett, what did you ultimately do to fix your problem? Does bleeding the second line do the trick?

Thanks

[BrettM]

I said screw it and got rid of the MJ proportioning valve at the MC and ran the lines unproportioned, but I'm going to add a Wilwood adjustable valve later.