MJ to XJ prop valve

O hell I am confused about this MJ to XJ pop valve thing.

Ok going in a circle staring at the nose were do the lines goes:

The nose one goes to the driver side front

On top first whole

Second one on top

Back side of the valve

On the bottom closes to the cab

And last the one on the bottom front

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And now the XJ pop valve:

The one on the nose is pluged

On top first whole

Second one on top

Back side of the valve

On the bottom closes to the cab

And last the one on the bottom front

Ok now with that out of the way here is the question?? Which whole do I need to plug off to make the XJ pop valve work in the MJ? I think if I can get the layout of which line goes where I will be able to make this work.

thanks pete i looked at that. Is that a MJ pop valve

Pete's photo is an MJ valve, with the lower front (rear prop valve) line plugged and the "nose" line feeding directly to the rear axle.

If you are swapping in an XJ proportioning valve, you don't plug anything. The two upper fittings are the inlets from the master cylinder and you leave them exactly as they were to the MJ valve. The lower rear outlet and the outlet at the "tail" feed the front brakes and are replaced exactly as they were in the MJ valve ... and as shown in Pete's photo. The line from the rear axle goes to the lower front outlet, the one that is shown plugged in Pete's photo. Run from that port directly to the upper end of the rear axle flex hose; do NOT use the rear proportioning valve when using an XJ combo valve in the front.

That was what i needed. I new that it was something like that but I wanted to make sure. Thanks Pete and Eagle :bowdown:

i was about to do the dual booster swap with the Xj valve and was about to ask that question but this post answered everything....sweet thx

Good luck getting the brake lines off I am a bought to rip all the brake lines out and start over. But good luck.

ive already had the pleasure of replacing my original master cylinder and replaced them at that time so i hope they come off easier now...i am swapping to a 97 mastercylinder now so ill have to make new lines again anyways

Sorry to revive an ancient topic, but I have a question about this picture:

With the bottom rear output port plugged, then is there just one single hard line running all the way to the rear soft line? With this set-up, would there still be rear breaks if the fronts go out?

Separately, in this picture, can someone identify where the two lines coming from the front originate ... and what is the reason for the two lines? How is this set-up different/same from the first picture?

And lastly, what is the benefit of using and XJ valve upfront in place of the MJ one. I realize that the front valve has no ability to detect load and adjust braking allocation, so whats the point?

I might be a bit confused on this, so feel free to set me straight.

The main reason to run the xj pop value is to get rid of the load thing in the rear by the axle.

Right??

That and everyone else is doing so why not :roll:

"With the bottom rear output port plugged, then is there just one single hard line running all the way to the rear soft line?"

Yes

The 'block' under the hood senses major brake failure through loss of pressure and turns on the brake light. On a MJ it sends full pressure to the rear axle and the height snesor reduces it accordingly. Whereas the XJ block does rescrict the flow to the rear so that the rear brakes don't lock up right away due to less weight. If you left the MJ block in without the height sensor, the rears would lock up too easily, the xj block would reduce it a bit. Did I sum that up well? Based on what I've read here and opening a XJ block.

The 2 lines to the front are right and left brakes.

Mr. Simon did you buy the one that was in the Lancaster paper a month ago?

So I'm still trying to figure out the options here. I made the following three diagrams. Do I have them set up right? Did I name things properly? I need some input here :cheers:

Options 1: Stock set-up. Front and rear MJ valves.

Options 2: Remove rear prop. valve and plug front valve. Lock-up issues and no by-pass in case of front failure.

Option 3: Remove rear valve and replace front MJ valve with an XJ valve. Reduces lock-up issues but still no by-pass in case of front failure.

Mr. Simon did you buy the one that was in the Lancaster paper a month ago?

I don't think so. I found mine on Craigslist. It was in Downingtown.

It looks good to me. There are alot of posts on this subject including a cross section of the prop valve. You caught the switch of the rear line when the prop valve is changed.

here's that cut valve, I put all the outputs on it.. Eagle did the milling on it, and a few IIRC,, The thing found from those cut apart is that the output on the mj valve wasn't bored correctly.. So the things not going to put fluid to the rear in case of a front failure.. I'm swapping my booster and I'm not 100% if I'm keeping the mj's valve and removing that saftey line yet or not..

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Here the problem with the valve.. You really couldn't see it in the above image

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So I'm still trying to figure out the options here. I made the following three diagrams. Do I have them set up right? Did I name things properly? I need some input here :cheers:

 

Options 1: Stock set-up. Front and rear MJ valves.

 

Options 2: Remove rear prop. valve and plug front valve. Lock-up issues and no by-pass in case of front failure.

 

Option 3: Remove rear valve and replace front MJ valve with an XJ valve. Reduces lock-up issues but still no by-pass in case of front failure.

You want Option #2. Option #3 is what Pete did on his first try, and then found out he had no rear brakes. That lower front (as in forward, not meaning "front wheels") output only gets pressurized if you lose the pressure in the front brake circuit.

I sent chrysler an email about the valve not being properly bored I want to see what they say.

did you hear backfrom them at all?

Is it possible it was bored through, but on a bit of an angle? When you cut the valve open, the rest of the hole ended up in the saw shavings.

Is it possible it was bored through, but on a bit of an angle? When you cut the valve open, the rest of the hole ended up in the saw shavings.

Nope. It was definitely not bored through.

BTW, I just replumbed my rear brakes. I plugged the lower (bypass) outlet and ran a single, new hard line from the "nose" outlet directly to the rear axle hose. It's amazing how much of a difference having rear brakes can make.

i got a question. i took out my hieght valvein the rear. i have both rear lines goin to the rear. can i just replace the front valve to make the rear brakes not lock up? now its only the left rear wheel that is lockin up on hard brakin. i am lookin to change the booster and master to a newer style. what would anyone recomend to use?

i got a question. i took out my hieght valvein the rear. i have both rear lines goin to the rear. can i just replace the front valve to make the rear brakes not lock up? now its only the left rear wheel that is lockin up on hard brakin. i am lookin to change the booster and master to a newer style. what would anyone recomend to use?

You should not have both lines going to the rear. You should block off the rear outlet on the combo valve/metering block and run a single line from the "nose" of the metering block to the rear.

If you get premature lockup of the rear wheels, either use smaller diameter rear wheel cylinders or buy a Wilwood adjustable proportioning valve from Summit Racing and put that in the single line to the rear.

did you hear backfrom them at all?

They pretty much ignored the fact that the part made wrong adn just said due to the age of the vehicle there was nothing they could do.

They completely missed the fact that i was pointing out a potentially dangerous error on their part and that I in no way ever mentioned anything about them fixing my valve.