Chrysler 8.25 disc brake swap

[88whitemanche]

What's up fellas I plan on swapping in an 8.25 to convert to disc brakes...

I've seen a lot of write ups for xjs but non for Comanches..

I do plan on swapping in a wj booster and master cylinder...

 

My main question is regarding the proportioning valve...

The videos for an xj shows to grab from one from an abs zj...but my Comanche doesn't have the proportion valve that can't be removed...

do I just leave it alone and just swap in the disc brakes and booster and master cylinder ?

 

What have you guys done?

[cruiser54]

You'll need the prop valve from a Cherokee with the "guts" in it from a Grand Cherokee 94 to 98. 

 

ORRRR, you can ditch the prop valve that's on there, and the one in the back for height sensing.

 

Then, marry the front brake tubes together and use an adjustable prop valve for the rear. 

[88whitemanche]

So what parts are needed to remove/replace the rear sensing valve?

I'll grab the prop valve off an xj with grand Cherokee guts...

[cruiser54]

Take the sensing valve and tubing off. 

[Rockfrog]

So what parts are needed to remove/replace the rear sensing valve?

I'll grab the prop valve off an xj with grand Cherokee guts...

Exactly, when my rear brake line blew behind the fuel tank, I tried replacing the line and the whole system crumbled. Replaced the entirety of the rear brake line with an XJ prop valve (uses the same size machined block) and re-ran a new rear main line (just one this time).

This can be done before the disc swap, and when you do the disc swap add ZJ "guts" to the prop valve if needed. My 2000 XJ still has stock guts with WJ fronts and TJ rear discs. Braking locks as it should (fronts lock first with rears trailing and tracking). There was some speculation that later XJ's may have gotten "whatever was on the shelf" which would also explain my lackluster braking pre-swap.

Bleed the system at the prop valve first, then start right rear and so on. Be prepared to re-bench the master as well.

My MJ's had an XJ prop for about 2yrs now, discs are still on the to do list (after the 8.25 swap).

 

 

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[88whitemanche]

 

So what parts are needed to remove/replace the rear sensing valve?

I'll grab the prop valve off an xj with grand Cherokee guts...

Exactly, when my rear brake line blew behind the fuel tank, I tried replacing the line and the whole system crumbled. Replaced the entirety of the rear brake line with an XJ prop valve (uses the same size machined block) and re-ran a new rear main line (just one this time).

This can be done before the disc swap, and when you do the disc swap add ZJ "guts" to the prop valve if needed. My 2000 XJ still has stock guts with WJ fronts and TJ rear discs. Braking locks as it should (fronts lock first with rears trailing and tracking). There was some speculation that later XJ's may have gotten "whatever was on the shelf" which would also explain my lackluster braking pre-swap.

Bleed the system at the prop valve first, then start right rear and so on. Be prepared to re-bench the master as well.

My MJ's had an XJ prop for about 2yrs now, discs are still on the to do list (after the 8.25 swap).

 

 

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Do you by any chance have any pics of your current rear brake line set up?

[Rockfrog]

I can get something when I get home after Tuesday night, I work out on the ocean so I'm about 1200km from my vehicles

 

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[88whitemanche]

I can get something when I get home after Tuesday night, I work out on the ocean so I'm about 1200km from my vehicles

 

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Ok cool

 

Question- the load sensing valve brake lines...

Is there a single one that runs all the way from prop valve to the array of lines leading to the valve itself?

[Newton]

You'll need the prop valve from a Cherokee with the "guts" in it from a Grand Cherokee 94 to 98. 

 

ORRRR, you can ditch the prop valve that's on there, and the one in the back for height sensing.

 

Then, marry the front brake tubes together and use an adjustable prop valve for the rear. 

do you have a diagram or pictures of how u marry the tubes together and the adjustable valve for the rear for the amateurs like me?

[cruiser54]

 

You'll need the prop valve from a Cherokee with the "guts" in it from a Grand Cherokee 94 to 98. 

 

ORRRR, you can ditch the prop valve that's on there, and the one in the back for height sensing.

 

Then, marry the front brake tubes together and use an adjustable prop valve for the rear. 

do you have a diagram or pictures of how u marry the tubes together and the adjustable valve for the rear for the amateurs like me?

 

No. I looked tonight and had nothing. Try going under the Jeep and tracing the lines. 

[88whitemanche]

Correct me if This picture is wrong...I picked it off of searching Comanche load sensing valve...

 

 

So I remove the front(load sensing brake line and everything behind it? And plug it?

[cruiser54]

That's what you do on the front. 

 

We need a diagram of the back. I can't remember what I did. 

 

I'll try to look tonight. I've got an MJ with that crap still on it...

[Rockfrog]

If you do that you need to add a proportioning valve. The MJ "valve" under the master is a simple distribution block, and the rear load sensing valve handles the proportioning. Swapping the MJ block for one from a ZJ or XJ solves this. All the lines plumb into the blocks the same. On the XJ/ZJ blocks the "loud sensing" output housed the proportion valve "guts" behind a cap. On the MJ block it's just a pass through with nothing else inside but the shuttle for the brake warning switch.

 

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[HOrnbrod]

If you do that you need to add a proportioning valve. The MJ "valve" under the master is a simple distribution block, and the rear load sensing valve handles the proportioning. Swapping the MJ block for one from a ZJ or XJ solves this. All the lines plumb into the blocks the same. On the XJ/ZJ blocks the "loud sensing" output housed the proportion valve "guts" behind a cap. On the MJ block it's just a pass through with nothing else inside but the shuttle for the brake warning switch.

 

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Can't remember - are there provisions in the MJ distribution block for installing the XJ proportioning valve "guts" w/o swapping the block itself?

[Rockfrog]

No, the internal cavity isn't drilled out for it.

 

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[Rockfrog]

 

 

 

 

Here's what I have on the MJ currently, my XJ with discs has the same basic routing pattern, but with the obvious disc at the rear.

The juncture at behind the Crossmember was made to allow use of a standard 6' off the shelf brake line. Only the portion from prop valve to that junction is non standard lengths. It is also original to the vehicle and kept because it was in good condition and at the cut point easy to remove/install. The only other original lines are the front brake lines and the rear axle lines. The front were in an oil bath from previous owners lack of maintenance so were rust free. The rear leaf new will leave with the current D35 when the 8.25 goes in so I left them (they also did not crumble in my hands like the rest of the rear circuits did).

 

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[Rockfrog]

And the layout,

 

 

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[cruiser54]

This is what I used.

[87Warrior]

And the layout,

 

 

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And just for clarification this is a picture of a XJ proportion valve, NOT a plugged MJ distribution block :) I know it can get very confusing when looking at these types of pictures for the first time.

[Rockfrog]

Yes, it's n XJ valve. The stock MJ block does not have provisions to be converted at all.

But, the stock MJ block does follow the same plumbing aspect.

 

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[xjrev10]

I have a WJ master/booster, rear discs in my 8.25.

 

Deleted the load sending valve and plugged the port in the prop valve and the line in the back of the truck. Works great. Never messed with internals of the prop valve. Couldn't be happier with my braking performance.

[WyoCherokee]

I have a WJ master/booster, rear discs in my 8.25.

 

Deleted the load sending valve and plugged the port in the prop valve and the line in the back of the truck. Works great. Never messed with internals of the prop valve. Couldn't be happier with my braking performance.

Fixing to do this myself. Do you have a  quick pic of the routing you did in the rear?  I have both the axle lines from my old XJ. I was thinking of plugging the prop valve port, running the "rear" hard line into a XJ soft line(the hard line should be the same nut size as an xj?) which drops down to the axle lines(same as an XJ). This is how i had them for my 8.8 discs.

[88whitemanche]

here is a write up on it,

 

http://comancheclub.com/topic/51268-load-height-sensing-valve-delete-bypass/?do=findComment&comment=524965

[88whitemanche]

Double post

[WyoCherokee]

I guess i don't understand why you wouldnt just swap in the prop valve from the donor ZJ with discs, and run the "rear" line into an extended braided line at the bracket, down to the wheel lines; retaining the 3/8 connection where it runs into the T and not having to reflare anything on that end. If you took the 8.25 from an xj, the brake lines, splitting block, and even the flexible line should all be attached. You could then remove the excess line running along the frame, the weight valve and all associated lines.