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  #1  
Old March 13th, 2006, 19:08
sycho15 sycho15 is offline
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Brake mod questions, different diaphrams and MC combo questions

On March 5th I surprised my girlfriend with a nice '93 XJ Country for her 24th Birthday, on the 11th we drove it up to some fellow Jeepers for a little wrench-a-thon and tossed on a 3.5" RE lift kit, and swung an '84 D30 with 3.73 gears under the front. We were going to put a matching D44AL with discs on the rear but none of the parts stores had the correct brake hoses and we were running out of time. I did put new calipers and pads on the D30 since they were different than the '93's and would not interchange. We drove up there with the 31s on the Jeep, and the braking on the way back was considerably worse (even though we did a lot of brake-bleeding after the caliper swap).

Anyhow- I've decided to swap the front axle for a '93-or-newer one with 4.10 gears, and put a Corporate 8.25 rear with 4.10s. This should get her speedometer reading correctly again. I'll put the ZJ disc brakes onto the 8.25.

I'll be ditching the stock proportioning valve and running the front lines directly off the MC, the rear will go to a Wilwood adjustable prop. valve.

So now I come to my question.
I can get a '96 XJ dual-diaphram brake booster to add to this mix, but can I put the '78 Grand Marquis MC ahead of it? Or the '84 E-350 MC? Or would the '96 MC be the best fit?
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Old March 13th, 2006, 19:45
ChicksDigWagons ChicksDigWagons is offline
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Re: Brake mod questions, different diaphrams and MC combo questions

I don't think the larger master cylinder is what you're looking for considering you haven't bumped up the front brakes. The bigger bore (1 1/4" IIRC) Grand Marquis/E-350 is needed when you upgrade the axles/brakes to 1/2-3/4 ton hardware and the caliper pistons consequently grow in size.

The Grand Marquis MC has equal size resevoirs, which is handy for rear disc brake conversions like you're planning, but the bore I fear is too large to get good braking (your pedal would be hard as a rock). The Stock XJ master would probably work okay but you will need to watch the rear-brake resevoir. Otherwise, consider an ZJ disk master cylinder which may or may not be a direct swap. Not sure about the boosters however. Ran a stock 87 booster with an E-350 MC on 79 Ford F250 twin piston calipers with a GM 1/2 caliper rear discs and stock combo-valve and it felt just about right. Though the residual pressure on the rear brakes makes them overheat...something that can supposedly be fixed by pulling the o-ring out of the combo valve.
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Old March 13th, 2006, 20:14
sycho15 sycho15 is offline
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Re: Brake mod questions, different diaphrams and MC combo questions

Supposedly the dual-diaphram boosters have some sort of angled mount for the MC that points it to the hood if it's not the matching MC? So I just don't know what would bolt up and work for dual disc brakes.

At the moment I'm leaning towards the '96 dual-diaphram booster and matching master cylinder, ditching the stock prop valve and hard-lining the front, adjustable valve in the rear. Does that sound good enough for 31" tires and what will mostly be street and mild trail?
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Old March 13th, 2006, 22:19
Tally_XJ Tally_XJ is offline
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Re: Brake mod questions, different diaphrams and MC combo questions

Hey Sycho. . . its me from FJOA.

The angled plate you are talking about is an aluminum spacer that goes betweeen the firewall and the booster. It kept the upward tilt of the assenbly down to a better angle so it was more level. I have heard it is not absolutely necessary to have, but would require some booster rod adjustment if left out or not left out.

Also, from my research, any Jeep master cylinder from those years will fit and a lot of Dodge full size truck M/C will also fit. As said above, the most important thing is not to get one with too large of a piston bore or it will be rock hard. Too small and you get spongy pedal. I used an F250 M/C on my stock booster and my brakes went to $hit. I shoulda kept the original.

I think the newer booster design came out in 2001, which is the year of the dual diaphragm booster that I got to do my upgrade with. I am in the same boat as you though on the master cylinder. Looks like I am just gonna get a WJ M/C so I know its right.
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Old March 13th, 2006, 22:28
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RWKHausSupply RWKHausSupply is offline
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Re: Brake mod questions, different diaphrams and MC combo questions

just do a WJ mc and booster, less work and easy!
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Old March 14th, 2006, 08:36
mjydrafter mjydrafter is offline
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Re: Brake mod questions, different diaphrams and MC combo questions

I did a '96 booster/mc on my '92 about 2 weeks ago. Awesome super easy swap. I had the right lines already from when I got my ZJ proportioning valve, when I did rear disc's last year. No modifications were required at all for the booster install. Seemed too easy to just use the '96 MC rather than switching to something else.
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Old March 14th, 2006, 09:48
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bj-666 bj-666 is offline
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Re: Brake mod questions, different diaphrams and MC combo questions

do the 96 swap for the dual diaphram and master that should be all you need with stock calipers/wheelcylinders. with disk rear and slightly bigger front calipers you may want to think about a master that can flow more fluid. i am running a E-350 master on a 96 booster with 8.8 calipers in the rear and ford single piston calipers in the front.
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Old March 14th, 2006, 10:23
sycho15 sycho15 is offline
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Re: Brake mod questions, different diaphrams and MC combo questions

I can get a '00 WJ dual-diaphram booster and MC for $75 at the local yard. As I understand it, the rod that goes to the brake pedal would be in the wrong position on the '00, while the '96 is fine. What would it take to make this work? What about buying a '96 booster and putting the '00 MC onto it?

I don't have the rear discs on the Jeep yet, and might not have them installed before I put that axle under it....
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