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Brake master cylinder questions.

Powerman

NAXJA Forum User
Location
Colorado
So I am going to put disks in the rear. I have a 2000 XJ. I've read that disk/drum MCs are not enough for disk/disk systems. I know a lot of people do 8.8 and change nothing, but is this really a good thing.
My question is does anyone have specs on master cylinders? what year, what sizes, how much brake can they do. I pulled a booster/MC/prop vlv from a 98 Grand Cherokee. It had 4 wheel disk. The whole thing only cost $20 so I figured what the hell. But some say that XJ and ZJ MCs are the same. Does anyone know this? Is the ZJ stuff going to do me any good since I have a 2000. What other MCs have others used. I will be using Isuzu 44 disks, or Explorer disks. Any help is most appriciated.
 
Dirt Surfer said:
So I am going to put disks in the rear. I have a 2000 XJ. I've read that disk/drum MCs are not enough for disk/disk systems. I know a lot of people do 8.8 and change nothing, but is this really a good thing.

You don't need to change the master cylinder to change from rear drums to discs. I have Explorer discs in the rear with a stock late model XJ M/C and it works just fine.
 
I forgot, I'm also going to bigger 44 brakes up front. Anyone? Thanks Goatman. Do you know if the XJ and ZJ MCs are the same?
 
Dirt Surfer said:
I forgot, I'm also going to bigger 44 brakes up front. Anyone? Thanks Goatman. Do you know if the XJ and ZJ MCs are the same?

Ok, you're still fine. I also have a D44 in the front. Many of us run this combination with the stock M/C, and there are no problems or weaknesses with doing it.
 
The difference is in the proportioning valve, the XJ and ZJ masters are the same. I'm running an SVO disc kit (same as Explorer) on my rear and they work well. I have a rear disc equipped ZJ prop valve on the shelf that I have yet to swap in.
 
its usually the early model XJ's like mine that convert the master cylinder and prop valve due to the single diaphram booster we have.
Can ya Dig?
 
What year did the new MC/ booster come out? I have friends that might be able to use what I have. I should use the prop valve though right.
This is not meant to imply that you guys don't know what you are doing. A lot of people say it works, but how do you know it work "well". 35's work on stock gearing, but it's debatable if they work well. I'm not tring to be a smart as*. Do you know what I mean? Does anyone know specs, or what larger vehicles use like half tons or even Dodge 1/2 or 3/4 tons use? Thanks for your help so far.
 
Dirt Surfer said:
What year did the new MC/ booster come out? I have friends that might be able to use what I have. I should use the prop valve though right.
This is not meant to imply that you guys don't know what you are doing. A lot of people say it works, but how do you know it work "well". 35's work on stock gearing, but it's debatable if they work well. I'm not tring to be a smart as*. Do you know what I mean? Does anyone know specs, or what larger vehicles use like half tons or even Dodge 1/2 or 3/4 tons use? Thanks for your help so far.

Look, comparing me saying it works well to someone saying 35's work fine with stock gears is borderline offensive. I've driven mine from Central CA to CO and Moab numerous times, plus tons of trips driving up to nine hours to do runs hear in CA and AZ and I can assure you that my brakes work perfectly. There are quite a few around here who have been doing this for a long time and who's advice is well respected who, like me, run the later model ('95 and up) M/C and booster with a D44 front and discs in the rear with 35" or larger tires. Most of us haven't even messed with the proportioning valve......just bolted it up.

If you want to use a different master cylinder, go for it, but you don't need to. You come here to get info, and there's some info for you. If you want specs on master cylinders and proportioning valves go to a brake parts catalog, you won't likely get that info here..........especially since most of us run the stock parts. :)
 
Goatman, I said I didn't mean to offend, but I should have known the gear thing to be that. My bad.
I'm the type that needs to know things. It gets worse when it is on a subjet I don't know s#@* about. I can accept an answer "it just does". I just want to know that it is based on some knowledge, especialy since I have none of my own. You know as well as I do that there are a lot of intelegent and knowledgeable people on the web, and then there are alot of others.... we will just leave it at that.

From the stuff I have seen, others experience, and your valuable input, I will probably change my prop valve when I tear out my brakes, and call it good. When I do things, I just like to know why I'm doing it. It's how I learn.
 
Heres what I’m getting here. If Goatman says its good it good and that’s that.
His rig is sick and he drives it everywhere on and off road. If it works for him it works.

[font=&quot]On the other hand if you have a proportioning valve from a similar rig but with disks in the back do the brake mod and drive it for a week or so then swap the valve and let us know if you find any improvement.[/font]
 
Well I figured I would change the prop valve when the brakes are empty, but that is a darn fine idea Bronco. I should do a little research for the common good. I have also read people just taking out the o-ring. I don't know if that is the difference between the 2 valves.
I'm really stoked about this. I just scored 2 D44s and am looking at what it would take to run them now. I would love better brakes. Mine do fine just stopping, but comming down from trails they fade real quick. And yes I use low gear. They just can't take much continued use. I have a Waggy 44, and an Isuzu 44. Thanke guys for all the input. I need all the help I can get.
 
The M/C's are the same, ( XJ-ZJ ) as they even carry the same part numbers. The p/valve however is not and I did change to it when I went rear disc.
The only problem I see is that you have not said which rear calipers you are going the use only the disc themselves which will have not bearing on M/C choice. The calipers can make a huge difference as it comes down to what size piston is used. If it is of similar size in volume to the wheel cylinder in the stock drum like the ZJ and Explorer calipers, then you will be fine. However if it is much bigger like a Chev caliper, then you need a bigger M/C to get the larger volume need to move the piston otherwise you will be at the floor before you stop. That will be your test if you have the right M/C size or not. The lower it goes before full braking means the bigger the M/C needed. Remember though that fitting a bigger one when it is not needed will increase the effort at the pedal.
 
i'm running the late model booster/master cylinder with a terra kit (explorer brakes)on my d44. 33" tires. the odd thing is that the proportioning valve i have out of a grand chickoree with rear discs doesn't seem to work that well. possibly i can't seem to get the air out it. with it installed my pedal wants to go most of the way down before it gets decent feel. with a wilwood installed at i get good pedal feel and good braking. it's odd because when i first did the swap i had the old non-rear disc p-valve in there and it was fine. ran the rubicon with it and the brakes were good. any ideas out there as to the possible issues in a p-valve that could cause this? i would rather have the factory valve working due to it's ability to switch circuts in case of a front or back circuit failure. sorry to hijack a bit of the thread but this may be good info for you when the swap gets done!
 
Good stuff to keep in mind. The Isuzu calipers look pretty small. I don't have exact piston size, but will look into it. Thanks for the tip.
 
mikeyl said:
i'm running the late model booster/master cylinder with a terra kit (explorer brakes)on my d44. 33" tires. the odd thing is that the proportioning valve i have out of a grand chickoree with rear discs doesn't seem to work that well. possibly i can't seem to get the air out it. with it installed my pedal wants to go most of the way down before it gets decent feel. with a wilwood installed at i get good pedal feel and good braking. it's odd because when i first did the swap i had the old non-rear disc p-valve in there and it was fine. ran the rubicon with it and the brakes were good. any ideas out there as to the possible issues in a p-valve that could cause this? i would rather have the factory valve working due to it's ability to switch circuts in case of a front or back circuit failure. sorry to hijack a bit of the thread but this may be good info for you when the swap gets done!

They can be hard to bleed at times and you have to do it from the p/valve itself at the front as well as each line where it leaves the valve.
 
I installed a M/C from a 1998-2003 Dodge Ram P/U 1500/2500/3500 PN: 23-21022. It has a 1.25 inch bore and 1/2" longer piston stroke.

I was a DIRECT swap for the OEM M/C on my 1999 XJ, EXCEPT for having to fab a 1/2" longer push rod.

Push rod modification:
After removing the OEM M/C, grab the knurled brass sleeve that is visible behind the push rod. Remove the push rod using a socket.
BUY a 2" Long x #10-28 machine screw (I bought a SS one).
Grind down the diameter of the crowned head until is is slightly larger than the threaded shaft. I then put a bevel on the top edge. This left the phillips + intact to reinstall the push rod. It was a lot easier with a screwdriver!

Install the new M/C. With he aid of a helper "bench bleed" the M/C using a bleed kit, before reconnecting the OEM brake lines.

Once the OEM brake lines are reconnected, use your helper to assist in bleeding off any trapped air.

I used this opportunity to swap over to DOT 4 fluid... can't hurt. And it absorbs water at a slower rate.

The XJ still did not lock up, but the brake pedal no longer traveled to the floor. The lack of "lock up" is probably due to the ABS - a complaint most guys have and a feature they forget they have!

Next I did the front Crown Victoria front rotors & calipers swap...
http://www.naxja.org/forum/showthread.php?t=1032731

The grab is AWESOME NOW! Finally an XJ that can stop.... before I felt like the energizer bunny... I kept going, and going, and going, and going.
 
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