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Thread: ZJ Master Cylinder Swap plus other info

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    ZJ Master Cylinder Swap plus other info

    So I did the axle swap to the 44/9" combo and the stock master cylinder would not keep up with the bigger calipers in the front and the disks combo that I put in the rear. Others I know of have not had this problem but I did.

    I tried to adjust the push rod to use the maximum amount of the stock master and it would not move enough fluid. I was putting the brake pedal to the floor if I put lots of force on it (Read: over 100lbs force).

    I had a 69 corvette disk/disk master cylinder that I was using on my YJ when I had the same axle combo under it and it did better than the stock YJ master cylinder but was still weak, and I could still put the pedal to the floor on the YJ with lots of force.

    I took all kinds of measurements of the grand booster and then took off to the pull your own junk yard.

    I came out with a 2001 BR (Dodge Ram) V8-318 4x2 disk/drum master cylinder. This master cylinder bolts up to a stock 1995 ZJ double diaphram brake booster (I have not tried on anything else, this was my combo) and uses the same brake line output (front and rear both fittings just bolted up). This is a larger bore master that is normally used on 1 ton applications but because of the double diaphram booster the pedal is not overly stiff.

    Master cylinder specs

    Stock 1995 ZJ Master cylinder (disk/disk) -- 1" Bore
    1969 Corvette Master Cylinder (disk/disk) -- 1.125" Bore
    2001 Dodge Ram Master Cylinder (disk/drum) -- 1.25 Bore

    All three of the above will work with the ZJ double diaphram booster that requires a seal between the master and the booster. BUT to use the 69 vette MC the seal from the stock ZJ master must be used to seal off the booster. There is a lip that the seal will sit in on the 69 vette Master, the vette master "may" also require some modification to fit on the ZJ booster to the bolt holes because the spread is not correct (required modification on my YJ bosster). This is usually just some light die grinding or just drilling the mounting holes out to 9/16 instead of the 1/2" dia that is currently there.

    Both the 69 vette MC and the 2001 Dodge ram MC require a different length push rod. There is adjustment in the stock rod but it does not extend out enough so a different rod must be made. The thread on the adjustment rod is 1/4-20 UNF, I just took a socket head cap screw that was 2 in longer and cut the head off plus about 1/2" then screwed it all the way into the stock push rod hole. I then test fit the master to see how much play was in the brake pedal, it was too much for my taste (>1" before master contact) so I adjusted the rod out about two rotations (small increments of adjustment move the pedal lots so move the rod slowly) to get the pedal to where i wanted it. I then put a drop of blue thread locker at the mating point of the adjustment rod and the stock pushrod (not too much incase if you have to move the rod at a different time).

    Then I just bench bled the master in the vise on the bench (loop the output lines into the master resovoire so that all air can be bled from the system as you pump piston and slowly release), put the master in the vehicle, hooked up the lines I have going into the proportioning valve and then bled the entire system.

    This modification gave me brakes that i am way more confident in, I still cannot lockup all 4 wheels but I belive that is because my pads are junk and the rotors appear glazed, I will be posting when i get this fixed about how the stopping changed with different (read: high quality) pads are used with the correct surface on the rotors.

    As you increase the size of the master cylinder you will move more volume (which was the problem with my system --> pedal going to the floor because of lack of volume) BUT you will lose hydraulic advantage because of the larger master cylinder diameter.

    Pressure = Force/area

    As the diameter of the MC increases the output pressure decreases. If you keep the calipers the same size the pedal will become stiffer (more fluid output by the MC decreases pedal travel and larger diameter MC piston reduces mechanical advantage as per the equation above) and requires more input at the pedal to compensate for the loss.

    I currently like the setup but do believe that the MC "might" be too large and has decreased my advantage to the point that I cannot generate enough force to lock all four tires up (37x12.5 MTR's). I am still betting that that is because of the garbage brake pads on there (incorrect choice at the parts store -- bought the cheapest pads I could at the time because these axles were not being daily driven, wheeling trips only, different story now).

    To conclude, I can no longer put the brake pedal into the floor, even with two feet on the pedal and pulling on the steering wheel. The pedal becomes stiff about 1/2 way to the floor and solid about 3/4 through the stock pedal stroke. With the engine running it requires about 15-20 lbs of force to comfortably stop the vehicle from 60 km/h to 0 with the double diaphram booster. My step dad says the feeling "instills confidence" for a rig on 37's (he drives a 2008 Nitro and is 58) and says it is not overly stiff. I stomped on it at about 80km/hr and it just barely locked up the front but didnt the rear (pads are total junk in the rear)

    Any questions please ask, I will be posting some pics in the next few days of the complete tear down and rebuild of the master cylinder, then the bench bleeding and install.

    Bradford

    Next is the SYE swap from the garbage 87 YJ 231 to the 2004 TJ 231 case that I have and install in the ZJ, Lots of info for people who want to do a 249 to 231 case.
    Attached Thumbnails Attached Thumbnails brake system 001.jpg   brake system 002.jpg   brake system 006.jpg   brake system 013.jpg   brake system 014.jpg  

    Last edited by Black88YJ; 06-17-2008 at 05:43 PM.
    95 ZJ 5.2L, Custom long arm 4 link Rear 3 link panhard front. D44/9" 4.88's locked and spooled,37x12.5 MTRs, 1 ton steering, Currently bumperless but rolling.

  2. #2
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    Nice write-up.
    I slapped in a 99 dakota master to mated up with my 44/9 and seems to stop better than the stock system did with 33's. Same bore as the vette 1.125". Bolted right up for me (TJ).
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    I wonder if that is the same as a durango, there are a few in my local junk yard. thanks for the knowledge, I'm going to go check that out and i'll make another write up and probably try it out to see how it feels.

    the cost is minimal vs the knowledge gained plus people here could probably use the info.

    I couldnt find a good source (there is info everywhere but nothing concrete.)

    based on the caliper size change on the 44/9 vs the stock 30/35 the 1.125in bore should have been large enough but would still have the pedal travel further, if i remember correctly. I am currently making a excel spreadsheet to calculate the correct master cyl size based on specific inputs.

    I believe the 44 front is usually 3"dia piston, my rears are 2.5" blazer/camaro fronts.

    The stock 30 front on my grand was 2.5 I believe and the rears were 2", so the change was big enough.

    The rest of the pictures for the above build up are below

    Bradford
    Attached Thumbnails Attached Thumbnails brake system 015.jpg   brake system 016.jpg   brake system 017.jpg   brake system 023.jpg   brake system 024.jpg  

    Last edited by Black88YJ; 06-17-2008 at 05:46 PM.

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    Pretty sure 98-01 dakota and durango's run the same master. Also the 98-01ram 1500, 2500, 3500 all run the same master (1.25" bore). Not sure if ya seen these but they have some good info for your hunting.

    http://www.pirate4x4.com/forum/showt...aster+cylinder

    http://www.pirate4x4.com/forum/showt...aster+cylinder


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    Curt,

    ya there is some info there but i couldnt stand all the hearsay, like is posted up during the thread. I just went to the local junk yard and found what I needed, I will post the pics here so people can see step by step.

    I measured both pistons and the primary and secondary are both 1.25in on the master I have.

    I saw your build up here and on pirate, I give you credit, most people wont/cant go that far, especially in a subdivision and in a garage that small.

    Follow this link to my build if you want.

    http://www.soxja.org/forum/viewtopic.php?t=912

    Bradford

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    I changed my front and rear calipers and didn't bleed my master cylinder, can this be done while the mc is still in the vehicle. I've tried bleeding the brakes the usual way starting from furthest to closest and the peddle has lots of pressure until I start the vehicle and the pedal goes right to the floor. Would this be my mc?
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    Quote Originally Posted by trafficticket View Post
    I changed my front and rear calipers and didn't bleed my master cylinder, can this be done while the mc is still in the vehicle. I've tried bleeding the brakes the usual way starting from furthest to closest and the peddle has lots of pressure until I start the vehicle and the pedal goes right to the floor. Would this be my mc?
    Con. Sounds like booster or MC. When my MC gave out i could tell by just hammering on it and hold it. Turn heep on and slam on the brake and hold. Is it solid? If you let off a little then it'll start going to the floor. Bad MC.

    To check your booster, with engine off..pump brakes several times to get rid of residual vacuum. Then while holding the brake pedal down, start the engine. If booster is working you will feel the pedal drop to normal. If your pedal is almost going all the way to the floor, it is usually adjustment or air in system. If the MC ever leaked the booster diaphram could be toast.

    Most of that shoud be right. LOL

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    Quote Originally Posted by Black88YJ View Post
    Follow this link to my build if you want.

    http://www.soxja.org/forum/viewtopic.php?t=912

    Bradford
    Nice, you lazer cuttin bastard. . Thats crazy. I must have gone through a couple hundred cuttin discs in the last 6 months. LOL.

    I'm PM'n ya. Need to pick your brain on a couple things.

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    TT,

    Sounds like curt is right on the money here.

    If you wish to bleed the master on the vehicle you will need to make up two lines that go from the output ports around and into the resovoire keeping them under the fluid and keep pumping the pedel until you no longer see any air bubbles coming from the lines.

    When you changed the calipers was this an upgrade? or just stock replacement and now you have this deep pedel situation?

    That will help with what is behind this problem

    Bradford

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    I swapped an older front end in and had to change calipers to the 89 style and a dana 44 rear end swap with 3/4 disc conversion. New calipers all around. I guess I'll try something this weekend but without the engine running the pedal is right at the top but when it's on it hits the floor. I assume that when the brake lines sat open then the master cylinder might have emptied out as well.

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    TT,

    you want to do something like in the pic here, that is the correct way to bench bleed a master. And just pump all the air out.
    Attached Thumbnails Attached Thumbnails brake system 021.jpg  

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    so should i disconnect my lines and do the mc first then the rest again?

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    could this still work if I just lifted the top of the resovoir and made sure to go slow as not to spill any fluid? Will it just suck in the fluid that is there?

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    In my opinion I would just disconnect the lines at the master, make some other lines that loop into the fluid and get all the air from the master.

    Then hook up the system lines and bleed the entire system.

    The air is in the master cylinder piston bore, I believe you are refering to the reservoire. You dont have to use hard lines to loop into the fluid, you can just use a small fitting and a rubber/plastic hose to loop the system.

    Brakes are important, just do them correctly

    Bradford
    Last edited by Black88YJ; 06-17-2008 at 09:08 PM.

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    Excellent right up man
    I've got a interesting question for ya
    Buddy of mine on out here has Scout axles on a CJ
    He has done a high steer over the winter and in the process of that he changed calipers and other junk
    He has Ford Calipers now(not sure if there f150 or 250)
    my question is this...when we went to bleed the brakes we got all the air out(as far as we can tell....brake fluid shoots about 5 feet...lol..and no air)
    but his pedal still goes to the floor with not effort....the only kind of resistance there is if from the return spring on the pedal..lol....if you pump it the crap outa the pedal it sorta get a little hard at the very bottom of the pedal but then if you let go the pressure goes away.
    He put a new master on it(YJ I believe) and still no change(he's bench blead both the old one and new one)
    I've heard somewhere that he needs a Master outa a Mustang or something because of the Fuild Volume being to low on the YJ master
    Any insight on this
    He and I are completely frustrated

    Thanks for any help
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    Does the gc master cylinder use metric brake lines and if so where can I find some?

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    Quote Originally Posted by muddy-lowrad View Post
    Excellent right up man
    I've got a interesting question for ya
    Buddy of mine on out here has Scout axles on a CJ
    He has done a high steer over the winter and in the process of that he changed calipers and other junk
    He has Ford Calipers now(not sure if there f150 or 250)
    my question is this...when we went to bleed the brakes we got all the air out(as far as we can tell....brake fluid shoots about 5 feet...lol..and no air)
    but his pedal still goes to the floor with not effort....the only kind of resistance there is if from the return spring on the pedal..lol....if you pump it the crap outa the pedal it sorta get a little hard at the very bottom of the pedal but then if you let go the pressure goes away.
    He put a new master on it(YJ I believe) and still no change(he's bench blead both the old one and new one)
    I've heard somewhere that he needs a Master outa a Mustang or something because of the Fuild Volume being to low on the YJ master
    Any insight on this
    He and I are completely frustrated

    Thanks for any help
    Sounds like you're right. Low volume (too small of a bore in the master) Don't know shit about CJ's but here, did a quick search for ya. Might help.
    http://www.pirate4x4.com/forum/searc...archid=3173344

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    Quote Originally Posted by trafficticket View Post
    Does the gc master cylinder use metric brake lines and if so where can I find some?

    Crappy, PS, Napa, Carquest, etc. all carry metric and imperial hard lines of various lengths. Ya just gotta bend'em yourself.

    I'd bring your ols sh!t to PS cause there fittings aren't packaged, they're in those sliding bin/drawers. Find a comfy spot on the floor and go to it. LOL

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