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Old June 3rd, 2008, 08:52 PM   #1
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Default YJ 8.8 Brake ?

Looking for help from those who have done an 8.8 swap into a yj or those with knowledge in the area of brakes. The yj was an 89.

Swapped a disk brake 8.8 from a 98 sploder into the yj and as I have read the mastercylinder is inadequate. After lots of bleeding the petal sinks almost down to the floor before starting to firm up but still goes to the floor under normal braking. After locking the rear lines the brakes firm right up. This is what has lead me to the conclusion that the stock mc is not generating enough pressure for the 4 wheel disks. I have read some of the writeups for the swaps of vette, e350, marquis mc's. Is there a reason why no one swaps a zj mc along with the prop valve? Are the rear brakes from the heavier exploder larger than those from the zj making the zj mc also inadequate? I'll also take any testimonials as to your setups.TIA
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Old June 3rd, 2008, 09:00 PM   #2
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Is the bleader on your caliper facing up or down?
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Old June 3rd, 2008, 10:03 PM   #3
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up
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Old June 4th, 2008, 07:35 AM   #4
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Hmmm, I have a soft pedal also, but I accidentally put the calipers on the wrong side so my bleeder was down.
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Old June 4th, 2008, 10:44 AM   #5
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the zj brakes and the 8.8 brakes are the exact same...I put the 8.8 in my tj and the only thing I've done as far as brakes is put a new prop valve from a 03 tj with disks. I'm not sure what and if there is a differance between the tj and yj master, but my stock tj master works fine...in fact the brakes feel exactly the same as they did before the swap
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Old June 4th, 2008, 11:51 AM   #6
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If the zj calipers and the 8.8 ccalipers are about the same size then I would think the zj mc will work. I guess the only way to know is to try it.
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Old June 4th, 2008, 11:56 AM   #7
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If the zj calipers and the 8.8 ccalipers are about the same size then I would think the zj mc will work. I guess the only way to know is to try it.
i'm pretty sure they are the same caliper
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Old June 4th, 2008, 12:13 PM   #8
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not running an 8.8 but when I converted the d44 to discs I had a problem with the rear m/c resivoir not holding enough fluid to activate the brakes enough. we swapped on a disc/disc mc from the 77 marquis with hydroboost. bolted right up, required almost no adjustment and pulled the oring from the stock yj prop valve, but since i have the cadillac
calipers I had to put a 10# rpv to the rear. stops the 35's very well with nice firm pedal.
I have a zj 4 wheel disc prop valve I still may install.
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Old June 9th, 2008, 12:37 PM   #9
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not running an 8.8 but when I converted the d44 to discs I had a problem with the rear m/c resivoir not holding enough fluid to activate the brakes enough. we swapped on a disc/disc mc from the 77 marquis with hydroboost. bolted right up, required almost no adjustment and pulled the oring from the stock yj prop valve, but since i have the cadillac
calipers I had to put a 10# rpv to the rear. stops the 35's very well with nice firm pedal.
I have a zj 4 wheel disc prop valve I still may install.

I installed the same master cylinder on my YJ with 14 bolt rear axle. Now I can lock up my 37" tires no problem. I think I paid $15.99 at autozone for it.
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Old June 9th, 2008, 12:43 PM   #10
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Hmmm, I have a soft pedal also, but I accidentally put the calipers on the wrong side so my bleeder was down.
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Old June 10th, 2008, 11:07 PM   #11
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Ended up just doing the MC from a 78 Mercury Marquis with 4 wheel disks. Ordered it from autozone here is town was 16$ plus 10$ core. Went to pick it up yesterday. Wrong part was shipped but they said they had one in stock in Saginaw. Pre4runner picked it up for me Yesterday. Bench bled the MC. Installed it today. Only problem was that the front output on the Marquis MC is 7/16-24 thread and the rear output is 1/2-20 thread. The jeep master cylinder was the oriented the opposite. Luckily I was able to just cut the line ends at the MC swap the ends and re flair the line ends. Bled the lines and the difference was night and day. Very firm petal works great.
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Old June 11th, 2008, 06:30 AM   #12
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It's funny, but I did the same thing once. After 3 hours of brake bleeding, with the pedal still soft (and my daughter learning a whole new vocabulary), I figured it out.. :miff:
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Old June 11th, 2008, 08:02 AM   #13
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Originally Posted by Stone View Post
Ended up just doing the MC from a 78 Mercury Marquis with 4 wheel disks. Ordered it from autozone here is town was 16$ plus 10$ core. Went to pick it up yesterday. Wrong part was shipped but they said they had one in stock in Saginaw. Pre4runner picked it up for me Yesterday. Bench bled the MC. Installed it today. Only problem was that the front output on the Marquis MC is 7/16-24 thread and the rear output is 1/2-20 thread. The jeep master cylinder was the oriented the opposite. Luckily I was able to just cut the line ends at the MC swap the ends and re flair the line ends. Bled the lines and the difference was night and day. Very firm petal works great.
good news
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