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Old 03-26-2014, 07:10 AM   #1
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94 yj brake upgrade w/8.8

Ok I have a 94 yj I put the 95 dual diagram booster and mc on it I also did the 8.8 axle swap with disc. I've bleed the brakes several times including vacuum bleeding but still can't get any peedle. Do I need to change my portioning valve and if so to what? Or is it something else?
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Old 03-26-2014, 02:03 PM   #2
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Are the 8.8 calipers on the correct side? The bleeder needs to be at the top. Just asking cause that is a common mistake that is made.

The only other thing it could be is the master cylinder, if you are not getting any pedal at all. Did the rod to the pedal come with the new MC? The dual diaphragm booster requires a longer rod, if I remember correctly.

I have an 8.8 disc on my 87, no new MC or booster. Doesn't even have a proportioning valve on it, and it stops fine with 35's.

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Old 03-26-2014, 03:18 PM   #3
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Yea there on the correct side. May be the angle they are at since I did the soa. But didn't know if my proportional valve would work with the new rear disc brakes.
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Old 03-26-2014, 07:00 PM   #4
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Post a pic of the brake calipers so we can see the angle. When I did my swap I bled them twice and they were ready to rock.... I take it you checked for leaks?
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Old 03-26-2014, 10:11 PM   #5
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Did the brake master get bench bled first??? And confirm the calipers are on the right side on your 8.8 as mentioned above.

When you mounted the master did you adjust the throw on the vacuum booster to engage the master cylinder piston.

Just did this haven't bled yet but all the same with an 8.8 that was working before.

Let me know what you got and pictures may help.
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Old 03-28-2014, 11:29 AM   #6
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I installed the 95 yj booster and a master cylinder for an e350 on my 89 YJ with 8.8 rear with discs. Results were not great, spongy brakes... deleted the e350 mc and put on the mc that came with the 95 booster, after bleeding, i can lock up all four wheels like nobodys business. Lots of adjusting that went on, but you do not need to replace the proportioning valve. Double check your vacuum and another thing you need to be sure of is that the rod inside the mc is pushing in far enough, if its not, then you need to extend it...
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Old 11-10-2016, 07:16 PM   #7
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So I'm considering doing this upgrade, can a 95 booster be purchased new or is it a bad idea and should I find one at a dismantler? I'm assuming I'll need a new master as well. Anyone have any insight and the best route to take and anything I should be aware of?
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Old 11-10-2016, 11:25 PM   #8
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Quote:
Originally Posted by steves92 View Post
So I'm considering doing this upgrade, can a 95 booster be purchased new or is it a bad idea and should I find one at a dismantler? I'm assuming I'll need a new master as well. Anyone have any insight and the best route to take and anything I should be aware of?
I pulled a booster from a late model xj and cut and welded my stock rod onto it for the right length and brake switch. I'm using a Dakota master because it has a better resevoir for a wrangler and is the same thing on TJ wranglers but easier to find at a pull yard. If you're going discs in the rear, I do suggest a zj proportioning valve. You can use a stock valve but there is a notable difference using the zj valve.
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Old 11-11-2016, 03:52 AM   #9
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Quote:
Originally Posted by c5wagner View Post
I pulled a booster from a late model xj and cut and welded my stock rod onto it for the right length and brake switch. I'm using a Dakota master because it has a better resevoir for a wrangler and is the same thing on TJ wranglers but easier to find at a pull yard. If you're going discs in the rear, I do suggest a zj proportioning valve. You can use a stock valve but there is a notable difference using the zj valve.
Thanks, I do have the 8.8 with discs. What year xj are we talking about when you say late model?

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Old 11-11-2016, 08:05 AM   #10
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Just buy this:

1974-1995 Jeep replacement 8" dual diaphragm brake booster master cylinder | Nelco Hotrods

It'll be an easy bolt-in. No welding. New parts, not unknown junkyard parts. Brakes are pretty important, so I always go new.

This kit uses a Corvette MC.

Search around - there are a lot of threads on the dual diaphragm upgrade. Cardone is one source for rebuilt dual diaphragm boosters, but they seem to have a TON of issues. Other people have used XJ or TJ boosters with the rod modification.
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Old 11-11-2016, 08:19 AM   #11
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Quote:
Originally Posted by StanF View Post
Just buy this:

1974-1995 Jeep replacement 8" dual diaphragm brake booster master cylinder | Nelco Hotrods

It'll be an easy bolt-in. No welding. New parts, not unknown junkyard parts. Brakes are pretty important, so I always go new.

This kit uses a Corvette MC.

Search around - there are a lot of threads on the dual diaphragm upgrade. Cardone is one source for rebuilt dual diaphragm boosters, but they seem to have a TON of issues. Other people have used XJ or TJ boosters with the rod modification.
That looks like a good deal. What about the valve? Did you use your stock valve or buy one of theirs?
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Old 11-11-2016, 03:14 PM   #12
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Quote:
Originally Posted by StanF View Post
Just buy this:

1974-1995 Jeep replacement 8" dual diaphragm brake booster master cylinder | Nelco Hotrods

It'll be an easy bolt-in. No welding. New parts, not unknown junkyard parts. Brakes are pretty important, so I always go new.

This kit uses a Corvette MC.

Search around - there are a lot of threads on the dual diaphragm upgrade. Cardone is one source for rebuilt dual diaphragm boosters, but they seem to have a TON of issues. Other people have used XJ or TJ boosters with the rod modification.
Well $30 for 2 boosters and masters wasn't too bad. 2001 and 97 xj boosters and 2 97 dakota brake master cylinders that I rebuilt..... Hasn't given me any problems what so ever. And at the first sign of problems, I have a plan B. That bolt in seems good to, but I personally would rather have easier to replace parts than expensive custom made parts..... If you have the money to buy that stuff, go for it!
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Old 11-11-2016, 10:28 PM   #13
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Wow, $30 for (2) boosters and MC? That's a screaming deal....the proportioning valve seems to be important also. What's the deal there? I can swing the new but im ok with a functioning used one.

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Old 11-12-2016, 12:02 AM   #14
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Quote:
Originally Posted by steves92 View Post
Wow, $30 for (2) boosters and MC? That's a screaming deal....the proportioning valve seems to be important also. What's the deal there? I can swing the new but im ok with a functioning used one.

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Half off at the pull yard. I guess I should have added a write up to my build thread to help others but I have a hard time taking pictures.... The proportioning valve comes out of any ZJ grand Cherokee without abs and with disc brakes. You just have to measure your stock rod length, cut it off and mate it to an xj booster with a welder or tap and die set. Your stock rod is thicker and the xj rod is skinny so either way is easy. You use the extension off your stock booster as well.
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Old 11-13-2016, 02:06 AM   #15
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When I did my disc 8.8 swap, I never had the need for any brake modifications. Stock 92 booster, master, and prop valve. Stopped like a champ on 35s. Lots of times, people upgrading to boosters and masters that are too big for the brakes have bad feeling brakes too. You can overdo it. Most people just seem to swap out the proportion valve to a ZJ valve, or pull out the o-ring in the YJ valve. The YJ booster and MC push enough fluid, you just need to make sure it gets where it needs to go.

Another option if you really feel the need to go bigger, is the 1978 Grand Marquis master cylinder made for cars with hydroboost. Bolts right onto the pre-dual diaphragm boosters, just have to unscrew the booster rod a little. That thing made it possible to lock up my 1 ton disc brakes with 35s.
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Old 11-20-2016, 01:35 AM   #16
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8.8 SOA will not affect the rear calipers for bleeding. Highly recommend the dual diaphragm booster with 35's. Is the adjustment rod to the master cylinder adjusted correctly? Start by placing all 4 tires on jack stands. With vehicle off, can your friend spin the tires while you press on the brake pedal?

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