Modified YJ brake problem - JeepForum.com
 
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post #1 of 7 Old 09-29-2013, 11:04 AM Thread Starter
JeepYJ350CI
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Location: West palm beach
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Modified YJ brake problem

Hi all. I've been searching but running out of time. My jeep has a serious stopping problem. And im moving from florida to the mountains in PA within one week. And still have alot of packing and stuff to do. Im looking for simple problems/solutions. Here is my setup

1992 jeep YJ
Throttle body fuel injected Chevy v8 mild cam all tuned for very high torque.
Rear ford 8.8 with disc brakes
Front stock d30 with standard pads and rotors.

Feels like soggy petal, I've bleed the system well using a vacum bleeder.

I can't really even hold it back on idle in 4lo. I mean it stops eventually with all I got on the brake system. The idle vac pressure is about 19" and I've changed the proportion valve before (for stock)

In some situations I can get the front right to lock up in dirt while in reverse.

I've done some reading about a corvette swap and a zj swap. I've also heard about removing some o ring in the proportion valve. Any help would be appreciated. I'm going to hit the junk yard tomorrow I really only have one day to get this figured out. I lost my old user name on here. But I've been around awhile. Thank you all in advance.

Jeff

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post #2 of 7 Old 09-29-2013, 07:07 PM
ROWA
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1994 YJ Wrangler 
 
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Location: Cary, NC
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I used a whole assembly from a 97 Grand Cherokee, Booster Master cylinder and Proportioning valve. You will need adapters Metric/Standard from the proportioning valve to your brake lines or you can re-flare the tubing with new tubing nuts. I had the hardest time with the rear flarenut not sealing, I ended up buying a piece of brakline and a flared coupling. Check all of your rubber brake lines for cracks or swelling, you might need someone to push on the brake pedal while checking for swelling.
With my current setup I can lock the front brakes on blacktop and the rear is a lot more responsive. I don't have any problems in Lo gear with stopping.
The modification I had to make to the booster to pedal rod was shorten it by about 1/2".
Good luck,

94 YJ Sahara

The best Engineering is no match against natural Stupidity.
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post #3 of 7 Old 09-29-2013, 08:17 PM
jokerchief462
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1989 YJ Wrangler 
 
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95 YJ 4.0 double diaphragm booster, 95 E 350 master cylinder and a prop vale from a WJ.

Biggest brake peddle ever.

I did all this when I out a 8.8 w/ discs in.

Lots if adapters from a line shop but finally got it all assembled.

Look for 8.8 brake threads or just YJ brake threads. There are many.

Sent from underneath my Jeep

89YJ 2.5L TBI, AX-5, NP231 SYE, Ford 8.8, Yukon Grizzly, Tom Woods Shaft, 33" BFG T/As, 4" lift, Warn VR10000s.

AF Jeep Club Tail #184
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post #4 of 7 Old 09-29-2013, 08:33 PM
rshbutch
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1990 YJ Wrangler 
 
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Location: fresno, ca.
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The problem you might be having is the cam. You are not making enough vacuum with that cam. Not sure if double booster will help. Might want to consider hydro boost style brakes. Did mine 6 months ago,simply awsome braking.
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post #5 of 7 Old 09-29-2013, 08:40 PM
jokerchief462
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1989 YJ Wrangler 
 
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Location: Sin City
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To run brakes you need 21 lbs vacuum.

Sent from underneath my Jeep

89YJ 2.5L TBI, AX-5, NP231 SYE, Ford 8.8, Yukon Grizzly, Tom Woods Shaft, 33" BFG T/As, 4" lift, Warn VR10000s.

AF Jeep Club Tail #184
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post #6 of 7 Old 09-29-2013, 08:43 PM
Dake
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1991 YJ Wrangler 
 
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I just did the 8.8 swap and my brakes are better than ever with 35s.

Waiting on my Rough Country lift to sag!
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post #7 of 7 Old 09-29-2013, 09:45 PM Thread Starter
JeepYJ350CI
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I really thank you all for the replys. My donor truck had a vac canister I omitted. I came directly out of the intake to the brake booster.

I am running somewhat new hard lines all the way around. And ss steel lines going to the fronts and 1 on the rear.

I have a budy with a Cherokee that did that newer ZJ upgrade. And he said night and day difference. And can lock his 33's.

I'm running 35's. the cam is really mild, but the info on the vac required to run brakes is good info. I'll do some IAC onboard tuning and try and increase the vacume some.

The jeep stops good enough down here in Florida. But it will be in extreme terrain in a week. I don't have alot of time for the conversion since I'm packing. If anyone knows what adapters I need so I can shave some time off. I will reflare the ZJ setup seems the easiest. For all I know it's just a bad master cylinder or booster. I am not a brake expert. I've rebuilt the trans myself. Installed and wired the ECM. But brakes is one thing I don't know much about.

Like I said. I really appreciate the input. And ps the cam is very mild. Mixed with small 2" dual exhaust, swirl port heads, makes it a torque bear. Very hard at idle speed to hold still in 4 lo.

P.s. when I first jack the brakes I feel a good bite. But it immediately falls off and hard to stop. Maybe some of you pros have some insight?
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