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booster swap

89 jeep

NAXJA Forum User
Location
FRESNO,CA
I took a master and booster from a 96 cherokee and installed it in my 89 cherokee xj. Brakes have double the stopping power, but now i have a little surging of the RPM while on the freeway. Idles fine, street driving fine, but when on the freeway, at 60-65, idle seems to jump then go back down. Any ideas.
Thanks
 
Sounds like the booster may have a vacuum leak. Check the hose from the manifold to the booster, the booster's valve and apply vacuum to the booster with a tester like mitty vac and see if it leaks.
 
Yep.. Sounds like a vacuum leak.

Double check everything that Talyn mentioned.

Also check your vacuum bottle reservoir and the lines going to it.

E
 
Check the adjustment of the switch on the pedal. Sounds like the torque converter lockup could be intermittent. When you step on the brake the TC unlocks, and if that switch isn't adjusted right the TC can run unlocked. This happened to me when I installed the later year master cylinder and booster.

(about 10 years ago) :)
 
Check the adjustment of the switch on the pedal. Sounds like the torque converter lockup could be intermittent. When you step on the brake the TC unlocks, and if that switch isn't adjusted right the TC can run unlocked. This happened to me when I installed the later year master cylinder and booster.

Thats a good point.
 
As luck would have it, I'm getting ready to do the same swap to my 90. I have a 96 booster/master as well. What do i need as far as supplies to adapt the brake lines and Goatman what did you do to solve the switch issue?
 
Use the fittings from the 96. Its easier to buy 3 ft of 3/16 brake line, some might have the bubble flare at each end, and the coerrct fitting for the new master, the metering needs a different flare. Youll need a tube bender and a flare tool. You might have to remove the spacer from the back of the 96 booster.

Goatman. What kind of adjustment do i need to make?
Thanks for the info. yall.
 
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is the 95/96 booster the most direct dual diaphragm swap out there?

...I just swapped in a '99 booster and m/c into my brother's '88 MJ to add braking power with the metric tonne swap and plow install. had to use two spacers, or would've had to chop the rod down.

I've got a couple '96 boosters and m/c's sitting here and would rather do a more direct swap than not...
 
The switch just needs to be disengaged when you're not stepping on the brake.......I think, I don't remember exactly how the switch button is. If the switch is telling the computor that you're stepping on the brake then the TC won't lock up.
 
The switch just needs to be disengaged when you're not stepping on the brake.......I think, I don't remember exactly how the switch button is. If the switch is telling the computor that you're stepping on the brake then the TC won't lock up.

On my '91, I had to take the brake light switch out, and pull the plunger all the way out. Then, install it. When you turn on the engine and press the brake pedal down, the plunger will be pushed down to the point where it needs to be.


Oh yeah.. That's how it is..


E
 
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I took a master and booster from a 96 cherokee and installed it in my 89 cherokee xj. Brakes have double the stopping power,

No, they don't.
They are the same brakes you have been using since the vehicle was built, they havent changed or been improved. The hydraulics may have been increased, but the brakes are the same junk they've always been.

We just can't get this concept............
 
No, they don't.
They are the same brakes you have been using since the vehicle was built, they havent changed or been improved. The hydraulics may have been increased, but the brakes are the same junk they've always been.

We just can't get this concept............

What rock have you been hiding under?

Switching to a later year double booster to replace the earlier years single booster has been a popular upgrade for many years, and has been written about extensively. The combination works in the same space since the master cylinder is shorter by the same amount that the booster is longer. I just happen to be the guy who discovered this and wrote about it, and it's been covered many, many times since then.
 
10-4 I went to barely skidding in the dirt to skidding on dry pavement. Pedal used to go almost all the way down, now, it doesnt go half way. One of the best things ive done to the XJ.

It still drives at 23-2500 rpm at 65, i guess thats right. I drop to 3rd gear at 65 and the rpm jumps to 3 grand, so i guess im fine, right?
 
time to put mine in my wheeling truck...


btw, I did this on my brother's '88 Mj when installing the 3.55 d30 and 3/55 d44 with m/t springs in the rear and plow up front. I gotta tell you, it blows the brakes on any other jeep I own (quite a few) right clear outta the water.
 
Question for those that have done this swap;

Did you reuse the stock proportioning valve or the one that is attached to the 96 MC? It looks to me that the 90 PV will not clear the booster from the 96 MC/booster. Otherwise the the PV's look the same between the year models.

Thats all I have for now but there will be more questions!
 
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