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Grand Cherokee Master Cylinder and Brake Booster Swap

Starboard M

NAXJA Member
NAXJA Member
Location
WA
Background: My 89 Cherokee has always had bad brakes. Never really cared all that much, and didn’t want to spend the money on new brakes. Tried new pads and shoes, which didn’t help very much. Bled the system, and while that helped a little, didn’t do all that much overall. After talking with a friend, I realized that I probably didn’t have power brakes, which would explain the rockhard pedal feel, as well as the really lousy braking. I assumed the brake booster went bad. Originally I was going to replace the MC and booster with stock parts, but I decided that I may as well upgrade after seeing posts about the braking power from a booster and master cylinder from a Grand Cherokee.

I found a master cylinder and brake booster on car-part.com from a 1999 Jeep WJ Grand Cherokee. Supposedly you can find them for around $60 shipped, but I didn’t want to wait for one to be shipped to me, and I wanted to make sure it was the right one, and in decent condition before I bought it. Ended up paying $135 for both the MC and booster that I picked up from a semi local junk yard. I figure that’s less then the cost of brand new parts from my local friendly car parts dealer, so I wasn’t too worried about the cost.

The Swap:

Started by taking out the old mc/booster combo.
Picture of the old stuff:
P1010527.jpg


Look under the dash, and finding where the booster rod connects to the pedal assembly.
P1010534.jpg

The four bolts that hold the booster to the fire wall are 14mm. Take those off with a deepwell socket. The top right nut is a pain to take off, and I ended up threading my hand around the steering column to get to that nut.

Next, disconnect the sensor from the pedal, and start to take the bolt and two nuts off of the pedal and booster rod.
P1010537.jpg

P1010552.jpg

P1010582.jpg

The locknut is a 16mm, as is the bolt. The nut is a 14mm. Take the bolt out, and put the nuts back on it so you don’t lose them. There is a metal sleeve with two clear plastic holders which needs to come off.

In the engine compartment there are a couple things that need to be taken out. Take off the vacuum line that goes into the booster, and the two hoses and three wire connectors that go into the window washer bottle. Remove the washer bottle, and set it aside making sure to not get fluid all over everything.

Use a turkey baster or something similar to drain the master cylinder reservoirs. Take off the brake lines that go from the master cylinder to the proportioning valve. Make sure to keep the fittings as you will reuse the ones going into the proportioning valve. Put something in the holes where the lines went so nothing falls in them. Don’t want any dirt or grime to fall in there.

Double check that nothing else is holding the booster and MC and pull them out.


Cleaning and fitting:

A simple comparison picture of the old and new:
P1010553.jpg


There is a small plastic sleeve in the old booster rod that you need to make sure to remove. Shown here on the old booster.
P1010561.jpg


Find a drill bit that is the same size as the hole on the old booster rod without the sleeve. In my case it was a 5/8’’ bit. Drill out the new booster rod.
The old rod uses a flat portion to sense when the brake lights should be turned on and off. This must be cut into the new rod. Cut off the old booster rod, and using vice grips clamp the cut off piece to the new booster. Use the drill bit to line up the holes. Make sure the cut off piece is in the right orientation, as you will have to grind down the new rod. You don’t want to mess this up. You can see the old piece clamped to the new here:
P1010564.jpg


Using a dremel or grinder, grind the new rod down so it is the same as the old one.
P1010569.jpg


Put the plastic sleeve that you took out into the new rod hole.

Now clean the firewall and anything else that you can reach if you want. I tried to get as much junk and mud out as possible, but this isn’t really needed. Also, you will need to hammer the pinch seam that is at the top, as well as the vertical one slightly to fit the larger booster. Picture of removed.
P1010570.jpg


Picture of pinch seams “massaged” and cleaned up a bit.
P1010573.jpg


Test fit the booster and see if any more pounding is needed. I have read that a ¼’’ spacer is needed to be added in between the firewall and booster to keep the brake pedal in the right position. I’m not sure why that ¼ would matter, but I ended up using washers to space the booster out, as it wouldn’t fit without them. So if you need a spacer, use one. Otherwise, I don’t think I would worry about it.
¼’’ of washers on the booster studs:
P1010575.jpg


Slide the booster and MC into position. You will need new nuts for the WJ booster studs. Don’t know what size they are, but they are 1.25 thread pitch. Make sure no wires or lines are pinched, and then bolt the booster down.

Hook up the brake pedal and everything else. At this time, make sure that the brake lights are only on when you’re stepping on the pedal.
 
Bending lines:

This was the hardest part for me. I’d never bent or flared brake lines, but luckily I only messed up once.
Use an old coat hanger and bend it to how you want your lines run. Realize that the lines run into the opposite side of the MC than the old one. Also, keep in mind you will want your washer bottle to be bolted back in.
P1010591.jpg


Using a couple of feet of 3/16’’ brake line, start bending. Now comes the complicated part. Make sure you keep the line fittings strait on where they go. Don’t want to bend up a line, and then realize the fittings are in the wrong place. Also, the flares are different on the proportioning valve and MC. The MC from the WJ uses a bubble flare while the proportioning valve uses a double flare.
The brake lines I got from NAPA were double flared, so I only had to use a bubble flare tool.

Showing a line bent with the coat hanger guild:
P1010594.jpg


Install the MC side of the lines, but keep the lower end free. You need to “bench bleed” the MC before you can finish the lines.

Technically the booster and MC should be out of the car to bench bleed them, but I decided it would be easier to do it while in the Jeep.
This is how I bench bleed them. Notice the salad dressing bottle in the foreground and clear lines.
P1010596.jpg


Once bench bleed, finish installing the brake lines. Took me a little while to get them in there, as everything is a tight fit but they did finally go in.
Installed:
P1010598.jpg


This shows how the lines were routed. Sorry about the bad lighting, but it should give you some idea.
P1010600.jpg


Make sure that all the fittings are tight. Bleed the brake system, starting with the wheel which is farthest away from the booster/mc, and working your way to the closest. In my case the farthest was the passenger rear.

Reinstall the washer bottle. Hopefully it will fit back in with how you have routed the brake lines. Make sure to install the right hoses on the right pumps and wires on fittings. I put the wires on wrong at first, so the front wouldn’t get water unless I pushed for the rear window wash, and when the front turned on, the wipers would move, and water would come out on the back window. Oops.

Reconnect the vacuum line going into the booster.


Make sure everything is tight, and nothing leaks, and go for a test drive. At first only go a couple inches and make sure the brakes are working before going onto public streets.

Final Impressions:

The braking is so much better. While I cannot lock up 35s, I can stop at least twice as fast as before with bad broken brakes. I would highly recommend this modification to anyone who has a problem with their brakes or people who have single diaphragm boosters.


Thanks to “cal” for answering my questions and being very helpful.


Other links that might be helpful in this swap:
How to bench bleed brakes
Original NAXJA thread
4x4wire swap


Notes:
-I assume no responsibility of anyone doing this modification. Do it at your own risk. If you aren’t comfortable with it, and don’t feel you are equipped to make this work, don’t do it.
-Make sure you don’t get any brake fluid on paint or it may start to take the paint off.
-There are many ways to do this install. Do it however you feel is easiest.
-Yes my wiring is ghetto. It will be fixed soon.
-I did this on my 1989 Cherokee 4.0 with no ABS. Other years might vary on required modifications.
-If you have disk brakes all the way around other mods might have to be done.
 
i just did the swap about 2 months ago on my 89. bought the booster and master for $80. went on car-parts.com also and found local yard that had the parts and picked them up. i did everthing you did except i didnt use any washer behind the booster. hardest part for me was make the damn double flare on the brake lines.

i have 31" tires and stopping power is like night and day. i would recommend this to any one that has the crappy single diaphram booster.

i got all the info on this from this site. there is a very long thread about this that you have to weed through to get the info. someone here as done this swap to about 6 xjs.
 
Starboard, Excellent writeup great pictures and very detailed explanation of everythig needed to do this swap. Now all I need is guts to geterdun.
 
89xj said:
i got all the info on this from this site. there is a very long thread about this that you have to weed through to get the info. someone here as done this swap to about 6 xjs.
Yep, I linked that site towards the end of my write up.

"cal" is the one who has done the swap so much, and he helped me with some questions I had.
 
I need to do exactly what you have done, except I have ABS on my '89. I wonder if any one has as fine a detailed example of how to deal with the ABS and convert to non ABS. Great pictures and detail. Good example of helpful article.
 
Will be doing the swap this weekend with Cal's help.
 
Went wheeling this weekend for the first time since doing the swap. All I have to say is wow.

I can now stop in 4low going down hills without having to put it in neutral. Makes it a lot more fun now that I am finally in control as well.

Had to do a semi emergency stop for a red light going 45 mph. Was almost able to lock up 35s. Very impressed with the stopping power.
 
Got an '89 with ABS I need to upgrade to regular non-ABS, I dig the upgrade however a few questions for the experts, (believe me I need help). What about the portioning valve? Must it be replaced? Can the current inplace brake lines be used or must they also be replaced. I plan a conversion to rear disk brakes how would this impact the upgrade, should I go ahead and do the rear disk brakes now if I can swing it.
 
Interesting idea - but I'm wondering if the ZJ loaded booster is the same as the 1996-up loaded booster commonly swapped in? I haven't found out yet.

The underbraking comes from using a single diaphragm booster, which was later replaced with a dual diaphragm unit. I'd like to do this swap meself sometime, but I'd also like to compare the early and late master cylinders. I'm not a huge fan of plastic, and I'd like to see about using an early M/cyl with a late vacuum booster, if somehow possible (I'm sure some machine work would be required, but I don't mind that.)

Apart from that - which hasn't anything at all to do with you! - very nicely done! Bravo Zulu for you...
 
starboard or cal,

can you please explain the difference in the flares from the old MC to the new one? are they different threads, or does one flare just not fit inside of the other fitting?

-Tim
 
2lazy2p said:
Got an '89 with ABS I need to upgrade to regular non-ABS, I dig the upgrade however a few questions for the experts, (believe me I need help). What about the portioning valve? Must it be replaced? Can the current inplace brake lines be used or must they also be replaced. I plan a conversion to rear disk brakes how would this impact the upgrade, should I go ahead and do the rear disk brakes now if I can swing it.

I used the stock proportioning valve.

You'll have to do one of two things to connect the WJ MC to the proportioning valve

1) build new lines w/ metric fittings at the MC and standard fittings at the proportioning valve

2) buy the metric/standard adapter fittings.

Can't help you on the disc brake conversion.
 
Sweet write-up, I just went 33's on my 89 xj and my brakes completely suck, Almost everything is new component wise including the booster and I'm sick of crappy brakes.I was searching for the 96 xj dual diaphram write-ups, I found a writeup on madxj. After reading and re reading and still scratching my head,I stumbled across this. I will be calling my local wrecking yards looking for a 99 grand cherokee booster and master setup!

wonder if braking will improve while the brakes are wet too? my brakes are almost non existent went wet?
 
bcmaxx said:
Sweet write-up, I just went 33's on my 89 xj and my brakes completely suck, Almost everything is new component wise including the booster and I'm sick of crappy brakes.I was searching for the 96 xj dual diaphram write-ups, I found a writeup on madxj. After reading and re reading and still scratching my head,I stumbled across this. I will be calling my local wrecking yards looking for a 99 grand cherokee booster and master setup!

wonder if braking will improve while the brakes are wet too? my brakes are almost non existent went wet?

after i did the swap, my overall braking in all conditions greatly improved.

btw, you can use the booster/master from 99-2004. why use an older 99 if you can find a newer 2004?
 
Picked up one from an 04 booster and cylinder for $35 dollars , installing it tonight,I'll post up my results and if I ran into any problems.
 
Swap went great ,well almost.....ground the tab for the brake switch at an inncorrect angle rendering my stock switch useless(believe me I tried everything). What other options do I have for a brake switch? I was thinking somsort of pull switch as used on some motorcycle rear brakes,or maybe some sort of hydraulic pressure switch. Help!! thanks

Brakes work unreal!!!:clap:
 
You can use a brake switch from a mid-90s XJ: they are a block with a plunger that fits in the bracket just above the booster rod connection. The nice part or these switches is that they have 6 wires (3 circuits), with 2 circuits normally open/one normally closed or vice-versa? Anyway, the circuits will work for an automatic with cruise, giving switch functions for the brake lights, the cruise cancellation, and the converter unlock. Of course, if you had a standard tranny with no cruise, you would only use one set of wires from the switch.
 
Slide the booster and MC into position. You will need new nuts for the WJ booster studs. Don’t know what size they are said:
the are a 8 mm nut...

also my 94 doesnt have a bolt and nut on the brake pedal..only a rod and a clip and the zj rod downt need to be enlared ..makes this even easier ..I cant seem to find and 3/16 brake lines witha a bubble flare on ends..only doubles

is a bubble flare the same as a single flare???
 
nope, buy some brakeline and a flaring kit, practice first
 
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