WJ Booster and Master Cylinder Upgrade

[Comanche County]

Alright it's time to do the brakes!

 

 

There are several good write ups on this mod around the net. But I thought I'd do it and post a few pics and lessons learned that may augment the great info that's already out there. Here's a couple of links:

 

http://www.4x4wire.com/jeep/tech/brakes ... 3/booster/

http://www.jpmagazine.com/techarticles/ ... index.html

 

Those articles are basically what I followed to get it done. James750 has also done this mod and lent his expert advice via pm. If you're thinking about this mod, DO IT, its not hard to complete and can be done in 2-3 hours and... yes, it greatly improves your stopping power.

 

First get ALL items and tools needed.

 

Get a WJ booster, Master Cylinder (MC), the two WJ lines with the flexible sections, all the hardware....and you're set...

 

Tools I used:

Metric and SAE sockets & wrenches.

Cheap flaring tool from Harbor Freight

4.5" grinder with a cut off disc

Drill

5/8" drill bit

Vice Grips

 

The articles above mention a custom spacer between the MC and firewall,,,,I did not use a spacer in this install.

 

The first JY I visited asked $150 for the MC and Booster, so I skipped them and found another (Hi-Way Auto Parts in Brownwood, TX) that pulled it for me for $80. Only problem was they did not include the hardware and the guy that pulled them also cut the WJ lines that run from the MC to the proportioning valve. You will need those lines! All I got was the MC disconnected from the booster. I was so excited to get started that I didn't even think about the hardware and lines. You will need the four nuts that hold the booster to the firewall. The MJ and WJ have different nuts - don't forget them. They're Metric 8mm 1.25 pitch lock nuts. The two that hold the MC on the booster are the same. That's 6 metric nuts total.

 

 

The part numbers:

 

 

 

I thought I'd just use my MJ hard lines (from the MC to the proportioning valve) but the MJ MC lines exit on opposite sides from the WJ - no joy.

 

I went back to the JY the next day and found the donor WJ. A 99' 2WD with 150K. I got the four booster nuts that were still laying in the floorboard as well as the cut lines and a couple of extras. I got the two more metric lock nuts I needed from Ace Hardware.

 

While at the yard I pulled an extra set of lines off a burned out 07-08ish Grand Caravan based on their extra length of flexible hose in the line. Turns out I did not need them....also they have different threads than either the MJ or WJ booster. However, if you have a Bubble flare tool you could attach the proper connectors and benefit from the extra flexibility. I also pulled the cut lines from the donor WJ and another set of cut lines from another WJ in the yard. I wasn't sure how the line issue was going to work out, so I grabbed whatever I thought I may use.

 

The Grand Caravan lines are on the left, the two cut WJ lines have the shorter flexible sections.

 

One of the MJ lines is next to the two cut WJ lines for comparison.

 

I didn't use these, but if you custom make your lines, couplers may come in handy.

 

First remove the washer bottle. The motor is attached to the bottom of the bottle. There is a two wire connector, the fluid hose and two 8mm screws that hold it on. Be prepared for washer fluid to leak out once you pull the hose.

 

Also disconnect the booster rod from the brake pedal. Here's the bolt that comes out. IIRC its 15mm. I used a ratchet wrench and a small crescent.

 

Disconnect the two hard brake lines at the MC and the four booster nuts on the inside of the firewall. A flexible ratchet extension would come in handy but I managed to get them out with a straight 3" and 6" extension. Use a deep socket.

 

Next pull the MC and booster as one unit.

 

Here they are side by side:

 

The MJ and early XJs have the same brake light switch that mounts on the end of the booster rod.

 

These are the sleeve and grommets that hold the switch on the booster rod. You'll need to drill out the hole in the WJ booster rod to 5/8" and use these items to mount the switch.

 

 

Comparison of the two rods. Notice that the MJ booster rod has a flat spot. That flat spot engages the brake light switch and has to be right distance relative to the hole in the rod.

 

The hole isn't clean, but the sleeve and grommets fit snug anyway.

 

In the JP article they removed the both rods from the boosters and aligned them with the 5/8's drill bit then ground the flat spot on the WJ rod to match the MJ rod. That would be a good way to do it. Since I didn't take the boosters apart, I inserted the sleeves and grommets in the newly drilled rod, measured the distance with a micrometer then ground the WJ rod until it was a match.

 

 

OK, once you've got the WJ rod set up with the brake light switch then mount it up in the vehicle. Next is connecting the lines. This one shows where the stock MJ lines orient to the WJ MC.

 

I wasn't sure how it would work and I thought I'd use the connectors here but it wasn't necessary.

 

I used the longest set of WJ lines and slid on the old MJ connectors then flared the ends using my handy dandy HF flare tool that I believe only cost me about 8 bucks. I only had to cut one of the MJ lines because it had both sizes needed to connect to the valve.

 

 

Here's the lines.

 

After some creative manipulation bending the lines my MJ now has brakes. Also, note that the WJ lines are reversed, that is --- the end that was connected to the WJ MC is now turned around and connected to the MJ proportioning valve. In the WJ, the flexible hose is closest to the MC now the flexible portion is nearest the valve. Clear as mud?

 

 

A couple more pics to show the difference in the flares. The WJ uses bubble flared ends and the MJ uses a double flare. The top line is the WJ style.

 

You'll need to make a little room for the top of the booster. The EGR tube must be moved above the booster but the clutch hard line can stay where it is,,,,there's room for it between the booster and the firewall.

 

 

After bleeding all the air out of the system I can vouch that this mod makes the brakes a lot better.

 

Overall, I spent about 100 bucks. That includes the parts, brake cleaner, and brake fluid. Money well spent. The truck stops a lot easier and is much safer to drive. :thumbsup:

[jimmy21669]

Nice write-up...thanks!

[txjeeptx]

Great writeup. How'd I not see it before? "Search" is only as smart as the user.

 

I had to modify the firewall more than you did to get my WJ booster to fit. I ground the large center hole larger to fit the WJ's larger booster pushrod section, and I ground down the two vertical ribs to either side of the booster mounting location. I also pushed the clutch hydraulic line over the booster instead of behind it, and did some minor rebending of the line to clear the booster on the engine side. I used a bottle jack and some scrap lumber to make the push upward on the horizontal firewall pinch seam to clear the booster. This allowed the booster to sit all the way on the firewall without being pushed up against any other part of the firewall or any hydraulic lines or the vacuum lines.

 

I rebent the WJ hard lines and cut them shorter, cut off the factory MJ distrubution block line fittings, and flared them onto the WJ lines. The install looks factory.

 

There is no problem with fitment for the factory MJ washer bottle.

 

I bled the system per the suggestion to "confuse" it into thinking there are no front brakes - ie, you bleed the rear brakes with one of the front brake bleed valves open (and attached to a hose and fluid container so no air gets back in the front brakes - basically, its like you are bleeding the front and the rear at the same time). This bleeds the line between the rear load sensing proportioning valve and the distribution block near the master cylinder.

 

The WJ dual diaphragm booster and master cylinder is one of the best modifications I've ever done to my MJ. It stops like a completely different truck.

[Comanche County]

Thanks for the compliments and extra info. Those are good tips that will help someone.

[JeepcoMJ]

Great writeup. How'd I not see it before? "Search" is only as smart as the user.

 

I had to modify the firewall more than you did to get my WJ booster to fit. I ground the large center hole larger to fit the WJ's larger booster pushrod section, and I ground down the two vertical ribs to either side of the booster mounting location. I also pushed the clutch hydraulic line over the booster instead of behind it, and did some minor rebending of the line to clear the booster on the engine side. I used a bottle jack and some scrap lumber to make the push upward on the horizontal firewall pinch seam to clear the booster. This allowed the booster to sit all the way on the firewall without being pushed up against any other part of the firewall or any hydraulic lines or the vacuum lines.

 

I rebent the WJ hard lines and cut them shorter, cut off the factory MJ distrubution block line fittings, and flared them onto the WJ lines. The install looks factory.

 

There is no problem with fitment for the factory MJ washer bottle.

 

I bled the system per the suggestion to "confuse" it into thinking there are no front brakes - ie, you bleed the rear brakes with one of the front brake bleed valves open (and attached to a hose and fluid container so no air gets back in the front brakes - basically, its like you are bleeding the front and the rear at the same time). This bleeds the line between the rear load sensing proportioning valve and the distribution block near the master cylinder.

 

The WJ dual diaphragm booster and master cylinder is one of the best modifications I've ever done to my MJ. It stops like a completely different truck.

 

 

you shouldn't have to modify anything at all...i've done this 4 times now using '95 or '96 xj brake boosters, which are the same identical setup as the WJ booster IIRC. even if not, the '95 or '96 xj dual diaphragm brake booster does the same thing. the difference IIRC is that the WJ does not have the aluminum spacer with it.

[Comanche County]

This is the only booster swap I've done. I can't speak for the the 95'-96' XJ/ZJ boosters, but from what I've researched, the WJ boosters offer slightly better braking power. However, the later XJ boosters are also an easier install. Having owned 3x 96 XJs, I can say that now my MJ with 35s stops almost as well as a stock 96 XJ. How do you rate the stopping power compared to the older MJ/XJ boosters? I have to give mad props to you my Jeepin friend for all the work you've put on here....would you recommend the 95-96 XJ boosters over the WJ? Just wondering?

[JeepcoMJ]

I'd definitely recommend the 95 or 96 over the later....same upgrade, 100% bolt-in.

 

 

Stopping power is flat out 200% or more, if comparing to factory stop power.

[ohiostate454]

This would work for all comanche years? correct

[Comanche County]

Yes, it will work for all MJs.

 

What we really need is input from someone who has done the swap with later XJ boosters and the WJ booster on an MJ or early XJ to receive balanced feedback and can accurately compare the two. I believe the consensus is that the WJ booster is a technical upgrade, whether the difference in braking power is noticeable or not. The 95-96 XJ booster may work just as well. If your running larger tires than stock, I think you'd be better off with the WJ booster. But if you've got an available 95-96 XJ (or ZJ) booster then go for it.

[Mike Stone]

I just done this swap with a 96 grand booster and mc and was 100% BOLT ON my mj is an 86 model. WHAT A DIFFERANCE!!!!!!!!!!! LOVE IT!!!

[MiNi Beast]

my next step. :yes:

[shawn]

excellent write-up.thank you. i just happen to have a 95 parts xj so I'm looking forward to seeing how this works. looks identical to the wj one that was shown.

[Comanche County]

The 95 XJ booster should be a direct swap.

[Red 1989 MJ]

Nice write-up thank's, will be useful in a near futur

[MiNi Beast]

working on mine now, went to get my booster at jy today and someone took the plastic resevoir off it, damnit so have to get one of them, like $20 I think, but got everything else. Doing something different with the brake light switch though as I no have grinder so will try it a different way. will post pics later. :D

[Comanche County]

I imagine it would be easy to grab a different style switch from any make of vehicle and adapt it also.

 

One thing to keep in mind that flat spot on the rod has got to be real close to the original spec. If too much material is left the brake lights will be on all the time. Too little and they don't come when your foot first touches the pedal. Best to ground some off then check it and repeat if necessary.

[MiNi Beast]

I imagine it would be easy to grab a different style switch from any make of vehicle and adapt it also.

 

One thing to keep in mind that flat spot on the rod has got to be real close to the original spec. If too much material is left the brake lights will be on all the time. Too little and they don't come when your foot first touches the pedal. Best to ground some off then check it and repeat if necessary.

 

with the pedel set up I have I do not have to grind on anything nor drill the hole in the WJ rod bigger, will be using a old school ford brake switch, something about simple really makes me smile. :yes:

[MiNi Beast]

stock MJ brake swith set up vs the bolt in WJ set up with a ford brake switch

 

[Comanche County]

What's the p/n for the ford brake switch?

[MiNi Beast]

What's the p/n for the ford brake switch?

 

had it left over from my old ford I had, just look up a 79 F250 and should pop right up. :thumbsup:

My MJ was converted from manual to auto so had the manual pedals in it when I got it so pulled the clutch pedal out when first got it, then figure I swap in a auto pedal later on and now was a good time, so just pulled a pedal from a 93 XJ and everything bolted right in. and you can see no grinding/ drilling was needed. :yes:

[Comanche County]

Ohhh, I'm telling on you, big cheater... :no: :D

[MiNi Beast]

i don't have a grinder as it burned up on me so I was hoping to not have to do that and well forgot to go to work Friday and spent half the day at the junk yard and cam up with this stuff and only got me with a bill for $55. and have an extra mc :D

[com_mako]

anyone try a WJ pedal with the MC/booster also from a WJ ?????

[btm24]

I did the 96 XJ BB and MC upgrade and its an amazing difference. It takes a bit getting the right size adapters and such but well worth it.

 

Brandon

[comanche12]

I'm planning to work on it this weekend! right now during lunch break at work, I'm researching now :wrench: :cheers:

 

edit: wj is '99-'04 grand cherokee, right? if yes, can i get any either those year to pull the parts?