91-94 Upgraded Brake Booster Swap to 95-96 Dual Diaphram Booster/Master Cylinder.

I used the www.madxj.com write up on swapping in a newer style dual diaphram booster MC combo. The 91-94 uses a single diaprahm vac assist booster. While it gets the job done, it leaves a lot to be desired in stopping power and pedal feel/effort.

91-94 single booster

95+ dual Booster

You will need a length of brake line, a line bender, a line cutting tool, a line flaring tool, and assorted hand tools. Pair of pliers, 1/2, 9/16, 7/16, and 13mm wrenches. You'll also need a deep socket 9/16 and socket wrench. I use a small extention to help get to the top nuts. I will add what I have forgotten as I remember.

This same swap can be done with the even older renix setups on the 87-90. Not sure about the 84-86 due to the power plant options (one being a GM V6 and the other a Renalt 4cyl). I'm sure the swap can be done, but if there isn't enough manifold vac then a stand alone vac motor can be installed. Several hot rod supply places sell these units for retro fitting older old rods with vac assist brakes.

I made the mistake of missreading the madxj article and actually purchased a 97 setup. The booster rod is WAY too long. That's with the aluminum spacer on there as well. Just not doable. Didn't pay too much ($30), so no biggy, but it cost me a couple of hours of mock up and a days worth of the XJ sitting while I hit a junk yard and pulled some stock lines to go back to stock.

I later picked up a 96 off of Ebay for an unbelieveably cheap price. $5 for the combo. I am using the 97 to represent the newer style booster/MC combo, sinse they are the same execpt the 95-96 uses a shorter booster rod. The 97 booster rod was cut in an attempt to get it to fit the pedal assembly. It didn't work. This is necessary however on the older swaps. The 91+ uses a button that is activated by the pedal rod itself. The older setup uses a switch that is activated by the

booster rod end. On a 91-94 the trimming of the rod is not necessary.

Removing the old setup is easy. You will remove the pressure sensor on the prop valve by disconnecting it and then using a 9/16 wrech to remove it. It's a tight fit in there ad you need all the room you can get. Loosen the brake lines to the prop valve. I had to put a pair of channel lock pliers in the block to steady it. Those fittings are pretty tight. Once those are loose, loosen the lines in the MC. Then crawl into the cab and pull the locking clip on the peadal that keeps the booster rod on. I slid a small screwdriver under the small lip and pushed the clip off. It comes out fairly easy. DO NOT PRY THE CLIP too much. You will reuse this piece. Once off, bend the lip back down so that is will lock when reinstalled.

Pedal clip

Booster nuts

With the clip off keep the rod on the pedal. There are 4 9/16 nuts that hold the booster in place. Remove these nuts. Then remove the booster rod off the pedal. Take a bungee cord and tie off the brake pedal to the steering wheel so the brake ligts stay off.

Come around to the front and remove the fittings on the prop valve and then with a firm tug, the booster and MC will pop right out. Once out, you'll want to remove the two fittings from the old setup that went into the prop valve. You will then move on to the new setup. There are two 13mm nuts that hold the prop valve bracket to the MC. Remove those and loosen and remove the two lines that run from the MC to the prop valve. Once the prop valve is removed, you will need

the fittings that attached the lines to the new MC. So now you will have the perfect size fittings to the new MC that will attach to the old prop valve.

Old fitting to reuse

New fittings to reuse

When putting the new booster/MC in, the fit into the firewall is tight. There is a "Floating" reinforcement plate that is behind the firewall inside the cab. The booster studs are tapered, so just kind of use the taper on one side to catch one of the holes in the plate and then give it a good push in and the plate will line up. Might take a few tries, but it will go in.

Biggest issue with the newer setup is the line routing. All the XJ came stock with disc front and drum rear brakes. The older style has the proportiong valve low and below the MC, and the lines come out on the pass side of the MC. The newer style has the Prop valve right next to and under the MC with the lines coming off the Drv's side of the MC.

The stock prop valve is setup so that the front and rear lines feed off the prop valve and the fluid is supplied by the MC above it. In order to use the new Booster/MC and the prop valve, it would have required redoing the front and rear lines. Too much work! So I just decided to use the old prop valve and route the lines to the old prop valve.

This is were the cost of a quaility bender pays for itself. This was my first attempt at bending sharp angles on brake lines. I bought a cheap bender and due to time restraints, worked them up fast. I will later go back and rework the lines to have a tighter fit. I used some pieces of close

hanger to mock up the bends and lengths needed to make the conections. Then bent the lines up using them as templates. I allowed myself some extra length on the line to make up for any slop. I used a 3ft section of brake line. I cut the line in half with a line cutter (fine hacksaw will also work). I then placed the fittings on the two sections.

The lines will come preflared on the ends. I used those ends so I wouldn't have to flare more than once on each line. Flare the ends with a flare tool, being careful not to over flare the end or the outer lip of the flare will crack. Once they are flared, hit the lip edges with some fine sand paper to deburr them.

I had lost enough fluid that the MC bottle was empty. I attached the new lines onto the MC and snugged them down. Then put the ends into a cup with brake fluid in it (not a lot, just enough to cover the fitting ends). I then filled the MC and pumped the brakes once. Then refilled the MC and repeated a couple of times. Then took the lines off.

I connected the lines to the prop valve first and snugged the fitting down. Just tight enough that there was a small amount of rotation on the line was possible. I then manipulated the ends on the MC so they threaded in nice and smooth. TAKE YOUR TIME DOING THIS! Stripping these threads would be a BAD thing. Use your fingers to thread the fittings in till snug. Then use a wrench. If I remember the fittings are 1/2 and 7/16.

Once this is done, reconnect the vac line from the manifold on there and install the pressure sensor on the Prop valve. I then called my brother over and bled the barkes. I did this several times to makes sure there was NO air in the system. Overkill on brakes in Okay. This is also the best time to check your connection again and again and make sure there are no leaks.

Go in afterwards and gave it a test drive. VERY impressed with this mod. It takes about 1/2 as much pedal to stop and the pedal feel is firm through the cycle.

1. After lift with Truck tires on. 2. DIY Bored Throttle body 3. Oil Filet Adapter housing Orings 4. Clean and with new Mud Rovers 5. RRO Adjustable Trac Bar 6. Various mods 7. DIY Intake and shield 8. Added lift for 4" 9. Greased Leaf Pack wheeling 10. Cat Back Exhaust and Cat 11. B&M Trans Cooler 12. Cheap Disconnects Upgraded 13. Hidden Hitch Installed 14. AJ's Offroad Rock Rails 15. Dual Diaphram Brake Booster install 16. Offroad with rails and hitch on 17. Water Pump Replacement