One ton xj brakes issues!!!!

Slut99 said:
Also the rear brakes will lock up and slide way before the front get good pressure
Click to expand...
That's a proportioning issue.

To get my brakes to feel great, I ran pushrod bolt out alot, then tested and adjust to get the feel I wanted.

Too far out, and the brakes lock without much pedal travel.

Too far in, it takes too much pedal travel to get them to lock, and feel like the front only start working when pedal is near the floor.

It the middle of all that, I adjusted and set my adjustable proportioning valve, so that the rear locks up just barely before the front.
 
When I went to four-wheel discs with four-piston Wilwood calipers at each corner I did the calculations for the stock hydraulic ratio then worked the math backwards to figure out what my new master cylinder needed to be. I ended up at 1-3/8" bore which the SuperDuty F-250s were using in the mid 2000s. A nice modern aluminum alloy master with a plastic reservoir.

I recommend you go figure out what your stock hydraulic ratio is (caliper piston area / master cylinder bore area), then figure out what your new calipers are and use the ratio to determine what your new master should be. Remember that there is also a mechanical leverage ratio tied to the linkage connected to the pedal that cannot be adjusted. The pushrod advice above is also spot-on, the easiest way to fix that once you have the new master is to measure the mounting surface to bottom of bore distance and replicate that with your new master cylinder. I also recommend finding a modern master cylinder to use. Those old cast iron MCs work but look like crap, leak around the reservoir seal, and are really heavy compared to something from the last decade, and there are a ton of choices out there. Mine is light, doesn't leak, and has a sensor/plug for fluid level which I was able to get the pigtail for and patch into my factory harness for the idiot light.

My brakes are great, stopping a truck that is quite literally in excess of a ton heavier than stock and still running the stock booster.

Read over this page for a more detailed write up of what I am talking about: Brake Upgrade

Also Pirate has a good article: Pirate4x4.Com - The largest off roading and 4x4 website in the world.
 
Last edited:
When doing the axle swap on mine, I used a 2001 Dodge 3500 MC. I bought a 1/4 28 grade 8 bolt from Fastenal and then measured for the correct length. I rounded the head of the bolt so that it fit into the MC. I also swapped to a 95 Cherokee brake booster because my stock unit was a single diaphragm. For the proportioning valve, I pulled the guts out of a 97 V8 Grand Cherokee prop valve. Essentially, the only real difference is the spring rate of the inner springs. What this allowed me to do was have the same braking proportions as a stock 4 wheel disk V8 ZJ. A Grand Cherokee is a tad heavier than a stock Cherokee so with the added weight from the new axles and tires, I was just over the weight of a stock V8 ZJ. Worked out great. The brakes are very effective. Coupled with my rear traction bar, I can lock up the tires and still keep the rear from wanting to topple over the front.
 
Back
Top