Having converted my TJ from manual to automatic with a nice low gear ratio I was shocked to find that the standard brakes lacked any real stopping power.  Even when stopped trying to hold the Jeep back when in low gear required an amazing amount of brake pressure. I started out looking for a rear disc brake conversion but having done one on my CJ-7 was still doubtful about their effectiveness.  I came across this article by Ron who's gearbox swap I'd copied.  I spoke at length with Harold Off about his kit for TJ's which consisted of a new master cylinder and booster (servo for us Brits).  They also supplied all new brake pipes and fittings making the installation nice and easy. 

Many of our regular readers are familiar with the many upgrades I have tried on Project Money Pit. Starting with a Dana 44 axle swap and 33" tires 5 years ago, I've gone through several brake upgrades trying to find the perfect setup. My braking system was working well after a swap to a full-size Ford passenger car master cylinder, so I thought I was finished. Then, I caught a bad case of upgrade fever last summer, and went through another round of axle swaps (see the Project Money Pit page for all the details). The new axles use Full-size GM disc brakes front and rear. At the same time I also upgraded to 35" Goodyear MTR tires. My YJ's braking system could handle the extra weight for day to day driving. Once I was in low range, however, the 5.13 gears and 4.3:1 transfer case made staying stopped on the trail a real challenge. The fact I was now running an automatic transmission intensified this effect. Add all of this to the larger piston size on the GM calipers, and it was time for another brake upgrade.

How to make it stop

One of the more common braking system upgrades for trail vehicles is swapping in a Hydroboost system. This system uses a master cylinder that is connected to the power steering pump for added pressure. While this works well on a trail rig, on the street the brakes tend to be too touchy for liking. They just lock up too easy. Since I had already upgraded the master cylinder, the only option open to me was to upgrade the brake booster itself. I didn't have any luck finding a junkyard swap for the stock YJ booster, so it was time to call in an expert. Harold Off and his white Jeep Scrambler are well known in the Southwest rock crawling scene. A steady stream of hard-core rigs comes out of his shop, Off Again Automotive, in Farmington, NM. One of the shop's specialties is the Navajo Brake Booster. This dual diaphragm booster and master cylinder combination is a direct bolt-in for a wide range of Jeep vehicles. After several informative conversations with Harold, I decided his was the setup I would go with.

The installation of the 9"; (an 8"; booster is also available) dual diaphragm booster couldn't have been easier on my YJ. The first step was to remove the stock booster and master cylinder. I first disconnected the rod from the brake pedal. Then I could disconnect the brake lines from the old master cylinder. All that was left was to unbolt the stock booster from the bracket on the firewall. Once I had removed the assembly from my YJ, I could measure the brake pedal rod length so I could make sure it was the same on the Navajo Booster. The new rod length is adjustable, but Harold had preset the length perfectly. The booster and master cylinder were shipped bolted together. I separated them so I could bench-bleed the master cylinder to remove all the air. This is simply a matter of filling the master cylinder with brake fluid, and using a long screwdriver to force the air out. Next I bolted the booster to the firewall bracket, and reconnected the brake pedal rod. The master cylinder could now be bolted to the Navajo Booster. The master cylinder was bled again to ensure no air was trapped in the system. As part of my axle swap, I had removed the stock proportioning valve since it was not designed for 4-wheel disc brakes. It was replaced by a Wilwood Engineering adjustable proportioning valve in the rear brake line to balance the front and rear brakes. The front brake lines had been replaced with a single drop brake line at the center of the axle. The line was split at the differential and connected to the front calipers with braided stainless steel hoses. Once the brake lines were connected, it was time for a thorough brake bleeding. Starting at the farthest rear caliper, each caliper was bled until no air was left in the system. The whole install took about an hour.

Test drive

It was now time for a test drive. I first tried it out on a gravel road in back of the shop. After adjusting the front to rear brake balance, it was time for a real road test. The difference was simply amazing. I could easily lock up my 35" tires from 60 mph. The braking system was as responsive as any 4 wheel disc system I had driven. Once back at the shop it was time for the low range test. I locked the hubs and put the transfer case in low range. I could easily stop while creeping across a hard surface, and with a little effort I could keep it stopped. I'm geared so low that Harold told me that it would be next to impossible to keep my YJ stopped for long periods of time on hard surfaces without some effort. I was pleasantly surprised to find out how little effort it took. With the automatic, I could easily put the transmission in neutral if needed. All in all I fell this was a huge improvement. I wish I had upgraded to the Navajo Brakes a long time ago.