YJ Brake Booster Upgrade

If you have ever driven a CJ with manual brakes you know that with larger tires they really suck, especially off-road. I had read about a YJ brake upgrade on the web and decided to do it. The brakes worked like crap after the modification until I extended the rod as shown below.

I basically copied the write-up HERE with a few very important modifications (very bottom). I copied the whole write up to this page.

Many people put larger tires on their Jeeps, add winches, tire carriers ect ect. With all that extra weight what people often overlook is upgrading the means by which you stop all that stuff when going down the highway or a steep grade on the trail. The braking system is one of the most important parts of your jeep, so it is imperative that this system is addressed once you've increased the vehicle weight in order to stay safe.

There are of course several options you have once you decide that is it time to upgrade. Prices can range up into the hundreds of dollars for hydro boost setups, or full units, such as the one from Navajo, which runs close to $400. Other options include trips to the junkyard to pull a unit from some other vehicle and "adapt" it to work in your CJ. I've heard of people using brake boosters from Cadillac's, Chevy trucks, as well as others. Although I have no personal experiences with these, I'm sure all of these could work, in some form or another. However, I chose the YJ setup for several reasons. Here are a few of them:

Tools List:

	Standard Socket Set
	Needle Nose Pliers
	9/16th drill bit optional
	Self Bleeder Kit optional

This particular install was done on an '82 CJ-7 with a AMC 258 with an auto.

Install:

Step 1 - Remove the old master cylinder

If you're running the stock carter carb , I would probably take the housing off and put it to the side so you have room to work.

A. First thing you'll probably do is remove the cotter pin that holds the brake rod to the pedal. You'll need to get under the dash, and look above the steering column to find this. I've found that needle nose pliers work well in pulling it out. Save this pin as you will need it to install the new master cylinder. If it breaks, they can be purchased at your local parts store.

B. Once you've removed the cotter pin, you can go back into the engine compartment and remove the 2 brake lines from the master cylinder. A flare nut wrench works well for this.

C. Now go ahead and remove the 2 bolts* that hold the master cylinder onto the firewall. These bolts are 9/16th. You may need another person to hold the nuts that are on the inside of the firewall while you back the bolts out.
* If you're currently running manual brakes, there are 2 bolts holding the master cylinder in. If you have power brakes then there are 4. You will use these same 4 holes for the new setup. I've seen some jeeps that have the 4 holes drilled, even though they have manual brakes, and some that do not. So, some people may need to drill those 4 holes out for the new master cylinder.

D. Once the 2 bolts are out you can completely remove the rod from the brake pedal and take the master cylinder all the way out.

******This Where I added a few steps. See the bottom of the page*****

Step 2 - Install the new YJ master cylinder:

A. Basically all you have to do here is hold the new master cylinder up to the firewall in the same spot the old one was, and bolt it in. As mentioned before, if you're converting from manual brakes, you may have to drill the 4 holes into the firewall.

B. Reconnect the brake rod to the pedal assembly and put the cotter pin back in the rod. Now your new master cylinder is attached, and its time to install the brake lines.

Step 3 - Attaching brake lines:

A. Take your new brake line unions and screw them into the YJ MC. Make sure they're tight.

B. First thing you'll notice is that the YJ MC has the threaded holes for the brake lines on the opposite side as the CJ MC. There are several ways to address this, but what I do is simply bend the lines around to the other side, while keeping several of the loops in the old brake lines in tact. Be sure to leave enough clearance for the throttle linkage on the carb. You want to make sure that nothing will rub on the brakelines under any circumstances. Also, be careful bending the lines so as not to put any kinks in it. A brake line bender may come in handy.

Note: This setup is utilizing the CJ proportioning valve in its stock location on the frame rail as well as all current brake lines.

Step 4 - Attaching Vacuum Line:

When you grabbed your YJ system from the junkyard you may or may have not grabbed the vacuum line that runs from the brake booster. I'd suggest you do. But if it is not available then just go to the parts store, and get about 12" of regular 3/8" Vacuum line. You'll also need the brass adapter mentioned above. The booster needs a vacuum source to operate correctly. You can really use any source you wish. What I do is use the one above the EGR valve as seen here.

Take the end of it off, (I believe it is a 3/8" bolt) and replace it with the threaded end of your brass fitting. Then you can attach the line and run it up to your booster. Its as easy as that. The pic shows an optional vacuum source for the booster..
****See modification #2 at the bottom of the page****

Step 5 - Bleeding your brakes:

Now it's time to get the air out of your newly improved system. I'll assume you already know how to bleed brakes. Start with the wheel furthest from the MC and work your way closer. This means the rear passenger side wheel, then the rear drivers side, passenger front, and finally drivers side front. You may have to go around a few times to get all of the air out. Don't forget to bench bleed your MC if you have a new one. I have not done this on units I've pulled from the yard and I've never had any issues.

If you're not familiar with bleeding brakes, and would like some more info on that, click here.

Notes:

1. Brake lights on all the time?
As seen in the picture below, the YJ booster rod is roughly 1/4" longer then the CJ rod. In some cases, we've had an issues where the brake lights would be on all the time because the brake pedal would not make contact with the switch which turns the light off. What you can do is bend the tab on the brake pedal slightly, and then it makes contact. Problem fixed.

2. Does the pedal feel soft?
This could be a combination of things. I'd first re-bleed the brakes several more times. This is probably the main cause of a soft pedal. Also, make sure you have no leaks, and check your self adjusters in your rear brake drums. Sometimes these need adjustment. This is done by simply jacking the vehicle up and turning the little cog wheels inside your drums with a flat head screw driver.

3. Which Proportioning Valve should I use?
As far as I can tell, the answer is either one. I've used both and they seem to be identical with the exception of where they are located. In the above application the stock CJ prop valve was used. In my personal jeep, I used the YJ valve. They are different part numbers (the CJ one is much more expensive for some reason), but they both work.

IMPORTANT Modifications

*******You can do this first or wait to see if your brakes still sucked like mine did. The reviews I read had it about 50/50 for people that needed to do this. If you don't do it first then you will need to remove the MC and reconnect and bleed your brakes again.********

Modification #1

I had read online that a few people needed to lengthen the rod on the YJ part since it caused the CJ pedal to be closer to the floor. This happened with me. Originally I wasn't going to do this but after I installed and bled the brakes they still sucked. What most people did was just to cut the rod and weld a nut or spacer into it. I read where someone used a coupler and so I decided to do that also. This is a much better idea since the coupler allows the unit to be adjustable for pedal pressure. You can set it to whatever pressure you like.

Steps

You will need a 1/2 x 13 die to thread the rod and a 1/2 inch coupler (mine was 1.5 inches long) and a welder.

Cut the rod with whatever you have leaving about an inch of usable rod on the end with the hoop.
Using a 1/2 by 13 die set thread the hoop end as far as you can.
You can then either thread the end that is attached to the Booster or do like I did and drill out the coupler about 1/2 an inch and weld it to the rod. ( I didn't thread it since I couldn't get enough of a hold to do that. In the end it worked better with a weld because it is easier to adjust while on the car.
That is basically it.

The beauty of having the weld on one end is that you can simply leave everything connected and adjust your brakes If you add a jam nut then you can lock it in place once you found the right pedal pressure for you.

Here is a shot of the coupler under the dash

Modification #2

The other modification I did was to add a check valve onto the booster. I don't know why they didn't do this on the original write-up but you do need it to keep nasty exhaust crap out of the vacuum booster.( I realize the vacuum pulls air out of the booster but the check valve has many purposes) You can get one at NAPA. I just took the grommet from the vacuum booster in and they matched it. It was the most common one. Here is a picture of it. It is the white plastic piece directly to the left of the top of the MC, directly under the angle iron, with the black hose coming off of it. It is connected to the Air intake direly to the left of the overflow tank, you can see the brass plug and hose clamp.