Brake booster on a 75 CJ-5 with manual brakes (part one)

I wrote this up for the forum used by the jeep club I am in but figured it would go over okay here, too. I'm going to copy from that site and paste the write up into the first 4 or 5 posts of the thread here:

Mongo is a 1975 CJ-5, 304, 3 speed, side pipes, D-44 rear, D-30 front. Manual steering, manual brakes, 4 wheel drums.

So far, the only installs I've done have been a new windshield wiper motor and switch, new speedometer/fuel gauge, a 4 inch lift, drop pitman arm, a double steering stabilizer and 35 inch super swampers.

My current project is replacing the wiring harness. This morning, I finished pulling the old one, but I had to start two other projects before I can start wiring. I needed to install a dual battery tray and the brake booster. These items had to be bolted on in order to determine where the wire loom can go across the firewall.

Part one covers mounting the brake booster. Part two will cover converting a 1985 Ford E-350 van MC to use with this booster and bench bleeding the MC. Part three will cover the modification of brake lines and attaching the booster to the brake pedal.

If you follow these instrutions, you won't be able to go backbecause you'll cut the original mounting position of the MC to such a degree that it won't bolt back in correctly.

 

Removing the MC:

First, remove the existing master cylinder. Using a 1/2 inch wrench, loosen the nuts holding the brake lines in the MC. Number 1 in the picture below will show the brake lines after MC removal. Next, use a 1/2 inch wrench to hold the retaining nuts on the inside of the firewall while you remove the bolts using a 1/2 inch socket under the hood. Remember, the brake pedal assembly is connected tot he firewall and the MC using these bolts.



Number 2 shows unused bolt holes, pre-drilled in the CJ firewall. Number 3 shows the hole in the firewall where the threaded rod is attached to the brake pedal assembly, as well as the holes used to bolt the MC to same. This is important, to note: The master cylinder was mounted with the rod centered between the two bottom holes. The booster we are installing has the rod centered between four mounting holes.



The second image shows the same items from a different angle.

 

The Booster and your tools:

Originally, I was going to use a booster from a 1995 Wrangler as, "supposedly," this was a direct bolt in. After talking with some of my friends, I found out that a lot of YJ owners swap in the booster from a grand Cherokee as an upgrade (also, supposedly a direct bolt in for THAT application). Why do I want to upgrade to a booster that other guys are upgrading away from? Having said that, I can't say that the 95 YJ booster is a direct bolt in, either, as I had to cut the firewall to mount this one.

As I said, this booster is from a 95 Grand Cherokee. Number 1 illustrates the mounting issue I mentioned in my prior post.



The second picture shows the tools I needed for the install, except for the fire extinguisher, which is mounted on either rear fenderwell on Mongo.



1 Flat grip channel lock pliers. This tool is great for working a piece of metal back and forth when you can't cut through it completely.

2. File. Used to remove burs and sharp edges after cutting

3 Air cutter. Some saws are better but I had my hands on this when I started.

4. BF Hammer. Used to "persuade" stubborn bolts that don't want to back out of a hole when you've removed the nut. Best when used with a punch or screwdriver.

5. Dremel: used to smooth sharp edges from a cut, grind away small amounts of metal in a tight spot.

6 7/32 drill bit, used to drill pilot holes

7 Tough drill, used to drill holes in the firewall.

8 Safety glasses: My Grandpa always used to tell me about an accident that his brother Clem had in the army in WWII. I always wear safety glasses, even when they fog up.

9 Fire extinguisher: The air cutter and Dremel throw sparks when you cut metal. About a foot and a half to the left of the area you are cutting, you've got your fuel induction. Sparks plus gas equals fire.

 

Cutting the firewall

Cautions:

You'll notice a large hole to the right side of my cut. This hole is where the wiring harness bulkhead is found in most jeeps. Because I've pulled my wiring harness and removed the dash, I didn't have to worry about my wiring. The air cutter throws a LOT of sparks. You should put up something to act as a shield to prevent sparks from burning your wiring. A shield to keep sparks away from fuel lines and your carb would also be a great idea.

In the picture below, number 1 shows the original, unmodified mounting holes.

Number 2 shows an enlarged, U-shaped cut made with the air cutter, then filed and de-burred. You cut the U-shaped notch because the rod is centered between the 4 mounting studs on the booster. The brake rod in the booster is larger than the original, so you need to make the hole bigger. You file and de-bur because the rod has a rubber boot. You don't want the boot cut during the use of the brake pedal.

Number 3 shows the bolt holes used to mount the original master cylinder. Using a small drill bit, I made two pilot holes below the original hole, the first half an inch below the original hole, the second, half an inch below that. I then used the large drill bit to drill additional holes, making a one and one half inch vertical slot. Using the air cutter and the Dremel's de-burring tip, I widened the indentations (drilling round holes doesn't make a slot by itself) in order to make the slots functional.

Let me explain why I did this. If you insert the top two studs and the rod into their respective holes, from the top, having slots for the lower holes means you don't have to force the booster in from straight on, which means that you need less room to remove and install it in case of part failure. Right now, this isn't necessary on Mongo. I'm about to convert from manual steering to power steering, so I need room for my power steering pump and my Dukes of Hazard air horn. I can save five inches of effective space, which is precious when you consider the larger MC going in, the pump, the booster, and 5 plastic horns of various lengths.



The second picture shows the same cuts from a different angle and without text in the way. Note that the surface should be sanded and painted (cheap rattle can paint is fine) to prevent rust, which you saw when the MC was removed. Do you want your brake pedal to rot off because of rust?

 

Booster mounted:

Number 1 shows the booster mounted flush against the firewall. I'm going to use a thin sheet of rubber with cutouts, along with gasket cement, to seal the firewall and the booster. I am about to replace the wiring harness and, at the same time, I am trying to waterproof the jeep. The gasket and cement will keep water out from my chop job.

Number 2 shows the loop for the wire loom. Now I know where I can run the wires along the firewall.

Number 3 shows where the harness bulkhead will be installed.

Number 4 shows what real Jeeps are made out of. if you have a real jeep, it will have stickers of similar color and style on any valve colors.



The second picture shows the booster mounted from a different angle.

 

Excellent writeup and photos.

 

Funny, my heep is just like yers, but I don't have the phansy chrome valve covers... R)

 

I had to do something frilly since I don't have a pretty pink avatar :twisted:

 

I could give you a pretty pink avatar if you'd like... Just another of our services here... R)

 

Mongo,

I am in the process of converting my 56 Cj5 to 11" brakes and I'd like to install a firewall mounted manual M/Cyl. with dual chambers. Looking at your pics, above, it looks like that's what you took off to be replaced. So maybe I should be looking at a 75 CJ5 as a donor vehicle for my setup. A couple of questions on your original setup:

1) What is the distance from the point where the brake pedal pivots to the point on the pedal arm where the m/cyl rod connects?

2) What type of clutch mechanism do you have? Cross tube, hydraulic, etc.? Is yours the model that has a firewall mounted clutch pedal with a rod that goes straight down to the clutch linkage under the floor?

3) What years of CJ5's have the same setup as your original?

Thanks for any info you can provide.

tommy b