CJ Brake Upgrade -

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CJ Brake Upgrade

#1 Guest_Mongo_*

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Posted 23 December 2005 - 05:28 PM

This post is for JimB, who said I should write up what I do for this forum, no matter how small the install :2thumup:

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.

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.

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.

#2 Guest_Mongo_*

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Posted 23 December 2005 - 05:28 PM

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.

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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 tot he 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.

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

#3 Guest_Mongo_*

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Posted 23 December 2005 - 05:29 PM

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.

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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.

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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.

#4 Guest_Mongo_*

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Posted 23 December 2005 - 05:29 PM

Cutting the firewall


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.

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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?

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#5 Guest_Mongo_*

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Posted 23 December 2005 - 05:29 PM

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.

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

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#6 User is offline   Jim B 

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  Posted 24 December 2005 - 08:30 AM


You've really outdone yourself, :amazed: :gossip: I enjoyed reading and learning a bit more about the CJ.

I got one question.... that booster is huge, I take it you upgraded for more power, is there that much difference vs the stock from what you have found out? What percentage would you say :2thumup:
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#7 Guest_Mongo_*

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Posted 24 December 2005 - 10:28 AM

Beaver the cat (my hurricane kitten) decided that the answer I had typed up wasnt right. She jumped on my laptop and hit an ALT-F4 combination, among other keys. Gotta love cats.

Anyway, I had manual brakes which just weren't good enough for 35s. I haven't finished the brake project yet, so i haven't tried them out to see what sort of difference the incremental canges will make. I will follow up with writeups on my other projects, though, and let you know what the end result was.

And yes, I got this booster mainly because YJ owners will sometimes upgrade their unit to tis one as an upgrade.

#8 Guest_Mongo_*

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Posted 29 December 2005 - 08:38 PM

I came to another roadblock while re-wiring Mongo today. The optimas and the dual battery relay haven't come in yet, so there isn't much more I can do on the wiring harness. I wanted to get in a few hours worth of work, though, so I went back to the brake system.

recap: Mongo is a 75 CJ-5, 304, t15 transmission, manual steering and manual brakes. I've mounted the vacuum brake booster from a 1995 Grand Cherokee. The next step is to add the master cylinder from a 1985 Ford E-350 van. I chose this MC because I anticipate installing a disk brake conversion on the front brakes far sooner than the rear conversion and the rear chamber is significantly larger than the front. Once I do the rear conversion I'll switch to the master cylinder from a 1969 Stingray.

#9 Guest_Mongo_*

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Posted 29 December 2005 - 08:40 PM

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In this picture, you'll note that I've clamped the MC in a standard bench vise. remember when your Dad would yell "do as I say, not as I do!" when you were a kid? This is the same principle. The body of the MC can be distorted if you clamp it too tightly. Since my drill press isn't large enough to handle this MC, I cheated and clamped it in the vise. Whatever you do, don't clamp it around the cap as this will distort the metal before you've tightened the vise enough to hold the MC still for drilling.

Select a drill bit that is larger than the hole you're drilling out. It's a matter of personal preference here, as the holes only require a slight enlargement. If you run the drill in reverse, it won't get stuck (as it may running forward). Once you've got the new hole started, you can put it back in forward and apply greater pressure.

This picture was taken after starting the right hand hole. You'll note a small difference between the hole on the left and that on the right.

#10 Guest_Mongo_*

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Posted 29 December 2005 - 08:41 PM

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Once the holes are drilled out, you can see that the MC mounts flush against the brake booster with no additional grinding required. It is possible that, in other combinations, you'll need to grind the flanges outside the bolt holes. If this had been necessary, I would have hit it on a bench grinders wheels a little at a time. When you are trying to make a mounting surface flush, Take as little as possible of it at a time. It's a lot harder to grind the entire surface down to flatten it if you take off too much while grinding the edge of the flange.

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This picture is another angle of the test mounting, now it's time to bench bleed this guy!

#11 Guest_Mongo_*

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Posted 29 December 2005 - 08:44 PM

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This is just a 1/4 inch extension from a ratchet/socket set. Use this to push the piston in.

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This angle shows the extension inside the piston. The MC is again held in the vise used to hold it during drilling.

Fill each cylinder of the MC reservoir half full of new brake fluid. Push the socket extension in 3/4 to 1 inch within the piston and hold it for 20 seconds. Slowly, release the pressure, which allows fluid to be drawn into the channel and wait 20 seconds, which will allow air to bubble up to the top of the channel and into the reservoir. Repeat the process until all of the air bubbles are free. Gradually, the depth you are able to depress the piston will decrease to about 1/8th of an inch. Once there are no bubbles returning to the chamber, you've finished. Now, mount the MC on the vacuum booster, connect the brake lines (as quickly and neatly as possible.. the air you introduce here has to be bled out at the tires), and bleed the system. All done!

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#12 User is offline   JeepinIan 

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Posted 31 December 2005 - 09:25 PM

To bleed master sylinders, I get a bleed kit from NAPA. It has plastic connections that screw into the portws on the side of the m/c and a short piece of hose that you route back to the reservour. No lost fluid that way.
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#13 Guest_Mongo_*

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Posted 01 January 2006 - 01:17 PM

Most MCs you get these days have the plugs in place so that you can bench bleed them this way. I've done it both ways and I find this way easier, plus I don't make a mess since I only fill the chambers half full.

#14 User is offline   kurplunk 

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Posted 28 February 2009 - 01:21 PM

This is a really great write-up, and I actually plan on doing it to my '79 CJ7... My only question is what you did for the brake pedal? Did you use a grand cherokee pedal? Or did you adjust push rod going into the booster to accomodate your stock brake pedal?

Also.. what were the improvements you noticed with this upgrade? I'm really interested!

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