brakes

Hi all, and thanks for the welcomes. I'd like to put power brakes on my 75 cj. I have a master cylinder and brake booster from a 75 wagoneer. I need to know what other parts I'm going to need. Will this work without the propotioning valve? Do I need disks on the front? I have the 304 with 31x10.50s and I don't plan on running anything bigger. Any advice will be greratly appreciated. I'll post pics as soon as I can figure it out.

 

I think the brake parts from the '75 Wagoneer won't work. It's a master cylinder (MC) for front disk brakes, and the power booster is probably too large in diameter to clear the engine. Wagoneers have a lot more room under the hood than CJs.

Here's a '72 Commando with power brakes: http://www.nmr.mgh.harvard.edu/~reese/Commando_under_hood.JPG The CJ setup looks like this too. CJs from this era had power brakes optional - both my Jeeps had full power. It seems that Jeep didn't sell many CJs with power brakes though, since all I've seen on ebay and elsewhere have had manual brakes.

The easiest route would be to find a CJ or Commando of this era and take the stock parts... I think you'll need to do a lot of searching and pay a lot to go that route.

If I were doing it, I'd use the stock PB MC and an aftermarket booster. Here's one place you can get the booster; I'm sure there are others. http://www.kugelkomponents.com/products/brake_systems/brakesystem.html It will require some cutting and fitting though.

 

I converted to power discs on my 72 this spring. I bought the disc setup on ebay from a 78 d30. I bought the booster/MC/prop valve on e-bay as well it was from a later model wrangler and fit nicely without any mods just bolted in. 8)

 

Thanks for the info. Guess I'll have to do some looking around. Not may CJs in the wrecking yards around here.

 

I bought and put on a MC/Booster from a YJ on my 73 cj5 and it worked with minimal modification. The push on this is about 1/4" too long and hence the brake switch would not trigger. I little mod to the brake switch and it works great. I am still running 11" drums all around but can stop much better than before. Next will be the front disc and crossdrilled drums.

 

Go to Jeeps Unlimited (www.jeepsunlimited.com). Scroll down about half way, maybe a little more. There is a good article on the upgrade. It is one I'm getting ready to do myself and I'll be using the article as a guide.

 

If you run the S10 setup like I have then you would have to swap to disc as it's a disc brake M/C. However the power booster would work I guess. Would take some modifying and it is close to the valve cover, although mine is a 69 with a 4.3 V6 so i'm not sure of other clearance issues you might have with your. Easiest thing to do is measure from the top of the valve cover to the center of where your master cylinder (bore) is, double that number and subtract about an inch for clearance you would probbaly be close. That's what I did for mine. I think it was like 6 inches from my valve cover to the cneter bore area in the firewall. I doubled that to 12 inches and took off 2 inches which gave me a booster of 10 inches. Disclaimer: Don't quote me on these measurements as exact It's just to give you an idea.

 

OK, this may be a dumb question, but what is the difference between a MC for drum brakes and a MC for disc brakes. If you used the MC for disc brakes on a drum brake setup, what would it hurt? Is it just putting too much pressure to the front to adjust with the proportioning valve? The main reason I ask is that I have drum brakes at all four corners and for now (just don't have the cash to swap out) I need to keep it that way. I'm going to begin searching for a MC/booster combo at the local yards and need to know for sure what to look for. Thanks.

 

What everybody refers to as a "proportioning valve" is actually, basically a distribution block. Factory units are not adjustable. the factory units you see with the wire coming out of them are actually just a way for the system to tell you if there is a pressure differential between front and rear braking systems. If you have a failure of either the front or rear brake system, then it causes a piston inside the block to move to one side or the other activating the switch (wire). I think the biggest difference between a 4 wheel drum brake M/C and the disc version is the amount of fluid the disc reservoir holds. A disc brake caliper probably holds at least twice as much fluid as a wheel cylinder. Also the front disc setup works at a higher pressure than front drums, which I think is built into the valving of the M/C.

On a positive note though, you should be able to use your existing M/C and just add in the power booster. I have done this with cars before. The M/C will likely bolt right to the booster, as long as you stick with american (bendix) style boosters. Sometimes you will find that the sensitivity of your brakes will go up quite a bit though. One of the fixes for this is to move the pivot point on the brake booster arm higher (further from the foot part of the pedal). Take this into account while looking for a booster. Usually the OEM booster for your model will already have this compensation allowed for in the mounting.

 

Thanks for the tip on that article. I'll go check it out when I'm done here.

 

Your welcome on the article.

Johnny:

Don't mean to keep harping on this, but I still have more questions. The proprtioning valve is not actually a valve b ut a distribution block? OK, that being said and understanding that disc brakes work at higher pressures, will using a disc brake MC harm a drum brake system or is the pressure simply high enough that the brakes will always lock up and become dangerous? I'm also looking into some brake proportioning valves from summit. They can be dash mounted and the braking characteristics can be changed on the fly by adjusting the valves. First things first though, I need to locate the proper MC booster combination. While I'm at it I will also be replacing all of the brake lines. After the scare I had last trip out, I'm not taking any chances.

Thanks for the info

 

Yes it's really just a safety warning/distribution block. It does not compensate for pressure back and forth. The front and rear fluid reservoirs are always seperate. I am by no means an expert on the subject, but from what all I have heard I have never tried to run a disc master on a drum system or vice versa. For as cheap as a master cylinder is it's not worth putting together a system that won't work when you need it most-IMHO. I would think that if you were to use a disc M/C on a drum system, that the front wheels would lock up almost instantly.

If you ever take a M/C apart, you will see 2 different pistons that are sperate from each other. The first piston does push against the second piston, but the position of the orifices in the body of the cylinder are different between the 2 M/C's. I think that as you push on the brake one starts to build pressure (to front) before the other. That being said, I think (uh oh there we go again) that the disc M/C builds up pressure sooner than the drum M/C.

The adjustable prop. valves you are referring to in Summit. Is it the one with a single knob and 2 fittings? In and out? I think those are designed to go in the rear brake line to adjust to keep from having the rear wheels lock up on you.

If it were me I would just keep the existing 4 wheel drum M/C since you are keeping drums for now and just add in the booster. Then when you do eventually change over to disc, just get the correct dist. valve and M/C. When I swapped over to disc on mine I just got the booster, block, and M/C from the 4 wheel drive S10 blazer.

I hope some others will chime in that know more about this stuff as well. Remeber err on the side of safety.