Power brake booster for 1972 CJ5 - JeepForum.com
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post #1 of 10 Old 08-13-2020, 04:57 PM Thread Starter
ACAMS
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Power brake booster for 1972 CJ5

I need all new brakes, and found a disk brake kit, but the booster kits are all for 74 up .... what do you guy's do to put Power disk brakes on a 72 or 72 CJ5?
I was kinda wanting to put a dual booster on it so I can have drum in the rear and disk on front.


THANKS FOR ANY HELP!

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post #2 of 10 Old 08-14-2020, 06:17 AM Thread Starter
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Is there some reason why the Navajo Power Booster for 74 to 85 won't work?
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post #3 of 10 Old 08-15-2020, 06:39 AM
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I'm not familiar enough with the 72-75 CJ5s to know what issues you might encounter with a brake booster install.

But we should clear something up. The stock power brake booster on 76-86 is a single diaphragm unit. Aftermarket dual diaphragm units are available. A dual diaphragm unit will provide more power assist, meaning your brake pedal will be easier to push. Using a single or dual unit has nothing to do with converting the front to disc brakes or running disc front/drum rear. What is important is to use the proper master cylinder for a disc/drum setup. This is due to the size of the reservoir (brake calipers generally require a larger reservoir than a drum brake wheel cylinder) and the built in residual valves, which hold a slight amount of pressure on the brake lines (drum brakes need slightly more residual pressure than disc brakes). Also be sure to hook up the brake lines correctly, some master cylinders use the front reservoir for the rear brakes.
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post #4 of 10 Old 08-15-2020, 07:55 AM
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Your current master cylinder was used for many models before and after the intermediate years' models. Go to Summit Racing and look it up. There will be a compatibility listing for the models it fits. Pick a year that a CJ has disc brakes and get everything you need including the proportioning valve to convert it to power disc brakes. Everything may bolt up but as we all know and you will find nothing ever goes as planned.

Good luck!

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post #5 of 10 Old 08-15-2020, 10:04 AM Thread Starter
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Thanks for the help ... I understand my Jeep has 11" drum brakes .... I plan on having 37" tires ... I don't plan on driving fast, and I am 6'5" 270# ... I can mash a pedal .... do you think I will even need disk brakes? ..... or can I just completely rebuild what is on it?
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post #6 of 10 Old 08-15-2020, 10:37 AM
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Even with smaller tires like the 31s on our 74 with four wheel drums panic stopping from speed is marginal. I was reminded of this a couple of days ago when I had to back up to clear an intersection when a hair triggered red light caught me going too fast. The added weight of 37s plus the momentum they generate will make stopping almost impossible. You will also have put a severe lift on it and change your gears. So let me ask why do you need 37s?

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post #7 of 10 Old 08-15-2020, 11:39 AM Thread Starter
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Quote:
Originally Posted by bob4703 View Post
Even with smaller tires like the 31s on our 74 with four wheel drums panic stopping from speed is marginal. I was reminded of this a couple of days ago when I had to back up to clear an intersection when a hair triggered red light caught me going too fast. The added weight of 37s plus the momentum they generate will make stopping almost impossible. You will also have put a severe lift on it and change your gears. So let me ask why do you need 37s?

East Texas mud that goes clear to China .... and the old man who owned it before me had Q78-15 mudders on it, which are 35.5 ... it has flipped springs.
I may go with 35x12.50R15 but either way, there is not a lot of stopping difference.


Should I put a disk brake conversion on it and put the proper Master cylinder and not worry about power brakes?
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post #8 of 10 Old 08-15-2020, 02:21 PM
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It seems 37s are the new 33s.
A front disc brake conversion is a great idea.
Power brakes is subjective. Some people like manual brakes because if the engine stalls, there is no change in brake performance. A properly setup manual system can be quite effective, you may have to push a little harder- but you said you can do that. Personally, I like power brakes. If you have power steering (or can add a PS pump to your engine) you might consider a Hydroboost system. It uses hydraulic pressure from the PS pump to provide brake boost instead of engine vacuum as vacuum boosters do. 3/4 & 1 ton trucks use it. I have it on my CJ and it is a night and day difference compared to a dual diaphragm vacuum unit.

Save the 11" drum setup (especially the backing plates). They are considered an old school upgrade for older Jeep Universals. Someone would probably be interested in them. I have a 67 CJ5 that I converted to 11" drums.

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post #9 of 10 Old 08-15-2020, 03:19 PM Thread Starter
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THANKS!!! .... Since I know I need to redo the brakes all around, I think I will convert to disk front, drum rear and not add power.
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post #10 of 10 Old 08-15-2020, 04:22 PM
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Been through this with my 74 recently so I’ll chime in. I’ll apologize for the wall of text up front but this story has been 10 years in the making.

My CJ5 had four wheel manual drums on it when I bought it. I upgraded to some 32s and wasn’t thrilled with how well it stopped. Living in a city with a half million people I really felt like I needed some better stopping power so I added in an 8” dual-diaphragm booster. That was how I ran it until I undertook a significant rebuild about 2 years ago that included going to 35s. It became clear quickly my braking was again insufficient so this summer I upgraded to front discs.

That’s the short version. Here are the details and pitfalls I ran into with each iteration.

By the time I got to thinking I needed a booster I had already rebuilt my brakes on all four corners. Replaced drums, linings, hardware, wheel cylinders and bled it all down. The drums were 11” all the way around. I bought a drum/drum master cylinder and an 8” dual diaphragm booster with firewall bracket from the-jeep-guy.com. First problem out of the box was that the bracket didn’t match up with the holes in the firewall. Undeterred, I modified what I needed to and went down the road.

Overall it worked ok. The brakes were “touchy” and it was super easy to lock up if not careful. Also, any of the drums being out of adjustment made it pull one way or the other. Sometimes violently. But I was pretty broke at that point so I just dealt with it as best I could.

Recently I went to 35s and have been focused on making the Jeep drive better. I replaced the tie rod, drag link, steering coupler, steering stabilizer and ball joints. All these resulted in incremental improvements but it became obvious the brakes were the weak link. So I bit the bullet and started mapping out a disc brake upgrade.

One thing I learned is that drum brakes are “self energizing”. I don’t understand the physics of how this works but what it means is that the drag between the linings and the drums increases spontaneously with little to no more input from the driver. While this is a neat fact what’s important to realize is that’s why old cars went round for years with no booster just fine. You don’t need help from a booster with drums because of their self-energizing nature. And when you add a booster to a drum brake setup they can be really hard to modulate due to the booster exaggerating your pedal input. This is why my setup on boosted drums was touchy and I was never thrilled with it.

Conversely, discs are not self-energizing and require a booster. Running discs without a booster or not enough boost will not inspire any kind of confidence in your ability to stop big tires. This is one reason you won’t find new cars without a booster. Without that self-energizing feature discs need the booster to be effective. I ended up with some personal experience with this too but I’ll get to that in a minute.

So after shopping around I settled on the Trackick Disc Brake Conversion. I’d looked at some other conversion kits but liked the Trackick conversion because it would allow me to spread the cost over time instead of having to pony up all at once. And in the long run it was a little less expensive. I also went to a Corvette-style disc/drum master cylinder, PV2 combination valve and a Wildwood 10lb residual pressure valve for the rear drums.

Here’s where you might run into trouble with your 72.

First thing you have to decide is if you really want to boost a full drum setup. If I personally had it to do again I wouldn’t. If you held a gun to my head and made me do it, I’d definitely take a different approach and maybe think about a smallish single-diaphragm booster.

I mentioned my initial boosted drum setup had to be modified to work on my 74. This is because the firewall bracket hole pattern matches up with the pedal bracket for newer model jeeps, not what was equipped on intermediates with hanging pedals. While my modification “worked” the support for the heavier booster and putting the weight of the whole setup further from the firewall wasn’t there. This resulted in the failure of the pedal bracket and the firewall over about eight years. I’m guessing your 72 has the same pedal bracket under the dash that my 74 does. You’re likely to run into the same problems and the solution is to either reinforce the firewall somehow or change out the pedals to the late model CJ/YJ style that we’re designed to work with a booster. This opens up a whole different can of worms on an intermediate as you have to relocate the booster (and clutch MC if you’re hydraulic) to work with the new pedals.

With my disc conversion I started out using the 8” dual-diaphragm booster I had from when I ran drums and I wasn’t thrilled with how well the setup performed. After some troubleshooting I theorized that the booster was crapping out so I ordered a new 7” dual-diaphragm booster and installed it (it was inexpensive). It worked a bit better than the 8” but it still wasn’t great. Back to doing more reading and I learned that the smaller the diaphragm the more engine vacuum is required to be effective, especially under hard braking. The inverse is also true. I run a semi-tired 304 that only pulls about 15 inHg at idle. So I bumped up to an 11” dual-diaphragm from a GMC full size truck and now it’ll pull my eyeballs right out of my head when I stomp on the pedal. Remember I was talking about personal experience with not enough boost? Front discs are pretty uninspiring without a booster, without a big enough booster or without sufficient vacuum to run the booster you install.

If you’re still reading you’re probably getting that what I’m saying is there are a ton of things to consider when changing your brake system to something other than what jeep designed. You’ve really gotta think about every part of the system from the bottom of your foot all the way out to the tires and make sure they all work together. The main takeaways are be careful boosting four wheel drums or not boosting discs, make sure your firewall can handle the stress of the gear you’re gonna hang on it and research, research, research.

Hope this helps.


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