I'm looking to do a brake upgrade on my GF's 79 CJ-7, but had a few questions that I couldn't find clear answers on after searching. First the CJ-7 already has the stock CJ brake booster, my question is does a Master Cylinder from a 86 Ford E350 directly fit the stock CJ brake booster or is does this master cylinder only bolt to the YJ brake booster? Same question for the 78 Mercury Marquis and 69 Chevy Corvette Master cyclinder as according to my searches these also might fit the stock CJ brake booster. Also from what I read the 95 YJ brake booster is the only year that was dual diaphragm and therefor better, so is a regular YJ brake booster that much better than the stock CJ brake booster? Thanks in advance for any help. :cheers2:

Thanks again,
Fred R.

Fred why does it need more hydrolic pressure? Does she have huge tires on the thing?
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

BigJim,
She does have 33's on the CJ but from what I have read, stock Jeep CJ's braking performance was already sub-par and thus adding the additional mass of bigger tires make for very poor brake performance. Right now as it is, she has to hit the brakes pretty hard and it goes almost to the floor. I have bled the brakes myself several times and then took it to a reputable 4x4 shop to get bled and after bleeding them they told me that the braking system needed to be upgraded and that it's current state is the best it will ever perform. When the jeep is in low range offroad it is very difficult for her to stop, on road it's the same thing as she has to start braking way in advance because of the brakes.

Thanks again,
Fred R.

Fred it is the 33's that are causing the problem. Check the advertised pressure to see if there is a difference before installing a different master cylinder.
In order to get 165 ft. stopping power back again you may have to upgrade the complete system.
The taller the tire is the more hydrolic pressure it will take to press the discs/shoes into the rotors/drums.
And the more pressure used the quicker the steel will wear out.
I'm thinking a couple of grand for a complete new system would be needed to get them 33's to stop as desired.
Others may prove me wrong.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Sounds like it is time for a disc brake conversion....

The assumption here is it is equipped with drum brakes all around.

I did a brake "improvement" by just replacing the drums on my old CJ5. Drums can be turned to the point where it will take more pressure to stop and a few thousandths of an inch on the drum does make a different.

So, new drums may help; however, an entire brake system upgrade may be necessary.

I have a '79 cj5. When I got it, it had manual brakes. I swapped in a jeep cj power booster/master cylinder setup. I also went from 32" to 33" tires. It stops real well.

There are writeups on doing a YJ booster installation in a CJ. It's supposed to be a step up from the CJ booster.

Moses Ludel says says NOT to put too big of a master cylinder in a small vehicle.

Totally confused, (oh wait...) anyhow, we build jeeps with 37" to 42" tires and run stock masters and boosters.
Even suggesting that a 33" tire is "big" is funny

Stopping power is proportional to the caliper, to the tire diameter, to the pedal ratio, and last and least is the bore of the master or diameter of the booster.

SD

I agree with you. The comment by Moses Ludel that another poster quoted was referring to stock Jeeps - when offroad, putting in a big braking system when operating on loose surface might lead to easy lock-up.

However, with larger tires, the increased rolling resistance, lowered leverage, and increased rotational weight can really benefit from an improved braking system.

Rather than go with rear discs or increased efficiency calipers when I went to 35" tires, I elected to go with improved brake fluid pressure application. I converted my CJ7 from manual brakes to power brakes by using a VANCO unit, which uses a Chevy pickup dual diaphram vacuum booster coupled with a 1968-1972 Corvette master cylinder, along with their custom push rods and mounting brackets. Has worked great. If I want to, I can lock the brakes at 45 mph on pavement. I have a bad foot, and the abiity to get good braking with significantly reduced pedal effort is a plus for me.

Good job Bob. Stopping is all about enough pressure to push the pads into the discs/drums hard enough to make the tires stop rolling. Using larger pads might help in some instances. The taller the tires are the more leverage they get over the stock brake setup.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks BobRowe,
That seems to be what I'm looking for. The jeep has D44's front and rear so it has disks. I can stop the jeep just fine as I'm used to how jeeps handle and brake with larger tires, but my GF is not used to driving a vehicle with what some would consider sub-par brakes. I've pretty much narrowed it down to master cylinder from Mercury Marquis or a 68-69 vette as from what I have read these bolt up right up to the CJ's stock brake booster... I'm figureing that the increased fluid volume should help out with the braking, if not I'll just upgrade the booster to a unit out of a YJ. I haven't had a chance to mess with it as it's been pretty cold and I've been busy with work.

Thanks again,
Fred R.