CJ Master Cylinder Upgrade

[cj5Dave]

Is there a bolt-on master cylinder upgrade for 76-86 cj's running one ton brakes? (stock D60 front and caddy rear)
I'm sure that the stock one on my 79 cj5 won't move enough fluid.
It would be sweet to have one that would bolt on to my stock booster.
I checked FAQ and searched but didn't find anything useful for this specific question. If you have a thread I need to read please post it.
Thanks in advance and flame away
Dave

[SanDiegoCJ]

IIRC it's a late 70's - early 80's Corvette master cyl. and booster can.

[Meyer]

search under corvette, was an easy swap for me

[JeepinDoug]

I'm running 1/2ton calipers in front, Exploder calipers in rear, an S10 dual diaphram booster, 68 Vette power m/c and the Jeep booster mount. Just had to massage the rod lengths and I lock up 37s easily. But like all vacume boosters, the brakes feel a little squishy. Besides the rod mods it was a direct bolt on.

[BlueCJeep]

I used the m/c from a '79 Firebird (w/ 4wheel disc option). Bolted right up to my '85 CJ with power brakes. The chambers in the m/c are reversed so you have to switch the brake lines. Super easy upgrade. I am running 4 wheel discs and they work great.

[bigchevy81]

im running the same set up as BlueCJ ive got a 60 up front and 14blt w/ 1/2t cali on it and im not happy with it im looking for somethin new to try now

[78304CJ-7]

I have a 68/69 Vet MC ready to go in my CJ. Will prob tackle it this week. Running Ford 60 dual pistons in the front anc 79 Chevy 1 tons in the rear. What did you have to do to the rod?

-RJ

[bigchevy81]

i didnt do anything to the rod, it bolted right up

[JeepinDoug]

Originally Posted by 78304CJ-7

I have a 68/69 Vet MC ready to go in my CJ. Will prob tackle it this week. Running Ford 60 dual pistons in the front anc 79 Chevy 1 tons in the rear. What did you have to do to the rod?

-RJ

Both rods will probably need their lengths adjusted. The pedal rod with my S10 booster needed a length change and the CJ yoke welded to the rod. The mating rod between the booster and m/c need a length adjust ment also.
I can't tell you how much, it's all cut and fit stuff.

[bobdog]

The 77-82 Corvette MC bolts up to the CJ Booster(80s CJs for sure but I have no first hand experience with the 70s CJs) with no rod length changes. The 79 Trans Am 4WDisc MC will also bolt up.

[Wes in TN]

Perfect timing on this thread. I was about to start researching this today. My father just bought a '79 CJ7 with a Dodge 44 front and a Ford 60 rear with drums and the Jeep needs a new MC. Can anyone confirm these MCs will bolt to the pre-80s CJs with power brakes? I had a friend recommend the MC from a '78-'79 2wd GM truck, would this be a better option since it still has drums on the rear?

[Meyer]

Corvette had 2 options, 4 wheel disc or front disc/rear drum.

I have the late 70's 3/4 ton chevy calipers all the way around (14 bolt in rear) and it locks up my 38.5's no problem. NO booster either.

[78304CJ-7]

What are you running for a propotioning (cobination) valve on that setup Meyer? Wondering if I am going to have to go with the adjustable one or not.

-RJ

[JeepinDoug]

Originally Posted by 78304CJ-7

What are you running for a propotioning (cobination) valve on that setup Meyer? Wondering if I am going to have to go with the adjustable one or not.

-RJ

You're asking Meyer but I'll answer for me, nothin, no porp.

[VancoPBS]

This is a copy and paste from another post, I am posting it cause I see another guy is not using a prop valve, which I personally am agasint (but to each his own).

First off is the duel job of a proportioning valve. I explained the how it holds pressure but it has a much more important job that I like to stress. You guys remember the old vehicles that came with single piston master cylinders. As we call them, suicidal master cylinders. Problem with these is once the 1 cup failed all your brakes failed, time to downshift and hit the e-brake and pray.

So along comes the duel master cylinder to solve this problem. If 1 cup fails then half your brake system failed and the other half will stop you. All good in theory but it’s only half the story. Those 2 pistons in the master operate together. If 1 fails they BOTH fail to the point where you can’t stop the vehicle. You guys have all heard this story right?

“I was driving down the road and was coming to a stop when my brake pedal hit the floor. I panicked and pumped my pedal and was barely able to come to a stop. Scared the crap out of me”.

This is what happened.

1. A master cylinder cup failed and both pistons followed each other and you lost all brakes.
2. Both master cylinder lines are attached to the proportioning valve; these lines put pressure on both sides of a piston inside the valve that’s sole job is to do nothing when you have pressure on both sides.
3. One side of the master cylinder had pressure (the good side) the other side did not (the failed cup). So the piston’s second job came in. That’s to be slid over by the pressurized side to block of the port to the bad side.
4. Now your good side of the master cylinder will operate enough to stop the vehicle. The bad side is blocked off and the good side can put the pressure out to your brake system instead of through the bad piston.

I stress this for a reason. I see many guys removing their proportioning valves and replacing them with metering valves. When you do this you just went from a duel master cylinder to a single (suicide) master cylinder. If you feel you have too much pressure and would like to put on a metering valve to fix it, go ahead. Just please leave the proportioning valve on, don’t remove it.

Note: If you need a metering valve there’s a reason. They where designed for racing vehicles not as a “fix” to your brake systems problems. Best bet if your modifying your brake system is to do what GM, or Ford, or the like did. Decide on a front caliper, see what the manufacturer used for the rears and use the same sizes. They did all the testing and engineering for you, take advantage of it.

[VancoPBS]

As for the corvette m/c, yes it has 2 listings. Tell the guy looking it up to look at the numbers, they are the same. 2wd and 4wd M/Cs are the same, the prop valve is what's different. You can use it on cjs, reverse the lines do not adjust any rods.

[Wes in TN]

There have been two date ranges for Vette MCs listed. Which is better 68-69 or 77-82?

[Meyer]

68, no proportioning valve

[bobdog]

Originally Posted by Wes in TN

There have been two date ranges for Vette MCs listed. Which is better 68-69 or 77-82?

For use with a CJ booster the 77-82 is a bolt on, the earllier ones have too deep a hole in the piston and will not work without rod modification, if at all.

[Wes in TN]

Looking over this thread and searching past threads there are completely different and conflicting answers about each of these MCs. Some say the 68-69 bolts up, some say the 77-82 bolt up. Some say to switch the lines coming out of the MC, some say don't. It's obvious there is some confusion. I guess I'll just buy both, see which will work the best, and take the one I don't use back.

[VancoPBS]

No reason to buy both. 77-87 CJs you need the 77-82 M/c. 75 and below you need the 68-76 m/c.

M/C lines work like this. The jeep used the primary piston for the front brakes and GM used the primary piston for the rear brakes. It really doesn't matter too much. but if you reversed the lines and went the way GM did the lines fit. If you leave them the same you need to buy fittings.

Been doing this for 20 years, have sold over 10,000 of those m/cs. I use that m/c in a ton of my kits.

[Wes in TN]

Originally Posted by VancoPBS

No reason to buy both. 77-87 CJs you need the 77-82 M/c. 75 and below you need the 68-76 m/c.

M/C lines work like this. The jeep used the primary piston for the front brakes and GM used the primary piston for the rear brakes. It really doesn't matter too much. but if you reversed the lines and went the way GM did the lines fit. If you leave them the same you need to buy fittings.

Been doing this for 20 years, have sold over 10,000 of those m/cs. I use that m/c in a ton of my kits.

Finally, some clarity. Thank you!

[RickyCJ7]

I am using a master and booster from a YJ 1994, bolt on, only the return line have to change the fiting.
Running dana 44 HD and 14 bolts with 3/4 ton disc brake.

Ricky

[CSP]

Originally Posted by VancoPBS

No reason to buy both. 77-87 CJs you need the 77-82 M/c. 75 and below you need the 68-76 m/c.

What's the reasoning for this? I have the '68-76 m/c in my '75 and still had to get a longer rod. This is with a manual m/c. I'm just curious why you're differentiating between the two or more importantly saying that the '68-76 m/c is a bolt in for pre-76 CJ's. It isn't if that's the case.