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post #1 of (permalink) Old 04-11-2002, 04:54 PM Thread Starter
 
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Disc vs. Drum master cylinder/booster question

Okay, I've got a '74 CJ5 with drums on all 4 corners. Fully manual brakes, no booster. I was wondering:

1. Can I use the master cylinder and booster off of a disc/drum set up? I know the master cylinders are different.
2. If not, will the drum only master cylinder bolt up to a jeep brake booster that had the disc front/drum rear set up?

Any help would be appreciated!
Thanks!
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post #2 of (permalink) Old 04-11-2002, 10:15 PM
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Re: Disc vs. Drum master cylinder/booster question

You probably can use the vacuum booster off a CJ or a fullsize Waggie/Chero, but you'll need the actuating rod because of the length.

Do yourself a favor though and upgrade to disc brakes in front. There's plenty of 77-79 CJ Dana 30s around that you can get parts from, but I would recommend the 77-78 units because they are larger. The master cylinders on the 77-78s are larger as well, I belive 1 1/16" bore verses the 1" bore of the 1979+ CJs. I switched to one of these MCs when I went to rear discs and it really made a difference.
post #3 of (permalink) Old 04-11-2002, 10:46 PM
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Re: Disc vs. Drum master cylinder/booster question

I'd agree with Hoghead, switch things over. You'll be happier in the end. I put the GM booster from an s10 onto my CJ5 and love the brakes. I'm still working out a smaller issue, but I can stop whenever I want.

Side note: when I swapped my standard brakes for power, I initially tried using the manual master cylinder (disk/drums). It wouldn't work. There is a slight difference in the piston where it meets the rod. It wouldn't allow contact until it was too late. But I just swapped it out for a power master cylinder, and all is good.
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post #4 of (permalink) Old 04-12-2002, 02:57 PM
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Re: Disc vs. Drum master cylinder/booster question

I could swear I once read somewhere that a caliper is a high volume, low pressure assembly (relatively) while drum wheel cylinders are high pressure low volume assemblies. This all makes sense to me....so wouldnt master cylinders have to be different? I.e. shouldnt a drum/drum master cylinder be changed to a disk/drum setup for front disks, since the fromt calipers will require more fluid to actuate than the old drum wheel cylinders did? Am I totally off base here?

-remy
post #5 of (permalink) Old 04-12-2002, 04:58 PM
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Re: Disc vs. Drum master cylinder/booster question

You aren't TOTALLY off base....but it's just a matter of degrees. Both master cylinders will push fluid. The differences are slight, and if you look at a spec sheet on them you'll see only a 1/16" or so difference in the bore of the cylinders. But it all adds up.

My problem was that my pedal was hitting the floor well before my brakes were functioning. CAN'T HAVE THAT!!
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post #6 of (permalink) Old 04-12-2002, 07:28 PM Thread Starter
 
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Re: Disc vs. Drum master cylinder/booster question

Thanks all. I'm actually trying to get a set of front discs off of a parted out post '76 CJ5 (not sure of the exact year, everything is STILL buried in snow here!) and if I get that, I'm pulling the master and booster too. I'd love to go discs on the front, and eventually on the back too, but for right now, I'm just looking for options to get what I have to stop better.

Thanks again!
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