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Old 09-11-2007, 02:28 AM   #1 (permalink)
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CJ7 brake booster upgrade?

So I've read and read just about every post there is on the internet about brake upgrades for CJ's. (least it feels like it)

Some background I have a 1981 CJ-7 stock power brakes with a Dana 30 up front (disc) and a Dana 44 in the rear (drums) Running 35" tires.

Recently "upgraded" to a '68 Corvette MC, (the one that needs the long push rod), not a problem, mine unscrewed about 1/2" and reached fine to raise the pedal back up.

The braking is not so good, with the increased bore, and the stock brakes, I'm using too much pedal effort to get enough pressure to stop quickly, no way I can lock up the tires. The pedal is firm, and has a short travel.

Just upgraded to all new PSC steering, so hydro is not in the pocket book right now. I was thinking a Dual Diaphragm booster would help a lot with the pedal effort. Got to thinking if a '68 Corvette MC bolted on No problem, then wouldn't a '68 Corvette booster work as well.

Well it seems the 1968 Corvette Booster is Dual Diaphragm. I'm pretty sure this will bolt up no problem,
has anyone tried?
Will I have a decent improvement from what I have with the single diaphragm CJ booster?
One Concern, its only 8 3/4" diameter, the CJ is 9" and I know a lot of the GM upgrades are 10+"

I can't really fabricate a new mounting bracket which I believe is required for the GM booster, and I have no idea about the linkages. The Corvette booster seemed appealing because it would just bolt in, about a 10min install.

Thoughts, ideas, questions? - Sorry for the long post, but wanted to be thorough.

THANKS!

Edit: Link and Part number for booster
Napa #NBB5491200
@ http://www.napaonline.com/masterpage...aster+Cylinder
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Last edited by cjarnesen; 09-11-2007 at 03:05 AM.
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Old 09-11-2007, 11:45 AM   #2 (permalink)
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O.K, the corvette master cyl is a 4 wheel disc master cyl. it does not have a residual pressure valve in it like your stock master cyl did. these valves are important to have for drum brake systems.
you also changed the bore size on the master cylinder. you went from a smaller to a larger piston diameter. it will help a lot if you change to a larger inside diameter wheel cyl. you have effectively decreased the pressure going to your rear brakes, therefore, a larger wheel cylinder will take less effort to move due to the larger surface area of the larger bore wheel cyl. hope that helps.
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Old 09-11-2007, 11:20 PM   #3 (permalink)
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Thank you!

I understand the physics of the MC, and I think I've heard you can put some sort of residual pressure valve inline with the brakes to keep pressure built up. Is this possible? How much will this help my situation? Will that Corvette Booster help with the pedal pressure needed?

For 90 bucks and about 5-10min of labor I am more than happy to swap in the booster, but I'd love to know of other easy options, and or issues I might run into.

Thanks!

-CJ
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'01 7.3L PSD Excursion AIS intake, rear sway bar, airbags, DP Tuner, etc

Last edited by cjarnesen; 09-11-2007 at 11:23 PM.
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Old 09-12-2007, 12:52 AM   #4 (permalink)
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The dual booster will definitely help increase rotor/drum pressure; my guess is it will add ~70% additional boost over your single diaphragm booster.
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Old 09-12-2007, 08:11 PM   #5 (permalink)
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I found this write up online last week. Uses a Grand cherokee MC and dual diaphragm booster. I think its for 4 wheel disk though.

http://www.jeepsunlimited.com/forums...d.php?t=155617

So... heres the write up to do a home brew disk swap an an AMC 20. I figure that the distance from the back of the axle flange to the WMS should be about the same, so you should be able to use the same rotors and calipers, and fab your own bracket in the same fashion that they did.

http://floridajeepers.net/viewtopic....e8bc13465209bd

Im going to the junk yard this weekend to pick up the parts to do this swap in a couple of weeks!
Hope this helps!
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Last edited by upj wheeler; 09-12-2007 at 08:11 PM.
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Old 09-12-2007, 08:42 PM   #6 (permalink)
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I think you started from the wrong end. You should look at upgrading the wheel ends before you start jackin with the master cyl. The stock master is sized right for the stock brakes, you just need the parts that do the work to do it better. What was so wrong with the stock master?
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Old 09-13-2007, 04:36 AM   #7 (permalink)
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Thanks for all the input. I'd love to run rear disc, that is on the list for future upgrades. I'm understanding more and more about the balance between wheel brake cylinders and the MC.

My braking was poor before the upgrade to the vette MC, hence the upgrade. With 35's and stock brakes, it just wasn't cutting it. It was fine for around town stuff, and fire roads. But heaven forbid I needed an emergency stop on the freeway, or did any kind of rock crawling, or technical wheeling.

The vette MC didn't make braking worse, just changed the feel, lot less pedal travel, and a lot more pedal pressure required. With low RPM's crawling, I didn't seem to get enough vacuum assist, and felt like I had manual brakes.

I was researching braking upgrades for the front, but you all think I should do the rear first? Anybody make rear D44 caliper brackets for the swap that upj was talking about, as I'm not really a metal fabricator (YET)?

Thanks for the help! I guess I just need a step by step, idiots guide for disc conversion/ HELP FIX MY BRAKES.

Any idea whether the grand cherokee booster will have better boost then the vette booster. I like the idea of the vette booster, cause it means no mods to the pushrod and or another new MC.

THANKS, CJ
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Last edited by cjarnesen; 09-13-2007 at 12:27 PM. Reason: For being dumb
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Old 09-13-2007, 07:42 AM   #8 (permalink)
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Did you read either of the links that I sent you???? The rear disk write up is a step by step guide for idiots!! and the Grand cherokee MC / booster swap is a bolt on (drill a couple of holes) and everything hooks up, including the push rod.
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Old 09-13-2007, 07:55 AM   #9 (permalink)
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Quote:
Originally Posted by upj wheeler View Post
Did you read either of the links that I sent you???? The rear disk write up is a step by step guide for idiots!! and the Grand cherokee MC / booster swap is a bolt on (drill a couple of holes) and everything hooks up, including the push rod.
I really want to do up that swap, I swear my brakes are going to kill me. Sad thing is, my rear brakes are a LOT better than my front and actually lock up before the front can catch..... think about how much fun that is in the rain trying to stop a light at the bottom of a big hill.

Already got the 1 piece shafts. Not Yuokon, dosn't matter though.

But, its my DD and I have to get my buddy to make a bracket at his work (Lazer cuttin and powder coating free... I win. ) but I have to drive it to work the next day.

I'll work something out I guess.
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Old 09-13-2007, 08:36 AM   #10 (permalink)
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sounds like you are looking in the wrong places to fix your problems here... swapping to rear discs is not going to help your braking if the drums are already locking up... I would recomend looking for a dual diaphram YJ booster ('95/'96 I believe). It will require lengthening the rod but it is not hard to do. Also, you need to get rid of that Vette MC because the bore size is too large. A larger bore pumps more fluid but requires more pressure to do it, that is why you are getting a hard pedal with little travel... Go back to a CJ or YJ MC for power brakes from a later year.
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Old 09-13-2007, 12:19 PM   #11 (permalink)
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Quote:
Originally Posted by upj wheeler View Post
Did you read either of the links that I sent you???? The rear disk write up is a step by step guide for idiots!! and the Grand cherokee MC / booster swap is a bolt on (drill a couple of holes) and everything hooks up, including the push rod.
I did read the links, sorry. It was 3 am when I was responding,so things seemed a tad bit more complicated and confusing at 3am. The axle guide is pretty sweet, very step by step. My D44 is somewhat different, but it looks like it all applies. My biggest worry is the bracket fabrication.

I looked at the ZJ booster, it looks like they are different between 93 and 98. Looks like the 98 is the big one, so I bet thats the one people are using. My new question is the ZJ booster has the same diameter as the Vette booster, 8.75" So would the Vette booster have the same boost as the ZJ?

I guess either would bolt up fine, the Vette is a little bit cheaper and wouldn't require another new MC. So I'm leaning towards it, but then i still have the 1.125" bore.

upj - I appreciated your thorough response, and didn't mean to make you think I ignored it.

ld50, I think your right, that I should go back to my old MC, I guess that makes me feel defeated. I would like to make the Vette MC work, and upgrade the rest of my brakes to work with it. But I'm learning its all about the balance of the braking system. My rears don't lock up yet, I think it has to do with the residual pressure valve that my Vette MC doesnt have. I don't think I need rear discs, if I can avoid it. Disc conversion is alot more money then a new booster, and it seems I should upgrade the booster anyway even if I went to rear discs. Doesn't like 80% of your stopping power come from the front anyway? Do the rears really make that much of a difference.

Anyways THANKS! I need to open my mind to other solutions, thank you!
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'01 7.3L PSD Excursion AIS intake, rear sway bar, airbags, DP Tuner, etc

Last edited by cjarnesen; 09-13-2007 at 12:23 PM.
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Old 09-13-2007, 01:05 PM   #12 (permalink)
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discs on the rear are good if you ever get in deep mud (drums fill up and are a pain to clean after), discs are eaisier to work on, remove, are lighter and provide better stopping power. With all that said it is still not likely that upgrading your rear drums to discs is going to be worth the effort. The residual pressure valve could help some but if you already have little travel in the pedal I do not think you are going to see much of a difference (the valve keeps the return springs in the drums from taking up too much, probably only effective with worn shoes). Back to the MC, the bore size is too big, it was made to work with disc brakes which require more volume and have larger pistons. YJ MC's are cheap, $30 or so, try one out before anything else....
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Old 09-13-2007, 02:03 PM   #13 (permalink)
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The residual valve only keeps air from being pulled into the system when the shoes retract, it will do nothing to help your braking. Put your old master back on and buy more aggressive pads and shoes and make sure everything in the system is top notch.

KiGrind; you need to put an adjustable proportioning valve in the rear brake system. That way you can cut the pressure down a bit and keep the rears from locking first.
Travis..
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Old 09-14-2007, 06:19 PM   #14 (permalink)
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Thanks.

What brand pads and shoes offer better stopping power? I know on my Dodge Durango (underpowered stock brakes) that pad upgrades seem to be for less brake dust, and not many offered better stopping power.

The rear shoes and drums were recently replaced after my drum got trashed from the mud and a stuck parking brake.

Thanks for all the suggestions everyone.
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'01 7.3L PSD Excursion AIS intake, rear sway bar, airbags, DP Tuner, etc

Last edited by cjarnesen; 09-14-2007 at 06:20 PM.
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