Do brake calipers have a "size"? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 03-13-2008, 08:25 PM Thread Starter
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Do brake calipers have a "size"?

I've never been completely confident in my "junk yard" rear disk set up. Mostly it's mental, with some physical re-enforcement. I've always been able to stop when I've wanted to. But the pedal has always been super soft to the touch.

My set up:
'84 S10 Brake booster
'69 Vette master cylinder
'93 Crown Vic rear brake calipers.

Nice mix of parts, eh?

So I've been doing a lot of searching and reading on here. Nothing has jumped out at me as to what would make my jeep stop on a dime. I did like the suggestion some body (RRICH?) had about comparing the setup the MC was originally equipped with, to the set up I have. I think that's a good idea. But how do I compare '93 Crown Vic calipers (single piston) to 69 corvette calipers (4 piston)?

Any ideas?
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post #2 of (permalink) Old 03-13-2008, 08:59 PM
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Sent you a PM.

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post #3 of (permalink) Old 03-13-2008, 09:41 PM
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Back a few years ago I wondered about the math myself. Sure there is a size, you ever look at the brakes on a compact car? Then you can look at a 2 ton truck... Size does matter.

So here are the balance of the links that still work from my "Brake Calc" list of shortcuts (sorry no new research). These are just write ups that I found useful, there were many others that don't come up anymore.

Outlaw Disc Brakes

StopTech : Balanced Brake Upgrades

Braking Systems... in Plain English

ECI Hot Rod Brakes...

Take a peek at those... From there you will find things you want to know more about... Put a phrase into Google and keep on reading.

Heck why not come back with a list of other sites that you found to be useful... I need a good brake link section.


Dale

Excellent Bad Example
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post #4 of (permalink) Old 03-13-2008, 09:49 PM
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Looks like you've found something your wife's known for years - it may fit, but it doesn't go together.

By super soft to the touch, you mean just a little pedal pressure is almost too much?
Or it means it takes alot of pedal movement to get it to stop?

You may be able to do a fairly easy fix for either.
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post #5 of (permalink) Old 03-13-2008, 10:53 PM Thread Starter
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Quote:
Originally Posted by RRich View Post
Or it means it takes alot of pedal movement to get it to stop?
The brakes react quickly, but the pedal goes way too low to the floor. They stop the jeep, but since I swapped in the rear disks I've never had a solid pedal. Seems too soft, and close to the floor.

I'd definitely trade some pedal movement, for better vehicle reaction.

I took the calipers loose tonight, and made sure the bleeder was at the VERTICAL top to get all the air out. Similar to all the people running eldorado calipers seem to have to do. I "think" I saw a little air come out while I gravity fed them. But I didn't get a chance to actually put the jeep on the road. That'll probably happen some time this weekend.

Any suggestions are appreciated.......

....... ... and how long have you been talking to my wife??!!
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post #6 of (permalink) Old 03-13-2008, 11:48 PM
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That's where thing can get really messy. It's all a mater of ratios.
Master dia and stroke to caliper piston dia and stroke, to pedal leverage and movement etc.
After a gravity feed bleed, try it with a friend. DON'T have him pump the pedal, just push down hard while you bleed it. Pumping turns the air into bubbles - impossible to get out.

Have a look at the pedal arm. Is there a way to LOWER where the pushrod attaches to the arm? Sometimes that will do it.
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post #7 of (permalink) Old 03-14-2008, 04:22 PM
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A good link.
Pirate4x4.com - The largest off roading website in the world.

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post #8 of (permalink) Old 03-14-2008, 08:28 PM
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Those S-10 dual boosters work nice though huh? I used import calipers , probabaly very similar to the Cadi style. I swapped in the S-10 dual booster and went through several different masters trying to cure the issue you are describing. I tried several different 4 wheel disc applications that I read about on-line. Finally I installed the S-10 master that came with the donor booster. This made the difference for me. Nice pedal and plenty of stopping power. Had to find the correct line adapters, but that wasn't too difficult.

Since I have swapped to the Wrangler tub I am using the Wrangler booster and went to a 4 wheel disc Mercury Marquis application to fit the booster. This is a good combo and I added a Wilwood adljustable valve to dial in the rears.

Is this the only hammer you've got?
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post #9 of (permalink) Old 03-14-2008, 10:44 PM Thread Starter
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Quote:
Originally Posted by RRich View Post
It's all a mater of ratios.
Master dia and stroke to caliper piston dia and stroke, to pedal leverage and movement etc.
This is the information that I think everybody is missing. All the discussion about 4 wheel disk brake master cylinders, the MC bore, and proportioning valves, nobody ever discusses the MC's STROKE. Of course this is mainly because the information isn't out there any where. At least not for the common man.

Jumping from website to website, and trusting all the information that is there, I can tell you that the Vette MC that I have has a bore of 1.125 (1 1/8). That's the same as the MC on the Crown Vic, that I pulled the rear calipers from.

So "simple" logic tells me that I should be stopping like a Crown Vic. No issues, straight swap. Obviously it's not that straight forward.

A master cylinder's bore is only half the equation....... how do we find the rest of the answers??......
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post #10 of (permalink) Old 03-15-2008, 12:35 AM
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Something that struck me just now - are you sure the problem is from the rear?
Try it on a flat gravel area - slam on the brakes hard - see which wheels lock up. One end might be doing all the braking. You might be surprised at which ones.

Check to make sure the front needs that MC dia too.

Then consider stroke. If both diameters are right, measure the stroke on a Crown Vic, and another Jeep. For the CV you can find one at a car lot - the salesman will think your are nuts measuring it. You can tell him it doesn't fit your needs afterwards - he'll talk about it for years!

And measure the pedal's ratio on both too - and amount of travel. That big article shows pedal ratios. Then measure yours.

I assume you are NOT using a prop valve - not needed or wanted with discs on both ends.

And - if you are using the super hard "lifetime pads" they are so hard you can cut concrete. Use the soft cheapies - that alone may be enough.

I wish those hard pads would be made illegal!
The soft ones last about as long but stop sooooo much nicer.
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