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Old 07-24-2009, 09:16 AM   #1
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Jegs mc

hey whats up guys thinking about getting a new master cylinder my brake light stays on and am not getting any pressure from the mc when i take the cap off. i did the mini diagnostic for the brake booster from the haynes manuals and it seems to be good but the mc isnt. Now my question is can one of the jegs mc work for my jeep i think it has the same mounting holes. what is the bore size for the oem mc on the yj 92? heres one of them iam thinking of getting the have four holes already so i could ditch the porportioning value and just use straight lines , they also have the same steel line thread size


Strange Tandem Master Cylinder Kits - JEGS


this is suppose to be for Chrysler vehicles but i know the brake booster in the jeep is a 7 diaphragm . .Tuff Stuff Chrome Master Cylinders & Brake Boosters - JEGS

right now iam running 31-10.5 -15 , i defaintly plan to go bigger and ive heard the stock mc just dont have the power to stop bigger tires.

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Old 07-24-2009, 11:19 AM   #2
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the stock ones seem to stop big tires ok

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Old 07-24-2009, 09:36 PM   #3
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well this is the problem i have a 89 undercraige frame and all the suspension but my mc and powerbooster is from a 92. i bled the brakes numerious of times and still have no pedal at least a couple minutes later after i depress the brake pedal. I figured i go with a bigger bore size and also a aftermarket one like the one from jegs. i plan to change axles so i just doubted the stock ones to even be able to stop me well enough with those mods.
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Old 07-24-2009, 09:40 PM   #4
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Another question can i use drums off a 91 with shoes and wheel cylinders for the 89 undercarriage i know both are different sizes so i figured i can change the drums ,shoes,and wheel cylinder and it would work . the bore size for the wheel cylinder on the 87-89 are 7/8 and for the 90-95 are 13/16 tell me what you guys think
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Old 07-24-2009, 11:43 PM   #5
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anyone?
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Old 07-25-2009, 07:48 AM   #6
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bigger master bore=more effort and less travel at pedal
smaller master bore=less effort and more travel at pedal

same holds for slaves but kinda reversed

smaller bore= more effort required
bigger bore= less effort required

if you want the best braking power you need a small mc bore and larger slave bores.(must be close or you might end up with a touchy pedal or a very soft pedal). all that said you must run a proportioning valve. if your gonna be swapping all sorts of different sizes to see what works you should get a manually adjustable valve.
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Old 07-25-2009, 11:22 AM   #7
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bigger master bore=more effort and less travel at pedal
smaller master bore=less effort and more travel at pedal

same holds for slaves but kinda reversed

smaller bore= more effort required
bigger bore= less effort required

Quote:
Originally Posted by dooder View Post
if you want the best braking power you need a small mc bore and larger slave bores.(must be close or you might end up with a touchy pedal or a very soft pedal). all that said you must run a proportioning valve. if your gonna be swapping all sorts of different sizes to see what works you should get a manually adjustable valve.
okay you lost me here can you explain that a litle better?
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Old 07-25-2009, 05:58 PM   #8
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The proportioning valve may already be adjustable IIRC.

This basically adjusts the pressure differential between the front & rear brakes.

Essential to have if you have front disc brakes, & rear drums. Nice to have, even if you have discs all around. If your back brakes are locking up in the rain, you can fool around with the P-valve & set it so it's just right.
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Old 07-27-2009, 05:07 PM   #9
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Quote:
Originally Posted by YjMopower View Post
bigger master bore=more effort and less travel at pedal
smaller master bore=less effort and more travel at pedal

same holds for slaves but kinda reversed

smaller bore= more effort required
bigger bore= less effort required


okay you lost me here can you explain that a litle better?
its all leverage. (for example) if your master piston is 1" bore and calipers are 2" bore. got that master 1" and slave 2". you apply 25lbs of pressure on master you will get 50lbs at slave. thats not exact because i didnt use the PI calculation to get exact ratio but you get the idea. but here is the kicker, you press the master down 2" but the slave only moves 1". again these are example numbers and are not anywhere near exact.

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