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  #1  
Old September 1st, 2017, 11:14
lxrubin lxrubin is offline
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MC upgrade without changing brakes?

I want a bit better braking performance and might go to WZ or WJ brakes in the future, but in the meantime, will going to a 1.125 master cylinder help braking performance?

Thinking about the hydraulics, it would push more fluid for the same travel, but would be more difficult to push. I have a 97 xj and with the dual diaphram, the pedal stiffness should not be an issue. So wouldn't this be essentially the same as increasing the piston sizes in the calipers and rear brake cylinders? Am I thinking of this correctly?
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Old September 1st, 2017, 11:30
VAhasnoWAVES VAhasnoWAVES is offline
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Re: MC upgrade without changing brakes?

as a general rule of thumb... a larger master will displace more fluid, not build more pressure.

technically speaking, yes, there is a pressure change. but it is not going to accomplish what you want. the right way to do things is choose the right size caliper for the job and size the master accordingly. for your desired change... changing the caliper is the way to go.
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Old September 2nd, 2017, 05:37
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cruiser54 cruiser54 is offline
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Re: MC upgrade without changing brakes?

Be nice to know what we're dealing with as far as year etc....
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Old September 2nd, 2017, 06:38
jmg222 jmg222 is offline
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Re: MC upgrade without changing brakes?

assuming this is for a pre-96 xj...

black magic brakes and add in a mc/booster from a 96 or newer xj, breaking power is amazing, even with 35" tires.
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Old September 2nd, 2017, 07:38
Jeep Driver Jeep Driver is offline
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Re: MC upgrade without changing brakes?

Quote:
Originally Posted by lxrubin View Post
I want a bit better braking performance and might go to WZ or WJ brakes in the future, but in the meantime, will going to a 1.125 master cylinder help braking performance?

Thinking about the hydraulics, it would push more fluid for the same travel, but would be more difficult to push. I have a 97 xj and with the dual diaphram, the pedal stiffness should not be an issue. So wouldn't this be essentially the same as increasing the piston sizes in the calipers and rear brake cylinders? Am I thinking of this correctly?
Short answer is, no.


Your theory is correct for a clutch master/slave where volume is relevant, increase the slave bore and you have to increase the master bore.......it's travel over pressure that is the concern here.

Next week I'm ordering Wilwood 4 pots, I'll be using my same 97 WJ master, no worries about volume, a 1" bore is more than adequate, even though I'm going from 2 pistons to 8 pistons.


If you want to increase braking performance.........

Drums suck, replace with rear discs.
Rubber soft lines suck, replace with braided SS.
Front stock calipers suck..........here's where you spend the big bucks.


Most of your loss is in the old rubber soft lines, replace those with SS and I guarantee you you'll see a 100% improvement.

Last edited by Jeep Driver; September 2nd, 2017 at 07:42.
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Old September 2nd, 2017, 10:22
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cal cal is offline
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Re: MC upgrade without changing brakes?

As said a bigger master gives you a firmer pedal that you have to push harder on. No upgrade to performance.
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Old September 2nd, 2017, 10:37
RCP Phx RCP Phx is offline
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Re: MC upgrade without changing brakes?

I just went thru this when doing a WJ/KJ disc swap. It is a "trade-off" between pressure required and pedal travel. I opted for the 1-1/16" bore Durango MC (and a direct fit) as a good compromise to both and I am extremely satisfied with it! Another thing that can make a difference is the rear axle type. My 8.25 has what I call excessive end play(for rear disc application) that I intend to shim tighter!

Last edited by RCP Phx; September 2nd, 2017 at 10:43.
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Old September 2nd, 2017, 11:54
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TRCM TRCM is offline
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Re: MC upgrade without changing brakes?

I put a 2000 MC on my 88, and changed nothing else.

It gave me much better brakes, but I wouldn't necessarily say better performing brakes.
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Old September 3rd, 2017, 08:31
trippled trippled is offline
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Re: MC upgrade without changing brakes?

IIRC, it goes like this: a 1 in bore creating 100psi will exert 200 psi force on a 2 in piston. A 2in bore creating 100psi will exert 100 psi on a 2 in piston. The initial pressure created would be you pushing the pedal. Yes the pedal travel would be less but you would have to push twice as hard to get the same force exerted.
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Old September 5th, 2017, 06:50
lxrubin lxrubin is offline
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Re: MC upgrade without changing brakes?

Thanks for all the replies, and sorry for the delay in responding. It's a 97 with 31" tires, but will likely go with 33" when these wear out. It stops "fine", but I've had a couple moments where I was doing an emergency stop and pulled into the shoulder to make sure I didn't hit the car in front.

I'll take your advice to replace the rubber lines to braided and that will hopefully still be usable when I go to WJ or WZ brakes. In the meantime, I'll run better pads like Hawks or something.
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Old September 5th, 2017, 07:05
VAhasnoWAVES VAhasnoWAVES is offline
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Re: MC upgrade without changing brakes?

good pads and rotors should be plenty for 33s. rear disks would make world of difference without changing the master/booster too.
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  #12  
Old September 7th, 2017, 18:50
Jeep Driver Jeep Driver is offline
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Re: MC upgrade without changing brakes?

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