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MC upgrade without changing brakes?

lxrubin

NAXJA Forum User
Location
MICHIGAN
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?
 
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.
 
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.
 
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.
 
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As said a bigger master gives you a firmer pedal that you have to push harder on. No upgrade to performance.
 
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!
 
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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.
 
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.
 
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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