Changing Master cylinder size.

[kevin12973]

I have been happy with my current set up but feel I can improve it. My current set up is 4 piston front and rear Wilwoods from Levy, 3/4" masters front and rear. There isn't much travel in the pedal so I'm thinking reducing down to 5/8" mc's for more power/ less effort. Anyone been there, done that ? Any problems running out of travel? Thanks for your time. Kevin

[Bob Cowan]

Tried it. Braking got worse, with a longer pedal travel. Went back to 3/4".

But, I have 6 pistons in the front, 4 in the back.

[AC Bill]

Isn't bigger better? What about the 15/16" master cylinder? This was the answer to many builders, when using disc brakes on the rear, instead of the donor drum brakes. The larger m/cylinder displaced more fluid than the 3/4" would.

[kevin12973]

Tried it. Braking got worse, with a longer pedal travel. Went back to 3/4".

But, I have 6 pistons in the front, 4 in the back.

Thanks for the feed back Bob. Did you change both front and rear mc at the same time or just one end? Not the result I was expecting. I don't know if there is much volume difference between Wildwood 4/6 piston calipers.

[CraigS]

I would certainly try 5/8 for the rear. Not sure about the fronts though. I have never found it, or thought to ask them, but I would think Wilwood would have a chart that gives minimum allowable MC size for a given caliper. Notice that they give piston area in all their caliper listings so maybe there is a max caliper piston area that each MC size can actuate.

[kevin12973]

Isn't bigger better? What about the 15/16" master cylinder? This was the answer to many builders, when using disc brakes on the rear, instead of the donor drum brakes. The larger m/cylinder displaced more fluid than the 3/4" would.
Perhaps better if brakes were power assist. With a larger mc the brake effort will be higher. I would like more leverage in my manual set up. A longer pedal would be acceptable/expected.

[kevin12973]

I would certainly try 5/8 for the rear. Not sure about the fronts though. I have never found it, or thought to ask them, but I would think Wilwood would have a chart that gives minimum allowable MC size for a given caliper. Notice that they give piston area in all their caliper listings so maybe there is a max caliper piston area that each MC size can actuate.


Thanks Craig, I started with 5/8" for rear but the balance bar ran out of adjustment to compensate. Switched to 3/4" and got the bias dialed in perfect. So seems the front rear mc needs to be same size. Im concerned with Bills findings, slightly different set up though.

[CraigS]

how about this in .70 bore size?
http://www.wilwood.com/MasterCylinders/MasterCylinderList.aspx?group=Compact%20Remote%20R eservoir%20Master%20Cylinder

[mikeinatlanta]

I'd give the smaller masters a try, but probably the .70. Keep in mind that the smaller the master, the more sensitive the entire system is to being soft due to too much or too soft flex line. If the smaller bores make it too soft you can try things like -2 flex lines before giving up on the smaller size master.