brake pedal pressure

rogthedodge · Post by **rogthedodge** » Sat Nov 28, 15 2:37 pm

Since doing my disc brake conversion I've been disappointed with the pedal pressure.Just had it pointed out to me that the master cylinder has" use dot 3 fluid" stamped in it .Would using later dot 4 fluid damage the piston seals?

68Runner · Post by **68Runner** » Sat Nov 28, 15 2:48 pm

DOT 3/4 are mineral so will both be OK to use.

Your pedal pressure feel is down to the fact you've gone from drums to discs and your master cylinder now has to move more fluid.
You will have to get a bigger bore m/cyl. You'll need a m/cyl which is for disc/drum setup. 1 1/8" I think.

Matt · Post by **Matt** » Sat Nov 28, 15 5:37 pm

No a bigger master will require even more pedal effort. Smaller bore is required to reduce effort.

It's got little to do with 'moving more fluid' . Pedal effort is a static calculation.

Mick70RR · Post by **Mick70RR** » Sat Nov 28, 15 7:02 pm

I had the same problem when I fitted front disks. Changed from a 1 1/8" master cylinder to a 15/16" and there was an improvement but still a lot of pressure required and the pedal travel increased. In the end I fitted a servo and went back to 1 1/8" MC and I'm happy with the brakes now.

Pete · Post by **Pete** » Sat Nov 28, 15 8:39 pm

Man sized brakes need man sized pressure, but a better and progressive feel in my opinion.

rogthedodge · Post by **rogthedodge** » Sun Nov 29, 15 11:43 am

Thanks for replies guys.new master cylinder and servo fitted with the kit,but the pedal travels too far before I get any pressure.there's no gap between the rod and the piston and no air, or fluid leeks in the system.might try a piston seal renewal kit if I can get one.

Pete · Post by **Pete** » Sun Nov 29, 15 1:52 pm

Did you bench bleed the MC before installing?