Upgrading to rear discs, need help deciding on a master cylinder!

[bmxmon]

Hello all, I don't post here much, just lurk. I have a question I can't seem to find an answer for anywhere!

First my car is a 65' Mustang with a Mustang II front suspension. I believe the brakes the kit came with (From Rod and Custom) are just your standard single piston GM caliper.

I just bought a rear end out of an 01' Ford Explorer for $150! Disc brakes, 3.73 gears, limited slip and 31 spline axles! Should work out pretty sweet for my end goal of a nice, mildly fast cruiser. (My Mustang will have a 5.3L Chevy and t56 in front of it)

What I need help figuring out is what piston bore and stroke I need for a master cylinder and if going power or manual brakes makes a difference. Hunting around I can't find any solid information. I don't expect an answer of "x" bore by "y" stroke, but a way to figure those values out would be great! I have yet to measure the piston size of the calipers, but I'm sure that is the key to it all.

Thanks for any help!

[Apogee]

Odds are your front calipers have 2-15/16" (6.77 in^2) or 2-1/2" (4.90 in^2) diameter pistons, for former being the more common of the two for most hot rod type disc brake conversion kits. Your rear Explorer calipers have 1-7/8" diameter pistons. Like you said, the first order of business should be to determine exactly what front calipers you're using.

After that, you need to determine whether you're running power or manual brakes. If power, what type of booster, vacuum or hydro? If vacuum, what size and configuration of booster.

For your reference, the Explorer uses a 1-1/16" bore MC mounted to a dual 9-3/4" diaphragm booster. The front calipers are twin-46mm piston units with ~4.77 square inches of piston area, so just a little smaller than the 2.5" GM units. Assuming a similar pedal ratio, that should at least get you close.

I would think that if you have the larger 2-15/16" GM calipers, a somewhat standard 1-1/8" bore disc/disc master cylinder mounted to a dual-9" diaphragm booster would work quite well. Any smaller of a booster and you'll want to decrease your bore size accordingly. Similarly, if you go manual, a 1" bore MC would probalby be the best fit given your volume/pressure requirements. Lot's of options for MC's either way.

Tobin
KORE3

[bmxmon]

Originally Posted by Apogee

Odds are your front calipers have 2-15/16" (6.77 in^2) or 2-1/2" (4.90 in^2) diameter pistons, for former being the more common of the two for most hot rod type disc brake conversion kits. Your rear Explorer calipers have 1-7/8" diameter pistons. Like you said, the first order of business should be to determine exactly what front calipers you're using.

After that, you need to determine whether you're running power or manual brakes. If power, what type of booster, vacuum or hydro? If vacuum, what size and configuration of booster.

For your reference, the Explorer uses a 1-1/16" bore MC mounted to a dual 9-3/4" diaphragm booster. The front calipers are twin-46mm piston units with ~4.77 square inches of piston area, so just a little smaller than the 2.5" GM units. Assuming a similar pedal ratio, that should at least get you close.

I would think that if you have the larger 2-15/16" GM calipers, a somewhat standard 1-1/8" bore disc/disc master cylinder mounted to a dual-9" diaphragm booster would work quite well. Any smaller of a booster and you'll want to decrease your bore size accordingly. Similarly, if you go manual, a 1" bore MC would probalby be the best fit given your volume/pressure requirements. Lot's of options for MC's either way.

Tobin
KORE3

Awesome, thanks for all the info! Greatly appreciated!

[Apogee]

Sure, no problem. I hope that's not your wife's/gf's Subaru Outback

Tobin
KORE3

[bmxmon]

Originally Posted by Apogee

Sure, no problem. I hope that's not your wife's/gf's Subaru Outback

Tobin
KORE3

Haha, I wish, unfortunately it's mine and now smells like crap! I used to have a perfectly good truck, but for the amount of miles I drive it just didn't make sense. The subie can still haul things! Just need to scrub the carpet now...