master cylinder bore question

Apr 7, 2003
Hi, i have drums on all four wheels but i just replaced rear drums, pads, and all cylinders. after spending some time adjusting all the wheels i still have to triple pump befor the brakes actually work. i was wondering where i could get a master cylinder from (what car at a wrecker) that has a substantially larger bore that would pump more fluid? thanks for your help
Nov 21, 2002
72fj40: You bled the air out of the cylinders, they were installed with the bleeder pointing up, the pads are the right ones and installed in the right place, so my 2cents, the master could be leaking internally so that the fluid doesn't get compressed{no fluid leaks out(rebuild it)} or the fluid is leaking out the back into the vacuum booster (rebuild it)
As far as a larger pump and resevoir I know nothing.
hope this helps
Jun 14, 2002
I would re-check your brake adjustment. Finding a m/c with the correct piston depth, stroke, fitting size could be difficult and by increasing your bore size you will increase your pedal effort and without power brakes, you may be unhappy. I would suggest going to power disc front brakes and self adjusting rear, much better than the older setup.
Mar 27, 2003
Bench bleed the master cylinder. You don't need a larger bore.
Feb 3, 2003
Am in the process of freshing up my system as well. I spoke to a mechanic friend and he suggested to check out a mid seventies chevy pickup master. I checked out a 74 1/2 ton and a 3/4 ton pick up master at Car Quest. The 1/2 ton is 1 1/8" bore and the 3/4 ton is 1 1/4" bore. It looks like a clean swap with minimal fabricating. Did the math and the 3/4 ton has 1/4 sq. in. more surface area. I believe the 1/2 ton exceeds the stock single lunger on my 66. Cost as I don't have a core is just over $25.00 for the 1/2 ton.
Yes I am staying with the drum brakes out of necessity.
Jan 28, 2003
Hey guys, I ran into the same issue when I bought my truck. I decided that I wanted a dual circuit MC, drums on all fours, and no power brakes.
I ended up with a mid 70's Ford PU cylinder. It has a typical of domestic 2 bolt flange, a 1" bore, and the fittings on the left side. I used a steel plate as an adaptor. It works well and is not as sensitive to loose shoes. I have no problem locking up all four tires on the street up to say 40mph (tested by a close call with a Porsche 911).
That said, if this cylinder ever goes, I will definitely replace it with a SMALLER bore cylinder, or see how it feels with a front disk conversion (minus residual pressure valve). The pedal effort is very heavy, and feels a bit marginal at highway speeds. It gets even heavier coming down out of the mountains when the lining heats up. I think a good option would be to use a booster. The spacer used on YJ's is about a 2-3" long and could be used with an early domestic MC to clear the firewall rib. If you don't want power brakes, look for a 7/8" bore MC.

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