i'll keep this short. I installed a dual master cyl. in place of my single one. it's from a 70' mustang, 1"bore. I mounted in original location. I plumbed it this way; resvior. closet to firewall, goes to front brakes. other resvior. to rear brakes. I keep the stock drum brakes all around. there all adjusted properly. I have bleed the system several times. I still end up with hardly any brake pedal. I know a lot of you guys proably have gone thru this? does any body have any good ideas. i'am lost?
is 1" bore same as original? is it a drum/drum master cylinder? did you change/adjust rod from MC to brake pedal?
Do you have residual valves in line between the master and the brakes? A 1 inch bore will work fine. That is what I have on my 51. Did you modify the original pedal for the new master? Is it an aftermarket pedal assembly? I had a pedal set up that I bought from speedway that had such a bad ratio it would not stop at al . Used all the same hydraulic parts on a Walton fab pedal and it works great.
there is a adjustment between the pedal and master rod plunger to small or to tight makes a difference, also does pump up when you pump the brakes??
thanks for all replies! 1st. did bench bleed with tubes in M.C. 1" bore is same as orig. I fabricated a mtg. brkt. (couldn't spend $200 for one). I do believe I have the right amount of rod travel. from what I have been reading I think I need to install prop.valve. drum/drum. hopefully this will do it? i'am open to any more ideas? thanks to all!!!!
You don't need a proportioning valve. You need 10 pound residual valves in line between the brake and the master cylinder, one for the front brake circuit and one for the rear. This will keep the brake fluid from running back from the wheel cylinders to the master cylinder.
Nailhead Jason is right. I mounted the same setup but with a power brake booster to my 50 Chevy and thought I could get away without the residual valve. I had a front disk kit so my setup was slightly different, but same principle applies. Make sure you have a drum/drum MC and do those residuals and you should be good to go. I also think the front residual is a 10lb and the rear is more? Don't quote me on that. I think TCI or Walton Fabrication has diagrams up with all the info. Sent from my iPhone using The H.A.M.B. mobile app
The master is under the floor board and if the car is lowered the master is below the level of wheel cylinders and calipers so the fluid will run back slightly towards the master. That causes you to lose your pedal pressure. The only way to fix the problem is with the residual valves. 2 pound valve to the disc brakes front and 10 pound residual valve to the rear drum brakes will do the trick. Sent from my iPhone using The H.A.M.B. mobile app
I spoke to a couple professional brake co.they said the master cylinder that I have. 1970 Mustang dual Reservoir.drum to drum. it's supposed to have built-in residual valve. I have not checked that yet? I'm waiting for my aftermarket residual valves.I will install them and go from there.
Even if it they say it has them built in you should put them in. It will help with keeping the pedal pressure up. Don't use the cheap ones from speedway, they suck, and always seem to leak. Use the good ones fro Willwood, and you wont have any problems.
A quick way to check is to undo the lines and look where they go. The is a cone in in each port where the flare seats. If those cones are made of the same Iron (or whatever the master cylinder body is made of), it does not have residual valves. If those cones are brass, sometimes with a hex head, it might have residual valves. Shown with one removed, in hand: The reason I say might is that some master cylinders have brass seats, and no residual valves, some have the residual valves removed, and others are repaired using brass cones during the rebuild process with them. You can verify, if you have brass seats, with a paperclip. Straighten it out, and gently press it in the hole in the center. If you feel a little rubbery resistance just past the brass, it has a residual valve. If not, it does not. This little duck billed dealy is the residual valve: It, if it is there, is inside the brass cone.