4-wheel disc brake question

['66427coupe]

i have a 1966 mustang with the factory 4-piston brake caliper setup in front with a versailles rear setup and 1967 master cylinder. i have never been happy with the performance with this setup from day one, it seems that the brake pedal initally sinks somewhat before you get a solid feel to it and you feel that you almost have to pump it to stop good.

i have ruled out a bad master cylinder because i will get a firm pedal after pumping a couple times. i bled the brakes well so i don't think it's air in the line, i went with small diameter brake lines and wonder if that has something to do with it? i also have a proportioning valve that was for a disc brake car along with a adjustable regulator for the rear brakes.

if anyone else familiar with this setup has any input it would be greatly appreciated. i solved my headlight problems with help from you guys and want to thank you all. one more step to making the car more streetable.

 

[Bullitt]

ok, you say you have a proportioning valve for a disc brake car AND an adustable one? did you take the guts out of the fixed proportioning valve?

when you run and adjustable valve, you have to gut the main valve so it is merely a splitter. if you don't, i imagine you'd get some interesting effects...

also, does your car have manual or power brakes?

 

[347Fastback]

We have the same setup but I changed the front to 69 mustang spindles and brakes. I am also using a willwood prop valve and the mustang steve power booster and pedal setup... My master cylinder is from a 86 SVO mustang...

 

[12sec67]

i'm running manual 4 wheel disc brakes on my 67. i used a T fitting to connect the front lines and took off the porportioning valve. i used the wilwood adjustable port valve on the back only - between the master cylinder and brake line to the rear disc. works great for my set up.

hope this helps- rich

 

[GT2K]

Are the brake hoses in good condition? All the fittings are seated well and properly? Condition of calipers?

There's more to the system than the MC...

 

['66427coupe]

it has been over ten years since i originally set the system up but from what i recall the proportioning valve from a disc brake car was supposed to keep a certain amount of pressure against the front caliper pistons and the seperate rear adjustable one i installed was to adjust the amount of braking pressure that the rear brakes get to help balance the system for best results? the adjustable controls only the rear brakes.

the hoses were new and the calipers completely rebuilt and work the same now as back then.

what is different regarding the wilwood proportioning unit?

how do i know if the brake lines diameter is big enough?what size did you guys use?

they are manual brakes with original 4 piston calipers that came on a 1966 mustang. and there are no visible leaks in the system.

 

[SandSprite]

Wouldn't a 1967 MC be set up for either drum/drum or disc/drum? You might want to try a MC made for disc/disc.

 

[Bullitt]

the '67 master cylinder is fine, same one i use on my setup (stock 67 front w/ versailles rear).

i'm really thinking it's your dbl proporitoning valve setup. either take the guts out of the non-adjustable one (remove the front screw in fitting and pull the spring and plunger rod out and reassemble) or replace it with a T fitting for the front lines and a straight connector for the rear. the first method i've used on my '67 and on my roomate's '86 GT with the M2300K kit (the instructions tell you to do this with the Cobra brake swap on Foxes). the second method i used with great success on my 90GT w/ 4 wheel disc. all the cars have a great, rock hard pedal with no "squish" travel.

you can easily pull the guts n put them back in later, all you have to do is bleed the brakes again. quick check to see if that fixes it or not.