Brakes

[timkins]

I currently have an under floor mounted non power assisted master cylinder with a 7/8" bore and I am thinking of installing a 7" power assisted master cylinder setup with a 1" bore. Do I have to change the brake pedal assembly with a different pedal ratio along with it. My current pedal ratio is 5.75 to 1 with 11" Grenada rotors and Chevy metric calipers with a 2.75" calipers with drum brakes on the rear.

[chimp koose]

I think there are factory power brakes at that ratio . Switching bores to bigger needs more ratio or a hard pedal . I would try it , it will probably be fine .

[chimp koose]

By the way , how do you like the pedal feel with the 7/8 bore and current ratio ? I am using a 7/8 bore on 11" rotors with gm metric calipers on my T . I am just starting to make a remote reservoir 90degree master cyl mount and need to make a pedal as well . I can pick the ratio and was thinking of 6:1

[timkins]

I am not impressed  with MY brakes. I think part of the problem is I am expecting them to act like a newer cars brakes. The pedal is firm and the car stops adequately but I cannot lock the brakes up no matter how hard I depress the pedal. I had a T with a similar setup and they worked fine. When I went to a heavier car is when I started to feel they were inadequate. My current ride is a an all steel full fendered 32 Ford 2dr sedan and the weight difference although not significant is greater. I think you will be fine with your plans for the T.[/b]

[kb426]

Do you have a proportioning valve on your current setup?

[timkins]

Yes there is a proportioning valve on the car. It has the 2# and 10# for disc/drum installed also. I have also tried a pair of 2 piston  Wilwood brakes but their total volume  size did not match the volume of the oversized Metric that was on the car so I went back to my original set. Extremely frustrated and it is probably JUST ME and my expectations.

[kb426]

I have a similar exp. with my 32. Same calipers on the front, Lincoln Mark six disks on the rear. I have experimented with 1" and 15/16" masters. With the proportioning valve on max, I stop but I don't think I can lock up the wheels. The pedal assembly I use is from a Datsun 240z and I never calculated pedal ratio. No power assist. Mine is firewall mounted and space in a pickup is very valuable. What size rotors do you have on the front?

[enjenjo]

If you do change it, use the dual diaphram 7" booster and you should be good.

[timkins]

I have 11" Grenada discs on the front. I have been experimenting with the front brakes for over 2 years. I have gone as far as having copper lined shoes custom fit to the rear drum brakes hoping  this would help stop the car. Not sure I have the room for a 7" dual diaphram. Have not had the ambition to get under the car here in western New York with the temps the way they have and no heat in the garage. Thanks for suggestions and help.

[kb426]

I've only driven a few 32's with under the floor masters, none of which had boosters. I don't think I could lock up the wheels on them. My 32 is manual trans so that has a benefit in decelerating. The 51 has hydroboost, 12" front rotors and 96 Mustang rear rotors that aren't very large. I can lock up the brakes easily. I've wondered if the electric pumps and hydroboost might not be the way to go in the future.

[PeterR]

I currently have an under floor mounted non power assisted master cylinder with a 7/8" bore and I am thinking of installing a 7" power assisted master cylinder setup with a 1" bore.


The pedal is firm and the car stops adequately but I cannot lock the brakes up no matter how hard I depress the pedal.

Remember, if you change from a 7/8" to a 1" bore, that by itself will increase your pedal effort by 30%.     A single diaphragm booster will barely compensate for the additional pedal effort due to the larger bore master cylinder.    You will need a dual diaphragm.

[Rochie]

IF you're having problems  take a look at this site.  It has helped me out a few times.
http://www.deanoshiro.com/brakes/master_cylinder_test.html