Now need to know M/C bore size, pedal ratio and rear wheel cylinder bore size
This is actually a very good question… with a not so easy answer.Quick question - Have you ever had good brake balance?
Ha! And that is why they are no longer on my Mustang! The only Granada part left is the spindle… all the other stop quick bits on the front end are now late-ish model Mustang parts, which are MUCH more capable than grandmas Sunday cruiser brakes. 😂I fear that if the new proportioning valve does not solve your problem, you need stop looking at the rear and concentrate on the front. I have never heard anyone at the track say..."man these Granada front brakes are the bomb".
The braking performance was fine for street driving, problems arose when I took it to the track and drove the thing like it has never been driven before! I’m not normally the type of driver to go from 100mph down to 30mph every minute or so (with a lot of intermediate braking in between)… the track really brings to light what is and isn’t going to work at that duty cycle!just some thoughts - locking up brakes at medium to low speed on the street may not be a good indicator of track performance. most any car should be able to lock up things a bit at lower speeds. on a front-heavy mustang, weight shifts forward under braking, and locking up the rear brakes is always easy to do if the brake balance is set too far rearward. as an example, i have to set my balance bar far to the front to get my rears not to lock up first. i have strong wilwoods up front and large drums in the rear. front brake performance is related to pressure on the front rotors - a large single piston caliper should be able to generate a lot of pressure if used with a booster. sticky tires may resist lock-up better. real brake performance is probably best measured with stopping distances from higher speed, and under repeat efforts, where brake fade is a bigger issue. brake fade depends on the system's ability to absorb and manage heat.... so many confusing issues when it comes to brakes.
PS - i hate the pedal feel and performance of the old fashioned sliding single piston calipers. modern calipers and systems do feel so much better although it is not always clear to me why that is the case
I thought that is essentially how the adjustable valves worked... taking a chart from the model Mark is using...I’m not sure what proportioning valve you are using now or the one you are changing to. However, the Tilton valve I use has a automatic diversion circuit for threshold braking. Essentially what happens is the valve allows pressure to the rears under normal braking. During threshold braking a larger portion of that pressure is diverted to the front.
For curiosity sake, what position is your lever in?I have this in my car.
Tilton Lever Style Brake Proportioning Valve - Pegasus Auto Racing SuppliesThe compact Tilton Brake Proportioning Valve allows a driver to rapidly select 7 distinct and repeatable settings for brake bias. Easy installation.www.pegasusautoracing.com
It takes all the guesswork out of, where the “knob” is. My version is 20 years older without the fancy wording
When I had stock size rear drums it was all to rear (full rear pressure) or up one. depending on fuel level and grip. With the current 11”x2 1/4” drums it’s the least rear brake pressure or one up. It will vary with how your weight is distributed. My car likes the full size battery over the RR and full fuel load. That is where it drives best for me on Blue Streaks. Once I got it sorted out, I rarely need to change it.For curiosity sake, what position is your lever in?
And hopefully your mind isn't in the gutter like mine is otherwise your answer might not be very helpful...