Datsun Roadster Forum-311s.org

Thanks guys...all excellent info. The long and short of it is...no.... I haven't figured out a fix yet as we are in the dead of winter and testing is a problem in my part of the world . I think the first thing to do is make sure the existing system is working properly starting with a master cylinder pressure test and go from there. The roadster brake system is not complicated so it's just a matter of increasing pressure on the rear brake shoes and dialing it out for track and tire conditions with a bias adjuster.

I made a brake pedal pressure tester that applies a constant pressure so you can measure the line pressure and calculate the braking bias. I use a small c-clamp to hold the cupped end to the pedal....it works with the clamp, but I am a belt and suspenders type of guy......LOL.....
By measuring the length of the spring I can calculate the exact pressure on the pedal.......As you can see in my calculations, try to keep your total pedal pressure near 110 lbs

Here's a trick I use for setting up brake bias on a new race car. Line pressure doesn't tell you much as the braking force is a function of cylinder size and lining surface area/friction material etc. Put the car on jack stands and depress the brake pedal with a broom stick or equivalent. Adjust the pressure on the brake pedal with shims of wood or equivalent so that when you put a torque wrench on one of the front lug nuts it just starts to rotate the wheel at about 40-50 ftlbs. Now check the rear, you want it at 50% of the front or 20-25 ftlbs. Adjust your bias by what ever means (I prefer twin master cylinders and a bias bar), changing cylinder size, pressure valve etc. to get the rear 50% of the torque to turn your fronts. Forces will be different when everything is hot but this will get you actually very close. I usually like more rear bias than most but I use that to help turn the car and save the front brakes in a race. Hope this makes sense and helps.

Mike

Thanks for all the great ideas, I appreciate the input.....Steve

Wow Steve, the brilliance in that is the simplicity. Very nice; thank you for the very helpful tip!

Well...maybe I boiled the problem down but getting more pressure to the rear is not so simple. Mike and Phil (fj20) have good experience with race car braking systems and they are right, having the ability to overload the rear is going to take a master cylinder change. And while, in the grand scheme of things, not terribly expensive it will be a lot of tinkering. But I think having control of the back end of the car as conditions change will be worth the effort and expense.