This page summarizes a series of tests performed to compare the performance of a 0.70 inch TR6 and a 0.875 inch Morgan/Sunbeam rear brake cylinder on a 74 TR6. At the start of the test the only modification from a stock configuration was the inclusion of Toyota front calipers and 240 Z finned aluminum brake drums. The rear brake shoes were a street composite.
The front wheel camber was set to 3/8 degree positive. All tests performed with a newly rebuilt master cylinder, dot 5 brake fluid. A proportional valve was installed on the rear brake lines but set to have no effect (completely backed out). I had predicted that the 7/8 cylinder would overpower the rear brakes, silly me!
Observations:
Testing was much harder to do than I expected. Left front tire
was about 1.5 pounds under inflated for all tests and would lock
prior to any other wheel for all tests. After installation of the
0.875 inch rear cylinder a rear wheel was locking up shortly
AFTER the front left but I was uncertain which it was (suspect
the right rear). My test method was to start braking when a bar
painted on the road disappeared under the hood. Brakes were
applied to start squealing the front left tire but not to lock it
up. Pedal travel increased as a result of the larger rear
cylinder diameter, initially a little alarming but fine once you
got use to it.
mean 243 std deviation 9
mean 215 std deviation 9
28 foot reduction due to 0.875 inch rear cylinder
11.5 % reduction in braking distance when compared to 0.70
TR6 cylinder
It is interesting to note that the standard deviation remained
the same for both sets of tests.
The distances are based a 74 TR6 running at 3000 rpm in 4th
gear with a 3.45 differential and 205-70 R15 tires.
The tire weight distribution was as follows:
These weights have been called into question and will be verified ASAP.
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