i put brake cyls from a 1 ton chevy truck in over the weekend.what i had was 15/16 and the ones now are 1-1/8
there is even one larger at 1-3/16 but i didnt want to go that far.
the modifications you have performed to the braking system would be best undone.The rear brakes need to be put back to the 9" drums and 3/4" wheel cylinders they once were.
the pedal def takes a bit more effor to stop now and i cant lock it up unless i stand on it.
You created a rear bias brake system with the 11" drums and 15/16" wheel cylinders. The bias is further rear with the increased wheel cylinders size of 1-1/8". You have already discovered to your chagrin that a rear biased brake system will cause the car to spin. Yet you continue to increase you're rear brake bias.
i dont think i would ever apply that much pressure.
Did you think that before you spun and kissed the guard rail?
FWIW you cannot modulate drums as well as discs, the self-energizing effect limits this.
it still seems to stop very well but i still also have my manual prop valve that i installed all the way shut.
The only reason you are still able to stop with this horrible bias is due to the quick take up design of the MC.
When the pedal is depressed, the large bore piston closes the quick take up valve and forces fluid past the primary piston seals until a backpressure seals the primary piston. This is called take up mode. After this occurs, fluid from the large bore is returned to the reservoir through check valve in the center of the valve. This is called compensation mode.
The stock MC is a 23.8mm/36mm quick-take up design. Initially the MC is effectively a large 36mm bore MC. This allows the pads/shoes into contact with the discs/drums quickly. When they make contact the system begins to build pressure, when it equalizes across the 23.8mm bore piston, this seals the smaller piston and the check valve in the MC opens. Then the MC effectively becomes a 23.8mm bore MC. Automakers did this to reduce drag while still maintaining normal brake pedal feel.
What you have done markg
with the larger rear wheel cylinders the MC is in 'take up mode' for a longer time as it requires more pedal travel to actuate the larger rear wheel cylinders. When the system begins to build pressure, the MC still requires even further pedal travel to build enough pressure to actuate the metering valve. Then finally the front brakes begin to work.
To compensate for this you now are using an adjustable PV to try and reduce pressure/flow to the rear wheel cylinders in an effort to have your car stop. This is not how the PV works. It is a fine tuning device on an optimized
brake system. Since you are no where near optimized with the jantastic wheel cylinders attempting to bandaid the problem by closing the PV as much as possibly has given you a car that stops, but not in a safe manner.
The brake system is just that, a SYSTEM
. Any changes done should be done with consideration to the system as a whole.
Remove that adjustable PV, reinstall the stock PV, install the original 9" rear drums and 3/4" wheel cylinders.
When you have done that, THEN we can begin improving your brake system.
Whomever is suggesting to use 11" rear drums and 1-1/8" wheel cylinders is going to get you killed... Unless you enjoy doing 180* spin outs on the freeway.
Center punching a pole with the rear of an G coupe does wonders for the gas tank.