Posted by Jesse Ybarra
on 10/6/2009, 2:21:10, in reply to "Re: Dual Master Cylinder Conversion"
64.12.117.15
Dennis,
I can be sure that if you research the manufacter of your brake rear wheel cylinders and front caliper pistons, a master cylinder exists for what you have that will have dimensions, that can be sized to match the demand, I can not give out the formula, I used because each vehicle has it's own needs.
The important issue is that of what the hydralic system does is easy. For me I look at the diameter x distance of each piston or cylinder x need, or:
size x movement = fluid cubic inches, this is going to be pushed by a master cylinder that is going to have a capacity to be pushed at the pedal with enough capacity + 25% of extra, size x movement with reserve, my rule of thumb is to have all mechanical components. But, I am not against power assist, for example a stock hydrovac can be sized to do this same thing, the original equipment late production DRW had big drums and a hyrovac these were great brakes. Hydrovacs add advantage and can be used to update earlier FCs or additionally, anything can be used, separate front and back dual hydrovacs can be used, but for me it gets ugly with complication.
What is important is that the proportion needs to work, what you have to push the fluid must be more than what you are pushing.
A friend has C20 Chevy discs and Chevy drums, 38" tall tires with 3.37 gears. The shop building his truck, used a popular streetrod product master cylinder with a sideway mount booster power brake and master cylinder, it could not stop the truck. The reason was simple the master cylinder had a smaller capacity, it works great on a small mustang disc front end and 10" rear drums on a 3,000lb street rod, with 26" tall x 8" wide tires (same is found on a 91-94 Bronco II or Explorer and works good on it). I suggested to my friend, that the repair, was that they used the same brackets with a stock C20 booster and master cylinder. it stops great now, Size does make a difference.
How it works for my needs, as I see it:
Discs/drums on FC trucks, need to have a master cylinder capable of making aproximately 2,000lb pressure for discs, 600lb for drums.
On the FCs the pedal arrangement is really good as it is, regular foot pressure multiplication of length of the pedal against the movement of the piston being pushed in, is really good, at the shaft is 200-250lbs (not boosted or power assisted) in between the lines need to be new.
The foot pressure is not changed when pushing one or two master cylinders, but the distance of the depth is reduced, by increasing the dual diameter. I try to do the math first, to avoid problems.
Jesse
--Previous Message--
:
: That looks great. Are there any calculations
: to size the master cylinder bores to the
: wheel cylinders? I have front disc with rear
: drums and this looks like a lot better
: set-up than what I have started. It would be
: nice to size it close from the start and not
: have to rely heavily on a proportioning
: valve.
:
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