Is there a way to size a master cylinder to the weight of your hot rod. I have done a lot of reserch but can't find any info on this. Thanks for any info. GCWRED
If you are using Disc brakes all around on a 2200 lb car, use a dual master cylinder with at least an inch and one/eighth bore. Most Chevy master cylinders from the 70's and 80's that had front wheel disc brakes are usable. If the MC is set up on the firewall you will not have to use the hold off valves. If it is located under the floor, you will have to use the hold off valves to maintain pressure.
Might want to have your doctor diagnose you throught the mail while you are at it. About as acurate as the info you got there. Usually helps to know a bit more before making a judgment.
Just to be clear on our terms here. There is a device called a METERING VALVE - it's function is to delay the application of the front brakes (disc/drum setup) until a preset pressure is achieved - reason being the backs need to overcome the return springs - without it the fronts would do nearly 100% of your braking under light brake conditions - this would also make stopping in slippery conditions potentially very bad as the front only condition decreases stability. I've often heard this valve called a HOLDOFF VALVE. Most metering valves are "hidden" inside the combination valve assy. The valves mentioned earlier are RPV's - Residual Pressure Valves. These maintain a vry low amount of pressure in the system when you are NOT on the brakes. Normally when the m/c s mounted high (above the calipers) you automatically have this effect because the discs are so efficient it doesn't take much pressure to keep the pads in close proximity to the rotors (hence the 2psi RPV typically in the disc system with the low mounted m/c . The drum brakes are typically using the 10psi RPV but for differrent reasons. One of those reasons being that upon brake retraction the system is prone to suck in air past the wheel cylinder rubbers. A differnt method used for this was the use of "lip spreaders" (I forget if that's the proper technical terms) - anyways those were the little tin washers you'd ocassionally find directly behind the seals in your wheel cyclinders. The entire braking system should be matched to your car. I think the "normal" method is to match the m/c to the brake components. The brake components having been matched to the weight of your car - that's one reason why you see so many different sized calipers. I would tend to think that the line pressure is a FINE TUNING tool - NOT a direct function of vehicle weight - although it would stand to reason that everything effects everything. Building a GOOD brake system on a Hot Rod is probably a lot more complicated than most of us really want to consider. Given this - a good starting point is to find an existing factory system that closely matches your own and copy it. Meaning find a car that is similar to yours in weight and brakes and copy it as much as possible. No sense in redesignign the wheel if you don't have to....
Where you gonna find a car that weighs 2200#s with four wheel discs to copy? Will he still need the aforementioned proportioning valve with the disc brakes all around? I personally like the idea of having a whole hell of a lot of brakes on something that is obviously intended to haul ass. The inch and an eighth master cylinder sounds like it's in the ballpark. Larger pistons move more volume but increase pedal effort, that size sounds like a good starting point. The old Corvette master should work, it's the one that is so common and is reproduced and sold by everybody and his dog.
Well I suppose that depends on how and where you look - in todays day and age - lighter cars are easier to find than ever. The point is you are likely to get a better baseline from soemthing that's close rather than soemthing that's at the opposite end of the spectrum. Pushing the limits - in difference will add to the confusion. I agree that I'd more brakes is better than less - to a point of course. A proportioning valve - is always a good idea - part of it's job is to vary the bias from front to rear based on the amount of pressure input to the system - as we all know - when the vehicle undergoes a shift in weight transfer - then ideally the brakes will adjust their bias to match - that is the job of the proportioning valve. Going rear disc may (or may not) make it difficult to find an appropriate factory proportiong valve - if that's the case then I'd explore the adjustable ones. The suggestion to visit Mater Power's website - is an excellent one (IMHO) - the more you know the better decisions one can make. I've got a 1-1/8" bore m/c in my convertible - disc/drum - (I forget the caliper piston dia) but I can tell you that I don't care for it very much - I am gonna sleeve it down first chance I get. Each car is different - it could be perfect for another - based on the particulars.
The best information I have ever received is to match the master to the front calipers. The front because they do most of the stopping. So, if you have Granada brake calipers, you're gonna have a Granada master cylinder. Next, we delve into the pedal arm ratio, and quickly realise that the Brake Handbook, by Fred Puhn, available from HPBooks, or Amazon.com will be the next, logical step. Cosmo
This is the new old guy, (GCWRED). Thanks for all your help. It's hard to find out this kind of info just any where. I have looked! It's tough trying to build a scarch built rod from a bunch of differant pieces. Thanks again.
In short.....As mentioned.... 1. Match brakes to suit car weight/use. 2. Power boosted or not...decide, cause that affects M/C bore size.... 3. Pedal throw length (Mechanical leverage) is the final factor. Example: I once had a car brought into the shop and the owner stated that his brakes pushed too hard and wouldnt lock up the wheels. I discovered he had eliminated the vacuum booster feature because of his radical cam didnt give enough vacuum to make the booster work. I immediately changed the 1-1/8" bore to a 1" bore M/C. Which made it stop better but with more pedal travel. I changed to a 15/16" bore M/C and it got really decent pedal and not too bad a travel. SOLVED But another car (Corvette with the same power booster eliminated issue) was different. I went to a 3/4 " bore before it would stop the car, but the travel (Fluid volume) required me to pump the brakes twice to get the piston out and stop the car. While the pedal pressure was nice and easy, the pedal travel made this combo not workable. These calipers will only work with a power assisted M/C. We changed to Brimbos and a 15/16" M/C bore and good to go. It is possible to use a short pedal, power booster and 7/8" M/C... OR a long pedal unboosted and a 7/8" M/C, OR a long pedal, booster and a 1-1/8" M/C and get the same pedal effort AND brake performance.....Think about it.
From New Old Guy, Boy, reading the articals at MPbrakes told me about all I need to get started on designing a brake system. All your replys were really helpful. I was about to install a system that would have given me nothing but trouble. Thanks again. GCWRED
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