Hello, i'm trying to figure out how to balance my brakes, more specifically my wheel cylinders. On the front end i have 11" drums, and on the rear 9" Should i use same diameter wheel cylinders to apply more force to the rear and compensate for the different drum sizes or should i still use smaller cylinders on the rear? Btw the vehicle in question is my truck, which will rarely, if ever, carry a load in the bed. Sent from my ASUS_X00DDA using The H.A.M.B. mobile app
Front brakes usually do a greater percentage of the braking than the rears. That is the main reason they are usually smaller size. What you don't want to happen is rear brake lockup as it leads to the vehicle skidding sideways and that is never a good thing on a public road. If you haven't already tested your brakes in various stopping modes, especially 'panic stop', from a moderate speed, say 50 mph (approx 80 kph), I'd suggest doing that, in a safe place, and seeing what happens...if you can lock the rear brakes. If they will lock, you do not need more braking power. If they don't quite lock up, but leave light rubber marks, I'd think they are about optimum. If they seem ineffective, maybe larger wheel cylinders would be worth trying...and testing.
Thanks, i should have said that right now i have no brakes at all, therefore i can't test them, but what you said matches what i had read I had doubts because having both smaller drums and cylinders than the front, i thought that i would have ineffective rear brakes right from the start. Sent from my ASUS_X00DDA using The H.A.M.B. mobile app
90 % of all drum brakes are designed with less lining surface area in contact with the drum on the rear brakes. You could do a quick check on the vehicle that the front brakes came off to see but I'd guess that they have 11x2 brakes. Those usually came with 11 x 1-3/4 on the rear. What you don't want as Hnstray said is more swept surface or larger cylinders on the rear. That could cause the rear to have more braking power than the front and if the rear brakes locked up first throw you into a spin. As it sits I don't think you will have a noticeable problem unless the rear shoes are real narrow.
11" up front and 9" out back is a big difference right there. Any drum brake cars that I've seen the front and back are the same drum diameter. You could probably use a little math to pick the right rear cylinders, which takes into consideration the area of the shoes. Take something that is known, work the numbers for that and compare it with what you have now, just to get an idea on ratios.
I bought a hold off valve from SSBrakes that doesnt allow pressure to the front brakes until the correct pressure is applied to the rear brakes. Talk to them.
On earlycj5.net some people have been satisfied with upgrading the 9" front brakes to 11" drums and leaving the stock 9" in the back.
Don't know what the english name is, but this is a popular solution to manage brake balance in racing. Two brake cylinders where you can adjust how much of the pedal pressure goes to each one, in racing sometimes even adjustable while driving to compensate for changing fuel load and tyre wear. (Just make sure if one of the systems develops a leak, the other main cylinder WILL apply the remaining half of the system before the pedal hits the floor.)
If all factory brake design, probably OK. With such a disparity in diameters, sounds like it's modified (maybe changed rear ends?), which adds another dimension to the quandary's parameters. Perhaps the replaced shoes are of a different arrangement, i.e., self-energizing, vs. non-self-energizing. Difficult to figure out the net effect of all the variables (add in front to rear weight distribution), so it will be a judgment call, and as previously suggested, some road testing. I've never had an application, but aren't there adjustable proortioning valves available for this problem?
Hold off valves were/are only used on disc/drum systems, not drum/drum. Curious what "correct pressure" is ???
Thanks everyone I looked it up, weirdly late 30's chevys have linings the same size, which happens to have the same width of the ones on my rear axle. That is a good idea, specially since i will be using a single reservoir MC. Yes, i swapped the rear end. looks like i have a lot of testing ahead... I tried to find the lining area of both the original and the ones i have, was kinda hard because most sources only say the applications and not the dimensions. It looks my lining area on the rear is only 78% of the front area, if i'm doing my math correctly, those areas, combined with a 7/8" cylinder (the biggest stock size for my rear end)on the back and 1" on the front, results in the rear brakes having 69% of the power of the front, and a balance of 59% front and 41% rear. Considering that the chevys of the era had a balance of 52.5/47.5% i think i'm not that far off, but like you guys said i will know for sure if it works only when assembling everything and testing...
I check the weight of the vehicle first , then I compare to GM cars or trucks , and then I reference rotor size , drum size and then use factory master cylinder and pro portioning valve to match...works every time...
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