I'm trying to grasp the difference in braking performance between single, dual, and 4-piston calipers, as well as the difference in performance between floating and fixed, and piston size. This past week, I've been looking through my books, and the older Vettes and Fords ran 4 piston, fixed calipers. In my mind, this would be a very efficient design, but newer Mustangs are running dual piston, floating calipers; Dodge diesels are running huge single piston calipers. Any input would be helpful. The LAST thing I want to do is set up a poor braking system.
First.......a fixed caliper design is just that, the caliper itself is bolted solidly to the steering knuckle or bracket, all of the "clamping force" is generated directly by the inner and outer pistons coming together to squeeze the rotor. Generally you will find multiple piston arrangements on each side to spread the clamp load evenly to allow for good wear and even pad loading. I have seen up to four pistons per side...inner & outer. The older 'Vettes had these and were known for their surfaces getting pitted and leaking. Several companies recondition these calipers with stainless sleeves. The calipers were usually split and the sealing of the two halves were critical at the fluid passage areas. A floating caliper is usually retained by threaded pins or bolts with smooth sleeved areas for the caliper to slide on and a machined surface on the knuckle to absorb rotational force. The pistons in these arrangements are commonly one or maybe two pistons on the inboard side with a pad on the outboard side fixed solidly to the sliding outer caliper bracket. The force applied by the inboard piston acts against the rotor and it's pushing motion clamps the outer pad by "sliding" the outer caliper bracket and squeezing the rotor. There are alot of variations and different engineering approaches to the exact same designs but the braking "power" is a matter of friction area, piston diameter, number of pistons and of course the selection of the correct master cylinder. I have a very well balanced system on my 1935 Ford, I used GM "B" car front brakes (big rotors and single piston floating calipers) with early Camaro/Firebird rear disc brakes which are also floating calipers and a slightly smaller rotor. The master cylinder is an early 'Vette piece, the cast iron 4 wheel disc part. I don't run any kind of combination valve but I do have residual valves in both front and rear and just in case I feel the need I have a Wilwood proportioning valve in the rear circuit. I am OLD......so I did include a 7" dual diaphram vac. booster to help my bad knees. The car stops awesome.
I didn't see an article relating specifically to your question, but there is lots of good brake info here that might help: http://www.stoptech.com/tech_info/tech_white_papers.shtml cheers Ed N.
Thank you for the responses. One 1.75" piston has a surface area of 2.404" and two 1.25" pistons have a combined surface area if 2.453". On paper, should these two calipers have comparable qualities since they share similar surface areas? Also, is there any reason that floating calipers seem to be over-abundant compared to fixed calipers on modern cars? Was it a common sleeve problem as mentioned?
what kind of car are you working on? even the worst disk setup is better than any drum setup. and even disc systems have their limits as i have experienced both type of braking systems fail and it isn't fun.
A fully custom project. 2100-2300 lbs, 15" wheels, tube axle. More than anything, I want to learn about everything that I can, because I'm sure any discs will be happy on the front of the truck. The purpose of the build is to have something really fun to build and drive.
Floating calipers are easier and cheaper to make and in MOST cases, work just as well as a fixed caliper setup. Fixed calipers do have one big advantage, that's the ability to shed heat in racing applications since they are firmly bolted to the suspension member and transfer the heat much better. The early four wheel disc Corvettes were really the only ones I have personal knowledge of. The brakes were so big and powerful that they never generated much heat and from what I can tell the fluid would gather moisture and start to eat up the iron surfaces. I've had alot of them apart that were really pitted bad. I think if they ran hotter it may have been less of a problem?? No matter, the stainless steel sleeved calipers were the 100% fix.
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