It would trip some people out seeing dual calipers under a 15in wheel and hold like a 1000lbs of boost at the line with hydroboost lol.

 

When I first thought about it, I just laughed but then I realized I really want to do it...

 

The obs front rotors only have slightly less pad contact area(4.255" vs 4.86") and of course less leverage due to the 1.18" less diameter but the OBS front caliper will have more clamping force from the larger piston. I think it will really come down to pad contact area. The OBS front has a slightly larger outer pad and a significantly smaller inner pad than the NBS rear. IMO, I think the higher clamping force will out weigh the size disadvantages of the OBS rotor and pad allowing for better rear breaking than the stock NBS single piston rears. Especially for you turbo guys that need more holding power on the line.

I did realize that but Rock Auto/Centric did not show the dimension diagram for the 1" thick rotor. I assumed the hat and outer diameter would be the same for both for comparison with the 3500 rotors.

Not a scientific or definitive analysis, but comparing the photos the spacing from the piston bore to the mounting hole seems reduced for each larger piston suggesting a common mounting position. However, the 3500 calipers do look taller from the mounting hole to the top of the caliper body suggesting that the increased piston diameter is all added to the outside of the caliper, where the piston already overhangs the pad on the 1500 calipers.

 

Actually, that is something I had though of doing if I were to ever add a large rotor/caliper setup in the front. Otherwise, I think it would completely screw up the brake bias. Deleting ABS and incorporating an adjustable proportioning valve, the dual rear calipers could prove beneficial to those running bigs&littles all the time on the street as you could apply more clamping force to the higher traction axle.

 

I don't know much about brake systems but I'd guess that the rear brake lines would have to be enlarged for more fluid volume to the calipers. The brake lines that feed the rear calipers are tiny so adding two more back there would do what??

I was thinking I could run -4 teflon line from the ABS module back to the rears and add a wye at each wheel. So it would go from -4 from the ABS to two -3AN teflon lines to each caliper. But I really don't know if that is necessary or if it would even have an effect on braking.. Any experts?

 

Larger lines would add even more volume the master cylinder would have to move when engaging the brakes. Since hydraulic fluid is not compressible, it moves very quickly thru the small lines. You would just need to make sure the master cylinder is capable of moving the volume of the extra piston. If the rears have more volume than the fronts, swapping line positions on the master may be needed.

 

So the master cylinder is set up to favorably send more fluid pressure to the front brakes?

 

Yes, most are setup this way. IIRC, the disk brake and drum brake trucks have different master cylinders for this reason.

 

In my quest to find the 1" rotors locally, I have discovered yet another caliper. In my previous post, I thought the 75mm/2.95" piston was the base or non-F44 pistion but isn't. The base piston for a 1990 model non-F44 is 2.5"/63mm. The 75mm pistion is the F44 option for the early year OBS(88-91) and eventually became standard in '92 with the 1.28"/32.7mm thick rotor.

 

So what is the Inside Diameter of your average 15 inch wheel where the calipers are. I have a 2005 VHO that came with drum brakes, a previous owner switched it to the single piston disc brakes which I about a year and a half ago changed to the dual piston disk brakes. At the time I never thought I would make enough HP to need a 15 inch wheel but I have since put a trick turbo kit on my truck and am currently making 708 rwhp. With my current setup I can roast my 20's at a 70mph roll. It would be nice to run the same DR Oakley has on his truck if I could because I really don't want to go down to a under 30" tire and I don't really want to go to a bias ply slick either, which are my only options in anything other than a 15" wheel. I have a 14 bolt rear end though and wonder if Oakley's brackets would work on my 14 bolt.

I was on Wilwoods website and they make a bunch of different calipers. I wonder if they have some 2 or 4 piston calipers that would be able to work with those brackets and rotors also. If traction wasn't a factor it would be nice to be able to build as much boost off the line as possible. I can't see those obs single piston calipers being as strong as the dual piston ones I have now but maybe the Wilwoods would hold the same or better even on a smaller rotor.

What do you guys think?