Brake and/or hydraulic experts caliper size question

I'm going to be putting discs brakes on the rear of my 92 D250. The brackets I have use a GM caliper off the front of a 4WD 3/4 ton pickup. My question is, there are two different calipers with a 2 15/16 size piston and a 3 5/32 size piston.

I'm wondering just how much difference between the two sizes would there be. I'm thinking that since these are going on the rear and 90% of the time or more I'm either running empty or hauling very light I would go with the smaller piston.

Curious what your thought s are.

I'd agree on the smaller of the two,especially on a pickup truck.

I would think a 7/32 diff in the bores would be significant. just me I would likely purchase the larger ones then use a prop valve later if need be but on a big truck I would be inclined to think you will be fine & I would want the most braking power at my disposal. I still refer to your oiling mods on occaision, good job there!

Thanks Robert. I will be doing a write up with pics of the disc swap as well. I'll post here in the truck forum and over at dieseltruckresource.com where I have a write up of converting the 518 trans in a 1st Gen to a lock up torque converter in the sticky section there. There are already a few write ups of disc swaps but most are out dated an no longer available.

I'll be doing the swap the last full week of May when I take my vacation.

I'm thinking the bigger calipers may not fit your bracket, if they're the ones I think they are, they're like the Dodge 1ton 4wd calipers and are slider type vs pin type.

They fit, they are near identical except for the piston size. I've had both on the brackets. Even the earlier '77 style fits. They are the smaller piston but the banjo bolt is 7/16 instead of 10mm. Kind of hard to find braided steel brake hoses with the 7/16 hole.

smaller piston is 6.777 square inch
larger piston is 7.284 square inch
The ratio is 0.866

How are you going to be using the truck? If it is unloaded most of the time I'd say go with the smaller caliper. In a panic braking situation if the rear brakes apply too hard, the rear end will come around. That's why the first ABS in trucks was on the rear axle.

What do newer trucks with your configuration use on their rear disk brakes? Figure out the area of the piston(s).

R.

I'm tired of the rear brakes locking up when it rains. Even though this truck has RWAL the shoes, cylinders and drums need to be replaced. It's a real PITA on these trucks to do that work and it doesn't make sense not to upgrade to the discs when the cost and work involved is pretty close.

So yeah, it's empty or loaded light 90% of the time. I've heard from others that used the larger piston caliper and they say the RWAL works fine with it. Still I'm over sliding down the highway sideways in the rain.

I have no access to a newer truck so I can't compare.

Speedway motors has steel braided wire hose with a 7/16 ID (AN 8) if that is what you are after.

If your truck has the rwal then get the bigger caliper. It will provide more braking force when you do have a load.

I have brembo 4-piston calipers on a 13" rotor on the back of my Dakota. Rwal keeps it from locking up