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Brake and/or hydraulic experts caliper size question #2284863
04/09/17 04:18 PM
04/09/17 04:18 PM
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in a cattle trailer down by th...
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Guitar Jones Offline OP
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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.


"Follow me the wise man said, but he walked behind"


'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost coming soon!
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Brake and/or hydraulic experts caliper size question [Re: Guitar Jones] #2284868
04/09/17 04:23 PM
04/09/17 04:23 PM
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Pittsburgh,PA
RTSrunner Offline
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I'd agree on the smaller of the two,especially on a pickup truck.

Re: Brake and/or hydraulic experts caliper size question [Re: Guitar Jones] #2284871
04/09/17 04:27 PM
04/09/17 04:27 PM
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Lincoln Nebraska
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RapidRobert Offline
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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!


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Re: Brake and/or hydraulic experts caliper size question [Re: RapidRobert] #2285043
04/09/17 10:31 PM
04/09/17 10:31 PM
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in a cattle trailer down by th...
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Guitar Jones Offline OP
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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.


"Follow me the wise man said, but he walked behind"


'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost coming soon!
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Brake and/or hydraulic experts caliper size question [Re: Guitar Jones] #2285202
04/10/17 10:11 AM
04/10/17 10:11 AM
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ohio
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ruderunner Offline
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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.


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Re: Brake and/or hydraulic experts caliper size question [Re: ruderunner] #2285267
04/10/17 12:56 PM
04/10/17 12:56 PM
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Posts: 20,600
in a cattle trailer down by th...
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Guitar Jones Offline OP
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Originally Posted By ruderunner
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.


"Follow me the wise man said, but he walked behind"


'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost coming soon!
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Brake and/or hydraulic experts caliper size question [Re: Guitar Jones] #2285308
04/10/17 02:37 PM
04/10/17 02:37 PM
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dogdays Offline
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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.

Re: Brake and/or hydraulic experts caliper size question [Re: dogdays] #2285335
04/10/17 03:45 PM
04/10/17 03:45 PM
Joined: Dec 2009
Posts: 20,600
in a cattle trailer down by th...
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Guitar Jones Offline OP
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in a cattle trailer down by th...
Originally Posted By dogdays
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.


"Follow me the wise man said, but he walked behind"


'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost coming soon!
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Brake and/or hydraulic experts caliper size question [Re: Guitar Jones] #2285621
04/11/17 12:45 AM
04/11/17 12:45 AM
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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RapidRobert Offline
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Quote:
but the banjo bolt is 7/16 instead of 10mm. Kind of hard to find braided steel brake hoses with the 7/16 hole.
Speedway motors has steel braided wire hose with a 7/16 ID (AN 8) if that is what you are after.


live every 24 hour block of time like it's your last day on earth
Re: Brake and/or hydraulic experts caliper size question [Re: Guitar Jones] #2285637
04/11/17 01:14 AM
04/11/17 01:14 AM
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383 Offline
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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


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