2wd 1500 vs 2500

[Schurkey]

Compared to my 1500, the 6 lug 2500 rotors were thicker, larger piston in the caliper, and different pads. Not sure of the specific RPO code, but by '90 those inferior front brakes were eliminated

The 1500 may also have the weak JB-3 front calipers and small master cylinder/booster. The extended-cab 1500s and the 2500s should have at least JB5 brakes--bigger caliper pistons, bigger master cylinder bore, bigger booster.

The RPO codes may have changed--JD3 vs. JB3, or something like that, but the functional difference between the xx3 vs. xx5 is as I described--bigger caliper piston, bigger master cylinder bore, and more-powerful vacuum booster. I forgot to mention the thicker rotor.

Photo 1. xx5 booster (left) and xx3 booster (right)
http://hbassociates.us/K1500_2020_Brake_Booster_02.jpg

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Photo 2. Rotor thickness difference between xx3 and xx5 front brakes. The diameter is the same, the way these rotors are positioned for the photo makes the thinner one seem to be smaller-diameter.
http://hbassociates.us/K1500_Front_Suspension_19.jpg

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Yes, the xx3 brakes were discontinued in the early '90s.

I converted my xx3 brakes to xx5 in front about a year ago.

Both the xx3 and xx5 brakes have low-drag front calipers, so you need the step-bore GMT400 master cylinder, NOT a GMT800 master cylinder!
Photo 3. Step-bore master cylinder. Note enormous piston at right side, supplying a large "gush" of low-pressure fluid to the low-drag calipers to push the caliper pistons up to the rotors. Then the smaller, high-pressure fluid actually applies the braking force.
http://hbassociates.us/K1500_Front_Suspension_54.jpg

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[Supercharged111]

The xx5 were found on 1500 and 6 lug 2500 though. Not sure about 2wd vs 4wd though as the hub and rotor designs are totally different.

 

[Schurkey]

The xx3 and xx5 both include the horse-**** 10" leading/trailing shoe rear drums.

I think--and I have not researched this in-depth--that only the 1500s have leading/trailing rear drums, and therefore the 2500s aren't optioned as xx3 or xx5.

When you get to a six-lug 2500, you have the xx5 parts IN FRONT, and at the master/booster, but you've got the bigger, duo-servo rear brakes. The upgraded rear axle, along the xx5 in front, is listed as xx6 on the option sheet.

Put another way, xx5 and xx6 are identical except for the rear axle, and the xx6 is what you get on a 6-lug 2500.

The 8-lug 2500 goes to xx7, bigger rotors compared to xx5/6, bigger drums compared to xx6, and no quick-take-up calipers, so no step-bore master. My '97 has hydroboost, there may be a vacuum-booster version.

One-ton (3500) brakes are even huger.

 

[Supercharged111]

OK that all sounds consistent with how I understand the trucks to be, just never paid much attention to the RPO codes. So then an F44 1500 would by default be an xx6 as it got the 9.5" out back but regular stuff up front.

 

[Schurkey]

OK that all sounds consistent with how I understand the trucks to be, just never paid much attention to the RPO codes. So then an F44 1500 would by default be an xx6 as it got the 9.5" out back but regular stuff up front.

I don't know enough about F44 to make an intelligent comment.

Check the glovebox door, see what RPO codes are listed.

 

[Supercharged111]

I don't know enough about F44 to make an intelligent comment.

Check the glovebox door, see what RPO codes are listed.

F44 is heavy duty chassis option. In the 1500 that means 9.5" rear diff, 4+1 leaf pack, and maybe some other stuff. In the 2500 and 3500 I can't say.

 

[stutaeng]

I thought F44 was only an option on the 1500? Not sure of the 2500LD... don't know much of those.

I thought on the 2500 (8 lug) and 3500 it was the Z82 or Z85 option? My K3500 has Z85 option, but I think it's the trailering package? I think Z82 was the chassis option?

 

[Supercharged111]

I thought F44 was only an option on the 1500? Not sure of the 2500LD... don't know much of those.

I thought on the 2500 (8 lug) and 3500 it was the Z82 or Z85 option? My K3500 has Z85 option, but I think it's the trailering package? I think Z82 was the chassis option?

You may be right, but I thought the C&C trucks had an F44/heavy option as well and no I don't mean the real 3500HD.

 

[stutaeng]

You may be right, but I thought the C&C trucks had an F44/heavy option as well and no I don't mean the real 3500HD.

Ok, think you are right on that. That's the ones with 15,000 lbs<GVWR>10,000 lbs. Was it like 12k lbs maybe? I read something on those here a while back...

Regular 3500 C&C, not the 3500HD beasts...?

 

[Supercharged111]

Ok, think you are right on that. That's the ones with 15,000 lbs<GVWR>10,000 lbs. Was it like 12k lbs maybe? I read something on those here a while back...

Regular 3500 C&C, not the 3500HD beasts...?

Those are the ones I'm thinking of.