JB3 with larger piston calipers?

[THOMASO1371]

I have a 90 K1500 RCSB and had a slight vibration under braking. Decided to just replace the braking system so ordered the 1" rotors, ACDelco calipers 743/744 non hd, and pads to go with it. After pulling the wheel off, I saw that it had the HD calipers 745/746, but still had 1" rotors. Will I be good to keep the larger piston calipers and the 1" rotor or should I put the smaller piston calipers on and go back to original?

 

[Schurkey]

DO NOT go back to the crappy, small-piston calipers.

When it was me, I added the wider 1.25" (but same diameter) rotors. I got the bigger-piston calipers, rotors, hubs/steering knuckles, master cylinder, and brake booster from the same extended-cab Treasure Yard donor vehicle. GM quit using the small/crappy JN3 brake system sometime around '93, and the extended-cab trucks got JN/JB5 from the beginning.

All of those parts are different--and better/more powerful--than the JN3 brake system. The rear brakes are the same, crappy 254mm (10") leading-trailing shoe drums.

Upgrading the rear brakes to the 11.x diameter Duo-Servo rear brakes from the JB6 brake system is a fabulous update, especially if you do it by removing the 8.5" ring gear axle in favor of a 9.5" ring gear axle of the same gear ratio, from a "light duty" 6-lug 3/4 ton.

 

[THOMASO1371]

Thanks. I saw your post on another thread outlining to ideal swap. It's a little outside my skill set to go that far for the hubs and steering knuckle.

I've had the truck for a little over a year and had no issues with the larger piston calipers with the 1" rotors other than the shudder when braking. I did replace the crappy 10" drums, but I'm pretty sure I screwed up the backing plate or had a bad new drum because I can hear the drum grind against the plate(have a thread posted about that issue).

I'll stick with the larger piston calipers, with the 1" rotors for now. I did order the NBS master cylinder, but didn't install due to seeing some issues based on brake booster/calipers and that's all above my understanding too. Just wanted to make sure I wasn't causing some long term harm by going large piston with 1" rotors.

Thanks again

 

[evilunclegrimace]

The steering Knuckles are the same for JB3 and JB5, it is the hub/bearing assembly that is different along with the rotors and calipers.

 

[Schurkey]

It's a little outside my skill set to go that far for the hubs and steering knuckle.

The hubs/bearings are different, the steering knuckle is the same. When it was me, the job was started because I had a worn-out, damaged steering knuckle--so replacing the whole steering knuckle/hub assembly was the main point of the work. I discovered the bigger-piston calipers and wider rotors kinda by accident. Then I had to go back to the Treasure Yard and grab the bigger master cylinder and booster.

I've had the truck for a little over a year and had no issues with the larger piston calipers with the 1" rotors other than the shudder when braking.

Then keep the JN3 rotors 'n' hubs. The calipers are the important part. I was just concerned that the calipers might be wider to match the wider rotor. If that was the case, when the pads wear out, the piston might be over-extended in the caliper casting so that it'd fall out.

I'll stick with the larger piston calipers, with the 1" rotors for now. I did order the NBS master cylinder, but didn't install due to seeing some issues based on brake booster/calipers and that's all above my understanding too.

The JN/JB3, 5, and 6 front brakes use low-drag calipers. The "NBS" master cylinder is not compatible with low-drag calipers.

You need a 3-chamber, Quick Take-Up master cylinder instead of the 2-chamber "NBS" master cylinder when used with Low-Drag calipers.

The steering Knuckles are the same for JB3 and JB5, it is the hub/bearing assembly that is different along with the rotors and calipers.

Yes. For those of us doing a Treasure-Yard brake upgrade, slapping on the entire steering knuckle and hub/bearing assembly gives us a chance to do a proper examination of the ball-joints; and a convenient time to replace them as required.

But all that's "really needed" is the different hubs/bearings to go along with the wider rotors.