JB5 Rear to JB6 Drums 6 Lug - Help with Models to pick

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Redsled

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I did the upgrade this weekend. After comparing the 86 to 80mm calipers side by side in the store, my gut said go with the 80mm since I knew that swap has been successfully done. So I went with the 80mm calipers.

I installed new (correct for the swap) hubs, new 1.25” rotors, new (reman) 80mm calipers and new 370 pads. It went together like a dream. The only thing I had to address was the bottom of the outer pad just barely made contact with the rotor hub like @1998_K1500_Sub noted in his thread. I took my grinder and removed just a touch of the metal material from the bottom edge of the outter pad to make clearance. This was very easy to do and only took a few minutes. It all when together without any issues.

Result - oh yesssss….much improved. Worth every penny!!
 

L31MaxExpress

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I have the largest calipers GM put on our trucks (no idea about piston diameter offhand), but that's 8-lug stuff. There are people that put "3/4-ton" calipers on their half tons, but I'm unsure of clearance issues, and I don't believe that's a combination that was ever factory. My setup was factory, just not on my truck.
The light 3/4 ton caliper setup was stock on many vehicles. There was also the GM option for the even larger piston SRW 8-lug caliper on the police Tahoes and Tahoe Limiteds, my 99 Tahoe had these. I put the larger SRW 1-ton calipers on my 1500 van without issues. I now have a 3500 DRW 1-ton calipers, pads and the 01-02 Van specific 39.1mm thick 8 lug rotors that make that combination possible.
 
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L31MaxExpress

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As for the rear brakes. I finally got around to comparing a few differentials in the wrecking yard. Atleast between the ones I looked at on mid 90s trucks and vans, the axle flange to backing plate distances were the exact same between a 10" drum and 11" drum. The axle tube bolt pattern was also the same. The wider 11" drums had a backing plate with more offset to the rear. It absolutely appears to be the same differential housing and axles, just different backing plates and drums.
 
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L31MaxExpress

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I also do not know if you guys realize this but the LT1 Impala SS/9C1 Caprice era rear disc setup is a direct bolt on to a 5 on 5" 8.5 or 9.5 rear axle. I put the Caprice rear brakes on my 83 G20 van nearly 2 decades ago. Required absolutely nothing changed as far as axle or differential housing aside from adding brake line/hose retention clips. Pull the axles out, remove the backing plates, install the drum parking brake setup and caliper brackets, re-install the axles, install the rotors, calipers, caprice brake lines and you are done. I put the Caprice master cylinder and proportioning valve in place of the G20 parts.

On my 83 G20 it had 1/2"-20 lug studs, the GMT800 trucks have M14-1.50 studs. The Caprice/Impala rotors fit over my 1/2"-20 studs but will likely need a small maching operation with a drill press to get them mounted over a 14mm stud.

I have also done a rear disc conversion on a G-body 7.5" rear using the OEM rear brake setup off a 4th gen Firebird. It was a direct bolt on using all GM parts.
 
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