Questions about JB7 Brakes

[NNK20]

Hey everyone, longtime “guest” reader here and I have learned so much from here, so thanks for having an awesome forum. I have a 1979 K20 with a 400sbc, TH400, NP203 that I am working on. Unfortunately the SPID is missing, I’m in the process of ordering an RPO list for the truck. The truck appears to have its original axles and does have the larger JB7 brakes however it’s a 6800 GVWR. I’ve read before that JB7 was a “heavy duty option” that could be ordered with the 6800 GVWR trucks but I’m wondering if anyone else has ever heard of that? Thanks for reading and I appreciate any help.

 

[Blue Ox]

You sure you don't mean 8600? That would be a JB7 / C6P option.

Otherwise it was probably retrofitted.

 

[Keith Seymore]

Here's the brake chart for the '79 JB-7 trucks.

Unfortunately the hole for the three ring binder goes right through where I want to see. I assume that is the K20 column (column 24).

If so, your two choices for GVW are either 6800 or 8400 lb GVW.

K

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[Keith Seymore]

Here's the generic info packet for some additional detail:

www.gm.com/content/dam/company/no_search/heritage-archive-docs/vehicle-information-kits/chevrolet-trucks/1979-Chevrolet-Truck.pdf

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[NNK20]

Great, thanks for the reply and information. It looks like according to that brake chart my truck may have been ordered with JB7 and the 6800lb GVWR. I really appreciate the help!

 

[carnutjw]

Reviving an old thread instead of starting my own since my "JB7" search led me here.
I bought my '87 Suburban R20/8600 gvw in August of 2024. It has always pulled left during any sort of braking. Steering and tire wear seemed to be reasonable so I attributed it to a brake issue.
After much deliberation I decided on some Hawk ceramic pads ($110 on Amazon), rebuilt calipers and stock replacement hoses from Oreilly auto. I cleaned and regreased the existing Timken bearings and reused my old rotors.
I've put about 300 miles on the truck since, both loaded and unloaded, and I must say the difference in braking ability is substantial. Pads are quiet so far, but I can't report on dusting yet due to frequent rain. Better yet- no more pulling left! The old pads had about .030" difference in wear so the caliper piston must have been sticking. The rotors were within a couple of thousandths.
The unfortunate part is that it appears Hawk may no longer be producing this exact pad. If they work out long term I guess I could reach out to them for a comparable pad.

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