Questions about JB7 Brakes

NNK20 · 2024-12-03T08:05:16-0500

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 · 2024-12-03T09:20:50-0500

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

Otherwise it was probably retrofitted.

Keith Seymore · 2024-12-03T09:50:49-0500

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 · 2024-12-03T09:52:43-0500

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 · 2024-12-03T13:41:01-0500

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!

Questions about JB7 Brakes

NNK20

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Blue Ox

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Keith Seymore

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Keith Seymore

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NNK20

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