JB5 vs JB7 Brake system

wobpb377 · Mar 23, 2023

How do you tell what brake system my truck has. It’s a 1986 Suburban 3/4t 454 with 400 trans. The SPID doesn’t list JB7 on there. Sites like napa or autozone say with our without JB7 for my truck. Maybe a visual inspection?

Doppleganger · Mar 23, 2023

If your master cylinder has a plastic cap (like a car) its a JB5. If steel, its a JB7. Also - iirc, the diameter of the rear drums is also a giveaway. 11" is JB5 and 13" is JB7.

Those are 2 ways I found mine out.

Scott91370 · Mar 24, 2023

Ignore the markings on it, those are for my truck.

Measuring the thickness of the front calipers and width of the drums is the best way to determine the size/system.

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Keith Seymore · Mar 24, 2023

The easiest way to tell: JB5 is a half ton brake system, so the hubs will be 5 lug (or 6 lug for a K truck).

I think what you meant to ask is: Do I have a JB6 or JB7?

JB6 = 6600 lb GVW
JB7 = 8600 lb GVW.

K

JB5 vs JB7 Brake system

wobpb377

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Doppleganger

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Scott91370

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Keith Seymore

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