JB5 vs JB7 Brake system

[wobpb377]

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]

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]

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]

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