JB5 vs JB7

[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?

[kipps]

J̶B̶5̶ (JB6) has 11" rear brake drums. JB7 has 13" rear brake drums. The difference is striking when you look at the rear drums on the truck. Unfortunately, I can't find any google photos that show the difference, and my truck is partially apart.

There's other differences with the front calipers and the master cylinder, but I can't say for sure how to measure those.

The 'Vehicle Information Kit' on the GM website for your 454-equipped Suburban indicates that it's a c20 with a 8600-gvwr. I almost positive that a 8600-gvwr vehicle is going to have JB7 brakes, since GM expects you to be pulling heavy campers with that rig.

https://www.gm.com/heritage/archive/...formation-kits

See if you have room to slip your fingers between the 16" rim and the drum. If not, then I'm going to say it's JB7.

Edit: I'm mistaken in saying "JB5". I should have said JB6 instead, as the lighter-weight alternative to JB7.

[Wobpb377]

Originally Posted by kipps

JB5 has 11" rear brake drums. JB7 has 13" rear brake drums. The difference is striking when you look at the rear drums on the truck. Unfortunately, I can't find any google photos that show the difference, and my truck is partially apart.

There's other differences with the front calipers and the master cylinder, but I can't say for sure how to measure those.

The 'Vehicle Information Kit' on the GM website for your 454-equipped Suburban indicates that it's a c20 with a 8600-gvwr. I almost positive that a 8600-gvwr vehicle is going to have JB7 brakes, since GM expects you to be pulling heavy campers with that rig.

https://www.gm.com/heritage/archive/...formation-kits



See if you have room to slip your fingers between the 16" rim and the drum. If not, then I'm going to say it's JB7.

Awesome. That’s exactly what I was
Looking for. I checked the rear drums it is essentially
The same size as the wheel.

[SCOTI]

Wider rear brake shoes = the HD brake package as well (if you don't trust your visual of the drum size). The HD brake package shoe width is 2.75" I recall vs 2" on the smaller brake set-up.

[Wobpb377]

I think I found another visual. The front brake line. The JB5 is a straighter cs the JB7 has a few kinks

[SCOTI]

Originally Posted by Wobpb377

I think I found another visual. The front brake line. The JB5 is a straighter cs the JB7 has a few kinks

But.... It's an '86 model. There is a possibility things have been changed (like rubber brake lines). So for a visual, there's a chance things aren't what they were originally.

[Wobpb377]

Point noted. Just. something I noticed on mine.

Thanks though for the help and the easy way to
Look at rear drum.

[Keith Seymore]

JB5 is a half ton, so it will have 5 lug wheels (or 6 lug for a K truck).

K

[kipps]

Originally Posted by Keith Seymore

JB5 is a half ton, so it will have 5 lug wheels (or 6 lug for a K truck).

K

I goofed. The non-c6p c20 and k20 trucks used JB6 brakes, instead of the JB7 that the c6p trucks used.

[Robert Crandall]

This photo shows a 1977 service manual. For 3/4 ton it shows: JB5 for GVW 6400, JB6 for GVW 6800 with JB7 being optional heavy duty, JB7 for GVW 7500 to 8000. If you have your GWV, then you can confirm with disc and drum measurements.

[Impact02]

Same information from a 86 service manual