JB3 or JB5 brakes?

kidego31 · Jul 20, 2018

I am starting to collect parts to get my resto going. I got a 85 c10 Silverado lwb. Factory was a 305 motor but someone has put a 350/350 in it. I have no power asst to the brakes so I figure the booster is gone. There are no vacuum leaks but I have vacuum to the booster. Looking at booster and master cylinder kits I keep finding about jb3 and jb5 brakes. I have no build sheet or stickers on the truck (thanks to whoever removed them). Is there an easy way to tell what one I have? Would it be better just to get the jb5 booster. I know if anyone can help it will be someone on here. Thanks

Keith Seymore · Jul 20, 2018

Your truck is JB5 brakes.

The V8/long wheel base combination puts you squarely at 6100 lb GVW; 6100 lb = JB5.

JB3 is the lightest duty power brake system so we didn't build very many.

K

73c20jim · Jul 20, 2018

How about a 73 c20 long bed?

dvdswan · Jul 20, 2018

If you don't have the RPO sticker in the glove box or it doesn't show. I guess you have the FF 14 Bolt rear axle and you would have to measure the shoes, I don't remember if it was the front or rear shoe but it will be 11" or 13" shoes IIRC.

73c20jim · Jul 20, 2018

no RPO sticker

kidego31 · Jul 20, 2018

Thank you. This site is amazing. Good People with a lot of knowledge

Keith Seymore · Jul 21, 2018

73c20jim said:
How about a 73 c20 long bed?

I'm not sure.

The '73 chart shows all the components and part numbers but does not link them back to an RPO code.

The comparable system in '74 is labeled JB7, so I would go with that: JB7.

K

73c20jim · Jul 21, 2018

Thanks. Some day I'll measure the rear brakes.

78C10BigTen · Jul 21, 2018

Keith Seymore said:
I'm not sure.

The '73 chart shows all the components and part numbers but does not link them back to an RPO code.

The comparable system in '74 is labeled JB7, so I would go with that: JB7.

K

Any idea what a 78 c10 big ten would be?

shiftpro · Jul 21, 2018

You might want to consider upgrading to 1 ton juice brakes, you know... should you want to actually stop in a hurry.

Keith Seymore · Jul 22, 2018

78c10bigten said:
Any idea what a 78 c10 big ten would be?

JB5.

K

78C10BigTen · Jul 22, 2018

Keith Seymore said:
JB5.

K

Thanks

MikeB · Jul 23, 2018

kidego31 said:
Looking at booster and master cylinder kits I keep finding about jb3 and jb5 brakes. I have no build sheet or stickers on the truck (thanks to whoever removed them). Is there an easy way to tell what one I have? Thanks

I'm not sure if all the codes below were used every year from 73-87, but here's what I've learned:

Brake codes JB1 and JB3 have 1.04" thick rotors and 2" wide brake shoes.

Brake codes JB5, JD3, and JD5 have 1.25" thick rotors and 2.75" wide brake shoes.

So, pull off a front wheel and see how thick the rotor is.

dabrogger · Feb 22, 2023

My JB3 truck booster is bad. Can I replace it with a JB5 booster? I see it’s 2” wider but anything else different?

MarineOne · Feb 24, 2023

Jb3 is single diaphragm jb5 is dual diaphragm so you will have more vacuum assist and braking will require lest pedal effort everything will bolt right up

JB3 or JB5 brakes?

kidego31

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