JB3 or JB5 brakes?

[kidego31]

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]

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]

How about a 73 c20 long bed?

 

[dvdswan]

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]

no RPO sticker

 

[kidego31]

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

 

[Keith Seymore]

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]

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

 

[78C10BigTen]

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]

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

 

[Keith Seymore]

Any idea what a 78 c10 big ten would be?

JB5.

K

 

[78C10BigTen]

JB5.

K

Thanks

 

[MikeB]

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]

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]

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