C14 or C17 Pedal Rod Booster

[tucsonjwt]

I can't get an answer from the parts stores on the proper booster for my 1983 C20.

The options are:

Pedal Rod #C14 - GM Code JB6 Brake (7200 LB.)
Option Codes are Located on the "GM Service Parts Identification" Sticker

Pedal Rod #C17 - GM Code JB7 Brake (8400 LB.)
Option Codes are Located on the "GM Service Parts Identification" Sticker

I don't have a GM Service Parts Identification Sticker, so which one is correct for my truck? How would I tell the difference?

I don't see any markings on the booster or pedal rod itself. I do have a cast iron master cylinder, if that makes any difference.

Thanks.

[hatzie]

JB6 = LD 3/4ton
JB7 = HD 3/4ton

JB6 should have 11 5/32" X 2 3/4" drum.
JB7 should have 13" x 2 1/2" drum.

[tucsonjwt]

Thanks. I guess I will have to pull off a rear wheel tomorrow and measure the drums.

[tucsonjwt]

I just remembered that I have a floating rear axle. LMC refers to 11" and 11-5/32" brake shoes. Can I determine which shoes I have by looking at the outside of the drum? My VIN has a 4th character "G", which is supposed to be 8001-9000 GVW (VIN tag says 8600 GVW).

[tucsonjwt]

I finally found it. A very faint stamped "C17" on the pedal rod at the booster end of the rod. What a search.