J55 Brakes

[custodian]

My 85 C10 is the heavy half ton truck. I'm changing from hydroboost to the power brake system. I have the brake RPO code of J55. It has the RPO code of GU4 for the rear axle (3.08). Can anyone tell me what size the rear brake shoes would be, and what front disc calipers and rotors I would need? Everything I look up ask if JB3, JB5 etc. I haven't taken anything apart yet.

 

[Scott91370]

I don't see them either and the entire list is here:
https://www.gmsquarebody.com/threads/front-brake-hoses.28411/

 

[Keith Seymore]

Here are the brake charts for 1985 C10 pickup, Blazer and Suburban. These are the working documents the engineers used to release the parts for production and service.

The reason you can't find JB3/JB5/JB6 etc on your truck is because the customer does not select those. The customer says "I want manual brakes" or "I want power brakes" and chooses the "Merchandised Option" J55. The engineering release chart then dictates the specific "Non Merchandised" brake option JB3/JB5/JB6 etc based on model, wheel base and GVW considerations.

More specifically, "03" is the model code for pickup, so find the columns that say either C10703 (short wheel base) or C10903 (long wheel base) and the appropriate GVW. "JBx" brake systems are vacuum; "JDx" systems are hydraboost.

Have fun!

K

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[custodian]

Thanks for all the info. I'll use it as a guide to determine what I have. I believe it's going to be the JB5 with 1.25 rotors and 2.75 rear brakes.