6400 lbs question

[Nunyadam]

I'm trying to determine whether I have 10 or 11 inch drums on my 92 Sierra SLE without having to go outside and take a tire off. (its cold and dark outside right now. lol)
A little research on the RPO codes tells me....

JB5 Brake System: Power, Front Disc, Rear Drum, 6400 Lbs.


I'm guessing its the 11" drum, just hoping somebody here can confirm or correct me if I'm wrong.

 

[Nunyadam]

Jb1 : Brake, manual, disc/drum, 4300 lbs
jb3 : Brake, power, disc/drum, 4600 lbs
jb5 : Brake, power, disc/drum, 6400 lbs
jb6 : Brake, power, disc, drum 7200 lbs
jb7 : Brake, power, disc, drum 8400 l85
jb8 : 8rake, power, disc, drum 10000 lbs

 

[Nunyadam]

the beast in question.

 

[Nunyadam]

According to the Chevrolet 10-30 series light truck service manual:

JB5= front disc 11.86X1.29 rear drum 11.15X2.75 Vacuum-Double Diaphragm

JB7= front disc 12.50X1.54 rear drum 13.00X2.50 Vacuum-Double Diaphragm

JB8= front disc 12.50X1.54 rear drum 13.00X3.50 Hydraulic-Hydro-Boost

JB7 is basically Dana 60 Front disc with the smaller 14FF drum brakes with a vacuum booster and JB8 is Dana 60 front disc with the Large 14FF drum brakes with Hydro-boost.

Ira