The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Redoing the Brakes... but the rear's are locking up on hard braking

sircrunch · 08-23-2016, 09:01 AM

I read some information last night that got me thinking.... There are 3 different types of brake systems for my truck. JB1 JB2 and JB5. These codes are on the service id sticker on each truck. My truck is originally a JB1 truck. That is manual, non-power brakes. JB3 and JB5 are power but it depends on the GVW of the truck. Because of my trucks lighter weight, when I upgraded to power brakes I went with all JB3 components. From what I read, JB1 and JB3 share most components anyway.

So I read a post on another message board from a fellow that said he converted his truck from JB3 to JB5 over time, piece at a time, and he said never mix JB3 and JB5 because "it will let the rear brakes lock up easily"

Sounds like what I have going on BUT as far as I know, I don't have any JB5 stuff on my truck.... Unless perhaps... the store gave me the wrong master/booster.

So right now, I've removed the master and booster for a return. I'm going to try to return it for a booster/master combo and install that to see what happens. If I'm still getting stronger rear brakes and weaker front brakes, I'm going to go to the next step, which I think would have to be.... the proportioning valve??

08-23-2016, 09:01 AM	#6
sircrunch Registered User Join Date: Apr 2016 Location: Anderson, SC Posts: 160	Re: Redoing the Brakes... but the rear's are locking up on hard braking I read some information last night that got me thinking.... There are 3 different types of brake systems for my truck. JB1 JB2 and JB5. These codes are on the service id sticker on each truck. My truck is originally a JB1 truck. That is manual, non-power brakes. JB3 and JB5 are power but it depends on the GVW of the truck. Because of my trucks lighter weight, when I upgraded to power brakes I went with all JB3 components. From what I read, JB1 and JB3 share most components anyway. So I read a post on another message board from a fellow that said he converted his truck from JB3 to JB5 over time, piece at a time, and he said never mix JB3 and JB5 because "it will let the rear brakes lock up easily" Sounds like what I have going on BUT as far as I know, I don't have any JB5 stuff on my truck.... Unless perhaps... the store gave me the wrong master/booster. So right now, I've removed the master and booster for a return. I'm going to try to return it for a booster/master combo and install that to see what happens. If I'm still getting stronger rear brakes and weaker front brakes, I'm going to go to the next step, which I think would have to be.... the proportioning valve??