RPO J55

[Craig 85]

that's what I'm working with. I guess I'll need to remove my rotor and take it in. I'm starting to work on the front end in my truck and the rotor thickness is 1-1/2" they can't seem to pull up the right ones at auto zone or Napa. I also need to figure out which hub nut socket I need for my locking hubs to get the rotors off in the first place...

@Frankenchevy I had to get new rotors when I did the brakes last summer. These are the ones I got at Napa. If you need the hub socket for the D60, text me, I have one.

https://www.napaonline.com/en/p/NB_4885843

 

[Craig 85]

What do they call the 1-1/2” rotors...JB8?

Yes, it also includes the 3.5" rear drums. 10,000 GVW

 

[Keith Seymore]

Posting the 1987 model year charts, since I have them handy, for your reference:

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[Jrgunn5150]

I was aware of the thinner rotors in the 80's, but you're saying even the Big 10 and Heavy Half has the same brakes as the standard half tons? So then what is RPO Code J55 HD Brakes mean? Maybe rears wider shoes???

My 79 was a 250/3speed truck, with nothing extra at all. It was the bare minimum you could order, and still has the 1.25 front brakes.

 

[Keith Seymore]

My 79 was a 250/3speed truck, with nothing extra at all. It was the bare minimum you could order, and still has the 1.25 front brakes.

The 1" rotors were for manual brakes and the lightest version of power brakes (JB3, @ 5600 lb GVW). We didn't build very many of those; I always assume the person has the 1.25" rotors and am surprised if/when they don't.

K

 

[Keith Seymore]

One other point of clarification, I guess, while I am here:

The J50 and J55 designations are what we call "Merchandised Options". The customer or dealer says "I want manual brakes" (those are base, so no option impact aka JB1) or "I want power brakes" (and therefore chooses RPO J50 or J55 as appropriate).

The engineering charts then pick the specific brake RPO, ie the "Non Merchandised Option", based on model, series, GVW and (sometimes) engine type. That is what the JB3JB5/JD5/JB6/JD6/JB7/JD7/JB8/JD8 represents.

You can see the same thing with transmissions. The customer chooses an automatic trans, or a three/four speed manual trans and then the engineering release picks the specific version based on the powertrain chart.

K

 

[Tlambert]

Keith, I read your last post above and your post above with the brake guides for 1987.
I’m pretty sure I understand it but can you confirm for me that my truck has the JB3 brakes.

My truck is a 1983 C10 Silverado 1/2 ton GVWR 5600. Master cylinder which I believe to be original has the ZF decal on the reservoir. Power assist front disk 1in thick I believe....(rotors are being machined at the moment) the pic I have of the measurement isn’t clear.

Rear drums are 11in with 2in shoes.
My service parts identification has J50-power brakes listed in the right colum. Here is a pic of the service label.

Thanks Tim

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[chengny]

RPO J50 is a non-specific code for power assisted brake systems - it only differentiates power brakes from manual brakes.

The 11" X 2" rear drum dimension was only used with the JB1 & JB3 systems. So, when taken together with the power assist feature, it would indicate that you have JB3 brakes:

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[Tlambert]

Thanks for the info. I appreciate the help.

 

[Keith Seymore]

Agree. The 5600 lb GVW makes it pretty clearly JB3.

K

 

[Tlambert]

Thanks Keith.