JB7, JD7, or JB8

[coachdtierney54]

New to the forum. I have an 85 C30 that needs a brake job. When I went to AutoZone, they asked what brake system I have. The tech told me to check the label inside the glove compartment. I checked, but none of these codes are present. Any idea what I need to buy?

Thanks!

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[Rusty Nail]

More information is necessary.

LIKE the brake rotor overall diameter.
The tire loading placard in the door jamb may have useful information.

Outside of that, with no RPO sticker, you can decode the VIN and that MAY help...

Oh. None present...yeap, itll likely be determined by the rotor size, because heavier duty brakes are bigger.

 

[bucket]

Depending on what you want to replace, those options may not even matter. But, if you have a SPID label in the glove box or under the hood, the option should be there if you want to take another look.

Those codes have to do with caliper bore sizes, wheel cylinder sizes, and brake drum/shoe size and width. So even if you can't find the code, you can match up the parts at the parts store. If the idiot says they can't help you without the code, tell them to quit being a putz and do their job

 

[coachdtierney54]

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[bucket]

Being that it's a dually with all the HD stuff, it's probably the JB8. Those brakes were probably standard with the other options.

 

[coachdtierney54]

The tech told me to take the tire off and take a picture. Then he could match it.

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[coachdtierney54]

The VIN has the capacity of 9000 to 10000

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[MikeB]

Pull off a rear drum and measure the shoe width. It will be either 2.5" or 3.5".
Typically the rear drum/shoe size is also used in the description of the front brake components.

Looks like 3.5" wide shoes means the braking system is JB8.

2.5" shoes = JB7 or JD7.

 

[coachdtierney54]

Very cool. Thanks again guys! I'll let you know how it goes. Probably have to wait until next weekend.

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[CSFJ]

And please, don't refer to the counter guy at the parts store as a "tech". Lol, as much as they'd like to think they are, they're not.

 

[MikeB]

Also found this:

JB7: POWER, DISC, DRUM 8,400 lbs GVW
JD7: Hyd Power, Disc/Drum, 8,400 lbs GVW (Hydro-Boost)

JB8: POWER, DISC, DRUM 10,000 lbs GVW

I'm pretty sure JB7 and JD7 systems use the same drums, shoes, rotors, pads, calipers. But JB8 is a different animal.

 

[1987 GMC Jimmy]

And please, don't refer to the counter guy at the parts store as a "tech". Lol, as much as they'd like to think they are, they're not.

Amen!

 

[Keith Seymore]

Also found this:

JB7: POWER, DISC, DRUM 8,400 lbs GVW
JD7: Hyd Power, Disc/Drum, 8,400 lbs GVW (Hydro-Boost)

JB8: POWER, DISC, DRUM 10,000 lbs GVW

I'm pretty sure JB7 and JD7 systems use the same drums, shoes, rotors, pads, calipers. But JB8 is a different animal.

This is correct. The OP's truck is a 10,000lb/JB8.

The SPID doesn't help because it will show the "merchandised option" of J50 = power brakes (that's the option the customer gets to pick) if it shows anything at all. J50 is standard on crew cab, CK30 models or when C6P HD chassis is ordered (which is standard with dually RPO R05). That's probably why J50 and C6P do not appear on the SPID.

The engineering release tables then convert that into the "non-merchandised" RPO (the one the customer doesn't get to pick) of JB3/JB5/JB6/JB7/JB8 as appropriate based on vehicle model and GVW.

K

 

[bucket]

This is correct. The OP's truck is a 10,000lb/JB8.

The SPID doesn't help because it will show the "merchandised option" of J50 = power brakes (that's the option the customer gets to pick) if it shows anything at all. J50 is standard on crew cab, CK30 models or when C6P HD chassis is ordered (which is standard with dually RPO R05). That's probably why J50 and C6P do not appear on the SPID.

The engineering release tables then convert that into the "non-merchandised" RPO (the one the customer doesn't get to pick) of JB3/JB5/JB6/JB7/JB8 as appropriate based on vehicle model and GVW.

K

Did that process change when the later style SPID came around? I know I've seen SPIDs with JB5/JB7/etc printed right on them. I think my '88 Burb is one of them.

 

[Keith Seymore]

Did that process change when the later style SPID came around? I know I've seen SPIDs with JB5/JB7/etc printed right on them. I think my '88 Burb is one of them.

Yes - there is variation between model years, and also from plant to plant within the same model year.

K