The Stupid Axle Questions Thread

[Schurkey]

We had another guy say that his sticker didn't list any "J" brake codes. I thought it was unusual.

It was awhile ago, and I don't remember what thread that was.

 

[someotherguy]

Alright, so I looked at my RPO sticker and I don't appear to have any "J" codes. Maybe someone can help me determine what I've got for front brakes?:

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We had another guy say that his sticker didn't list any "J" brake codes. I thought it was unusual.

It was awhile ago, and I don't remember what thread that was.

It is indeed pretty weird no codes are on there. However, Derek's truck being an '89 1500 regular cab, it would normally come with the "small" brakes unless optioned with HD brakes. So the "small" brakes would have the 1" rotors, while HD would be 1.25" (though specs on the rotors seem to indicate around 1.29")

Going through the few early parts truck SPID labels I had that were legible, I have found, sorted by year:

1988 C1500 extended cab longbed, 350/SM465, no brake code, though being an extended cab, it certainly came with the larger brakes by default

1989 C1500 regular cab longbed, 305/700R4, no brake code

1989 C2500 (7200 gvwr) regular cab longbed, 350/700R4, no brake code, though being a C2500 (6 lug) it certainly came with the larger brakes by default (and the 9.5" 14 bolt)

1990 C1500 extended cab shortbed, 350/700R4, showing JB5 brake code

So this small sample size kind of implies the brake code hit the scene on the SPID label starting with 1990.

Then, 1992 was when GM equipped all 1500 pickups with the bigger brakes by default, regardless of regular or extended cab.

Richard

 

[GrimsterGMC]

It is indeed pretty weird no codes are on there. However, Derek's truck being an '89 1500 regular cab, it would normally come with the "small" brakes unless optioned with HD brakes. So the "small" brakes would have the 1" rotors, while HD would be 1.25" (though specs on the rotors seem to indicate around 1.29")

Going through the few early parts truck SPID labels I had that were legible, I have found, sorted by year:

1988 C1500 extended cab longbed, 350/SM465, no brake code, though being an extended cab, it certainly came with the larger brakes by default

1989 C1500 regular cab longbed, 305/700R4, no brake code

1989 C2500 (7200 gvwr) regular cab longbed, 350/700R4, no brake code, though being a C2500 (6 lug) it certainly came with the larger brakes by default (and the 9.5" 14 bolt)

1990 C1500 extended cab shortbed, 350/700R4, showing JB5 brake code

So this small sample size kind of implies the brake code hit the scene on the SPID label starting with 1990.

Then, 1992 was when GM equipped all 1500 pickups with the bigger brakes by default, regardless of regular or extended cab.

Richard

My 1988 K1500 has J50 on the sticker that relates as "Brake system, power". It has the tiny JB3 brakes on it.

 

[someotherguy]

My 1988 K1500 has J50 on the sticker that relates as "Brake system, power". It has the tiny JB3 brakes on it.

Right, we see J50 on all these SPIDs (edit for clarification: the 1988-1989 SPIDs) but all the 1988-1989 ones I have are lacking the code indicating the brake package itself - JB3, JB5, etc.

Richard

 

[DerekTheGreat]

Man, I love you guys, resourceful as can be!: "J50." That must be the illegible code between GT4 and KC4 on my sticker.

Is it possible my truck was optioned with JB5? Weren't JB3 trucks equipped with the small, pancake looking brake booster? I've never seen that little guy anywhere, not even in a yard. My truck has the biggun, and I'm too lazy to pop off a front tire to measure one of the rotors. So I'm trying to figure out another way to see what I've got. I had the fronts off about 2k miles ago and foggy memory would say the rotors looked to be about an inch thick. But what's 0.25" amidst friends?

Edit:
Found a picture from 2018, back when I replaced my wheel bearings & axle shafts. Are they the little guys?:

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[someotherguy]

Man, I love you guys, resourceful as can be!: "J50." That must be the illegible code between GT4 and KC4 on my sticker.

Is it possible my truck was optioned with JB5? Weren't JB3 trucks equipped with the small, pancake looking brake booster? I've never seen that little guy anywhere, not even in a yard. My truck has the biggun, and I'm too lazy to pop off a front tire to measure one of the rotors. So I'm trying to figure out another way to see what I've got. I had the fronts off about 2k miles ago and foggy memory would say the rotors looked to be about an inch thick. But what's 0.25" amidst friends?

Do you have the 14 bolt SF? If not, I'd say you have the little brakes almost for sure.

Richard

 

[DerekTheGreat]

Nope, just the dinker-doo 10 bolt. If all goes well, I'll have a 14 bolt SF G80 in my possession by Tuesday. I updated my last post with an old picture I found. Is it visibly obvious as to what I've got?

 

[someotherguy]

Nope, just the dinker-doo 10 bolt. If all goes well, I'll have a 14 bolt SF G80 in my possession by Tuesday. I updated my last post with an old picture I found. Is it visibly obvious as to what I've got?

Not really, IMO. The "small" rotors are about 11.6" diameter, 1" thick - the "big" ones are the same 11.6" diameter, but 1.29" thick. So if you can get out there and put a ruler across the edge of the rotor, you'll have your answer.

Richard

 

[Schurkey]

The smaller rotor is just leaned-up against the bigger one. They're the same diameter, but different widths.

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A person is unlikely to see the difference without something to compare to...or your eyes are calibrated better than mine.

 

[DerekTheGreat]

Hmm. From the looks of it, I've got the bigguns. The only difference is the rotor diameter? Calipers are the same? I think measuring my rotors now would be a wash, there's 60k miles and six years of wear & tear on 'em now.