Odd frame rail stamping numbers?

[RenoKeene]

The first pic is of a 69 Chevy SWB 1/2 ton
The second is a 70 GMC LWB 1/2 ton....the 58131 matches the last 5 of the vin. Whats up with the S prefix?
Are all GMC's different like this?

[special-K]

Good question. I'm curious to now the answer.

[ls1nova71]

My '71 GMC has a letter before the 6 numbers that match the VIN, but it's a J not an S. I thought that meant where it was made?

[RenoKeene]

Here is the whole GMC VIN CE134-SZ58131
I believe the prefix (S) is the mfg plant...St Louis
C=2WD
E=V8
1=1/2 TON
34=FLEETSIDE
S=ST LOUIS
Z=1970
58131= 8131st truck built

So.....GMC only stamped the Plant and the build number?

This truck seems to have been an oddball anyway....1/2 ton FACTORY BIG BLOCK A/C 6 lug CST 127", with aux fuel tank switch in the floor (exactly the same as my 72 Custom Camper). The tank was gone but the mounts were still there, this is where it gets strange...the hangers for a tool stowage box were still mounted to the bed floor but that bedside had been replaced. Leads me to believe it was a Custom Camper but there were only 3 holes in the door above the door handle for the Custom emblem, no Camper emblem.
Did they even make a 1/2 ton Custom Camper?
BTW instead of a SPID I got a chrome glovebox door.

[RenoKeene]

More info on this...
The GMC S 58131 breaks down like this:
S=St Louis
the (5)XXXX denotes 1970 only. 68,69 & 71 begin 10001 and 72 begins 500001, this comes from LMC's catalog (for what thats worth).

So I can tell it was made in St Louis in 70 and was the 8131st truck built.
What it doesn't tell me is if it is a 1/2 or 3/4 ton frame. The VIN tells me it's a 1/2 ton.

I read some old threads about different steel thicknesses between 1/2 and 3/4 tons, according to the above info there is no difference on GMC's.

I have answered all my own questions except WHY SUCH A DIFFERENCE BETWEEN CHEVY AND GMC STAMPINGS? And if the build number was (1)XXXX how would you know if it was a 68, 69 or 71?

[RenoKeene]

Any more thouhgts on this?
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[special-K]

I don't believe a longbed 1/2 frame is any different than a 3/4t. One frame would be strong enough for the difference is GVW,which isn't very much. The springs and axles are enough for that.
In '69 there were Custom Camper/10s. I'm not sure about '70. I know in '69 a factory auxiliary tank was offered and was located in the rear,not the side. I have only seen '72s with the driver side tank. But,I have a '71 Custom Camper brochure that lists the auxiliary tank as a suggested option. But,it's not offered in the dealer data book. The tool & stowage compartment has nothing to do with the Custom Camper option. They were available on any longbed.

[RenoKeene]

Thanks Tim, I'm still confused about the build sequence numbers..

I have answered all my own questions except WHY SUCH A DIFFERENCE BETWEEN CHEVY AND GMC STAMPINGS? And if the build number was (1)XXXX how would you know if it was a 68, 69 or 71?

Also were all big block 70 GMC 1/2 tons 6 lug? Seems that there is a limited amount of build data for GMC's compared to Chevys.

Thanks, Brad

[too much stuff]

Any 1/2 ton 2wd from 67-70 would be 6 lug originally. Any 71-72 1/2 ton would be 5 lug. Shouldn't matter if gmc or big block or not.

[Vintage Windmills]

I'll look at the stamping on the frame from a 69 GMC BB C20 when I get home.

[RenoKeene]

Originally Posted by too much stuff

Any 1/2 ton 2wd from 67-70 would be 6 lug originally. Any 71-72 1/2 ton would be 5 lug. Shouldn't matter if gmc or big block or not.

I see, Thanks.
Any info on the stamping numbers?

[RenoKeene]

Originally Posted by Vintage Windmills

I'll look at the stamping on the frame from a 69 GMC BB C20 when I get home.

Let me know what you find. I'm very curious about all this.

[Vintage Windmills]

They match on my 69 GMC BB C2500:

stamped on frame: SA29914
last 7 digits on title: SA29914

It seems like they forgot to stamp the Z on your truck.