I need some help decoding an axle

[Keith Seymore]

Thanks for all the input people. I started the post because I searched for info on axle codes with no luck until HR showed me the link. I was just researching the trucks history and after getting stumped by the engine number, which I still am, I moved on to the rear end number. I'm just trying to learn more about the truck and square bodys in general.
As far as the SPI goes, there is no differential listed. it came with a LF4 400ci 4 barrel and a MX1 Auto trans. the power train chart shows the standard ratio is 3.07. the truck is a 78 k10 cheyenne, build date is Dec 18 77. would the cheyenne package bump the gears up?

No - powertrain options stand alone, and are not tied with trim options (like Cheyenne or Scottsdale).

Normally if you have the base axle the SPID will show GQ1, but not tell you what the ratio is numerically.

I'd be looking for GU6 (3.42) on your SPID, and then as mentioned above, possibly G80 if it has the locker/limited slip.

I think you are going about it a bit backwards; normally people use those codes to figure out what they have, by not having any other info available to them. You already know what you have, via the RPO codes, so the specific coding on the parts and date coding is actually redundant and of no added interest.

Here's the generic info packet from the Heritage Center, which it sounds like you may already have:

https://www.gmheritagecenter.com/do...its/Chevrolet-Trucks/1978-Chevrolet-Truck.pdf

If you are a glutton for documentation, like me, you can send your VIN and $50 to the Heritage Center and they will give you the invoice for your specific truck, including build timing, option content and pricing, and the original selling dealership and possibly even the original owner's name (if it was a customer order, not for dealer stock).

http://www.gmmediaarchive.com/?page=1

K

 

[DanMcG]

Here's the SPID, Unless I'm looking in the wrong place there is no Tranny shown.

You must be registered for see images

Keith, thanks for the link to the Heritage Center, I was looking for that the other day. I think it might be worth $50 just to get some history on it.

 

[HotRodPC]

Here's the SPID, Unless I'm looking in the wrong place there is no Tranny shown.

You must be registered for see images

Keith, thanks for the link to the Heritage Center, I was looking for that the other day. I think it might be worth $50 just to get some history on it.

That label is way small for me to read, but it appears you have a code starting with M, probably 1 of the MX codes 0 or 1 for Automatic Transmission.

 

[DanMcG]

Yes mx1

 

[HotRodPC]

That's likely the Th350. Keith probably knows more about the Trans codes. I've seen the MX codes in both Th350 and 700r4, It might be Th400 is the MX0. Not positive cuz I haven't studied that, but I bet he clears it up.

 

[RetroC10Sport]

MX1 was just the code for an automatic trans. You could only get an automatic with the 400 V8. Did not specify whether it was a TH350 or TH400.

Standard gears were 3.07s with 2.76, 3.40 and 3.73 optional.

 

[RetroC10Sport]

KAN axle code is a 3.07 non locking 12 bolt 4x4 axle.

 

[Keith Seymore]

MX1 was just the code for an automatic trans. You could only get an automatic with the 400 V8. Did not specify whether it was a TH350 or TH400.

Standard gears were 3.07s with 2.76, 3.40 and 3.73 optional.

This is correct.

MX1 was the "merchandised" option code for the non-overdrive automatic. The engineering release determined from that if it was to be a TH400 or TH350 based on powertrain and GVW information.

MX0 is the merchandised option for an automatic overdrive trans, when appropriate.

K