Let's decode an actual VIN. The vin is 2505ZF2807B.

This is what we know about this truck from this number, It's 1965-66 Model 2500, with a
157" wheelbase built in Fremont California, with a GVW rating of GVW 6,001 - 10,000.
It was truck number 1807 off the line at the Freemont plant of "F" series trucks.

There may also be a letter before the first number Here is a list of light truck model prefixes;
I = Inline Engine, K = 4-Wheel Drive, P = Forward Control Chassis,
PB = Forward Control Chassis with Body, G = Handi-Van

The first two numbers is for the model, the next two are for the wheelbase,
Models -------------------Wheelbases
10 = 1000 ------------------------------------- 01 = 115" --- 02 = 127"
15 = 1500 ------------------------------------------------------ 02 = 127"
25 = 2500 -------------------- 02 = 121" --- 03 =133" --- 05 = 157"
30 = 3000 ------------------------------------- 01 = 133" --- 05 = 157"
The above wheelbases are for light trucks, Handi-Van is 90 inches.

The next letter is the plant code or were the truck was built,
plants with * are GMC Plants, the others are Chevrolet Plants.

A = Atlanta, Geogia
B = Baltimore, Maryland
* C = Oakland California
F = Flint, Michigan
* H = Oakland California
J = Janesville, Wisconsin
N = Norwood, Ohio
* P = Pontiac, Michigan
S = St. Louis, Missouri
T = Tarrytown, New York
* Z = Fremont, California

The next letter is the truck "Series". GMC used a "Series" letter in the VIN number,
& you can narrow down the year of a GMC truck this way. If there was no major change
made in the truck line, the series letter stayed the same, like on a school bus chassis.
This 60-66 body style was first built for the 1960 model year, the first series letter is
"N" & was used in 1960 & 1961. In 1962 GMC changed the hood & dash on the trucks,
the series letter used for 1962 was "J". 1963 saw the torsion bar front end replaced
with coil springs & the rear coil replaced with leaf springs. The series letter for 1963
is "G". The next major change came in 1964 with the restyle of the cab, & the option of
an inline 6 cylinder engine. The series letter for 1964 to 1966 is "F". There was not any
more major changes for this body style. But there was a series letter "E" used on some
1965 trucks (have not seen any yet) & "D" used on all inline engined 1966 trucks. More
info has been found for "F" Series Trucks, GMC built truck in two plants from 1964 to
1966, the Pontiac Michigan plant & one of two plants in California, Oakland or Fremont.
If your trucks vin shows "HF" it was built in the Oakland California plant which GMC shut
down after the 1964 Model year, so all "HF" trucks are 1964. Production was moved to an
ALL NEW plant built in Fremont California for 1965, so "ZF" trucks are 1965 or 1966.

So here is a break down of the series letters;
N = 1960-1961, J = 1962, G = 1963, F =1964-1966, E = 1965, D = 1966

The next group of numbers is the Serial number or unit built number, all series at all plants
started with Serial number 1001. For the 1966 year run, GMC started most series with Serial
number 10,001, but some series not used in 1965 started with 1001. I have found that GMC had
a lot of left over trucks from 1965 & they sold them NEW in 1966 as 1966 Models, this was
done to rid the dealers of any older trucks still on the lot to make way for the NEW body
Style coming in 1967. If you have a GMC "PF" or "ZF" series truck titled as a 1966, but the
Serial number is lower then 10,000, it mite really be a 1965 model year truck. One way to
tell is to check the engine for a spin-on oil filter, no spin-on filter, then it's a 1965.
GMC swithed to the spin-on oil filter for the 1966 model year on V6 powered trucks.

The last letter is GVW class.
A = 6000 lbs or less, B = 6001 to 10,000, C= 10,001 to 14,000

There was some overlap with the Series Letters - GMC just liked to confuse people I guess.
Conrad has a couple books that show that the "N" series started in 1960 & actually going
to 1966, the "J" series started in 1962 & went to 1966, the "G" series started in 1963 &
went to 1966, the "F" series started in 1964 & went to 1966. The "D" series was Used on all
1966 model with Inline 6 engines. So a "D" series is a true 1966 truck while a 1966 "F"
series is a continuation of when GMC started building the "F" series in 1964. Most of the
overlap in series letters is with BIG GMC TRUCKS like the Model 4000 & up. We haven't seen
a Model 1000-3000 "N" series past 1961, a "J" series other than a 1962, or a "G" series other
than a 1963 on what most folks call "Light Duty Trucks". Starting in the mid sixties is
when auto manufacturers started putting more emphasis on the year of production, rather
than the "series". It was common for Trucks to get titled for the year they sold instead
of the year they were built. My truck is a 1965 model, but it's title said 1966.

I can Translate your VIN number for you if you can't figure it out. Send me the following
info about your truck to get it listed on the Vin listing. Use e-mail link below.

1) The year of your truck if known.

2) Trucks VIN number, found on a tag in drivers door frame. See tags on GMC ID Page.

3) Stock V6 Engine number, see the Engine Data Page for were to find that.
3a) If a 1963, Do you have PLAID Valve Covers?

4) Stock Transmission Type & number of speeds (gears).

5) Type of body, Pickup Wide-side (Fleetside) or Fender side (stepside), Suburban, Panel, Stake....

6) For Trucks, size of rear cab window Big or small. For Panels, Suburbans, Gate or doors.

7) Your Name, Home Town, & State.