Information provided by Howard Pletcher. This is an updated version (June 29, 2004)
There is little to decode from IH serial numbers. If you have a table of them, they do identify the time frame a truck was built in, but that is not hidden within the serial number. The system used depends upon what time frame you have in mind.
For many years starting in the 1930”s or earlier, each individual model had its own serial number sequence starting with 501 when the model was introduced. For example, there was an R100-501, R120-501, R130-501, etc.
When the S-line was introduced in 1955, it also started with serial S501, but there was no separate sequence for the various S models. S501 may have been a 110, S502 a 130 or 150, etc.
Serial numbers started over with SA501 with the A-models in 1957 and again with SB501 with the B-line in 1959. However, when the 1961 C-line was introduced, the serial numbers kept going with the SB numbers rather than starting over. This sequence continued until 10/65 when a new 13 digit VIN was introduced.
There were various other prefixes besides SB used for other models–FC’s were Scouts, W’s were Emeryville DCO-405’s, FW’s were the DCO-405’s built at Fort Wayne, and there were more for different models at Fort Wayne in particular.
The VIN structure used from 10/65 until the start of the 1973 model production consisted of a 6 digit model code followed by a letter indicating the plant it was built in followed by a 6 digit serial number. The model code was a specifications code that basically meant what model the truck was sold as. There is some meaning to the codes if you have the code table to interpret them.
The plant code was a G for Fort Wayne, H for Springfield, C for Chatham, Y for San Leandro, and L for Bridgeport Metros, and the serial was a sequential number. Trucks were generally built in serial number order, but not exactly for numerous reasons. Example: 781956G200123
For the 1973 model year, the VIN was modified to consist of a 5 character model code, followed by a letter indicating the model year of production, the plant indicator, a production line within the plant indicator, and a 5 digit serial number that started with 10001 each year. The plant indicators were the same as above. The model year indicator was a C for 1972, D for 1974, etc. The production line was either Line A or Line B for Fort Wayne and Springfield and A for Chatham. The Scout line was always line D in Fort Wayne (there had been a C line for a time, but it was discontinued about 1970). C and D were used at Springfield when the A and B serial numbers passed 99999 and started over. Example: H0062HGD39515.
This system continued through 1980, and then was modified by a US Federal Standard that specified the VIN structure to be used by all manufacturers. This system added 3 characters at the start of the IH VIN to indicate the country of origin, manufacturer, and type of vehicle and another character just ahead of the model year letter that was calculated from the rest of the characters to produce a check digit to help detect alterations to the VIN or errors in computer processing. The year indicator was B for 1981 and continued through Y in 2000 (skipping I, O, and Z ) followed by the numerals 1 through 9 through 2009. The sequence will restart with A in 2010. In the mid-1980”s, Navistar dropped the production line indicator which wasn”t required by the law and quit restarting the serial numbers each year. A similar system is in use today on any vehicle you may purchase in the US–and probably anywhere in the world. Using this you can tell if your vehicle was built in the US or not–1 for the first character=US, 2=Canada, and every country has a particular number or letter, although I”m not sure what they do after the first 36 countries. Example: 1HT36B2C9CHA12345.
One question often asked is ?Where was my truck built?? Prior to the use of the plant indicator in the VIN beginning in 1965, there is little indication on the truck itself. The VIN plate does not indicate. It says ?International Harvester Company, Chicago Illinois? or ?International Harvester Company, Hamilton, Ontario? for trucks built in Canada. The city is the location of the IH Headquarters for that country, not the plant where the truck was built. IH built only the first 100 Autobuggies in Chicago and a hundred or so trucks in Hamilton in the 1920?s, but all trucks say Chicago or Hamilton on the VIN plate.
As a rule, the lighter duty models were built in Springfield and the heavier ones at Fort Wayne. The dividing line appeared to be around the 1 ton models?K3, or the 130 series in the early years, although it varied from year to year according to production needs. By the 1960s, all the light line vehicles were built at Springfield up through the 150/1500 and the light end of the Loadstars–the 1600 and 1700–were also added.
All, or virtually all, IH vehicles sold in Canada were assembled at Chatham including Light Line and Scouts up through 1967. These were assembled from parts both built in Canada and shipped in from the US. After this, an Automotive Trade Act permitted manufacturers to trade production across the border and all manufacturers began to concentrate production of specific models in their Canadian plants. Chatham then built the CO-Loadstar/Cargostar models and the heavy end of the Loadstar line until the Fort Wayne Plant closed in 1982, after which Chatham built the heavy-duty conventional models.