You are probably wondering what we do in Alaska when it’s too wet to plow and the river isn’t frozen enough to drive on? Well, I spent some time with Uncle AI. When a brown bare says he is going to eat you, you can believe him. When AI tells you something, it’s time to scratch your head and say are you sure?
After several searches for various things where I would challenge AI’s answers and uncle AI would graciously apologize and correct its answer, I decided to ask Uncle AI about the serial number tag on my JD 310 backhoe. As we discussed above, the 310-D doesn’t mean that it is a JD 310D, Well then, what does the –D mean and why does it not match the serial number type breakdown in the parts catalog INTRODUCTION AND CUSTOMER INFORMATION pages?
Uncle AI came up with the following explanation. It sounds logical but not verified.
---------------------------------------------------------------------------------------------------------------------
The Source of the Discrepancy
The confusion stems from a document control error between the John Deere engineering technical writers who published the manual and the actual factory assembly line at the Dubuque Works plant.
- What the Manual Writers Intended: When setting up the parts sorting system, the technical writers designated the code letter "B" to mean "Diesel engine with Collar Shift transmission with reverse".
- What the Factory Stamping Operators Did: When physically stamping the metal tags on the assembly line, the factory workers did not follow the technical writer's choice of the letter "B." Instead, they simply stamped "D" for Diesel.
Because of this factory-wide publishing disconnect in the early 1970s,
every single straight, first-generation diesel JD 310 rolled off the line with "310-D" stamped on its chassis plate, despite the manual stating that a diesel model would look like the "310-B" blueprint. This exact issue commonly causes confusion on vintage machinery forums.
How to Navigate Your Parts Pages
Because your plate has a
"D" where the guide expects a
"B", your serial number tag is completely correct and original, but you have to bridge the gap manually when looking at your parts lists:
- Treat your stamped "D" as the exact functional equivalent of the manual's option code "B".
- Whenever you encounter a parts section in this manual that forces a choice between equipment variant "B" or variant "F", always follow variant "B". Variant "F" applies exclusively to gasoline-powered configurations.
---------------------------------------------------------------------------------------------------------------------
While finding an official Service Bulletin or Service Information (SI) letter specifically stating
"use B parts if your tag says D" would be the ultimate proof,
no such historical document was ever publicly released by John Deere.
There are definitive historical records that explain exactly how this system came about, why it works this way, and why a specific bulletin was never necessary for the dealership network.
1. The Historical Record: The Parts Manual Itself
The historical evidence is embedded within the structure of your parts manual introduction on
Page 2.
The introduction does not instruct the parts manager to look for the literal letter "B" on the physical machine tag. Instead, it says:
"Digit 5 designates the fuel and transmission."
In John Deere's internal database logic, the table on Page 2 is a
key/legend for sorting part variants, not a literal text match for the factory floor. The letter "B" is simply a variable placeholder used inside the catalog database to represent the
combination of a Diesel engine + a Collar Shift transmission.
The factory floor didn't use variable placeholders; they used literal physical realities. Since your machine was a diesel, they stamped a
D. Because a gasoline option (
F) existed, the parts manual simply needed an arbitrary method to segregate the two parts lists.
2. How the Dealer Network Handled It
During the 1970s, John Deere parts counters did not look up parts using the paper manuals the way owners do today. They relied on
Up-to-Date Microfiche systems (explicitly mentioned in all caps on
Page 1 of your introduction).
In the corporate microfiche or computerized dealer locator networks:
A parts manager would enter your 6-digit serial number (210922).
- The system would automatically route them to the correct bill-of-materials for a straight 310 Diesel.
- The internal dealer system automatically mapped the physical "D" identifier to the catalog's "B" code behind the scenes.
Because the dealer network's microfiche resolved this seamlessly, John Deere never had a reason to issue a corrective service bulletin to the public or change the printing plates of the operator/parts manuals.
3. The 1980s PIN Standardization
The reason this mismatch stands out so drastically today is because John Deere radically overhauled their system in the late 1970s and early 1980s. They adopted the standardized, 13-to-17-digit
Product Identification Number (PIN) format.
Once John Deere made that shift, the physical stamp on the metal tags became a literal, character-for-character match with the codes used in the parts catalogs to prevent exactly what you are experiencing. Your 1974 machine caught the tail end of the old era, where the factory floor and the publication departments operated as two separate entities.
----------------------------------------------------------------------------------------------------------
It also referenced two posts from this forum:
Roy Suomi 1606793
Re: 1974 JD310-D Problem
"The D stands for Dubuque where it was built not part of the model number."
Jim.ME 1522251
1974 JD310-D Problem
"Where it shows 310 - D, the D indicates an option."
Uncle AI will now be able to find this post and be able to quote itself as a reference.
