Model T vs Model TT Parts
I think that part of the confusion about T vs TT can be cleared by thinking about the Factory Number, also known as the Factory Symbol Number, used to designate different models and parts. About 1920 FMC adopted a Factory Symbol Number system for all components of the vehicles manufactured by FMC.
There are three parts to the Factory Symbol Number. First a prefix that indicated the model of the vehicle the part was used on, followed by a base number, followed by a suffix indicating the revision of the part. The prefixes FMC used during the 1920's were A,B, C, F, K,N, R, S, T, TT, L and FT. The first 7 letter prefixes represent the pre-T letter series cars. T is for Model T, and TT is for Ton Truck, L is for Lincoln, and FT is Fordson Tractor.
The middle part of the Factory Number, the base number, represented a unique part number ( this was a change from earlier years of Model T production where if there was a change in a part, even a small change, an entirely new part number was given to the redesigned part. FYI - this practice had made life challenging for today's researchers trying to trace the development of a particular Model T part because the part number kept changing.). When the Model A came out in 1927, the part numbering protocol changed so that the base number would be the same for all models. If 4040 was the base number for a motor block, then 4040 would always represent a motor block. After 1920 the base number always stayed the same. The final piece of the Factory Symbol Number was a suffix that represented the revision of a part. A newly designed part had no revision number, but if it was redesigned the original part was given the suffix A and the new part had the same model and base number but had the suffix B assigned after the base number. If the original part was to remain in production to service cars that used the original design, then the letter R was also added to the suffix letter.
An example of the symbol numbers is T-173, the Hub Brake Cam Bushing (Catalog Numbers 2559 and 2559B). The Hub Brake Cam Bushing carries the Factory Number 173 and the same interchangeable bushing was used from 1909 through 1925. With the introduction of the "Improved Cars" for 1926 the hub brake and hub brake cam were redesigned for for the large drum rear brakes. The Hub Brake Cam Bushing was also redesigned for the new hub brake cam. The new brake cam bushing carries the Factory Number T-173-B because it is not interchangeable with the old Hub Brake Cam Bushing. However, since there were still 13 million Models Ts running around using the old style Hub Brake Cam Bushing, the earlier T-173 needed to be retained for service (repairs). The old style Hub Brake Cam Bushing was redesignated as T-173-AR and production of this style bushing continued to be supplied for repairs to the small drum rear ends.
OK, so,I digress. The way to tell TT from T parts is by looking in the parts catalog for Model TT designations before the Factory Part Number. The front Spring Assembly for a 1909-1925 Model T carries the factory number T-332-AR (7 Leaf), and the Factory Part Number for the Front Spring Assembly for a Model TT carries the Factory Number TT-332 (9 leaf). The Front Spring Assembly used on 1926-27 Improved Cars is different from that used on 1909-1925 cars and it carries the Factory Symbol Number T-332-B.
Ford also compiled a parts list for both the Model T and TT chassis. The parts lists was just that: a list of all the parts and the number used in a chassis assembly. The list for a TT chassis included not only all the TT specific parts, but also the parts with T Factory Symbol Number that were also used on a TT chassis.
The two terms Factory Number and Factory Symbol Number appear to have been used interchangeably by the Ford Engineers. I suspect the Factory Symbol Number term comes from the parts drawings themselves. At the lower left hand corner of the parts drawings the Factory Number can be found enclosed in a circle, which tends to make it more of a symbol rather than just a plain number.
Excellent lesson as always Professor!
Thank you Trent for this clear, easy to understand explanation of Ford part numbers.
I think I speak for all of us when I say that we appreciate very much your time consuming and scholarly research into our Model T's and TT's.
Thank you so much for all your years of research, sharing, and support to our hobby!
For those who would like to look at the TT discussion it is located at: http://www.mtfca.com/discus/messages/411944/478116.html?1410376941
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