55 Thunderbird Gears in 39 Trans

[Mac VP]

Last year we purchased a pickup truck load of used and NOS Ford trans parts from some nice guys in western Michigan. After getting home and sorting thru everything, I set the 51a-7061 mainshafts in the bin. When I went to use one a few weeks later, I couldn't get the 01A-7100 low/rev gear to slide on. I've been down that road before so I grabbed a 1A-7100 gear and tested the fit on the splines....perfect! In all other respects the main shaft was identical to an ordinary 51A-7061 closed drive shaft.

There was no box. There was no marking of any kind on the shaft. I finished the job with a regular 51a shaft but put the oddball aside. I did a test fit to assemble this shaft in a normal 78 case with 81A shifter assy. Used the 51-54 cluster gear (1A-7113) plus the 28 tooth 1A-7100 slider, a 1A-7141 rev idler, the 1A-7102 second gear, and a 1C-7017 main drive gear, and the usual 8M-7124 synchro assy. In other words I built a "39 style" closed drive trans using the 51-54 gears. It fit and worked perfectly. Ended up building two trannies for customers who wanted the slightly higher gear ratios this delivered, and sold the combo of gear to another customer who built it itself.

I scoured ALL my gear catalogs and could not find any reference to this shaft. To this day I still wonder who made them. I'd love to come up with a few more.