The Chief Overdrive transmission project began while Mark Hanlon was returning from a business trip with a friend and long time Indian rider, Thaine Morris. They were discussing the various idiosyncrasies of Thaines’ ‘50 Chief, when he lamented that he was unable to ride his bike at speeds greater than 65mph for long distances. While short trips were ok, the engine was “unhappy” running above 3000 rpm for sustained periods.

Thus, the idea for an overdrive transmission was born.

In order for this project to work several criterion needed to be met. First, the gearbox had to look the same as the original Indian transmission. Second, the gearbox would preferably be a constant mesh style as the “crash” style had too many reliability problems. Third, the gear ratios of the original three-speed gearbox needed to be preserved and an overdrive gear added for highway cruising.

Engineering began in earnest March 1999 with Frank Byford joining the team. Frank began his engineering career in the 1950’s working and riding for Greeves Motorcycles in England. In 1953 he went to work for Associated Motorcycles who built AJS Matchless, Norton, James and Francis Barnett bikes. One of his first projects was to design four-speed constant mesh transmission for this line of motorcycles. Frank’s designs were very popular in England and emulated by many of the other motorcycle manufacturers for several years.

The stock Indian three-speed transmission design was reviewed and the available space inside the case checked to see if a 4 speed gear set would fit without compromising the integrity of the power train. The initial result was that there would be insufficient room for conventional sliders with dogs. Packaging was constrained by the engine in the front, the frame underneath and behind, the generator drive, the clutch on the left and the sprocket on the right. Many approaches were considered and several unconventional concepts eventually had to be employed to cram the proverbial quart into the pint pot.

With some careful juggling of material, undercutting into some of the gears to use pockets instead of dogs the design gradually came alive. Using 12 instead of 8 D.P. gears also provided a little more room, and as a bonus opened up the number of gear ratio combinations considerably. The reduced thickness of the teeth would reduce tooth strength so it was decided that a stronger material was needed to make up for the loss. After a little research AISI 9310 was selected for both the gears, the secondary shaft and the mainshaft. This material has a 25% core strength increase and a 3 point case hardness increase over AISI 8620. The design was then detailed, the casting patterns purchased and the parts ordered.

The prototype was completed utilizing an original case with a specially cast cover made with a homemade pattern. The parts were machined and heat treated and assembled in record time. This prototype box was installed on Thaines ’50 Chief at Dave Hansens “The Shop” in Ventura and a couple of quick test runs made by Thaine and Dave. With a big Grin on his face Thaine left for his shop about 50 miles away, being able to cruise comfortably at 75mph with no problems. Unfortunately not all went well, a couple of days later Thaine was rammed by a car changing lanes that made his bike unrideable and Thaine sustained an injured shoulder.

The box was removed from the damaged bike and the insides studied for wear and damage. Although there were only a few miles on the box it appeared that cruising in overdrive caused some indication of ‘blue shaft’ due to the output bushing rotating faster than the mainshaft while under load with insufficient lubrication. This led to opening up a few clearances and adding figure 8 oil grooves in the output bushing.

This prototype box eventually ended up on a machine prepared by Dave Hansen for a second Bonneville speed record attempt in September 2000. After the record setting run Dave Hanson was asked how every thing went. He replied, “When you are at Bonneville you don’t have time to be nice to your equipment, or worry about its functionality. We abused the four speed overdrive transmission for over ten runs at top speed and it performed flawlessly.” The reason that the Chief box was used for this second run is because the first run was plagued with the machine jumping out of second gear with the crash box during acceleration. The Chief box, being constant mesh, did not jump out of gear.

More thought went into the design and the whole gear cluster was revamped to use a larger diameter mainshaft. Caged needle bearings were used instead of bushings and a thrust bearing installed to take care of the axial thrust caused by operating the clutch. With the use of a bigger mainshaft and caged needle roller bearings, larger diameter case bearings were required. This necessitated making an internally beefed up case casting to accommodate the larger bearings.

Seals were added to all of the external rotating leak paths and the production run of 20 started.

The first production transmission was shipped to Carl Sorenson at Apopka Indian. Carl installed it in his daily rider, a 1948 Chief. To date, he has put over 8000 miles on it with no problems. Carl and three other Chief Overdrive riders took their bikes up to the Springfield Indian Centennial in July 2001.

The first transmission design was for a late model (1940-1953) Chief. Then parts for the rigid frame (1935-1939) Chief were added to the inventory. An overdrive unit for the Scout will probably be in the future plans if there is sufficient demand.

As Mark Hanlons’ other business interests blossomed, he found that the Chief project was taking too much time away from them and decided to sell the project, with the result that in 2002 the designer, (Frank Byford), and Irongate Machine, (Kerry Byford and Rick Rudy) bought the project complete. After the Lawyers, paperwork and all the bureaucratic stuff was completed the current production run of 50 was started in June 2002 with deliveries the first week in February 2003.

A number of wonderful people helped throughout the project for which a hearty thank-you is in order. Some of those who helped the project along the way were Thaine Morris, Dave Hansen, Carl Sorenson, Wilson Plank, Greg Hutchinson, Bob Stark, Gary Stark; Mike “Kiwi” Thomas; Jerry Greer, Jody van Meter, those loving and understanding wives, all of the vendors and other participants, because, without their help and perseverance, the project would have taken much longer to complete.