Terry McGean: Hydramatic is actually the name of the General Motors division responsible for the design and manufacture of automatic transmissions, but its first widely used product was the four-speed automatic trans usually referred to as simply Hydramatic, though its actual name was Hydramatic Drive. There are variations, but the original dual-range unit was introduced in 1939 and continued through the mid '50s. Although this transmission did have four forward gears, it did not feature overdrive-Fourth gear was direct-drive, while First was extra low by today's standards. The Hydramatic used a fluid coupling called a torus instead of a friction clutch, but it was not considered a torque converter as it did not use a stator and therefore did not multiply the engine's torque as modern torque converters do. In fact, four gears were used to make up for the lack of a torque converter; more modern three-speed automatics are sometimes considered "four-stage" automatics, as the torque converter can provide the effects of an extra-low gear though torque multiplication. The term dual-range was not a reference to multiple levels of gearing, but rather to the different positions of the shift selector, which could provide Second-gear starts if desired (to aid in low-traction situations), or delayed Fourth gear engagement (for towing or steep grades), in addition to typical automatic shifting though all four gears.
The Hydramatic was durable and was even used in heavy trucks like military-spec GMC 6x6 trucks and some WWII Cadillac-powered tanks (one engine and trans for each set of tracks). B&M recognized the performance potential of the Hydramatic's strength and four gears early on and founded the business on the practice of modifying the GM Hydramatic in its Hydro-Stick for drag racing. These units proved to be quite reliable, and B&M offered versions rated to 800 hp, as well as street versions that retained automatic shifting. There was even a Traveler model for trucks, offered as an alternative to the clunky heavy-duty four-speed manuals of the day, for towing or camper hauling. B&M offered the Hydro-Stick through the early '70s, though even the catalog informed consumers that the efficiency of the modern "four-stage" three-speed automatics would "eventually supplant the popularity of the old-design Hydro-Stick." Of course they were right, and even then B&M was deeply involved with prepping modern automatics like the TH350 and 400, TorqueFlites, and the C4 and C6 from Ford.
Today, the Hydro-Stick is really only suitable for nostalgia purposes and would not serve your LeMans particularly well even if you could find one. If you want overdrive, try a 200-4R four-speed that will bolt in place of your TH350 by sliding the stock crossmember back to the TH400 position; the holes are already drilled in your frame. You should be able to retain your existing driveshaft without modification, but you will have to utilize the throttle-valve linkage to the carburetor, and it will have to be adjusted correctly. Check out the story we just ran in the Apr. '05 issue on a 200-4R swap in a '65 El Camino ("The Forgotten Overdrive"). David Freiburger: That was cool.
More Info
B&M Racing & Performance Products; Chatsworth, CA; 818/882-6422;
bmracing.com
Olds And Slow
Carey Saab, Cincinnati, OH: I own a '71 Olds Cutlass Supreme convertible. This summer I built a 455 Olds engine from a basket of parts supplied by a supposed Olds expert. I am using an Offenhauser dual-quad manifold with 660 carbs, a Mallory electronic ignition, and a camshaft with unknown specs. The crank and rods are stock. The pistons are forged dome tops that have been milled flat. The cylinder heads are modified and are believed to be Oldsmobile "C" heads. Cranking compression is 185 psi across the board. It has a Turbo 400 trans with a 2,200-stall converter and a stock rearend (for the time being).