WORKING ON A DYNAFLOW, PART 1
Post WII America was ready for conveniences, and was fascinated with things automatic. More and more products were push-button controlled and advertised as "doing the work for you", cars being no exception. Before the war, early attempts at making an automatic shift car were generally semi-automatic, vacuum shifts. GM's Hydramatic introduced in the Oldsmobile was by far the most successful. Buick built a torque converter drive for the M-18 "Hellcat" tank destroyer, and, with the advent of new, tougher war materials, Buick was developing its own automatic for postwar production. The new automatic was to be called "Dynaflow", and would first be available on the 1948 Roadmaster Series as an option. It was a very smooth transmission without the Hydramatic feel of gear changes. However, owners complained that the transmission had to "catch up" with the engine, and dubbed it the "Dynashlush"! Even with its idiosyncrasies, the Dynaflow caught on.
The early Dynaflow was made up of 5 basic pieces contained in a sealed drum filled with transmission fluid. These are the Pump P that is connected to the engine flywheel. The Turbine T which fits inside the pump facing it. The turbine is connected to the drive shaft that turns the rear wheels through a torque tube. As the engine increases speed, the turning pump throws fluid against the blades of the turbine, making it revolve and move the wheels. The unit acts like a fluid coupling. The motor can turn while the car is standing still, and the fluid, rather than a clutch, starts it moving. The torque converter multiplies the turning effort of the engine. The three small wheels with vanes are the Stator S and secondary pump. They fit in between the pump and the turbine, and redirect the fluid as it flows from the turbine back to the pump. Oil flows from the pump to the turbine, around the outside, and returns through the center openings. The stators are free to spin in one direction about the shaft upon which they are mounted, through a free-wheeling configuration, but they can not turn the opposite way. This means that during early acceleration when the engine and pump are turning faster than the turbine and drive shaft, the stators are locked in place and redirect the returning fluid into such channels that will multiply the thrust, so that you get the effect of a first gear. As the car picks up speed, first one stator, then the other ceases to re-angle the flow of fluid, and floats idly on the shaft. That's because less conversion of the engine torque (turning effort) is needed. The need now is for more direct transfer of power at higher speeds. As the stators reach their free wheeling stage (cruising speed), and you let off of the accelerator, the pump and turbine are turning at nearly the same speed, approximately one revolution of the drive shaft for each revolution of the engine. When you need power for passing, all you have to do is step down on the accelerator. When the engine speeds up and the pump is turning faster than the turbine, the stators lock up again, redirecting the flow of fluid to convert its speed to extra torque (torque multiplication). Buick summed it up this way: Instead of the old manual shift, First, Second, and Third, with Dynaflow, you now have an infinite number of gear ratios. And you don't have to select them--they're automatic!
By 1953, the first generation Dynaflow evolved into a "twin turbine" unit that was available in all Series 40s, 50s and 70s. It had a 4-element torque converter featuring two turbines interconnected through a planetary gear set comparing the twin turbine with the first generation Dynaflow. The Twin had one pump instead of two, one stator instead of two and one free stator instead of three. This new setup provided a more positive connection between the engine and the drive shaft, reducing the slippage and improving the gas mileage. On our '53, we are doing a thorough restoration of the drive train, so the transmission was removed for rebuilding. When we rebuilt our engine, the Dynaflow was pulled at the same time, and re-installed along with installing the newly-rebuilt engine. The engine ran great, but the transmission leaked, slipped and didn't have Park, so we had to pull it again, this time leaving the engine in the car.
In the past, we dropped the rear end and torque tube assembly, so that the transmission could be pulled back and removed. This is a lot of work, and after doing it several times, we figured out that we could disconnect the torque tube from the transmission, disconnect the rear brake line (rubber hose), hook up 2 hold-down straps: One around the axle housing on the left side to the rear of the frame, and another the same way on the right side. Then, disconnect the torque tube from the torque ball and move the rear axle back to disengage the propeller shaft from the universal and ratchet each strap back, pulling the torque tube from the transmission with about an inch of clearance, which is just enough to let the transmission come down. To remove the transmission, we first dropped it and disconnected the two water hoses at the trans-cooler, plugging them to keep from losing our coolant. We then removed the engine's splash pan, bell housing cover and bell housing hand hole cover, turned the flywheel until one converter drain plug could be loosened to provide an air vent, then turned the flywheel until the opposite drain plug was straight down, removed that plug and drained the fluid from the converter. We then removed the plug from the transmission oil pan, and drained the transmission. We disconnected the oil filler pipe at the rubber hose and disconnected the exhaust pipe hanger at the right accumulator, then disconnected the shift rod and speedometer cable, then the rubber thrust pad from the transmission support. We positioned our transmis-sion jack high enough to relieve the load on the transmission support, then removed the support from the frame X-member and removed the thrust pad. We marked the flywheel, converter pump and cover with paint, so that the pump can be installed in the same position, and removed the three "drive bolts", then lowered the transmission just enough to remove the bell housing bolts. We then moved the transmission rearward, to disengage the hub of the converter pump cover from the crankshaft, and lowered the transmission and removed it from the car. We wrote down our casting number, to help in ordering any needed parts. Next month, we will tell you what we found inside this old Dynaflow. It will surprise you--it sure did us! Keep 'em driving!