Aside from its awesome appearance, the Lenco Street five-speed transmission offers Pro Street enthusiasts the capability of racing as well as driving their vehicles on the street.
Lenco transmissions were first made popular in the early '70s when NHRA Pro Stockers needed a gearbox that was up to the task of 9-second elapsed times. The Lenco provided unbreakable performance and lightening-quick gear changes, which made these clutchless wonders the tranny of choice among the ultimate door slammer crowd. Over the years, there have been many in-car-cameras showing Pro Stock drivers grabbing and shifting the trademark five levers as they power their vehicles toward the finish line. Although there have been many attempts to create similar shifters for stock-type transmissions, Chevy enthusiasts have long aspired to duplicate the multi-lever design of the Lenco for their hot street machines. But extreme cost-among other things--has always been a huge inhibitor for all but the stoutest of street-driven machinery.
Despite its reputation among racers and its many uses today, which include everything from boats to alcohol dragsters, many enthusiasts have not caught on to the fact that there IS a street version available. Gary Sumek of Lenco mentioned that they have been producing a five-speed street version for a few years. The ST-1200 is not one of their most popular transmissions (they still sell more racing models), but it is the answer to many problems facing high-horsepower street cars and trucks that need a compromise between a stout race and street transmission.
The transmission is made up of sections, each holding a planetary gear set and an intermediate shaft. These can be easily removed and replaced in the case for changing ratios or servicing.
Lenco transmissions essentially combine the best of a manual and automatic transmission into one unit. It uses a clutch and flywheel assembly only to engage the transmission into first and reverse gears. Once engaged, the gears are shifted without a clutch. How is this done? Simply put, once the transmission is in gear, the power runs through a set of planetary gears. Each planetary gear set is in its own housing and carries a higher ratio. Each gear is engaged by pulling down on the shift lever, to activate the clutch mechanism for each gear set. Think of it as manually shifting an automatic transmission. The only difference is that in an automatic, the transmission fluid moves internal valves to close the clutch pack. In the Lenco, the shift lever actually moves the clutch pack together to engage the gear in each housing.
Adding progressively different ratio independent gear housings behind each other allows Lenco to create two-speed, four-speed, five-speed, and even six-speed transmissions. The total amount of gear reduction depends on the amount of housings and the overall application of the transmission. On the street five-speed model the ratios start at 3.25 in first gear, 2.26 in second, 1.64 in third, 1.25 in fourth, and fifth gear is 1:1. What does this mean, you wonder? As an example, this tranny with a set of 4.30:1 rear axle gears, coupled to 32-inch-tall Mickey Thompson tires should allow any Pro Street Chevy to cruise on the highway, averaging 60 mph at slightly above 2,800 rpms.
The planetary gear set in each housing is almost identical to that used in an automatic transmission. Three planet gears rotate around a central sun gear. Differences in gear sizing create different percentages in gear reduction. | 
When assembled, the planetary carrier holds the gears and clutch housing in place. | 
The clutch pack assembly is then held in place with a snap ring. |
Floaters and clutch plates are installed in the carrier. Each carrier holds seven clutch discs and eight floaters. | 
The plates are measured with the center clutch hub in place and when the clearance is correct, a pressure plate and spring sit down on the clutch pack hub. | 
The shaft carries the sun gear that all the other gears rotate around. The outer gear on the shaft is what is engaged when the clutches are activated and keeps the gears from rotating. |