Picking The Right Automatic Transmission - How It Works

Hard-core drag racing calls for durable, lightweight, and efficient automatic transmissions. The pros explain how to pick the right one

Stephen Kim Jul 18, 2011 0 Comment(s)
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Stan Poff: Vasco and 9310 are both of the “vaccumelt” family of metals. There are different grades of these metals, and some are more suitable for certain applications than others. We used 4340 metal when it was popular 15 years ago. Then we graduated to 9310, which is pretty much what pro ring gears in rearends are made from. The next step in progression was moving on to Vasco, which is available in different grades. Some grades are better for gears and other grades are better for input shafts. Today, some of the Vasco materials used in transmissions have been surpassed by other aerospace materials that double or even triple the strength of Vasco.

Surface Area

Jim Beattie Sr.: Increasing the number of clutch packs and using oversized sprags and bands are common tricks to increase the surface area of a transmission’s power-holding components. The catch is that more surface area equates to greater frictional horsepower loss, so there must be a balance between these two factors. From a durability standpoint, increasing the number of clutches is a good thing, provided you have enough clearance for the additional clutches. More clutches equal more surface area that is capable of more holding power, but with the trade-off of increased drag. If you have disposable horsepower, then there is no point of diminishing returns. Just make your transmission as strong as possible. However, if you are running Stock Eliminator then you really don’t want to overdo it, and having the correct number of clutches for your horsepower and weight is very important. Of course, oversized or an increased number of elements in a sprag increases its holding power as well, as do oversized band.

Heat

Stan Poff: Heat is the big monster lurking in the shadows that will destroy a transmission once the fluid has broken down and lost its viscosity. I recommend always running a temperature gauge to know how hot the transmission is getting. If it is staying between 160 and 180 degrees, change it every 40-50 passes. If at the end of a run you see temperatures ranging in the 200-230 degree mark, measures should be taken to reduce the operating temperature and fluid changes should be performed more frequently. In applications where temperature stays low, thinner fluids can be used. In cars where temperatures run high, thicker fluid needs to be used. Stockers, Super Stockers, and Comp Eliminator racers often use thinner fluids for e.t. purposes. The big horsepower engines equipped with automatics—some of which can reach 3,200-plus horsepower—usually run thicker fluids. TCI Automotive offers its Max Shift transmission fluids in several different weights to better cover all applications.

Maintenance

Zack Farah: For maximum longevity, a drag transmission should be serviced every week. After the race weekend, the pan should be dropped and inspected on Monday so in the event there is any unusual debris there will be time to get it out and serviced before the next race day. In a Powerglide or a TH350, the filter is a screen and should be removed and cleaned. TH400s use either a felt or screen element type of filter. If it is a felt-type filter, it should be replaced weekly, and new ones can be purchased from a GM dealership. The pan gasket should also be replaced if necessary and torqued to 12-15 lb-ft. I recommend topping the trans off with high-quality brand-name Dexron/Mercon fluid whenever it is serviced.

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