A torque converter is a simple automatic transmission that has a low and high gear. They are commonly found on go karts, ATV’s, mini-bikes, and snowmobiles. The low gear is ideal for when you’re going up hills or driving slowly, and the high gear lets you achieve top speed. They are also a good choice for stop and go riding.
Torque Converters – Advantages
Compared to a centrifugal clutch, torque converters offer better acceleration from a stand still. They also allow karts to be geared for a higher top speed.
Torque Converters – Disadvantages
Unless the engine is idling, a T/C belt is constantly under tension. The friction from the belt tension lowers rear-wheel horse power slightly. For this reason, centrifugal clutches are preferred over torque converters in most forms of paved kart racing. An exception to this would be a small kart track with lots of tight turns and low-speed corners.
To choose the best torque converter, here are five things to consider:
Live Axle or Fixed Axle
O.D. of Crankshaft
Off-road or Pavement Driving
Go karts can use a variety of rear axle types. The most common for yard karts is the fixed, or “dead” axle. A single wheel drive runs a chain from the engine clutch straight to the drive wheel, which has a sprocket mounted directly to it. This means that the rear axle does not turn and the rear wheels spin freely.
Since power is applied to one wheel only, the other rear wheel is left to spin, or “free wheel”. This allows better steering and cornering. For pavement and hard-packed dirt, single wheel drive with a centrifugal clutch works satisfactory.
Live Axle (Two Wheel Drive)
Off-road karts work best with two wheel drive. In sand or loose dirt, where a single wheel would often spin out, a live axle has both wheels turning at the same time, giving you twice the traction. Having a torque converter is ideal for climbing hills and inclines.
A centrifugal clutch does not work well with a live axle, and under constant use, will burn out. If you plan to use your kart for off-roading, live axle with torque converter is the way to go.
Driver Pulley vs Driven Pulley
On small engine torque converters, the front pulley is called the driver, and the rear pulley is called the driven. The driven pulley can be swapped out to a different size, giving you the option to change gear ratios. By having two or three different pulleys you can best adapt your kart to different riding scenarios.
The three most common sizes of go kart torque converters are 20 series (light duty), 30 series (medium duty), and 40 series (heavy duty).
20-Series Torque Converter
For small engines putting out no more than eight horsepower, a 20-series torque converter works fine. Driven clutches are available in both 6″ or 7″ diameter, for either 5/8″ or 3/4″ shaft diameter. Applications generally include lawn and garden tractors, yard karts, mini-bikes, and others. A 20 series converter uses a conventional (symmetrical) belt.
30 Series Torque Converter
The most common of the three sizes, 30-series torque converters work best with 3 to 8 horsepower engines. They are available for either 3/4″ or 1″ engine shaft size. Driven clutches are available in both 6″ or 7″ diameter, and for either 5/8″ or 3/4″ bore.
The 30-series torque converters are asymmetric, which means one side of the pulleys are flat. Both the driven’s and the driver’s movable faces and the spring mechanism are on the outboard side of the belt. Asymmetrical belts are also flat on one side, and have a top width of 3/4″.
40 Series Torque Converter
If you’re running an off-road kart, ATV, or LTV with 10 horsepower or more, you need a 40-series torque converter. These are rated for 8 horsepower minimum and 25 horsepower maximum. The 40-series torque converters have a 1:1 final drive ratio.
Drive clutches are available for 3/4″, 1″, and 1-1/8″ diameters. Driven clutches are available with 5/8″, 3/4″ and 7/8″ diameters. A symmetrical belt is used with the 40-series torque converters and they require the use of a jack shaft.
Torque converters are compatible with most horizontal-shaft small engines, including Briggs and Stratton, Honda, Honda clones, Robin, Tecumseh, Kohler, and others. Check your engines output shaft diameter, and order the kit to match the chain-size/pitch of your kart’s axle sprocket.
Most T/C kits come with everything you need to bolt them on, however you may need to lengthen/shorten your chain.
Most karts use either a #35 or #40/41 chain and sprocket pitch/size. An easy way to check to see what size chain you have, is to measure the distance between any two teeth on your axle sprocket. 3/8″ is a #35 pitch, and 1/2″ is #40/41 pitch.
Torque Converter Maintenance
All you need for maintenance are a few hand tools and a dry molybdenum spray for lubrication. In addition to cleaning, older torque converters may need a new belt, as the rubber will eventually harden and crack from age. They also get narrower through wear, which effects both low-end torque and top-end speed.