Ruff Torq's new transaxles for lawn & garden

Diesel Progress North American Edition, July, 1999 by Mike Mercer

New "Narrow Drive" K series units target low noise, compactness; "more flexibility for the OEM"

Tuff Torq Corp., Morristown, Tenn., has introduced the latest generation of its K series hydrostatic transaxles for lawn and garden tractor applications. The new "Narrow Drive" K series hydrostatic transaxle line includes four products, the model K46, model K62, model K66 and the model K71, which replace the K51, K55, K61, K65 and the K70 transaxles. All are designed with reduced package size and lower noise emissions than the previous generation.

"A compact design and lower noise emissions were the two most important design criteria for the new narrow drive K series line of transaxles," said Robert Abend, Tuff Torq vice president. "The narrow drive design provides more flexibility to the OEM when it comes time to mount the transaxle to the tractor. This new design is engineered with flexibility in mind to fit a wider range of applications than the previous generation transaxles."

The four new transmissions use aluminum die cast housings that incorporate a diagonal bulkhead designed into the casting to increase stiffness and reduce noise. A second significant design feature is the "d"-shaped center section, engineered to make the overall transaxle package smaller and narrower. An additional benefit is that this design allows the transaxle's input shaft to be centered on the casing, according to the company.

"When designing this latest generation of K series products, we wanted high power out of a small package," said Krista Winfree, supervisor of applications engineering at Tuff Torq. "We wanted to make the OEM's job as easy as possible when it came to designing a new piece of equipment around these units or modifying current products to accept these new transaxles."

The K series narrow drive axles use an internal wet disc brake configuration allowing several brake lever mounting orientations, depending on the reduction ratio. Brake capacity is 181 or 139 lb.ft, at 94 lb.in, of brake arm force for the K46; 432, 347 or 240 lb.ft, at 92.6 lb. of brake arm force for the K62; 243 or 159 lb.ft, at 67.5 lb. of brake arm force for the K66; and 535 lb.ft, at 21.2 lb.ft. of brake arm torque for the K71 transaxle.

All four K series narrow drive transaxle models use automotive-type heat-treated bevel gears in the differential. A differential lock is not available on the K46, but is optional on the K62, K66 and K71. A factory set return-to-neutral mechanism is standard on the K46, K62, K66 and K71 transaxles with foot control applications. All four narrow drive transaxle models include a roll release mechanism.

"The refinements on the new K series transaxles are based on past experience with previous generation models and the input we received from the marketplace," said Abend.

Added Winfree, "Making available options, such as changeable oil filters, differential lock, outside hydraulics, higher travel speeds with small diameter tires and foot or hand control were all features demanded by our customers."

The K46 is designed for rear-engined riders and lawn tractors. The standard axle torque rating for the K46 is 166 lb. ft. with the standard 20 in. maximum diameter tires and a reduction ratio of 28.04:1. The axle is also available with a 127 lb.ft. rating and 21.53:1 reduction ratio and a maximum tire diameter of 18 in., giving travel speeds of 5.5 mph.

The K46 transaxle hydraulic pump and motor have displacements of 7.06 cc and 10.93 cc respectively. Maximum input speed is 3000 rpm through a 0.58 in. input shaft. The axle shaft diameter measures 0.75 in. Maximum static weight capacity for the K46 transaxle is 675 lb. and its dry weight is 27.6 lb.

All of the narrow drive transaxles use 10W 30 class CD motor oil. The K66 uses 5W 50 synthetic motor oil for ground engagement applications. The K46 has an oil capacity of 0.63 gallons while the K62 and K66 have a 0.66 gallon capacity and the K71 has a 1.22 gallon capacity. The K46 and K62 models use a non-changeable internal oil filter while the K66 and K71 units are available with an external changeable filter. All transaxles are prefilled and air bled at the factory.

The K62 is designed for heavy-duty lawn tractor and yard tractor applications. Pump and motor displacement for the K62 is 10 cc each. Maximum input shaft speed is 3000 rpm. The input shaft has a 0.58 in. diameter and the axle shaft is 1.0 in. in diameter.

The K62 has a maximum static weight rating of 584 lb. and a dry weight of 38.6 lb. The K62 has rated axle torque of 268, 215, and 149 lb.ft. with reduction ratios of 33.50:1, 26.90:1 and 18.65:1 using 23, 20 and 18 in. maximum diameter tires respectively. The standard axle is available with a reduction ratio of 26.90:1 at 215 lb.ft.

Tuff Torq's New K Series Transaxles

Model    Type             Standard           Maximum      dry weight
                       Continuous Axle     Input Shaft        lb.
                       Torque (lb. ft.)       Speed

K46     Hydrostatic           166              3000           27.6
K62     Hydrostatic           215              3000           38.6
K66     Hydrostatic           310              3400           50.7
K71     Hydrostatic           406              3400           60.5