Ease of servicing automatic transmissions

MHUB - April 20, 2015

Considering the increased acceptance of automatic transmissions in medium- and heavy-duty trucks, as well as vocations like fire, refuse, bus and utility operations, we explored the availability of service information that might help our readers.

According to Allison, servicing an automatic transmission almost parallels a driver’s operation of the unit—put it in “D” and drive. A few safety and fuel efficiency features are available with the transmission electronic controls that fleet managers can select.

“We have experienced this no-worry performance to be the case for customers operating 67-ton GVW off-highway articulated dump trucks, 170-ton GCVW log haulers, city transit buses, high-use dock spotters and others,” said Steve Graddy, service engineer, Allison Transmission.

But what about the basics, like fluid and filter changes? Acceptable transmission fluids are listed on the Allison website under: Service—Fluid—TES295 (synthetic) approved fluids or Schedule #1 TES389 (non-synthetic) fluids. According to Graddy, both fluids provide proper performance and equal transmission durability when used within the company’s recommended fluid change intervals or fluid oxidation limits.

“Synthetic fluids provide increased oxidation resistance, which increases the operational life of the fluid when compared to mineral-based fluids, which translates into extended fluid change intervals,” said Graddy. Allison requires TES295 fluid when a customer has extended transmission coverage.

Using a synthetic fluid versus a mineral fluid is typically based on severity of duty cycle—including on/off-highway, off-highway, refuse, transit, intercity coaches, or transmissions equipped with an output retarder. Such vocational transmissions can operate at higher temperatures, and for every 18° F increase in fluid temperature, the rate of fluid oxidation is doubled.

Graddy suggests the following three methods to determine when the transmission fluid and filters must be changed:

1) Customers may elect to use the company’s recommended fluid/filter change intervals (allisontransmission.com—Service: Fluid/Filter Change Intervals or Service Tip #1099).

2) A unique Allison feature called Prognostics monitors various operating parameters and alerts the operator when the transmission fluid and filters must be changed.

3) Fluid analysis is employed when a customer desires to use the fluid beyond the recommended change interval or Prognostics alert point. Fluid oxidation limits/fluid analysis is available at the same location of Service Tip #1099.

Graddy itemized a few other items to monitor and manage—aside from changing transmission fluid/filters when required and simple routine inspections—including: determine the frequency of periodic inspection for fluid leaks, loose bolts, clogged breather, damaged or loose hoses, damaged or loose electrical wiring or connectors, worn driveline components, damaged drive axle suspension components and correct suspension ride height for vehicles equipped with air suspension. Allison engineers note that if ambient temperature is below -13° F, the transmission should be operated in neutral at idle speed for at least 20 minutes before range selection is attempted.

What about total fluid life cycle cost? If a customer expects the transmission to operate approximately 18,000 hours before the first overhaul, 36 fluid changes would be required. A typical fluid refill quantity is 39 quarts for a 4000 series transmission in a refuse truck. Typical fleet price for TES389 fluid is $3 per quart. Fluid cost alone before the first overhaul would be $4,212 (excluding labor and disposal costs).

A TES295 fluid in this same vocation has a recommended fluid change interval of every 6000 hours. A TES295 fluid is approximately $9 per quart. Fluid cost alone before the first overhaul with TES295 fluid would be $1,053—a savings of more than $3,000.

Allison technical assistance is available by calling 800-252-5283. Fleet managers may obtain a free Operator’s Manual and Mechanic’s Tips at www.allisontransmission.com.