A step-by-step guide to Allison transmission service and how to maintain this vital motorhome component.
By Mark Quasius, F333630
Most diesel-powered Type A motorhomes and a fair number of gasoline-powered coaches are equipped with Allison transmissions. Such transmissions have set the industry standard for longevity and reliability, but like any chassis component, they require regular maintenance.
The nine most common Allison motorhome transmissions on the road today range from model 1000 MH to model 4000 MH. Each transmission is rated for horsepower, torque, gross vehicle weight rating (GVWR), and gross combination weight rating (GCWR).
This article serves as a guide for do-it-yourselfers. And for others, it helps to know what’s involved in servicing your Allison transmission.
The first step in determining service requirements is to find the model and serial number of your Allison transmission. This information typically is available from the manufacturer of the motorhome or the chassis. You also can crawl under the transmission and look for the serial number, which usually is stamped into a steel plate on the right side. On a diesel pusher, the transmission identification plate is on the driver’s side.
Then, go to the Allison website and visit the My Transmission page at www.allisontransmission.com/parts-service/my-transmission. Enter your transmission’s serial number to display the service requirements.
Also on the website is Transmission Fluid/Filter Change Recommendations bulletin #1099T. To find it, place your cursor on the Parts + Service tab, click on FAQ/Service Tips, and then click on Fluid + Filter Information. The bulletin covers a range of transmissions and includes tables based on the series, fluid type, and age of a transmission. Service intervals are separated by vocation type.
If you have a 3000 or 4000 series transmission, you must know the sump size in order to determine the fluid capacity and filter part numbers. Such transmissions come with either a 2-inch or a 4-inch sump. Determine the size by measuring the cast-aluminum pan that is bolted to the bottom of the transmission housing. A 2-inch sump’s height is approximately 1.75 inches, while a 4-inch sump measures about 3.5 inches high. Or, look for this information on the My Transmission page on Allison’s website.
Unlike diagnostics, which help with troubleshooting, prognostics proactively prevent problems. Prognostics first appeared in 2009 model-year coaches. Prognostics electronically monitor the transmission and interface with the Allison shift pad in the cockpit. Although previous shift pads displayed error codes and transmission fluid levels, prognostics-enabled electronic controls offer much more, including an oil-life monitor, filter-life monitor, and transmission-health monitor.
With prognostics, the transmission fluid and filters no longer must be serviced solely on a time or mileage basis. Their life is displayed as a percentage that more accurately reflects the condition of the transmission and its serviceable items. To view the oil life on a transmission with prognostics, simultaneously press both the “up” and “down” arrows on the keypad two times. To view the filter life, press the buttons a third time. Various other operations are available in prognostics; check the owners manual for the procedure to retrieve additional data from the Allison shift pad.
Allison worked with Castrol to produce a superior product, Allison’s TranSynd synthetic transmission fluid, which has gained favor among most chassis manufacturers the past several years. In older transmissions that still have nonsynthetic fluid, your best bet is to replace it with TranSynd; otherwise, the fluid and filters must be changed more frequently. Two complete fluid changes are needed to purge enough of the nonsynthetic fluid before you can begin the extended service schedules.
Since the introduction of TranSynd, other manufacturers have developed synthetic transmission fluids. The accompanying chart lists fluids tested and approved by Allison to meet Allison’s TES 295 certification, as of September 2017. For the most current list, visit www.allisontransmission.com/parts-service/approved-fluids.
Allison highly recommends using TES 295 synthetic fluids. The typical fluid change interval for a motorhome equipped with a 3000 or 4000 series Allison transmission filled with TES 295 is 300,000 miles or 48 months; for a coach using non-TES 295 fluids, the interval is 25,000 miles or 12 months.
The seven Allison transmissions in the 1000 and 2000 series utilize a drain plug, a spin-on filter, and an internal filter. The internal filter is serviced only during a transmission overhaul, so don’t worry about that one. Changing the spin-on filter and fluid is a simple task; it’s basically the same as changing the oil in a car.
The Allison 3000 and 4000 series transmissions used in most diesel pushers are designed for higher power levels and coach weights. Servicing them is a bit more involved, but not overly so. The biggest difference is that cartridge-style filters are inside the transmission. You get to them by removing access plates in the transmission’s bottom pan.
Prior to 2006, the main filter was a Gold series product that had to be changed at 5,000 miles. Gold series filters are no longer made and have been replaced by high-capacity filters that do not require a change at 5,000 miles. Both the main and lube filters have identical part numbers and are commonly sold as a two-filter kit, complete with the necessary gaskets and O-rings.
Allison 3000 transmissions can hold approximately 29 quarts of fluid; the larger Allison 4000 can hold approximately 48 quarts. But not all of this fluid is in the transmission pan. Much is contained in the transmission cooler, cooler lines, and torque converter. Therefore, an Allison 3000 could require only 19 quarts on a refill (rather than 29 quarts when changing fluids), and an Allison 4000 could require only 39 quarts on a refill (instead of 48 quarts when changing fluids). If filters only are changed, these numbers drop markedly. Only two quarts are lost when changing the main filter. Eight quarts are lost when changing the lube filter.
Before changing filters, have the following items on hand:
- A drain pan large enough to hold the drained fluid.
- A replacement set of genuine Allison filters, complete with O-rings and gaskets.
- A 3/8-inch-drive socket set with ratchet, extension, and metric sockets.
- A 3/8-inch-drive torque wrench.
- Enough TranSynd or TES 295 fluid to replace what is drained.
- Shop rags or absorbent paper towels.
Begin by cleaning the bottom of the transmission so dirt won’t get in. Dawn dish soap, a garden hose and nozzle, and a stiff brush work well. Then warm the engine. The transmission fluid need not be excessively hot, but it should be warm enough to facilitate draining. Then shut down the engine.
Place a drain pan beneath the transmission. If you are doing a complete fluid change, remove the drain plug in the bottom of the transmission’s pan, near the rear of the transmission. The plug can be identified by its 3/8-inch internal square drive. Insert a 3/8-inch-drive ratchet’s extension into the square recess and remove the drain plug, allowing fluid to drain. If the drain pan isn’t large enough, you’ll have to halt the flow partway through the process, which can get messy. If you are changing only the filters, this won’t be as big of a concern, because 10 quarts is approximately what will drain.
A six-bolt cover holds each filter in place. As you begin to remove the bolts, fluid will start to drain, so have the drain pan in place. Once all six bolts have been removed, the filter and cover plate can drop out of the transmission pan. Usually, they won’t fall out by themselves. Use a screwdriver to pry the filter from the case; be careful not to damage the sealing surface of the cover plate or transmission pan, which could result in a leak. The large filter is attached to the plate, so be ready to hold it once it is free to prevent dropping the entire assembly. After removing the filter assembly, take it to a workbench where you will swap out the filter, gaskets, and O-rings.
The filter is pressed onto a stub on the cover plate. Remove the filter by gently pulling it off the plate using a rotating motion. Place the oil-soaked filter in a container suitable for disposal. Generally, the filter cap can be cleaned by wiping it with a clean rag or towel. The use of solvent usually isn’t necessary unless the exterior is particularly greasy.
Once the cover plate is clean, open the genuine Allison filter pack and remove the O-rings and gaskets. The kit may have extra O-ring seals, so match what is in the kit with what is on your cover plate, and set that aside. Then remove the old seals and replace with the new. Remove the paper gasket as well, ensuring that no pieces remain. Apply a bit of transmission fluid to the O-ring seals, slide the new filter over the cover plate stub, and install the gasket.
Next, remove dirt or gasket material from the filter area in the transmission pan. Then, place the filter in the cavity and insert some bolts. Using a metric socket, lightly tighten the filter cover retaining bolts by hand to snug up the cover. Use the torque wrench to tighten the bolts to the final torque specs. Both the 3000 and 4000 series transmissions put torque specs at 38 to 45 pound-feet. That’s not a lot, so be careful. Overtightening the bolts might strip the threads in the aluminum transmission pan.
Repeat the above procedure for the lube filter.
If you previously removed the drain plug from the bottom of the transmission pan, reinstall it before refilling the transmission with fresh fluid. Use the 3/8-inch-drive torque wrench and insert the 3/8-inch-drive extension into the drain plug. Tighten the plug to 27 pound-feet of torque. Again, do not overtighten the plug to avoid stripping the threads in the aluminum pan.
Finally, add fresh transmission fluid. When checking the fluid level, the temperature must be between 140 degrees and 220 degrees Fahrenheit; driving the motorhome for at least 25 highway miles will accomplish that. The level can be checked with the dipstick, but it’s best to use the transmission’s electronic control pad. If your transmission has WTEC II or later controls, the fluid level can be checked from the cockpit. It’s the most accurate method, and the one preferred by Allison. The steps are as follows:
- Park the vehicle on a level surface, shift to N (neutral), and apply the parking brake.
- Simultaneously press the “up” and “down” arrows.
- The fluid-level check might be delayed until the following conditions are met: The fluid temperature is above 140 degrees and below 220 degrees Fahrenheit; the transmission is in neutral; the engine is at idle; the vehicle has been stationary for approximately two minutes to allow the fluid to settle.
With a fourth-generation transmission control pad, results are displayed as follows:
- If the fluid check is delayed, the window will display a hyphen (—) followed by a numerical countdown, starting at 8, indicating the time remaining in the two-minute settling period.
- If the fluid level is correct, “o L” will be displayed, which stands for oil (fluid) level, followed by “o K.”
- If the fluid level is low, “o L” will be displayed, followed by “Lo,” followed by the number of quarts it is low. For example, “o L Lo 02” indicates two quarts low.
- If the fluid level is high, “o L” will be displayed, followed by “HI,” followed by the number of quarts it is high. An example is “o L HI 01,” which indicates one quart high.
For more information about the procedure, including error codes that may be displayed, refer to your Allison transmission owners manual. For fifth-generation transmissions with prognostics, the procedure is similar but the results are displayed in an easy-to-read format.
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Indianapolis, IN 46222