Transmission Service

Weekend Project:
TRANSMISSION SERVICE

A step-by-step do-it-yourself guide to servicing your coach’s Allison transmission

by Jake Elliot

Servicing your coach not only provides a cost savings, but also the satisfaction of knowing the service was performed to your expectations, and in accordance with the manufacturer’s recommended procedures.

Servicing the Allison 3000MH, common on Cummins ISC-powered coaches, proved to be one of the easier maintenance items we have performed. Outside of a nine-gallon bucket (which you already bought from Home Depot to drain your ISC’s engine oil into) and a calibrated torque wrench (up 50 lbs.), no special tools are required. A flat level spot and a couple of hours is all it takes.

We purchased the parts, including filter kit (part number 29526898) and the fluid TranSynd, (part number 27101-CTCS), from our local Allison dealer. We opted to use TranSynd in lieu of Dextron III, as the former is a synthetic fluid made for Allison meeting all of the specifications of Dextron III (G34010) and Allison C4-27403598. Using TranSynd will allow for increased maintenance intervals (50,000 to 100,000 miles when supported by oil analysis) while maintaining the warranty according to Allison. The filter kit (O-rings and gaskets and instructions for performing the service) runs about $80, and the fluid runs about $38 per gallon, of which we used five. The manual states that the 3000MH will take approximately 19 quarts on a refill service. That figure may vary, depending on the size and length of the cooling lines used in your coach’s application. It is always safer to have more on hand than not enough, and your dealer should allow you to return any unused fluid as long as the seal has not been broken (you can locate the dealer nearest you on Allison’s website (www.allisontransmission.com). While you are visiting the web site you may want to take a couple of extra minutes to download Mechanics Tips #MT3004EN. This 50-page bulletin will give you most of the information required to perform your 3000MH service.

After bringing the transmission fluid up to operating temperature, we parked our coach on level ground and set the parking brake. Take the time to manually check the fluid level prior to draining so that you have a reference point to fill to later. You can do this by starting the engine, moving the gear keypad selector from D to N to R and back to N. With the engine running, parking brake set and the key pad selector in N, check the fluid level on the dipstick. Mark that level for future reference.

Shut down the engine and place some protective plastic or plywood under the transmission pan. The draining fluids tend to splash easily; however, if you are careful the mess is minimal. Position a drain container under the transmission. The container should be large enough that the transmission’s pan fits inside of the circle of the pan. We found a nine gallon galvanized tub at Home Depot that fits perfectly. You will want the pan to be tall enough to eliminate fluid from splashing, or worse, the wind blowing the stream of draining fluid out of the pan on to the ground, but short enough to slide easily under the Allison’s pan and allow room to remove the bolts and filters. Be sure to have plenty of rags on hand.

Start by removing the six 15mm bolts from the filter covers. Loosen the bolts and remove all but two in opposing configuration. Carefully pull down the filter cover from the outer edge. You are attempting to break the seal of the flat gasket and O-ring. If you pull down a little at a time, the fluid will drain slowly into the pan. There are six bolts on each cover, we would recommend removing the filter covers one at a time. If you are performing the 5,000-mile break-in service, you will not drain the pan at this service. Carefully remove the filters. They are a little tough to remove from the cover as the filters are held in place on the filter cover by an O-ring inside the filter itself. Lubricate the new O-rings. There are three, two on the filter cover and one inside the new filter. Make sure that the old flat gasket has been removed completely from both the pan and the machined surface on the filter cover. Push the new filter onto the cover, install the two new O-rings on the filter cover and place the new flat gasket on the machined surface of the filter cover. Place the assembly into the pocket (it will go only one way) and finger-tighten the bolts. You will need to firmly press the filter cover into place, seating the O-ring.

Checking that the cover is firmly seated against the pan, begin to tighten the bolts in a cross pattern. Using a torque wrench, torque the bolts to 38-45 lbs. ft. Repeat the procedure for the other filter. You will want to carefully examine the drain pan contents for foreign metallic particles. If you have found particles, or the fluid you have drained is dark or brown in color with a burnt smell, notify your Allison dealer for further corrective action. If you are performing the 5,000-mile service, you are complete with the exception of filling the fluid. Add only the enough fluid to bring the transmission’s fluid level back to the line you had established at the beginning of the service. If you are performing one of the regular services, you can drain the pan at the same time you are draining the second filter pocket. Once all of the fluid is drained, clean the magnetic tip on the drain plug, again looking for large metallic debris, lube and replace the O-ring on the drain plug and reinstall on the transmission pan. Remember to torque the drain plug to 18-24 lbs. ft.

On our project coach (a ’98 Monaco Windsor), the transmission fill can easily be accomplished through the access cover by lifting the bed. We started by filling approximately 19 quarts. Close the bed hatch, and start the engine. Check for leaks and correct immediately if required. If no corrective action is required, allow the transmission to warm and remove the drain pan from under the coach.

Once the transmission has reached temperature, manually check the dipstick following the same procedure as you did when you established the baseline prior to draining the fluid. Add or drain fluid as needed to bring the fluid level to the same mark you established at the beginning of the service.

Driving the coach at this point will bring the fluid to full operating temperature. Once operating temperature has been obtained, you can electronically check the fluid level in the transmission by simultaneously pressing the up and down shift arrows, and the fluid level will be displayed in the keypad; Allison, also uses this as a diagnostic tool. For more complete information regarding the keypads functions consult your owner’s manual.
With the exception of responsibly disposing of the old fluid at a waste disposal center, and logging the service in your manual, the service is complete. You now have first-hand knowledge of your transmission’s condition, and the satisfaction of knowing the service was completed not only to Allison’s specifications, but to your own as well.

Servicing your coach’s equipment gives you the opportunity to become familiar with the intricacies of each component’s operation, and the little quirks that surround the mystique of their functions and their interrelationship to the other components. This information can become very useful in times when there are no repair shops within miles to assist you with a problem. It has been my experience that maintenance procedures usually appear much more complicated and messy (at first glance) than they actually are, so don’t allow that to become a deterrent from knowing your coach better.

Jake Elliot has been involved with road-going diesels for more than 25 years, including 20 years in operations and driving for heavy equipment rental outfit. His current coach is a Monaco Windsor, his third-owned diesel-powered RV. He is a regular contributor to the Turbo Diesel Register and joined the Lifestyles family in 2001.