Transmission Maintenance

IMPORTANT: There is a filling procedure in the book. (See link below). There is one part to that they assume you know. I didn’t, but it eventually became clear. First it has you adding fluid until you are in the COLD range. Then it has you fire it up and bring it to 160ºF plus and bring it up to the hot range. At this point it actually takes several more quarts. Once you have done that the cold reading is no longer valid, in fact it will show waay too much. The cold level is ONLY to establish a safe minimum amount to start it up. It has to be running and up to temperature to get the level to the actual required. At this point the cold level is meaningless. Now, sitting in the driveway you will not get it to the required temperature. Mine takes hills and a few hours to get above 160ºF. So I have now learned to bring a few quarts and stop every so often to check and add.


But, by all means, read the Allison book that came with your coach, or download from the web…

For starters the book calls for changing the “External Transmission Control Filter” at 5000 miles. Then you’re off the hook until many miles later. (50,000/24M but more on that later). I suspect it’s to assure that if there was any matter from manufacture which collected in the filter it is not reducing the flow.

This one’s easy….. Here it is:

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You’ll find it on the bottom of the transmission, can’t miss it. There’s a magnet there…. clean and place on new filter! You’ll need a little fluid about a pint, Allison TES 295 approved, to top it off again when you’re done. I got some Fleetrite Synthetic ATF…. I bought a gallon, some people bring a small container and schmooze the shop out of a few ounces out of the bulk barrel.

The book mentions another filter, the auxiliary lube filter. The best I can tell it is NOT installed on the 2500MH. And after extensive debate on social media (some of it with people that actually know what they are talking about) and a phone call to Allison I have confirmed there is no internal filter that needs replacing. There is a screen in there that is replaced when the transmission is ever rebuilt.


Fast forward about 20,000 miles and I know a bit more. There’s ATF (Automatic Transmission Fluid) that meet Allison TES 295 and then there’s Allison Transynd (Made for Allison by Castrol). After chatting with the guy that wrote the TES 295 spec  it turns out that if you run Transynd in it, you don’t heave to replace that until it wears out, which you can determine via analysis. Take a small sample and send it to a lab. They will tell you how your fluid is doing. This is how truck fleets maintain their transmissions, as an occasional $20-$40 analysis versus thousands of gallons of fluid translates into hundreds of thousands of dollars.

I am not sure whether that’s the route I want to take,  but for starters I don’t know what is in there. ANY fluid you put in there needs to meet the Allison TES 295 spec, but they are not  the same as Transynd. There’s a tag on the dipstick and it’s not telling me much more than that whatever is in there, which was put in by Freightliner, is Allison approved and meets TES 295….


Also, there’s an interesting maintenance calculator on the Allison website. Based on the usage numbers I put in it gave me a 50,000 miles, or 48 month (versus the book 24 months) change interval.

Now, something else that I keep in mind is that the tow rating for this coach, 5000#, is limited by the transmissions. Most other Berkshires have an Allison 3000 with is rated to 10K. I do occasionally tow at the limit. I keep the transmission temp up on the LBCU at all times and have never seen a temp even close to the upper limits (220º IIRC) but it does play into my thinking about maintenance.

Right now I plan on doing a complete fluid/filter change with Transynd at 50K/48 months, which should be about the same thing at our usage. Now, when you drain and change the fluid, there’s a lot that stays behind in the torque converter, so “the man who wrote the spec” recommends that to change over to Transynd you drain all that will drain, refill with Transynd, drive for a half hour and repeat. So right now that’s what’s probably going to happen.

Stay tuned.


And then it was time…… 45K miles, but a little over 4 years. So, ordered a new control filter and went out and got a few gallons of Transynd. Pull the plug and let it drain into a clean container so I can measure how much comes out. About 9-10 qts. Replaced with Transynd.

One note. Not unlike the generator getting a nice clean reading on the dip stick is not easy. I have found that the best method is to remove the dipstick and then go do something else for a while so that all the fluid in the tube is out. Then do the reading.

Looked pretty clean coming out of the hole, but all in the tub I could see that it was a little dirty. No burned smell though so that’s good. Glad I did it. And, you don’t get ALL of it out like this, so I think I will do it again in 25,000 miles. As an interesting side note, SEVERE duty requires a change every 12,000 miles…. On page 56 of the manual referred to above a “Motor Home” is under severe duty.