Transmission Fluids

Introduction

Allison Transmissions are pretty much standard on most motorhomes so this topic will deal exclusively with them. We'll discuss the various transmission fluids used in them as well as filters and service requirements. Hopefully this information will help you plan a realistic service schedule for your Allison Transmission so that you can keep it running smoothly and strongly. Note that this tutorial only serves to help illustrate the differences between the various lubricants and service schedules. It does not replace your owner's manual, which will be the ultimate guideline to the service schedule that pertains to your RV. For additional information please refer to the Allison website at www.allisontransmission.com/ for specific details.

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Automatic Transmission Fluids

Automatic Transmission Fluid, or ATF, is different than motor oil. Motor oil is designed for engines, where combustion takes place. Motor oil has viscosity ratings that must be adhered too. Automatic transmissions use ATF, which is a reddish colored oil. It's not designed for a combustion type environment, such as an engine. Instead it is designed to transfer power through a complex system of servos, fluid couplings, pumps, etc. In addition to transferring power, it also needs to provide proper lubrication to all of the moving parts within the transmission. Just like engine oil, it will be picking up contaminants as it works so filters will be incorporated into the transmission to remove and trap these particles. An engine has a water based cooling system but a transmission does not. An automatic transmission will utilize an oil cooler to prevent overheating of the fluid, which would lead to it's eventual breakdown and failure to adequately lubricate the transmission's many moving parts.

Therefore we can forget about API Service Categories and the various SAE viscosity numbers. We really have only two choices to make - whether to use conventional lubricants or synthetic. If you choose to use conventional transmission fluids Allison limits the warranty coverage and requires more frequent service intervals. However, if you use approved synthetic transmission fluids you can extend both your warranty and your service intervals. Unlike the choice between conventional and synthetic engine oils, this choice is a no-brainer. In fact Allison runs all of their transmissions with synthetic oil prior to shipping. Most of the oil is drained before shipment so it's up to the chassis manufacturer as to what type of fluid they will refill the system with. Sometime in the 2004 model year both Freightliner and Spartan began shipping all of their chassis with synthetic transmission fluid so most all of the conventional fluid has pretty much disappeared from RVs by now.

The biggest question is "Which brands of synthetic ATF can I run in my transmission?". Originally Allison only approved their own brand of synthetic ATF, which was called Transynd. Transynd was made by Castrol and privately labeled and sold through authorized Allison service centers. Since that time Allison has published a set of specifications, called TES-295, and has tested various synthetic fluids to see which ones were compatible. The ones that were approved are listed on the Allison site. As of today's date, the following fluid are approved by Allison. For any changes to this table please refer to the Allison website at the above link.

TES 295 Approved Fluids

As the above chart shows, you don't have to buy Transynd any more in order to get the benefits of synthetic oil that is approved for your Allison transmission. You can use Mobil Delvac, BP's Autran, or any other of the approved fluids as well. Running approved synthetic fluids will increase the time between fluid changes. For example, an Allison 3000 series transmission running non-synthetic fluids requires a fluid change at 25,000 miles but when filled with synthetic fluids that increases to 300,000 miles. The smaller Allison 1000 series goes from 50,000 miles with non-synthetic fluid up to 150,000 miles with synthetics. The filters also get extended treatment with synthetics. For exact details on these check out Allison's Fluid and Filter Change Recommendations at www.rvcruzer.com/docs/AllisonSvcSchedule.pdf.

Transmission Filters

Transmission filters are just as important as the oil that passes through them. And, just like transmission fluid, they too have a limited service life. Refer to the above service schedule for exact requirements for when they need to be changed. The Allison 3000 and 4000 series transmissions used to require an initial change of the primary filter at 5,000. This was to remove any contaminants or machining residue from when the transmission was built. however, effective with serial number 6510670912 (3000 series) and 6610205144 (4000 series) some Allison transmissions were equipped with high capacity filters. This change began around July of 2006. If you have these high capacity filters you do not need to perform the initial 5,000 mile filter change and you can go right to the normal service schedule. High capacity filters can be identified by P/N 29545777 or P/N 29545780 stamped into the end of the filter cap. If you have the standard filters instead of high capacity, those part numbers will be P/N 29538231 or P/N 29538232. More info on this can be found in the above mentioned link.

Do Your Own Service

Servicing your own Allison transmission isn't all that hard. Assuming that you are using synthetic fluid you won't have to do it very often. If you have the Allison 1000 series transmission you'll have a spin-on oil filter and all you'll need is a drain pan and an oil filter strap wrench. If you have the Allison 3000 or 4000 series it's bit more complex, but not difficult. You'll need a metric socket set to remove the flanges that retain the filters from the cast aluminum pan on the bottom of the transmission. A small amount of fluid will escape into the drain pan but it's not the entire contents so you won't need huge buckets to handle this. After removing the old filters, simply wipe everything clean and install new o-rings onto the flanges, and insert the new filters. The o-rings are supplied with the filters so you don't need to go searching for them. Allison offers a handy two filter kit that includes everything you need, including illustrated instructions. Be sure to refer to the Allison tech document, referenced above, for more detailed information.

If you have non-synthetic fluid in your transmission, this would be a good time to upgrade to the synthetic fluid so that you can gain the benefits of synthetic. If you drain the transmission and change the filter(s) you won't get all of the old fluid out. There will still be plenty of the old fluid left in the cooler, lines, and torque converter. If you do this Allison does not recognize this as meeting the extended service interval requirement of synthetic. You'll have to run this 50/50 mix a bit and then change it once again. After the second change it will be considered full synthetic and you may use the extended service intervals. This second change can be done the same day if you want to get it over with, or you can wait for the next scheduled non-synthetic service interval It's your choice. An alternative is to take your coach to an Allison approved service center and have them flush the entire system, then fill with synthetic. This will meet Allison's requirements for extended service intervals because it will be full synthetic. The downside is that you have to pay someone to flush the system.

This article written 11/10/09