Toyota Prius “Transmission Service”

The other day I made the mistake of recommending a “transmission service” to a customer who owns a 2007 Prius. I will admit the terminology I used could have been more specific but after 27+ years of using the term, it just slipped out. Technically however I was correct. A quick google search answered the question this way. The definition of a transmission is: “the mechanism by which power is transmitted from an engine to the wheels of a motor vehicle.” Yep, that about describes it.
So why then do hybrid experts, some owners, and enthusiasts bristle when you refer to the mechanism by which power is transmitted from the engine to the wheels of their motor vehicle simply as a transmission.
I have a theory. The transmission in a Toyota Prius is a unique, complex, simple and in my opinion beautiful example of engineering. In a first and second generation Prius (all through 2009) it contains only one major component that someone intimately familiar with a conventional transmission would recognize. This, a planetary gear set, and just one. A conventional transmission with just one planetary gear set would have just two forwards speeds. However, brilliant Toyota engineers, by coupling this one gear set with two electric motors created a very simple, very durable, infinitely variable gear ratio transmission. Or as I usually refer to it, “hybrid transaxle”. So my theory is that calling it simply a transmission just sells it a little short.
This hybrid transaxle also contains many of the same smaller components that a conventional automatic transmission contains. Ball bearings, taper roller bearings, torrington bearings, a drive chain, final drive gears, a parking pawl are some. I have known these facts about this hybrid transaxle for many years having attended countless training seminars, read the internet endlessly I thought I had a pretty clear picture of what was inside. But, until recently I had never had occasion to take one apart completely.
This brings me back to the reason I was trying to sell the “transmission service” in the first place. All those little components are moving parts that require lubrication. The lubrication in the Toyota hybrid transaxle is the same fluid that is used in all current Toyota automatics, namely Toyota WS (for World Standard I am told) Fluid. Toyota says this fluid is good for the life of the transmission in a Prius so no need to change it right? Wrong! Last week I learned that the “life” of a Prius hybrid transaxle is about 250 thousand miles, if you never change the fluid. Bearings fail, steel parts begin to move against aluminum parts, wear occurs, your Prius stops moving somewhere between San Diego and San Jose. Lucky for me it was in Gilroy.
A new Prius transmission from Toyota is in the ball park of $3500.00. Used, around $1000.00. Plus labor. I think used is a good bet here because with just a little care and maintenance I think a life well beyond 250k is to be expected.
I change the WS fluid in our 07 Camry Hybrid and the 2003 Prius ever 30k. You should consider requesting yours be done as often. Oh, and the Generation 1 Prius takes the Toyota Type IV fluid, not WS.

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