I've had this service done too, at the dealer. But now I'm wondering if there is, in fact, some documentation that states it is not recommended, why would the dealer recommend it? I suspect there is no official documentation stating it is not recommended. I've seen the posts from Tom (former Allison engineer) stating that Allison does not recommend it, but I've found no "official" documentation. Just wondering if any actually exists, and if so, where?I've had every duramax I've owned flushed properly with a good machine by people who know what they are doing. Never any issues.
MIkey52, I've read this before and do not contest Mr. Johnson's info (the former Allison engineer). I'm just curious if there is an official policy statement from Allison Transmissions that can be referenced?Allison strictly recommends against flushing a transmission system. Just do a drain and if changing to an approved TES-295 fluid, do a double drain and refill. The method is on this forum under my thread: "Former Allison Transmission Fluids Engineer".
For two reasons: First, we ran a test where we "doped" the fluid with 500 ppm (parts per million) manganese. We did a normal drain and a flush using this doped fluid and found little difference in the amount of fluid actually exchanged using the two methods. Also, if you're not careful when using the flush method, you can potentially starve the pump for fluid and damage the pump. It has happened before.
That's why Allison does not recommend flushing. Can it be done and not damage the pump? Yes, I'm sure it can; however, if you did damage the pump, you've trashed the transmission and Allison will not pay to have it repaired. Just use the standard drain procedure (or the double drain if changing from a DEXRON-III product to an Allison TES-295 product). It will be much more simple, less messy and a whole loss less risky.