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Discussion Starter · #1 ·
Hello,

I've read that it is not recommended to flush the Allison transmission. Can anyone tell me where this information is officially posted? Either on Allison's website or, more preferably, in the owner's manual? Particulalry for an '07 Classic. Thanks.
 

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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.
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?
 

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People use the word FLUSH to mean different things. One would be the use of a machine that pushes fluid thru the trans under pressure, captures the old, and fills with new fluid, and many people think this is harmful. Other people use FLUSH to mean that they exchange the fluid from the trans by using the transmission (with the engine running) to push out the old fluid while simultaneously adding new fluid, and others mean to just do the double drain. Hard to know unless they describe what they mean by FLUSH.
 

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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".

Bucketlist,

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.
 

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Discussion Starter · #9 ·
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".

Bucketlist,

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.
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?
 

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@Markusj ,
I will check the ACdelco factory service manual when I get home later tonight. I know it's a different generation, but at least it might help you. You could also locate and purchase the factory service manual as well.
 

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@Markusj ,

Well I didn't find exactly what you're looking for. The only thing the service manual talks about flushing is the external cooler, not the transmission. Its in a diagnostic section for checking the cooler and lines to make sure it's all clear and flowing. The truck is not running, and the only thing the flushing system is hooked up to is the cooler and lines, not the transmission. If I'm reading it correctly.

The service manual says that if you want to change the fluid, drain the pan and refill. So, while nowhere does it say, "don't do a transmission flush", the manual says to drain and refill the pan.

Not sure if any of that helps, or the scenario you're in, but I read enough on this forum that flushing the trans is risky. Sure, you don't get every ounce of old fluid out, but a double drain and fill, while time consuming, is safer.

And, for whatever it's worth, I'm looking at the '17-'19 manual.

I can only guess that a flushing setup might be slightly faster in overall service time. Since the machine puts in the exact amount it takes out. When you drain the pan, you're basically somewhere from 6 quarts to 7 quarts. So you have to guess, refill, then go drive the truck and get it hot enough to do a "hot check" and topoff. Once again, a lot of guessing there, I'm sure some dealer techs on here can elaborate more.

Also, read the post #30 in the thread below. @ChevyTech77 is a verified dealer tech and helpful dude:

 
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