Originally Posted by whitetmw

He said the over the road units like Allison never need to have a fluid change, but do require additives at prescribed intervals. With only one or two exceptions, these transmissions are only pulled when they fail and need rebuilding. Although they have prescribed intervals for fluid analysis to "catch thing early".

Originally Posted by A/Ox4

I don't think the 4r100 is a "sealed" unit. Correct me if I am wrong but this was how I understood it.

I had a Tundra with a "sealed" transmission. It had no transmission dipstick and from the factory they say never replace the fluid unless there's a leak, failure, etc.

That is what I was under the impression is a "sealed" unit.

Originally Posted by whitetmw

As I said in my post "I'm not a Transmission Technician". This is kind of long but I was educated and I'll try to pass what he said on for you.

So , I spoke with my Transmission Buddy Shop Owner today (he co-owns a shop that does cars up to over the road trucks, Busses, and who know what else - He must do a $1M business a year. He's open Mon-Sat 16 hrs. a day with two shifts).

I asked him about the "Myth" of not changing anything if there was high mileage and no maintenance.

His response was that it's not a Myth. And, if you ask any reputable transmission shop they'll tell you the same: Leave it be. He said The Transmission Institute (I forget the name) has a whole chapter on how to advise customers who want it done and why not to do it.

Why? According to him its more of a seal issue than anything. Additives in the ATF (which he said is nothing more than Hydraulic Fluid in a sealed unit) are designed to keep seals pliable and extend life. However, with high mileage units not being maintained the additive is either tired or destroyed by naturally occurring acidity and other things and the seals, while wet are probably beyond there life span because of it.

He said the over the road units like Allison never need to have a fluid change, but do require additives at prescribed intervals. With only one or two exceptions, these transmissions are only pulled when they fail and need rebuilding. Although they have prescribed intervals for fluid analysis to "catch thing early".

He said introducing new ATF will cause seals to swell, built up deposits, caked dirt, and sludge (if it were overheated) to loosen and enter the system. Most probable result will be leaking following a few thousand miles. And, it will get worse until your loosing quarts, then gallons, etc. The next thing to go will be the pump seals, and then the unit due to lack of fluid lubrication.

So, with all this I asked him what he personally suggested. His suggestion was:

Have the unit pulled, cleaned, lines flushed, a new cooler, and reseal it. While they're in there they'll have a good idea of what may need to be replaced, providing there is no other parts requiring replacement you're in good shape. And if there are parts which need replacing they were on their way out anyway. He also said an oil analysis would give insight into just how good or bad the additives are.

I also asked him about external filters (because I have one mainly). His response is if it makes you feel better that's fine. The over the road trucks have them but a light duty truck?

I said what? His response was look, the transmission is not like an engine, there is no combustion byproducts, water, condensation, and so on contaminating the fluid. Trans Units are a sealed hydraulic system which only sees environmental conditions such as cold and heat. If you control heat and perform maintenance you should not have a failure other than normal wear and tear.

I said what about trapping particles? He said if you've got particles, you've got problems. The Magnet should be more than enough to contain the designed wear particles.

Hmm. I still keeping mine. But a guy with almost 40 years and the biggest shop in 500 miles, you've got to take some of what he says as knowledgeable. So this is all Bull or Fact. I'll have to start doing some serious reading and research.