Many customers seem to think that the oil in their automatic transmission must have been changed, because a major service must include that, and the service cost so much. Or else they believe the dealership when they get told that you never have to get a transmission service, it’s a sealed unit, not recommended, can’t even check it……..Whatever! The reality is that transmission fluid is just oil, like any other oil. You change it on a regular basis, or pay for the new transmission eventually.
Each model has its scoreboard on when the automatic transmission is likely to fail if you never change the oil. Higher power, bigger cars and bigger engines mean they fail earlier. Eurovans and most early V8 cars have the worst reputation: 30% or more do not make it to 100,000 miles. Hot weather and city driving contributes to the demise rate. We see many transmissions in the process of failing, most of them are between 100,000 and 160,000 miles. We pretty much never see a good automatic transmission over 200,000 miles unless the transmission has been serviced. If somebody told you that you never had to change your engine oil, would you believe them? Of course, pretty much every transmission we see failed or failing is long past the factory warranty. We advise customers looking for used cars to pay more for lower mileage cars to help avoid the failing transmission scourge. Enough said.
Ideally, H&B Karmakanix should perform an automatic transmission service with every major service. Most need the fluid changed every 40,000 miles, this includes Golf, Jetta, Passat, Audi A4 and Audi A6. For V8 Audi’s and for VW Eurovans, we often find that is not often enough. The fluid should be changed every 30,000 miles, or 20,000 if you are cautious or drive mostly in hot weather and/or city traffic. When serviced, only about 1/3 to 1/2 of the fluid is actually changed, so one has to view the process as progressive dilution. Which makes it all the more important to have a service done. Most units that we service are already older, and we may recommend shorter interval drain-and-fill to continue cleaning it up. The filter inside only really needs changed every 40K. Note that some units have a filter that is NOT replaceable, making servicing even more important. Most automatic transmissions have a separate section full of gear oil called the differential. This gear oil needs replacing with every other automatic transmission service.
Some say that servicing an old transmission will cause it to fail. In our experience, that advice just leads to early transmission failure by training people to avoid needed maintenance. There are some transmissions where the fluid is already sludged up and burned, and the transmission may be worn and have slight damage. Changing the fluid is very likely to extend the service life of that unit. When we find metal flake and large chunks of clutch material in the pan of an automatic transmission, then a fluid change will not help, and could accelerate the inevitable demise of the unit. Hard to conceptualize, but the larger chunks suspended in the fluid may be helping a very damaged clutch, a bit like adding sand to increase the grip. That transmission is not just old, it is badly damaged.
The real story is that all modern transmissions are adaptive, and the speed and force of the hydraulics changes according to the driver’s habits and the transmission’s condition. When the fluid gets old and has lost much of its friction modifiers, it is now too thin and too slick. The transmission has adapted to shifting faster and with more pressure to compensate. Changing to fresh fluid with fresh additives could contribute to wear and damage until the transmission adapts. The real fix is to disconnect the Transmission Control Unit, which resets the shifting adaptation tables in the TCU. The TCU will then quickly “learn” how to operate the clutches with the new fluid. One also needs to manually reset the adaptations for the engine throttle body.
Customers with standard transmissions, 5 speed or 6 speed, need the transmission fluid changed every 80K. For standard transmissions, we use Amsoil synthetic GL4 gear lubricant. Modern DSG (Direct Shift Gearbox) transmissions and CVT (Continuously Variable Transmission) transmissions now have a factory required transmission service, usually performed during the 40K or 55,000 mile service. This mainly applies to many Diesels after 2005.5 and 2 wheel drive Volkswagens and Audis. At H&B Karmakanix, we only use the best synthetic fluids, often buying them directly from the dealer who refused or neglected to change your transmission oil.