I've read several posts on this topic made over the years but don't have a clear idea if this whooping sound that occurs on acceleration is simply a cosmetic problem with no mechanical consequences or an indication that an expensive transmission failure is inevitable. The "additive" mentioned in several posts is apparently no longer available. I've seen several posts where people have changed out the fluid with no lasting benefit, even when this additive was available. Hate to open up the transmission if there is nothing that really is guaranteed to fix this problem. Any thoughts?

 

The noise is cosmetic and a fluid change will usually cure it. If you don't get all of it drained out of the torque converter, it may take two changes though.

The recommended interval to change the fluid and filter is 60k miles, so sooner or later you will take care of it as part of normal maintenance.

 

I have been told that the genuine ZF oil has the aditive in it.

 

During a couple of phone conversations I had with ZF tech support back in March 2010, I was told that the noise is supposedly nothing more than an annoyance. It is caused by the internal clutch packs grabbing for a micro-second too long before releasing. The reason is generally attributed to the friction modifiers in the ATF breaking down and losing some of their effectiveness over time and heat cycles. Doing an ATF drain-and-fill is regarded as a better and potentially longer-lasting solution than going the additive route. As previously mentioned, it may require multiple drain-and-fills to completely silence the "bark" since each drain-and-fill typically removes only 6 to 7 litres of fluid in the 10-litre 6HP26 system....