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It’s mostly noticeable in reverse but I can hear it in drive too.
Car is on jack stands, haven’t driven it yet due to the noise.
Background: I had the front end off for months and the transmission fuel lines drained abut 1-2 quarts during this time, and one of my suspicions is that there is an air gap in the transmission now?
The other possibility I’m thinking is the filter I used might not be good: it’s a Vaico filter. Anyone have experience with those?
I went through the filling procedure and brought the fluid up to spec temperature and after going through the gears I hear the suction noise. It did take an extra 2 quarts from what the service manual suggested, but that was because of the front end being off for months.
What do you guys think?

Could be that it's the wrong filter with the pickup pipe too close to the sump pan and it's restricting the inflow / cavitating. There are 2 versions and it's common for aftermarket versions to be too long. I would get the ZF filter. There's a link in a recent thread.

I had a similar noise after having my gearbox oil and filter changed.
To cut a long story short.
The o ring on the filter neck was too small.
Instead of being an interference fit it was a clearance fit.

Just hate paying a garage to do a job. Then having to do it yourself to correct their mistakes.

As Shoppinit says above.
Filter neck should be 20mm long. Not the 25mm one.

Thanks guys for the input!
I’m in US so I’ll try to source a ZF filter here.
It sucks that I have to redo the job, but I guess sometimes it doesn’t pay to go aftermarket.

Are they still available at the dealer?

The "genuine ZF" filter is actually a Filtran filter : viewtopic.php?f=2&t=133598
As Steve says, 20mm neck - but I've never actually seen a 25mm one in the wild.
Anyway, that thread gives you the correct ZF part numbers that you can find a supplier of in the US.

If you can hear a sucking noise, I'd also question if they followed the refill procedure - potentially it's just underfilled.

Also here's the link to ZF Aftermarket with oil included, but do also see my caveat on my original post about quantities:
https://aftermarket.zf.com/en/catalog/p ... 58.298.047

My service kit has just arrived and the filer neck is 22mm and it is a Filtram part

That’s weird. Measured mine with a vernier caliper and mine is definitely 20mm. Also a filtran filter.

The old one I removed was also 20mm.

I also check over the new filter in great detail. As they are very fragile and easily crack.

Steve its 20mm if i put the O ring on Theres is a recess which is 2mm below the rest of the filters housing.

You're good. I didn't actually quite show in my original pic on my DIY, but the 20mm is from the flat surface, not the recess. If you look closely at the pic you can see the caliper is standing out a bit from the tube - but it's not clear. For completeness, would you mind taking a pic from the flat surface with the measuring stick on that I could use & add to my Filter thread above?

And as long as you have the part numbers matching my links above, it's spot on (which you do)
(FWIW I never saw a 25mm one - I know they exist for the 5HP24 box, but not for any of your Audis that I know of)

Hi bilco1.
Yes mate 22mm to bottom of recess.
20 mm was to flat surface of filter.
Although I used a vernier caliper. The garage used a steel rule. Hence 20mm became the norm for me.

After reading all of the above. I guess my original problem stems from the garage installing the wrong o ring.
Like Matt. I have never seen a 25mm long neck.
But they do exist apparently.

Yeah. Wrong or incorrectly fitted o-ring could cause aspiration and reduce atf pick up