[ainarssems]

I have attached list of 5 speed boxes. I believe they should be physically the same and if you swap boxes with the same final drive ratios it should be only gearbox and TCU swap but might be OK with the original TCU. If different final drive ratio then matching rear diff also needed. I have heard of somebody having vibrations in car which were traced back to gearbox being changed to different without changing to matching rear diff. Don't know if TCU were changed as well.

You might start with checking fluid level and topping up if required and do a diagnostics scan to see if anything comes up.

I think you need to go to Audi for it all.. 190 quid for all the bits sounds about right, though if your mate is a mechanic, try TPS with all the audi codes and see what they come back with.

Last time I checked it was about £130 for oil and parts and £200 including labour at local ZF specialist.

changing the oil dislodges all the gunk that was resting peacefully and finishes the box off ! Ive heard this all over many forums. I don't believe in this theory (So it will 100% happen to me now ) I cant believe changing the gearbox fluid will do a gearbox any hard if done properly. Maybe those boxes were just on there last legs ?

The problem is that if oil have not been changed for 100K+ miles it does not work properly and do not keep all the gunk in oil and it settles out. When you put fresh oil in it starts washing and lifting it all up again. If gunk dissolves slowly you are fine if it comes off in lumps you are in trouble. Theoretically you could take box apart, clean it and still be fine.

Here is Tozo's post when he did his S8. For the A8 you either have to re-code the ECU so it doesnt look for the Auto gearbox signal, or trick it into getting a signal, thats what Tozo did on his A8

The problem is there is no manual box coding for 4.2 A8 as they never came with manual boxes, only S8. So it is either bodge job with TCU and other gobbins in place or custom software rewrite for ECU so that it can be coded for manual.

The main part is the gearbox, if you can get one of those cheap, you have a good chance of limiting parts costs to under £3k

You can use gearbox from A6/Allroad TDI quattro, you can get them for less then £300 and also have longer gears for better economy