A8 Parts Forum - Know your Transmission Sticky

The gearbox in the A8 / S8 (and in deed the autos in the A6 and other marques) are all considered to be the weak spot in the Audi design.

Under the covers, it is nothing more than a ZF gearbox (HP24a, where a stands for Audi, or HP19a on the 3.7 pre facelift) which is also used in BMW, Range Rover and countless others.

The gearboxes are generally designed well, but 2 main factors cause premature failure in our eyes:

1) The A8's do throw out considerably more power than most other ZF based vehicles, and also the quattro drive train gives no room for wheel spin like in the BMW's

2) Audi's service plan on the D2 didnt include a regular oil and filter change for the gearbox. They did this breifly at the start of production on the 4 speed boxes and stopped around 1997 when the 5 speeds came out. If you speak to any transmission specialist, they will suggest a gearbox service around every 20,000 miles.

There are many different gearboxes fitted over the years. There are different gearboxes based on engine code, (14 engine codes pre facelift, 17 facelift) and then again differing on whether its quattro or front wheel drive

The 4.2 Quattros in the UK were 4 speed upto mid 1996 using a gearbox with a code of CML, after which they started fitting the 5 speed DTD gearbox which statistically seems to be the weakest box out there.

The 4 speed quattros seem bullet proof, and we've yet to see one fail, even after 330,000 miles which we noted on a car that we got recently.

The 2 wheel drive boxes seem more robust, but still wouldnt expect to see 200,000 miles without a refurb.

We've seen the later 5 speed gearboxes fail at anything between 40,000 and 177,000 miles without servicing. Servicing should prolong the life somewhat, but nothing it guaranteed.

The S8 gearboxes share the same inner workings as the A8 4.2, however they have different final drive ratios built into the front diff, which is inside the gearbox.

All the A8/S8 gearboxes have the front diff built in, with all the quattros also having the center diff built in at the rear onto which the prop shaft for the rear axles connect.

The need for servicing is clear, but we do recommend that under no circumstances this be left to an Audi main dealer for a number of reasons:

1) They have time and time again proven to various A8 customers that they dont really have the experience as they nearly always get it wrong

2) When they change the oil, that is literally what their process tells them. Without further prompting, they wouldnt consider changing the filter, or cleaning the sump & magnets.

3) They will charge £100 / hour for a job that a competent Transmission specialist will charge half that for.

There are two transmission specialists that we would recommend in the North:

Chester Auto Transmissions: http://www.transcentre.co.uk/

Advance Transmissions: 01642 563237, TS23 3TA

For those that are still reading and want to know more, we can't recommend enough the excellent documents by Paul Waterloo on the subject, including how to check / change your own transmission fluid:

http://www.audipages.com/Tech_Articl...nsmission.html