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D2 - Transmission Gearboxes, diffs, drive shafts.

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Old 21st January 2009, 12:55 PM
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Default 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:

For parts enquiries and Forum User Administration please contact customer services directly, not me - enquiry@a8parts.co.uk, www.a8parts.co.uk, or call 01642 783537

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2001 D2 4.2 QS Silver, 1997 D2 S8 Silver, 1999 D2 4.2 Silver, 2002 D2 S8 Dolphin Grey,
2003 C5 RS6 Blue, 1998 D2 S8 Black, 2000 D2 4.2 QS/S8 Ming Blue, 2003 D3 4.2 Ming Blue,
2005 B7 S4 Blue, 2006 D3 3.0 Tdi Black, 1999 D2 4.2 Silver, 2003 D3 4.2 LPG Crystal Blue,
2000 D2 S8 Silver, 2007 3.0 Tdi Q7 Black, 2009 B8 S4 Black, 1998 D2 S8 Agate Grey,
2006 D3 4.2 Tdi Blue, 2006 D3 S8, 2007 Q7 3.0 Tdi, 2006 C6 S6,

The Second 20 Audis:

2011 A7 Sline, 2001 A2 1.4 Tdi Black, 2002 A2 1.4 Tdi Silver, 2006 A8 4.2 Tdi Blue,
2007 4.2 Tdi Q7, 2006 S4 Cab Silver, 2010 RS6 Saloon Black , 2007 TT Roadster,
2010 A8 D4 4.2 Silver, 2006 C6 A6 2.7 Tdi Quattro, 2000 D2 4.2 QS/S8 Ming Blue (again), 2008 Q7 4.2 Black,
2009 C6 RS6 Saloon Daytona Grey, 2001 Fully Loaded A2 Tdi, 2006 Avant S6 Black, 2007 VW Caravelle Exec Black (almost an Audi)
2009 TT Roadster Daytona, 2015 Q7 4.2 tdi lava grey, 2002 GmbH D2 demonstrator, 2006 D3 A8 LWB 4.2 Tdi Black

Most Recent Audis:

2001 A2 1.4 Tdi Black, 2007 4.2 FSi Q7 ABT Blue, 2016 S5 Coupe Launch model, 2004 S4 B6 Cabriolet, 2016 Q7 Sline White

Last edited by Conan_the_Librarian; 21st January 2009 at 06:45 PM.
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Old 17th September 2009, 07:07 AM
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An interesting read there.
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Old 24th March 2017, 08:47 PM
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Default Still teaching Newbies

3.7 to the stars... D2, LPG kit, March 2000(road tax...)
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