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muddy924 · Joined: 12 Sep 2007 Posts: 9 Location: Shropshire. UK

The 5 speed box in the NA 924's is often described as "Audi based".

I need to drastically lower the gearing of my '82 car for motorsport.

Are any of the 1980's Audi 100 transaxles a straight swap i.e. is the bellhousing the same as a 924 or is it as I suspect a completely different casting?

If they are different then does anyone know if I could fit all the internals of an Audi 100 diesel box (4.56 diff.) into a 924 casing ?

Or by the same route, just fit the CWP (4.7 ratio) itself and fifth-gear pair (0.64) from an Audi Coupe - into a 924 box thus retaining the 924's first gear reduction of 3.6 and thereby getting the benefit of a really low overall first gear AND keeping a decent overdrive fifth ?

bass gt · Posted: Wed Apr 02, 2008 1:47 am Post subject:

Hi,

How low do you need to go?? what kind of motorsport? i am using a 944 box in my '24 turbo, and with 21"Dia tyres, the g=earing iss very low. Check out the video's i posted here. You can see what gear I'm in at places like Gurston, Harewood ect.

Steve
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Front Wheel Drive is the Devil's work.

924RACR · Posted: Wed Apr 02, 2008 1:51 am Post subject:

If he's not running a turbo, then yes, the stock gearing is too high - 5th gear is virtually unnecessary. I've run mine up to 110 in 4th (with stock gearing including 4.111 R+P), only gets to 6500rpm at 108mph with my tires (225/45/15 Hoosier R6's)...

Sadly, I've never found time to investigate different ratios, though I could certainly benefit from them!!
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

bass gt · Posted: Wed Apr 02, 2008 2:11 am Post subject:

Vaughan,

The answers simple then.....run a turbo!!

The 944 box has a R+P gearing of 3.889, so maybe that is an answer. I don't know hespecific ratios however, but i do know the final is 3.889

Steve
_________________
Front Wheel Drive is the Devil's work.

924RACR · Posted: Wed Apr 02, 2008 4:01 am Post subject:

Ah, if only it were that simple. SCCA doesn't really allow turbos to compete, not anywhere near the same way I'm racing, let alone worry the added cost...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

muddy924 · Joined: 12 Sep 2007 Posts: 9 Location: Shropshire. UK

Hi Steve/all

The 924 is being prepared for Classic Trials of the muddy variety. That uniquely British motorsport where we attempt to drive roadgoing 2WD cars up steep slippery slopes, mainly old unsurfaced roads or forest tracks. Unlike rallying there is no emphasis on speed, just an ability to get the car up hills as steep as 1 in 3 and do 'restarts' from wet rocky slabs/deep mud/loose stones on the steeper parts.

Main requirements are :- high ground clearance, sump guard, plenty of traction aided by large diameter wheels and a lightened car with weight shifted rearward, robust drive-train, torquey engine - and a first gear with an overall reduction ratio of around 16 or 17:1
For the road section when driving back 100+ miles home after the event then a decent high 5th gear helps progress and fuel economy.

Standard UK NA 924 has a 3.6 first and a 3.9 diff giving an overall ratio of 14:1.

The '86 Audi 100 diesel 'box has 3.6 first and 4.556 diff giving 16.4 overall.

The Coupe GT had a 4.7 diff (or a 4.9 in some books) - but a 2.8 first gear - so it needs to be put in a 924 box to produce a decent overall ratio of around 17:1.

I will initially run on 185/80x14 tyres but may go up to high profile 15" tyres (possibly even 16") - if I can get the gearing low enough.

v8carreragts · Joined: 05 Sep 2003 Posts: 665 Location: Tucson, AZ

The AUDI 016 ratios. There is a 4.56 as well as a 4.77.

trans ID#

AMM; AMN 4.77

AAX; AAY; 2U; 6U 4.77

v8carreragts · Joined: 05 Sep 2003 Posts: 665 Location: Tucson, AZ

oops, the AAX; AAY; 2U; 6U is 4.56

Rich H · Posted: Wed Apr 02, 2008 5:06 pm Post subject:

If you are feeling really stupid the VW vans had an option of a 3:1 reduction box that fits on the outboard end of the driveshaft... Bolts to the swinging arm.

Might be a bit on the low side.

MY Dad used to be very competative in Production car trials in the 70's and 80's (before it got serious) in his Hillman Imp, we have a loft full of trophies. Compete in it at the weekend then go shopping in it on monday sort of thing.
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

muddy924 · Joined: 12 Sep 2007 Posts: 9 Location: Shropshire. UK

Rich. I have a memory of seeing a buggy doing trials with the reduction hubs - very effective !

v8
Now we are getting somewhere. Thanks. This ID# is the one stamped along with the date on the topmost part of the bellhousing?

Does your source happen to say which models had the AMM and AMN ?

These Audi 100's are getting very thin in UK breakers yards but today I found a late '87 100 GT Coupe. I could see enough of the bellhousing to tell it was NOT the same as a 924 - there being no hole for the gearchange link. I am still hoping that an earlier 4.56 diesel box might be the same as a 924.

Update :-
Following your lead on these codes I found a fairly detailed table of ratios on http://www.gt40club.com/technics.htm#Audiaxles

All I need now is to find which models of Audi had the gearbox I'm chasing.