ZF 5HP24A - Rear axle ratios – just the two?
 

Hi everyone. My first post on the forum – please be gentle :)

I have an interest in the ZF 5HP24 transmission and I have a fair amount of experience of its use in Jaguar, BMW and Range Rover applications but none, unfortunately, of the 5HP24A variant used in the Audis.

Clearly the 5HP24A is quite a bit different to the 5HP24, having the integrated front ‘axle’ and the Torsen differential unit in the transmission itself.

http://i260.photobucket.com/albums/i...psb74c0909.jpg

From what I can gather there are three different front 'axle' bevel gear sets used :

3.0909 (34/11)
2.9091 (32/11)
2.7273 (30/11)

as well as three alternative ratios for the front propshaft idler gear drive :

1.2069 (35/43/29)
1.1724 (34/43/29)
1.0000 (29/39/29)

and five alternative rear gearset ratios to drive the rear propshaft :

0.9063 (29/32)
0.8529 (29/34)
0.7838 (29/37)
0.7742 (24/31)
0.7368 (28/38)

All the potential combinations are actually reduced down to (just) five overall options, shown in the list below, which covers all 27 Audi variants of the transmission :

http://i260.photobucket.com/albums/i...ps9943bc10.jpg

My question is, am I right in thinking that there are just the two rear axle ratios available i.e. 3.7000 (37/10) and 4.111 (37/9) for Audis fitted with the 5HP24A? If that is the case then drive to the front axle from the Torsen unit will always lead the rear slightly by between 0.04% and 0.46% depending on the model. Not that this is a large amount as, at worst, this speed difference is only equivalent to having 1.5mm less tread on the front tyres than the rears if the gearing at the front & rear was absolutely identical. I just wondered if any other rear axle ratios were offered by Audi with this transmission?

Phil

Hi Phil,

Nice to see you in the forum. I'm afraid I can't answer your question in any detail whatsoever but I'm fairly sure there are only 2, one in he A8 and the other in the S8. The S8 is certainly more rev happy than the A8. I know that is the case for the face lift models but not sure about the pre-face lift. Hopefully someone else and clarify in more detail.

I really shouldn't type so quickly on my phone!

S8 revs much higher both PF and FL. So probably the same/similar ratios though the controllers and programmes are different.
My PF and FL seemed to be very similar revs at "motorway" speeds. Or in the back lanes out in the East Midlands today. :ROFL:

If the ratios where the same front and rear gears can chatter causing wear and noise, the tinny difference keeps the gears meshed
Dave