Rear diff ratios

[pete2144]

Are all C6 Rear diffs the same, so do they have the same ratios, I’ve just got hold of a second hand one and although most of the numbers on it are the same it does have some different?






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[Jim Haseltine]

This isn't going to help much. Can't speak for the RS6 but going from over 20 years of playing with Audis, 0AR525083 is likely to be a generic casting number. Any more specific information (like the diff code HNL if it exists) would be stamped into a piece of the case that has been machined flat.
Far as I can find out, the rear diff for the C6 RS6 is 0AR500043A - but that's the entire thing, casing, diff and drive shafts. It's also the only one I can find listed in parts breakdowns for the RS6 so I suspect that there was only one ratio available.
Looking through various on-line versions of Etka 0AR500043A is also listed against various automatic C6 models and has a notation of 31/10 whilst similar diff number 0AR500043C has notation 32/9 - the notations could be diff ratios but who can say for sure?
Unless I knew for certain that the diff came off a C6 RS6 I'd try to find some way of checking the ratio - probably by marking the flanges then ensuring that the amount of rotation is the same. That's if it's possible, some diffs have a habit of not wanting to play when you try that sort of thing.

[pete2144]

thanks for your reply!
yes its definitely from a C6 RS6, I've checked the ratio and its the same!
I was just confused as to the difference in some of the numbers on the casing, but I guess the casing is used on other models just with different internals.
And they both have HNL stamped on them so I'm good to go!
cheers.

[ATinOf]

The rear diff ratios on the HNL diff paired with he 09EA code box as fitted to the 5.0 FSI;

Gearbox code....Gearbox Primary Drive....Spur Gear Front Axle....Front Axle Bevel Gear....Overall Front Ratio....Rear Diff Ratio....Overall Rear Ration....Torque Converter
KBD................???.............................???..........................???............................???........................???..................???..........................???
KUE................???.............................???..........................???............................???........................???..................???..........................???
KZH................32:30.........................31:29.......................32:11........................3.317....................31:10...............3.307......................K110
KZQ................32:30.........................31:29.......................32:11........................3.317....................31:10...............3.307......................K110
LLJ.................32:30.........................31:29.......................32:11........................3.317....................31:10...............3.307......................K110
MKT................32:30.........................31:29.......................32:11........................3.317....................31:10...............3.307......................K110

Note the blanks above, if anyone has the data chip in

To the OP - the HNL was paired with 2 other gearboxes in the A6's (codes 09LC, 09LD) but I dont have data to say whether the ratios were the same or different in those scenarios

You would like to think if they were different it would carry a different code identifier, as it does on the 5.2 FSI (HNN, ratio 32:9)

[ATinOf]

Hmmm, that table ^^ didnt turn out as expected, I will try and tidy that up

It would appear tables are disabled on the forum, improvised

[welwynnick]

So the front and rear differentials have different gear ratios!?!

Nick

[ATinOf]

So the front and rear differentials have different gear ratios!?!

Nick

According to the data, but don't forget the gearbox has the Torsen Diff on the rear output

[welwynnick]

According to the data, but don't forget the gearbox has the Torsen Diff on the rear output

The centre diff was what I was thinking about. In the Mercedes world, people are paranoid about using front and rear tyres with slightly different rolling radii, which results in the centre diff having to accommodate a slow but continuous speed difference. I presume that differentials are designed for intermittent rather continuous rotation, and the latter would wear them out. I always assumed the F&R ratios were the same for that reason.

Nick

[ATinOf]

Every time a car goes round a corner there are differences in wheel rotational speeds even when they have the same size tyres which is what the Torsen diff was invented for

[Jim Haseltine]

Tyre radius matters on vehicles with viscous couplings as any marked difference between the front and rear axles is supposed to cause the coupling to work continuously, overheat and eventually fail. With mechanical diffs it's not such an issue although I seem to remember reading somewhere in my owner's manual a warning about it.
Strangely, by design the rear axles of Freelanders are over-driven compared to the front axles and the drive passes through a viscous coupling so maybe it's not as big a problem as it's held up to be.
During the really bad winter we had around 15 years ago I ran some rally wheels on my quattro - started with chunky M&S tyres on the rear and wets on the front. The noise from the Torsen diff was both surprising and rather concerning so I swapped out the wets for another set of M&S.

[welwynnick]

Strangely, by design the rear axles of Freelanders are over-driven compared to the front axles and the drive passes through a viscous coupling so maybe it's not as big a problem as it's held up to be.

Interesting. I think the Freelander has a different transmission configuration to Audis and LandRovers with longitudinal engines, where there's a centre differential.

With just two exception, I believe that with 4WD cars with transverse engines the drive goes directly to the front differential, and the rear is only connected by a clutch or viscous coupling. There's no centre differential, so rotational speed difference won't matter so much. Moreover, if the rear axle is over-driven, that will allow the centre coupling to divert MORE than 50% of the torque to the rear axle.

Nick

[RS_BROKE]

two gearboxes for the c6 the 26 and 28 maybe that's why its different.