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D2 - Transmission Gearboxes, diffs, drive shafts.

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Old 22nd May 2020, 12:06 PM
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Default Could a D2 be converted to RWD?

I was talking to a mate the other day about cars ( heís a BMW but ) and he was saying how great the 5 and 7 series are because the front wheels do the steering and rear wheels provide the go.....typical BMW talk

I was thinking afterwards how hard would it be to convert a D2 to RWD? Iím not sure it would improve handling much, but my inquisitive mind would like to see it done to see the weight saving.

Iíve heard of people doing it with Lamborghiniís so surely the D2 could be done also
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Old 22nd May 2020, 12:46 PM
tintin tintin is offline
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I don't get why you'd want to do this: if you want weight saving, there was the option of a front wheel 2.8 instead ( https://www.ultimatespecs.com/car-sp...D2)-28-5v.html)
- and none of that silly sliding about on snowy/icy roads and needing to be pushed or pulled, which would be really embarrassing in an '8
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Old 22nd May 2020, 01:27 PM
ainarssems ainarssems is offline
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The simple way would be remove shafts from front drive shafts but leave CV joints and weld up centre diff. But hardly any weight saving. And handling is not that great mostly because engine is way up front and front wheels further down to back on Audi compared to BMW not because it's 4WD or weight.

The main reason I stick to Audi is quattro and while it could be a bit of fun to kick out the rear with RWD for daily driver 4WD all the way.
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Old 22nd May 2020, 05:07 PM
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Typical BMW propaganda IMHO. What a load of tosh. Next time we have a snowy winter, see which cars are abandoned: FWD - nope; 4WD - nope; RWD - there the ones!
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Old 22nd May 2020, 06:44 PM
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Quote:
Originally Posted by The_Laird View Post
Next time we have a snowy winter
Maybe never again...….
But I used to drive over the Chilterns to work a few years back, to Stokenchurch, and in winter we had an office sweepstake on how many BMW 3-series you could count stuffed up the M40 banking when it snowed!


As an aside, that coincided with the reintroduction of Red Kites at a sanctuary very near, I recall the first time one flew right by my first-floor office window looking for dead rabbits in the office grounds.
It was literally only about 6' away through the glass and my response was "F*** me where did that Eagle come from!"
Now they're as common as muck where I live and bloody noisy! If I look out of the window I'd expect to see at least half a dozen any time of day.
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Old 22nd May 2020, 09:17 PM
sarg sarg is offline
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Quote:
Originally Posted by The_Laird View Post
Typical BMW propaganda IMHO. What a load of tosh. Next time we have a snowy winter, see which cars are abandoned: FWD - nope; 4WD - nope; RWD - there the ones!
As a driver of high powered rear drive cars, I can say with experience that this depends more on your tyres than anything else, which is why I now try to have two sets of wheels for each car, one set with winter tyres.

Having said that, will still be looking for 4wd AND winter tyres for my next daily driver, best of both worlds
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Old 23rd May 2020, 06:48 AM
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Quote:
Originally Posted by RICKY D View Post
I was talking to a mate the other day about cars ( heís a BMW but ) and he was saying how great the 5 and 7 series are because the front wheels do the steering and rear wheels provide the go.....typical BMW talk

I was thinking afterwards how hard would it be to convert a D2 to RWD? Iím not sure it would improve handling much, but my inquisitive mind would like to see it done to see the weight saving.

Iíve heard of people doing it with Lamborghiniís so surely the D2 could be done also

Ricky - don't miss out on the sorts of opportunities I've had in the past, one of which involved pulling/towing a BMW 3-series out of a car park opposite Cinderella's/Jaz in Purley. To be fair to the 3 chaps, they were really grateful I offered my assistance. I'd seen them as I drove past, with two leaning heavily on the boot of the BMW in order to gain traction. Once I'd hooked up my tow-rope, I pulled them out at barely more than tickover speed. I think that there was a grudging appreciation of the car's ability. Always makes me smile...
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Old 23rd May 2020, 08:24 AM
MikkiJayne MikkiJayne is offline
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BMW handling isn't just about driving the rear tyres - its about weight distribution. Because of the drivetrain architecture the front axle line is halfway along the engine so they can get 50/50 weight distribution on each axle which gives the tyres a much easier time, and also has a significant impact on turning inertia of the whole car. I've seen a completely flogged 520 outrun a well sorted VR6 Golf across Milton Keynes simply because the knackered BMW could turn for the roundabouts without slowing down whereas the Golf's heavy engine meant it would just understeer in to the bushes at the same speed.

Have a look at this pic of a BMW E39 (5-series) engine bay. You can see not only how far back the engine is in the bay, but also where the front struts are relative to the engine:



On twisty dry tarmac an E39 would just scamper away from a D2, even a manual one. But when traction becomes questionable, quattro takes the win every time. Its why Audi was dominant in every motorsport they entered, until quattro was banned in pretty much every tarmac racing format.

Mechanically it is simple to RWD a quattro car, and indeed there are a number of RWD-converted A4s used for drifting for some unfathomable reason. However, the compromise we make to have a driven front axle is that the entire engine is in front of that front axle making the weight distribution and moment of inertia fairly terrible for changing direction. If you converted to RWD, you still have the FWD physics to contend with, but now you have half the traction. It doesn't really make sense, unless you want to spend the day going sideways, and really RWD is simply a crutch for not having enough horsepower to to quattro drifts (search Gatbil on Youtube for quattros going sideways).

Our drivetrain architecture can be traced right back to the Horch (I think) cars which first introduced the layout of having a longitudinal engine with front wheel drive, in order to make more room in the cabin for people and things by not having a propshaft or driven rear axle. The layout was slightly different to what we have now, but it evolved in to a 4 cylinder engine in front of the axle with the geartrain behind the axle in the very first Audi models, and they have stuck with it to this day.

Audi have taken some fairly extreme measures to change that weight distribution characteristic in later models (a bit like Porsche stubbornly developing the 911 for decades even though the engine is really in the wrong place). From the D3 onwards, they have gradually moved the gearbox output shafts further and further forwards, to the extent that the front diff is actually beside the engine block on some recent models, with the axle centre line almost parallel with the back of the engine. The clutch & flywheel, or torque converter are mounted on a spacer and sit a few inches off the back of the block then, so there is room for the output shaft in front of them. Coupled with active torque vectoring in the recent 'sport diff' they are engineering out the FWD understeer characteristic, chasing after BMW's 50/50 handling.

A B8 generation gearbox:

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Old 23rd May 2020, 11:36 AM
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Great reading all the inputs. This certainly wouldnít be something Iíd ever want to do on my D2...itís the USP vs. itís BMW, Mercedes, Lexus counterparts of the era, however I was curious to know how easy it would be to do.

Thatís Interesting MJ that people are using converted RWD A4ís to drift with. My head tells me that would be terrible due to the fact they were never designed that way vs. something Jap or BMW. Iím curious to see how they perform so Iím going to see if I can find some footage on YouTube.

John, thatís a pretty funny story regarding the BMW in the snow
Iím not one to gloat, and my D2 is far from ideal with it being lowered, but the snow and icy conditions Iíve driven in with it has been very compliant and very predictable .
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Old 23rd May 2020, 12:15 PM
MikkiJayne MikkiJayne is offline
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Quote:
Originally Posted by RICKY D View Post
Thatís Interesting MJ that people are using converted RWD A4ís to drift with. My head tells me that would be terrible due to the fact they were never designed that way vs. something Jap or BMW. Iím curious to see how they perform so Iím going to see if I can find some footage on YouTube.
Someone has even completely redesigned the front suspension to give more steering angle Now I'm pretty open minded when it comes to modifying things, but that makes no sense at all to me.
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