Gearbox swapping.

[blackie781]

Hi guys. I have been thinking lately about swapping my gearbox on my 2.7 ARE engine (allroad) for the diesel 2.5 AKE gearbox. Looking on the old VagCat for part numbers, there seems only to be one.

I was wondering if anyone had done it before or even if anyone knows if it possible? I know for example the petrol has a spacer inbetween box and engine, does the diesel, and also is the mounting face the same for both???

[Peter D]

Why do you want to do this. The ratios are different and the diff ratio will be different. Add to this you may have to source replacement drive shafts, you will have to check. Regards Peter

[blackie781]

I was thinking because the ratios were different.

Let me explain,

If the disel cruises at 70 at say 2000rpm, (needs verified, my diesel passat 5spd cruised at 70 at 2200rpm) thats about 1000 rpm less than the petrol so I was thinking about fuel consumption on long jouneys (of which I do alot app avg 35k a year). At 1000 rpm difference thats 60,000 revs per hour, so over one 9 hour journey thats about 540,000 revs, thats alot of wear on the engine and equates to about 4.5 hours driving at 2000rpm (70mph) so over a return journey from glasgow to barnstaple my engine is possibly doing an extra journey, in wear and in fuel!

In light of the diff ratios, are not most quattros 60/40 bias to the rear wheels? The by product of putting a diesel box on a petrol one assumed would be that top speed would possibly be increased somewhat again because of the ratios.

To be honest I didnt even consider that the driveshafts could need replaced. (and with that maybe the hubs)

I think it will maybe take alot more research, a small call to the dealership (for g/box part numbers and driveshaft part numbers etc) or maybe even just the old 'give it a bash' routine and see if it works! One question for any diesel allroaders, do the diesel gearboxes have the oil cooler at the front of the motor?

[Peter D]

Have you looked at the power and torque curves. 2000 rpm at 70 the car is running inefficientlywith the turbo's only just cracked open and I suspect you fuel consumption would increase. There is a lot to consider, why do you think Audi do not offer such a box. There may be some advantages but non come to mind other than the waer factor you mentioned. Regards Peter

[blackie781]

Hmmm, food for thought one thinks! The more one thinks the more variables are getting thrown into the mix. I clearly wasn't thinking of the negatives. I think this will be going on hold until a bucket load more research has been done! Thankyou Peter for helping me see the light!

[zollaf]

i think i can say with some certainty that audi would have selected the gearbox very carefully to optimize the driving pleasure. if another box with taller ratio's would have worked, i think they may have used it.
personally, i would leave it as it is. comes back to the old saying 'deviate from standard at your peril'.
not many people have a huge budget and lots of workers to be able to try things out, so one person and a hunch probably isn't going to be able to better a world leading manufacturer.

[JimTraining]

Go for it Blackie, you can be our trial and error development department. C5's are getting some serious mileage and we may all have to mix and match one day, it would be interesting to see the result if you can do it for the right money. We will start a development budget, where do you want the tenner sending?

Having worked at a manufacturer of machinery that was on tyres (and tracks) for five years, I was always amazed by the clever boys in R&D who could spend hours calculating combinations of diff / gear ratios and suitable torque / power curves as all are variable, if you have torque converters, they have variability too on ratio until they are 1:1 in lock up. They would combine what they considered optimum and then some hairy end user would spot a glaring problem on the road / site. Net result was that the old boys in design would set up 3 or more combinations and let the end users / testers take the pick.

540,000 revolutions less on a journey does sound lovely though! Let me know the fighting fund details and I will happily contribute.

[blackie781]

Like I say, afew phone calls will need to be made, and over the next few months I will look into it quite in depth. I will post my findings on here and get some feedback, see what the general concensus is, I do however propose to 'give it a bash' just need to convince the missus it will be moolah well spent, and we all know what a daunting task that can be!

Thanks for the moral support Jim!

[adamss24]

Without sounding negative or against Peter's side, i would say to go for it ! The 2.7TT allroad has already enough power and with a remap and some hybrid turbo's even more can be achieved. It's common practice in europe to put diesel gearboxes on petrol engines as you get closer ratio + a higher top speed whilst fuel economy increases. I can tell you whatever you do don't pick a allroad v6 tdi gearbox, i would put one from the 2.5 tdi audi a4 b5 auto. The reason is the ratio's are much better and the top speed is much higher but it does not have oil cooling provision although that can be easily sorted by drilling and tapping new pick-up's ! If you want the a6 saloon tdi quattro will drop in and have the required gearbox oil cooling provision however it wont feel as sporty as the a4 one ! One thing to watch is the final ratio on the center diff (it's built into the gearbox) and rear diff- they need to match otherwise you'll need the diesel rear diff as well. The AKE allroad/a6 does not have the spacer between the engine and gearbox so you will need to keep that as well . I don't see the reason why they uses the spacer as the flywheel/clutch combo is the same between the two models. The allroad uses the self adjusting LUK clutch and DMF just like the b5 rs4 does...I think is has more to do with space against the bulkhead as the turbo's sit in a different position in the petrol engine and they can foul onto the bulkhead hence the spacer.

[blackie781]

I think the easiet way to reply is to just insert where I need to so;

Without sounding negative or against Peter's side, i would say to go for it ! The 2.7TT allroad has already enough power and with a remap and some hybrid turbo's even more can be achieved. It's common practice in europe to put diesel gearboxes on petrol engines as you get closer ratio + a higher top speed whilst fuel economy increases. I can tell you whatever you do don't pick a allroad v6 tdi gearbox, i would put one from the 2.5 tdi audi a4 b5 auto.

I want to keep it manual sorry I should have stipulated this in my first post.

The reason is the ratio's are much better and the top speed is much higher but it does not have oil cooling provision although that can be easily sorted by drilling and tapping new pick-up's ! If you want the a6 saloon tdi quattro will drop in and have the required gearbox oil cooling provision however it wont feel as sporty as the a4 one ! One thing to watch is the final ratio on the center diff (it's built into the gearbox) and rear diff- they need to match otherwise you'll need the diesel rear diff as well.

Thanks I will definately keep that one in mind.

The AKE allroad/a6 does not have the spacer between the engine and gearbox so you will need to keep that as well . I don't see the reason why they uses the spacer as the flywheel/clutch combo is the same between the two models. The allroad uses the self adjusting LUK clutch and DMF just like the b5 rs4 does...I think is has more to do with space against the bulkhead as the turbo's sit in a different position in the petrol engine and they can foul onto the bulkhead hence the spacer.

If the petrol has a spacer and the Diesel does not, does that then not mean there is a difference in the length of the input shaft as the flywheel/ clutch assembly will be that bit further away on the petrol? I don't know if I explained that too well.