Transfer box kaputt - big money...

[philsayer]

A few months ago, I noticed a small cloud of smoke drifting from underneath the car - thought no more about it, as it didn't recur.

Yesterday, my pride and joy (complete with family and self) were Green Flagged home 200 miles, as the transfer box had destroyed itself....

Gradually, as we headed towards London on the M40, the knocking noise was getting louder and more worrying, so we decided to get some advice. (One of those moments when you're grateful for smartphones...)

I owe a big thank you to Mark at MDM Technik in Marlow... wife and twin 5 yr olds were offered warmth, comfy sofa, and juice and coffee while Mark and I went out to listen to the noises from under the car and then put it on the lift. This on a freezing cold Saturday afternoon, when the Big Boys have pretty much shut up shop... and a very reasonable bill for his time, I thought.

Anyway, it would appear that the smoke would have been the oil exiting from the transfer box, and evaporating as it hit the exhaust that runs under it. Since when, I guess, the box has been running without lubrication. It finally did what you'd expect it to do, and disintegrated. Although the car was still driveable (but making nasty noises) the mechanism or the heat had cracked the transfer box casing.

(For those who don't know, this is the box that takes the drive to the rear wheels - it's between the prop shaft and the gearbox.)

Cost of new parts around £1400, plus around 3hrs labour, it would seem.

Softening the blow is the Momentum warranty we stumped up for when we bought the car (not from a franchised dealer) last year. But the claim limit is £1000... didn't spot THAT in the small print at the time!

Does anyone have any idea if this is a common failure? Any thoughts as to what has caused it? My own guess is that it's the result of a previous owner replacing tyres haphazardly, rather than as a set of four. (I was warned of the dire consequences of doing that when we had a Touareg - same applies to quattros and 4motions, I believe.)

But I'd like to know if it could have simply been a manufacturing fault, rather than the box being stressed by unequally-circumferenced tyres.

I'm guessing that, on top of having to pay a few hundred towards the repair, I really ought to buy a set of tyres immediately - but is this issue of relative wear really that big a deal? Or just VAG covering themselves? (A sort of automotive equivalent of Dry Clean Only labels...)

I'd be grateful for your thoughts, folks. Thank you.

[Micha_elD]

I think I've read the handbook cover-to-cover, and don't remember anything about the tyres needing to be replaced as a set of 4. Mine all wore out together, so did that anyway, but have never heard that its essential to change all 4 together, what if only 1 had to be replaced as a result of a puncture? Surely you'd expect the car to be able to cope with that?

Why was the oil escaping from the transfer box?

[philsayer]

I think I've read the handbook cover-to-cover, and don't remember anything about the tyres needing to be replaced as a set of 4. Mine all wore out together, so did that anyway, but have never heard that its essential to change all 4 together, what if only 1 had to be replaced as a result of a puncture? Surely you'd expect the car to be able to cope with that?

Why was the oil escaping from the transfer box?

Although I can figure out that a worn tyre has a smaller circumference than a new tyre, and that it therefore makes a slightly greater number of revolutions in a given distance, I confess I don't understand why the differential gear (in conjunction with the transfer box) doesn't cope... but apparently, it doesn't.

The more I think about it, the less I understand it, though... because when the car turns a tight left hand corner, the left rear wheel must cover a smaller distance than the left front wheel (and a full lock turn did indeed send my knackered transmission into convulsions), so why should it matter that there's a slight difference between front and rear in a straight line?

Trawling other forums isn't helpful - a lot of semi-informed talk about the differences between Haldex and Torsen diffs (Audi seem to use both, depending on model) and some saying replacing a single tyre matters, others saying it doesn't.

Regarding the oil loss - I really don't know which happened first, but that suspect cloud of smoke I mentioned was a few months ago. I'm only guessing that it was oil from the transfer box - can't be certain. The first noticeable mechanical transmission problem was on that journey, this weekend. The casing is cracked but I can't be sure why - the techie suggested it was probably the disintegrating gears thrashing around inside that caused it to crack. I'd guess a failed seal caused the oil loss way back when, and it's been under-lubricated ever since, until the failure. Either that, or the tyres issue (if it really IS an issue) has slowly "killed" the transfer box, which has disintegrated under the pressure long term. But if all concerned are to be believed, it's only a 64,000 mile car...

Anyway, what is for certain is that continuing to drive the car isn't a sensible option... because it could impact on the gearbox, at which point you're looking at a FIVE grand repair, possibly!

[Micha_elD]

Really sorry to hear that a repair is likely to be so expensive.

I can't believe that Audi would build cars that are wrecked by having odd tyres, it might put a bit more wear on the mechanics, but they can be built stronger to cope with that, so surely they would have done that.

It seems likely that a seal went, oil drained away, then the problem arose. Or maybe the car hit a rock or something that cracked the case and the oil went that way. Apart from the smoke some time ago, there probably weren't any further clues until lack of oil wrecked the box.

[philsayer]

Really sorry to hear that a repair is likely to be so expensive.

I can't believe that Audi would build cars that are wrecked by having odd tyres, it might put a bit more wear on the mechanics, but they can be built stronger to cope with that, so surely they would have done that.

It seems likely that a seal went, oil drained away, then the problem arose. Or maybe the car hit a rock or something that cracked the case and the oil went that way. Apart from the smoke some time ago, there probably weren't any further clues until lack of oil wrecked the box.

I agree your first theory is more likely, Michael - there's a strong aluminium cross member that helps to protect the box.

Jury is still out on whether having differently-worn tyres is damaging or not - a lot of conflicting advice and opinions out there!

A quick thought - there have never been any signs of visible oil leaks on my drive, probably because the leaking oil was evaporating on the hot exhaust that runs right underneath. So a word to the wise - a suspicious cloud of smoke (quite short-lived) at the end of a journey might indicate a similar fault. I'm now kicking myself for not checking when I saw it!

[Architex_mA8tey]

Theres a known issue with the oil seal failing on the output shaft end of the transfer box which normally results in a slow leak and regular noticeable smells as the oil hits the warm parts of the exhaust and burns off again. I guess it would be possible to lose enough over time that the while lot heats up and then as parts start to come apart inside it would blow the seal completely.

A lot of 8 owners that get "that smell" change the output shaft seal which isnt too expensive. I did exactly that but then the good ol tiptronic box decided to get me another way and 4th gear failed and I ended up getting a service replacement box. . ouch!

[philsayer]

Theres a known issue with the oil seal failing on the output shaft end of the transfer box which normally results in a slow leak and regular noticeable smells as the oil hits the warm parts of the exhaust and burns off again. I guess it would be possible to lose enough over time that the while lot heats up and then as parts start to come apart inside it would blow the seal completely.

A lot of 8 owners that get "that smell" change the output shaft seal which isnt too expensive. I did exactly that but then the good ol tiptronic box decided to get me another way and 4th gear failed and I ended up getting a service replacement box. . ouch!

Sorry to hear that - but your post has helped me a lot... it'd take an age to explain why!

Does the gearbox need to be removed to replace the transfer box? I'm being given the runaround, I suspect, by a car sales/service outfit that is out of its depth... and they've had the car for nearly two weeks. Grrrr....

[johnloaderuk]

Jury is still out on whether having differently-worn tyres is damaging or not - a lot of conflicting advice and opinions out there!

Seems to vary depending on the type of 4WD system fitted, does it say anything in the handbook ?. As you say, lots of conflicting advice on the internet.

http://www.etyres.co.uk/changing-tyres-4wd

[Architex_mA8tey]

Sorry to hear that - but your post has helped me a lot... it'd take an age to explain why!

Does the gearbox need to be removed to replace the transfer box? I'm being given the runaround, I suspect, by a car sales/service outfit that is out of its depth... and they've had the car for nearly two weeks. Grrrr....

I think the transfer box can be unbolted from the end if you can drop everything away but you have to consider how many miles has the rest of the box done and therefore how long will the rest last? One of the resons I went for a service exchange box in the end was because for the difference in cost between a refurb at say £1500 and a service exchange box was under £1000 difference but you are getting a complete new box with all parts, torque converter, transfer box, tcu and even filled with oil ready to go and also it had an unlimited mileage warranty for 2 years. If you're on a budget try A8 parts and see if they've got a suitable transfer box and fit it plus a gearbox oil change and see how you go. Good luck!

[wakeffra]

I have a 2002 A4 Quattro and have been noticeing a slight burning smell from the underneath of the car for a month or so now. I planned to check / change the gear oil in all the final drives anyhow so brought this forward a bit. Front and rear final drives were ok with the right ammounts comeing out and the right ammounts going back in. The transfer box on the other hand was coverd in oil and only let out when draining aprox 200ml. It took 800ml to fill.

My understanding is that the seal is very prone to failure due to it's location so close to the catts which get extremely hot very quickly. I also beleive that Audi now recomends a diffarent output flange and seal on repair.