2005 3.0 tdi quattro won't engage drive

[ejenner]

Hi all.

New here. Got a problem with my 2005 Audi A6 C6 3.0tdi Quattro.

Was driving along all fine and suddenly lost drive. Since then I've not been able to get it to engage drive at all.

There's no fault codes, no nasty noises.

With the engine running you can put your foot on the brake, move the gear selector into any position and it'll show the position on the dash. Take your foot off and nothing happens. The engine revs smoothly.

It does not seem to even know it is faulty... just nothing at all happening. No drive.

Has anybody ever seen this fault before? Thanks.

[Crasher]

The ZF6HP19…, type 09L, what a joy they have been, well to gearbox builders they have. Common reasons for loss of drive are torque converter and mechatronic failure or catastrophic failure internaly.

[ejenner]

I'm leaning towards the idea that it might be as simple as changing the bridge seal in the gearbox.... I say 'simple'... it'll still be a pain of a job laying under the car with automatic transmission fluid everywhere but that just about beats taking out the whole transmission. I've seen that you have to code a transmission if you're changing the mechatronic unit... which is what would happen if you changed the box entirely.

[Crasher]

Part number 09L 325 443?

[ejenner]

I have in my hand.. a genuine ZF part with P/N: ZF 0501 216 014

It arrived very quickly and I'm told this is the one which matches the reg number for the car. There's two types for these gearboxes.

I just thought before going to the trouble of taking out the transmission entirely I may as well check this seal as it's a common failure point. I've been told if it has failed it'll be obvious when you see it. So I thought if I take it out it would be handy to have the replacement in my hand to switch straight in. That'll reduce the chances of getting debris in the box or forgetting where any of the parts go. Just a quick swap. I imagine this might take a couple of hours and will be great if that fixes it.

[Crasher]

https://a.allegroimg.com/s1024/0c5696/5db7f71f4289a1728bced029f9a2

[ejenner]

that's the chap

[Crasher]

how much?

[ejenner]

The bridge seal was fine. Not broken or cracked like they are in some of the videos on YouTube. I think because it's the bigger one which you find on earlier versions of this transmission there is less chance of it failing. It's thicker with more reinforcement.

I can't see any other major problems in the gearbox after taking out the valve body.

Does anyone know if the rear propshaft coupler fails just at the back of the gearbox would it still drive the front wheels or is the whole system set up so all the torque goes to one rear wheel via the propshaft and diff? The only reason I ask is there's a black line on the bottom of the car around the propshaft where the propshaft is spraying something off around the rubber coupling. It could just be that the line is there on every car because the propshaft naturally flings off tiny bits of rubber or dirt over many 10s of thousands of miles and what I'm seeing is normal on every A6 Quattro.

[Crasher]

The centre diff would send all the power to the front diff if the rear propshaft failed, the box has failed internally.

[ejenner]

The work on this is ongoing. I've taken out the box and stripped it down. Bad news is there's no evidence of any specific faults in the box. So the suspects at this stage are torque converter and the valve body. I hope the problem does not turn out to be the valve body as I could have fixed that without removing the gearbox.

The torque converter has a slight rattle when rocking it which could be a signal that something has fallen out of place and might be the reason the car has no drive.

So I'm going to try and obtain a replacement transmission with torque converter.

[ejenner]

I've bought a gearbox from an A8 with a torque converter which is supposedly a match to my A6. i.e. the box didn't come with a torque converter but I was able to get one separately.

The variants of the ZF6HP which are available are many in number. Even from two 3.0 TDI motors of the same approximate age there are different valve bodies and model numbers. The sandwich plate which sits between the top and bottom halves of the valve body are one number different. My existing sandwich plate is 1068 327 179 and the A8 gearbox is 1068 327 180.

The three digit code of the old box was HKG and the new one is GZV.

It has taken a lot of research pouring over very minor details. It's worth the effort though as the car isn't worth a lot of money so it would be a mistake to do anything drastic like overpaying for a secondhand transmission. I could never justify spending a lot on a secondhand gearbox as they're usually well worn when you get them and if somebody is asking £800 for a secondhand box it's not worth it. Having an automatic gearbox professionally rebuilt costs around £3000 and I've seen that work out badly before as well! i.e. the 'professional' doing the rebuild gets something a little bit wrong and the whole thing is a waste of time.

I've got two options for reassembly. Either fit everything new from the new parts and transfer only the gearbox control module (it is coded to the car I believe). I think without the original gearbox control module it is going to be limited to 8mph. So whatever I do I must refit the original gearbox module. The choice is between the two different valve bodies. But as these can be changed after the box has been fitted I'm not massively persuaded to pick one or the other. There is a really good chance the old valve body was causing all of the problems so that's an incentive to use the new valve body. But the new valve body is what makes this A8 gearbox different to the A6 gearbox so that tips the balance back in favour of the old one.

I think I am going to use the old valve body in the new gearbox and see if that works. I have the option to switch to the new valve body if it turns out after everything that the old valve body was the problem. The mechanical parts of the gearbox seem to be identical. The only slight issue with this strategy is that I didn't find any mechanical problems in the old box. I still don't know if it was the box, torque converter or valve body. But I am eliminating things bit by bit and will get to the bottom of it eventually. The hold up at the moment is the car being outside and the weather being terrible. I will go out to work on it as soon as the weather picks up.

[ejenner]

Another little difference with the A8 box v.s. the A6 box is the way the shifter cable works. On the A6 the cable approaches from the propshaft end in quite a horizontal attitude. Two little bolts hold the cable bracket to the side of the box. The moulding in the casting for the case exists the same on both boxes but the tapped holes for bolting the cable bracket are unused on the A8 box. Out of the side of the box itself you have the shifter rod which goes inside the box to physically select. At the end is a sort-of cam which connects to the cable with a ball and socket. This cam-thing on the end of the shift rod is different on the A6 v.s. the A8 box. It is held on with a roll pin. So I swapped that between the two boxes.

I decided first attempt to put the box in with the new valve body and old control module. I really hope not to be taking this box apart again but as the info as to whether or not this will work isn't really out there I'm having to make my best guess.


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I made a little cradle to fix the box to the jack so it didn't slip around while I was trying to get it in the car. It was mostly successful except I got the balance a bit wrong and when I had it about 10-inches up in the air it pivoted on the jack and stripped two of the screws which were supposed to be holding it to the top of the jack, I should have bolted it in that spot = hindsight. Wasn't the end of the world, the back of the box was easy to lift as most of the weight was still on the jack. I stuck an axle stand under the back of the box and just notched it up a step at a time while raising the jack at the front. Overall the cradle was successful. The gearbox wouldn't actually balance long on top of the jack without tipping one way or the other and it's not really the sort of gearbox you can manipulate by hand as it's very heavy.

By this stage it is bolted to the engine but that's as far as I got, plenty of progress for one session.

[ejenner]

Well it's all done and working. The new valve body wasn't ideal so I drained the fluid and put the old valve body back. I think in the end it's most likely the torque converter was the faulty part. I couldn't find any problems in the box itself and I'm using the old valve body.

This was my technique for filling the transmission. Just gravity feed. The bottle at the top is higher than the transmission so the fluid has no choice but to flow to the lower point. I put a little fitting with a tap on it onto the bottom of the pan. Then when full turn the tap off so it can't come out. Cut the hose off the bottom and replace the tap with the drain plug... if you swap them real quick only a tiny bit of fluid leaks. The point is this cost about £7 for plastic hose and fittings. A proper auto transmission filling pump is about £80... this works fine... I filled the fluid three times in total.

38971

[Crasher]

You put some hours into that job.

[ejenner]

Not gonna lie... it was a bit of an epic.

However... it's not my profession, just messing about at home on the driveway. So I did it all in about 4 or 5 'sessions' when the weather was okay. At a relaxed pace and broken up it feels like much less work. The only downside with it taking so long is that it does challenge my memory undoing hundreds of bolts and then doing them all back up without putting a single foot wrong when there are gaps of weeks between touching it.

[Crasher]

On job like that I take pictures all the way through plus having ETKA to look at the fastener spec and pictures is a huge help or that seemingly simple part of the job can eat up a dipropionate amount of time and of course putting it in the wrong hole is not recommended.