A4 B7 Multitronic - please help figure out this strange gearbox phenomenon

Hi all!

I have a 2005 A4 B7 with the 2.0 TDI engine and Multitronic transmission. I bought the car used from my uncle last year. I love the multitronic (when it works as it should), but I have this strange behaviour randomly ever since I got the car and it's annoying the hell out of me now. Sometimes when I start the car and get going, it feels like the gearbox behaves like it thinks I'm driving on an incline, or pushing the accelerator very much. It just keeps the revs high constantly (2000-2200 RPM) and only goes to a higher ratio if I barely even touch the gas pedal. Even then, it just slooowly puts a higher ratio that's suitable for cruising at the given speed. If I push on the gas just a tad bit more, it instantly goes back to high RPMs, it just feels super sensitive if that makes sense. I can use Tiptronic (manual) mode without issues, but when I put lever back in "D", the gearbox suddenly puts a low "gear" and revs shoot up to 2000+ RPM. If I do this on the highway while going 130 km/h in "gear" 7, then I put it in D, it again puts a low ratio and the revs skyrocket to almost 3000 RPM and slooowly climb back down to 2300-2400, again, only if I'm just barely touching the gas. Now, I can fix this problem when it happens. If I stop and shut down the car, then start it again, the problem is gone. The gearbox behaves as it should and it's perfectly drivable. Gearbox oil was changed 4 months ago, gearbox ECU was repaired at the same time because of intermittent PRNDS flashing and random switching to Sport mode without moving the gear selector. Since then, every other gearbox issue is gone, I get no PRNDS flashing or any other anomalies except the above described one. This makes me think the problem is outside the gearbox. I'm thinking some kind of sensor that is part of calculating the engine load that the gearbox works with, but no fault codes anywhere. I'm running out of ideas here. If I don't restart the car, sometimes it fixes itself while running, after 30-40 minutes.

Any help and ideas in this would be greatly appreciated.

Thanks.

Sounds like torque converter lock up issues

Have a google of a lock up torque converter and you will understand.

The reason it works in sport or tiptronic mode may be due to a higher line pressure in those modes (means shifts are quicker)

The Multitronic CVT that I have has a 7-plate clutch assembly with 7 friction plates like these:

https://cimg1.ibsrv.net/cimg/www.aud...738-177165.jpg

So it doesn't use a torque converter, but basically a multi-plate clutch. Can the problem be related to this?

Ah, sorry I get confused with the multitronic, s-tropic, Tipttonic jargon. The multi-plate wet clutches are not used as you would use a clutch in a manual transmission, they are only used to engage a planetary gearbox to enable reverse. So in short no, these will not be the problem.

The way the CVT works is by having two sets of opposing cones and a special chain wedged in the middle which is know on as the variator. The chain only transmits torque if it is compressed (similar to a clutch). The pressure in between the cones is controlled by a hydraulic valve, giving you your constantly varying ratio. However, when at a standstill, the chain is allowed to slip on the cones so that it acts like a torque converter, then when you pull away the cones are clamped together with more pressure and the chain locks.

When you put it into tiptronic mode, what happens is it will work in defined steps of ratio and apply more pressure to keep it at that ratio and only change when you hit gear up/down. So this is why you don't see slip when in tiptronic. I believe in sport there is just more pressure on the cones to transmit the increased torque, again why you don't see slip in sport mode.

Now I have explained how it works, your problem could be a few things:
1) The chain that links the variator set could be worn and it not locking properly, so it is slipping and not transmitting torque and your engine rpms are flaring. (Solution: Transmission Rebuild)
2) Old oil is causing poor hydraulic performance. Meaning the transmission is sending what it thinks is enough pressure to lock the variator, but due to the gloopy oil it is not enough and consequently the variator chain is slipping and your engine rpm is flaring (Solution: Transmission Oil Change)

Have a look at this is my explanation wasn't clear:

http://autos.ca/articles/jk/at_011212.htm

Audi Multitronic - YouTube

Thanks guys for your reply basically it was doing it in low rpm and when i floor it its fine plus when breaking revs coming down it would start shaking (vibrating) but today i took it for a drive and oil line leaked all the oil out from the cooler can this be a pressure problem plus on vcds no codes at all how much oil should i put back in 5l or more? Cheers

Should i use audi cvt fluid or the cvt fluid from.eurocarparts cheers

I would imagine there is a filling procedure that you do with VCDS which requires a certain oil temperature and then a gear selection procedure on a road drive then a level check. I would probably do a complete oil change if it has dumped half it's oil already.

However, cleanliness is paramount when working on transmissions. Unless you are experienced in working on transmissions (which it sounds like you aren't) I would get a professional to do it.

I presume that you have replaced the faulty oil line? the leaking oil line could be the root of your problems...

A4 tdi cvt noise - YouTube i have recorded the noise it makes, does it sound like driveshaft? all help appreciated thank you

It is incredibly hard to tell you what that noise is, I assume this is another problem that you have?! I would check the following:

1) Check the boots on the driveshaft. If they are split and there is grease all over the boot it is possible it is the driveshaft. If no split then it is unlikely. Driveshaft problems don't just happen, they get gradually worse.

2) Check the brake rotor for wear, remove any large lips/corrosion on the outside edge if it still has life in it. Could be the rotor catching on the pads.

3) I see you are running spacers, so I would check the wheel bearing. Get a long screw driver and use it as a stethoscope to home in on where the noise is coming from. Obviously don't do this on spinning parts.... if it is wheel bearing it will be loudest on the upright. However I would check various locations to find where is loudest: transmission (more than 1 place), upright, brake calliper, etc.

I get the feeling you have no idea what you are doing though so my main advice again would be to get a professional to look at it.

How To Find A Noise - EricTheCarGuy - YouTube