Gearbox problem after fluid change Help
 

I recently bought an A8 2.8 2002, and didn't have any service history with it, I have changed the multifunction transmission switch as it had the dreaded PRNDS lights on, after that job was done the car drove great with no problems, I thought I would do a service on the gearbox and change the ATF fluid and filter, but now I have problems, the gearchanges are not smooth, and I am noticing that the rev counter is moving slightly and not stable when in 5th gear, it feels like its slightly jolting, the fluid that was drained off was a dirty red in colour, with no contamination, just a very slight sludge build up, I fitted a new Meyle filter and gasket and filled the transmission with Febi Bilstein atf fluid 29738, this is clear/yellow in colour and according to Febi this fluid is the one for my car, I am concerned that this fluid maybe wrong, the service was carried out exactly to ZF specs, any ideas on this please.

You can’t get all the ATF fluid out by draining it, so you’ll now have a mix. DIY fluid changes have caused problems for others and it’s usually recommended to have them flushed - but this requires specialist equipment. I’m not sure if there’s a ZF specialist near Leicester, but hopefully someone here will be along shortly with a more positive reply!

BTW, was it you at Belvoir Castle a few weeks ago?

Hi, thanks for the info, no it wasn't me at Belvoir Castle, I just got back from a run up the A46, I noticed that its driving ok at 60mph and above, but when driving at 40mph or below I noticed that the rev counter is fluctuating slightly and I can feel the car bumping slightly, hard to explain really, I wonder if its the mix of fluid thats causing it. it was fine before I changed the fluid and filter

my local mechanic [ audi fan but not A8 or auto ] doesn't have a slurpy machine but recommends draining overnight to get as much out as possible , fill up and give it a run for half an hour then drain again , change filter and top up again ensuring correct temperature /fill level

maybe not perfect but with 75% or so fresh ATF gives a reasonable clean box , and using the correct AG52 mannol available in bulk from germany at a reasonable price [ multitronic/steptronic/ tiptronic ] not too expensive

don't forget , getting the level absolutely correct is critical

wonder if mikki could set up to do this , it's a long way to glasgow for us southerners!

Just in case, this is the detailed procedure, Cycling through the gears and checking temps is, apparently, key to getting it right.

The fluctuation in RPM is a common characteristic of the 5HP gearboxes and is supposedly down to the torque converter - a couple of American transmission specialists offer a modified converter to solve it. My S8 does it too at ~1800rpm, just before the converter clutch locks up. Its highly annoying but I just put it in S if it bothers me. Its curious this started for you after a fluid change though. Febi 29738 is the correct specification.

I still haven't figured out why some gearboxes are just fine after a fluid change and some aren't. I have a feeling it could be down to the re-filling period when the level is some 3-litres short due to the stupid design of the filling solution, although I couldn't say what specifically gets upset during that time.
I was going to contrive a device which could get the full load of oil in with the engine stopped so that it didn't have this (albeit short) period of running low on oil, but I've been working on the manual swap instead :p

The suggestion to refill, run it for a bit then drain and refill again is good, however since the gearbox has to be at 40° to set the level it would be an overnight job so that it could cool down. Still, there are a couple of nice hotels near the workshop ;)

don't quite follow that mikki ; after it has drained overnight and then filled how is it 3 litres too low for the half hour drive ?

my methodology is
leave on the ramp overnight
first thing in the morning fill
before lunch half hour drive
drain again during 2 hour french lunch at local restaurant [ menu de jour !]
refill at correct temperature in approved manner [ I hope my £10 temperature gun from amazon is accurate enough , works well on brake disc temperatures ]

Its about 3 litres short between when you fill it with the engine off and then top it up with the engine running as it comes up to temperature. Its only a few minutes with it idling, but I still don't like it since if you drove it 3 litres short it would kill the box in pretty short order.

I've never checked to see how long it takes to cool down tbh. If 2 hours will do it then it is practical to flush like that +++