Rell309

Please help someone... changed transmission fluid and filter with Mercon Sp, shifts perfect from 1st to 6th but when slowing down all down shifts are smooth EXCEPT 5th to 4th??? When car is cold Illinois December nights 30 degrees and I drive car cold the downshift is almost smooth but when transmission warms up the downshifting is more prevalent. Could it be overfilled or under filled causing this? I'm sure as car warms fluid is expanding and this is when downshift 5 to 4 begins harder???

I added fluid at 33 degrees to 38 degrees cel until overflow out fill plug. Car exact level? My snub mount looks cracked and dry rotten but I didn't think this would be problem since all other shifting is smooth even UPSHIFT from 4 to 5th is smooth??? Can anyone help me???

Do I need to do anytype of transmission adaption with VCDS after the fluid change could this be the problem?

Rell309

Audi A6 2006 181k miles

dzywicki

I assume you filled it while the car was running? Did you shift through all of the gears and then fill one last time until it over flowed?

If you did these two things, then I don't have anything else to add

Rell309

Yes I filled while it was running and went through gears. Did this until fluid starting com Bg out after cycling through the gears. Do you think there is possibility it could be overfilled? I did underfill it once and it wouldn't engage Drive until car and fluid warmed up but when it did it went into Drive quietly and smooth. I'm just lost thinking maybe valve body or some type of solenoid because it only happens 4-5th downshift? Crazy!!!

markcm

Did you find any resolution to this? I am having the exact same issue. I've read lots about it being the N91 as well. Mine only hard shifts once the trans temp reaches 40C and only under deceleration; the slightest bit of acceleration and it will downshift from 5-4 smoothly, even when fully warmed up.

I have already swapped the complete valvebody including solenoids and it still hard down shifts from 5th to 4th exactly the same as before which makes me nervous that my problem may not be the N91 yet my symptoms are exactly the same as many others which were resolved by replacing the N91 valve. Granted I replaced mine with a used unit.

UPDATED / RESOLVED: I ended up installing a Transgo ZF5HP-19 Pressure Regulator Valve Renewal/Repair kit with a new N91 which completely resolved the hard 5th to 4th downshift issue. It is now 2.5 years later and the car still shifts perfect. I've since also had a friend with an All Road (about 2003 as I recall) who was having the same issue; the transmission shop told him "transmission is toast, needs a full rebuild, $4000", he replaced the N91 and installed the transgo kit which also fully resolved the issue for him.

DreewMcK

Not too much to add but I left the plug in, cycled through gears, put in P, took out plug and filled up till overflow at 38 and put plug back in. Took ~5L, which is pretty much what came out.


I couldn't figure out how to manually go to gears 2 and 3 which is recommended in the ZF instructions. It mentions a manual/winter program???


It's been good but I haven't driven it hard yet and it hasn't been overly cold.

kelisko

I've been reading a lot about the transmission fluid change on the C6. Most people who decide to perform the fluid change at high mileage, usually for the first time end up with issues. At that stage, the debris in the fluid sort of "marry" the transmission parts and breaking the bond kind of make the transmission go crazy.

If you have a high mileage and the car's transmission was never serviced, leave it.

DreewMcK

While I have heard this from a number of people, and it seems like a general rule of thumb, particularly when flushing anything, I will give a different perspective.


On the weekend I changed mine at 100K miles, first change, and my friends at 200K miles. I can't guarantee that his wasn't done before but looking at the fluid color compared to mine I would bet that it was the first time. There wasn't noticeable debris in his, aside from on the magnets, and even then it wasn't metal it was just some sediment. Someone in the shop even commented that the fluid 'looked' like it was still good when they were swirling it around the bucket.


I'll try to post back if anything bad happens to his sooner rather than later.


He did mention though that one of his mounts is bad and he noticed a jerking on downshift too (before and after), so I would venture to say its the mount.

findalex

1. Did you reset the transmission ("basic settings") and do an adaptation run? If not, find someone with a VAG-COM to help you with it.

2. Drain and fill is safer, even though it only replaces 50% of the fluid. If you only changed 4 - 5 liters, then I'd recommend do another so more of the old fluid is replaced. The new filter should be good for a while.

3. It's possible you overfilled. 40 C is supposed to be the mid-point of fluid level. The range is between 35 C and 45 C (50 C for hot climates).

4. Get a VAG-COM to ensure the temperature measurement is accurate. Some people use an infrared temp gun, but that's just the surface temperature of the transmission pan/housing.

FormulaElement

This! Changing the fluid can never hurt newer transmissions. That rule of thumb is for older cars without electric solenoids!! Electric solenoids will adjust the pressure until it doesn't slip and shifts smooth. The old fluid is generally stickier and will hold the gear in place better.

I recommend cleaning the MAF with a special cleaner (go to any auto part store and buy Mass Airflow Cleaner. Then do a adaptation.

After Changing the solenoids and fluid, then cleaning the MAF. If it's still shifting bad, it's most likely your valve body or transmission.