skiwi

there has been a considerable amount of activity on this list to do with the issue of the "lifetime" fill of the zf auto transmissions. the observation made (and consequently followed) whether the transmission be they 5hp24a, or the 5hp19a, is that they benefit from a fluid and filter change at least once in the 1st 4-5 years of life.

although not an expert, i have been looking at this issue, and perusing the various technical resources that i have available to me. my conclusions (worth what you have paid for them) are:

1) the issue is primarily one of temperature. atf is sensitive to temperature - and the service life of atf is dependent upon the temperature it's experienced. if your temperatures have been high for long enough (i'll define this later), then you are not longer in the "lifetime fill" category, and must consider an atf fluid and filter change.

2) how do you know that you have exceeded recommended temps? in the latest zf 6-speed (6hp26a), partly because the mechatronik module is fully immersed in atf, there is now more information available. the new 6-speeder logs temperature data using the temperature sender. this will provide an accurate record of the gearbox's thermal load. once this has been exceeded, a fault code (18167 - multiple gear oil temperature overshoot) is recorded. dealers *are* instructed to replace the atf if this fault is logged. for the rest of us, with the older transmissions, while there is the ability to record atf temperature using the temperature sensor (embedded in the wiring loom), it is more a case of understanding what heavy use (towing, hills, and particularly racing) will lead to high temps - and whether we need to factor in fluid changes as a matter of course.

3) temperature control of the older transmissions is of course not possible except in retrospect, whereas the new transmissions do this. some parameters for the new zf unit are interesting for a frame of reference. the new 6-speeder has 3 levels of high-temperature control triggering at >124c, >139c, and >141c. once 124c is triggered, the shift program is changed to allow the torque converter clutch to operate for longer, and shift points are changed up. above 139c things get more serious with engine torque reduced by upwards of 60%. above 141c, the gearbox switches into emergency mode.

with older transmissions our options are more limited. the tcm does not signal temperature to the motronic, so there is no feedback loop as there is with the new 6-speed. i suggest that those with laptops and vag-com should monitor display group 4, field #1, while driving their favourite bit of road hard to ascertain the parameters of atf temperature for their transmission, driving style and attempt to understand the limits. better still, use the "capture": facility of the tool to record the temperature (#4/1), gear (#1/4), engine rpm (#1/1), output rpm (#1/3), speed (#3/3), throttle position (#8/2), engine torque (#9/1 or 4) & dynamic indication number (#12/2) to get a better understanding of your "worse case" scenario. nerd city and all that....

note: where would we be without vag-com?, or, to put it another way, why are people happy to spend so much money for a car, and then balk at the small amount needed for the best dealer-independent diagnostic device around?

hth,
dave
'01 s8

JimR

I don't feel a compelling need to do all the monitoring. Does this look like a lifetime fluid? I rest my case. ;-)

<img src="http://pictureposter.audiworld.com/1018/a6_service_015.jpg">

Personally, I think every 35,000 or 40,000 miles is right for these cars. And most people aren't going to drive around with their VAG-COM (if they have one) in data logger mode enough to get the data points required.

PaulW

Or at least that's my opinion. The oil filter clogs up with foreign material and starves the hydraulic pump which causes the damage in the transmission.

I have two or three oil analysis from A8's and all show that the oil was in better shape than JimR's A6 oil after analysis. And one car had 80K on it and the transmission was scretching for some time before it was changed.

pw

GDJT Allroad^2

... and probably what the fluid in mine looks like. Hopefully I'll have it fixed this weekend. Ugh!

JimR

We put the car up on jackstands about 5 weeks later, and did a drain and fill. I figure I got about 2/3rds of the fluid changed out. I've mentally tagged around 75k-80k miles for another service. It's at around 64k now.

skiwi

multi-plate clutches are not noted for their production of foreign bodies - they are remarkably benign. note also that the gear boxes (transfer case and front diff) where gear wear is high, do not have a filter.

my theory is that high temperatures cause the atf to breakdown and contribute to higher wear in the clutches and planetary gear sets - and this clogs the filters.

note that high temps (not filtering) are fingered specifically by zf in the new 6-speed by way of the gearbox logging temperatures and avoiding high temperature running.

note also that high speed running is not the culprit, it is periods of high acceleration primarily - periods where slip in the transmission is at its highest, and the tcc remains open.

$0.02
dave
'01 s8