JimR

He's in ATL.

ryoung

Their web site list GM Dexron IIIH and Ford Mercon.<ul><li><a href="http://www.mobiloil.com/USA-English/MotorOil/Other_Products/Mobil_1_Synthetic_ATF.aspx">Mobil synthetic ATF</a></li></ul>

ttuling

if it lasts that long. Our torque converter clutch is rare among automatic transmission clutches in that it's programmed to slip for minutes at a time, albeit when it's not carrying much torque. ZF was happy to use Dexron IID/III until they introduced such a slipping clutch, if I'm interpreting the Lubrizol page correctly. If most manufacturers don't use continuously slipping clutches, I wouldn't expect most ATFs to accommodate them.

It is entirely possibly that other fluids make the TC clutch work in a way that tends to prevent hunting, but at what cost?

I admire tozoA8's inquisitiveness and generosity in sharing his results.

Tom

ttuling

It's not for our LT 71141 spec (you'll have to go to ExxonMobil's Esso brand for that) but it is interesting how they set apart that fluid as being for certain cars with slipping torque converter clutches.

It's said to contain "specially selected friction modifiers and highly refined base oils to meet the demanding requirements of Aisin slip controlled lock up converter automatic transmissions." That, in a different forumlation, is probably the difference between LT 71141 and what came before.

Tom<ul><li><a href="http://www.mobiloil.com/USA-English/MotorOil/Other_Products/Mobil_ATF_3309.aspx">http://www.mobiloil.com/USA-English/MotorOil/Other_Products/Mobil_ATF_3309.aspx</a</li></ul>

JimR

I'm wondering if the G-055-025-AZ it references is for the DSG transmission.

ttuling

Agreed that slipping clutches are not ideal. Somebody tell ZF. Our torque converter clutches slip when coasting at speed. They can slip during moderate acceleration in D. The TCU controls it, and VAG-COM shows it as described in the URL below.

I suspect if Dexron III breaks the hunting cycle, it's by letting the torque converter clutch slip more, not less, and therefore engage more gradually. If so, I'm not sure this is better for the clutch than hunting.

But if it is the case that Dexron III breaks the hunting cycle by smoothing TC clutch engagement, whether or not it does it in a way that's healthy for the clutch, that would suggest that it is suppressing the hunting not curing its cause, like aspirin suppresses a fever.

(Ask yourself: why have no users of 2000 or newer cars reported hunting, even at mileages well beyond where it started on certain earlier models? The transmission didn't change to prevent it -- tozoA8 showed that by getting hunting with a low mileage 2002 transmission in his 1997 car. But the control system may well have changed with the move in 2000 to throttle-by-wire. Specifically the ECU's near-coasting engine torque calculations may remain more accurate or linear in the presence of inaccurate sensor readings.)

Tom<ul><li><a href="https://forums.audiworld.com/a8/msgs/73293.phtml">https://forums.audiworld.com/a8/msgs/73293.phtml</a</li></ul>

ttuling

That's what others have seen when they've looked. It wasn't hunting between gears. Whether to lock the converter clutch probably depends on engine torque readings from the ECU.

The slip-to-lockup transition is supposed to happen once when reapplying the throttle after coasting, but for some reason repeats in a cycle in cars with hunting. Slip, not total unlock, is the normal mode for the torque converter clutch when coasting without braking at speed, lockup is the normal mode for light throttle at speed, especially in Tip.

I wasn't saying that your car hunts because the converter clutch slips, or that it should be slipping instead of hunting, but that tozoA8's hunting may be suppressed because something about how the converter clutch behaves during that slip-to-lockup transition is different enough with Dexron III -- slower maybe -- that the cycle is broken (perhaps by allowing the O2 sensors time to contribute to an accurate engine torque reading in light of nonlinear MAF sensor readings).

The times that I'd expect a mile of converter clutch slip are (1) coasting downhill at speed and (2) driving up a slight incline above 40 km/h in D with an apparently "unlocked" torque converter (i.e. VAG-COM could show it to be only partially unlocked).

In summary, our cars have intentionally slipping torque converter clutches. They can slip for a long time. This is different from older automatics. Aisin and ZF seem to want special fluids in such transmissions. That makes me reluctant to use other fluids without understanding how they will affect the durability of the torque converter clutch.

Tom

tozoM8

The TC locks at 30 mph and after that it was hunting every time I took my foot off of the pedal and then I stepped on it. It was doing the same thing at any speed and any gear after 30 mph. When the TC regulating, it will maintain 30-100 rpm difference between the tranny and the engine. When you step on it, it will lock up the TC, but it has a little time delay. I monitored it with Vag-com and it still has the time delay, but the lock up is smooth, so I don't have the hunt anymore. So what I am guessing here is, that either it has to have the delay ( more likely yes )but the Audi fluid let the TC slip too much, or it doesn't have to have delay, but that would make a big thump at aggressive acceleration. I think Jack was on the right track with the MAF sensor. I think that the signal to lock the TC comes from the MAF sensor to the TCU because I advanced the TPS a lot and I still had the hunting. Only a few people had switched to synthetic ATF, but nobody reported any damage yet. I thought if Audi lied about the lifetime fluid, why would I believe it will damage my tranny. So far the damage to my tranny happened, because the previous owner believed Audi about the maintenance free tranny.

Hex168

I can't vouch for this; it was a link on some BMW site. See near the bottom of Page 2.

They claim D4ATF is a substitute for Esso LT71141 (amber).<ul><li><a href="http://www.hrpworld.com/client_images/ecommerce/client_39/cat_header/480_1.pdf">http://www.hrpworld.com/client_images/ecommerce/client_39/cat_header/480_1.pdf</a</li></ul>

ttuling

It must be nice having the hunting gone. Not sure I'd use that fluid for the long term because of TC clutch wear uncertainty. Hopefully we find and can fix an external trigger for the hunting.

I think a delay of about a second to lockup after stepping on the gas is normal. Several people with non-hunting transmissions report it.

Tom