hessteh@aol.com

what is meant by these terms. My 2001 transmission seems to make a slight, intermittent clicking type of noise when car is stationary, transmission in Drive, foot on brake (like at a stop light). Runs smooth when in neutral. No noticeable oddities while driving. Does thus sound normal?

KaMaKaZieP -ALUMIN8-

Hunting is when you are driving with light pressure or up a hill. the transmission will shift back and forth between 4th and 5th gear. It is very annoying and i dont think you can miss it.

The thumping is when you are coasting at 40 or so MPH and you put your foot back on the gas pedal, there feals like there is some play in the drivetrain because the engine will THUMP when you accelerate again.

PaulW

I wanted to get in my car with vag-com and look at it....but I need to drive out to the nearest nuclear power plant to do it safely......

I will have to check it out.

KaMaKaZieP -ALUMIN8-

Well what are we waiting for lets get on them!

Sven_S8

I love that car! :-)

ttuling

not completely freewheeling like the Saab, but with less engine braking through the torque converter than if the clutch were locked. This was normal behavior on, e.g., early GM cars with lockup converters.

Tom

mclarenm8d

I consider this to be a case of the TCU "stuffing" a selection at a time that is not mechanically good to do so. Doesn't matter if it is a gear selection or torque convertor lock-up. The TCU is being lazy on duration and it misses a window of opportunity to have the RPM "matched" reasonably close.

This is why I always upshift and downshift in tip mode :-), and never let the TCU decide.
If you are experiencing the thump in the "coast scenario", try putting the car in tip mode and then braking hard up to a stop. My guess is that it will "thump" when the TCU decides to make the downshift from 3 to 2.

In essence, in the amount of time the TCU is taking to downshift while coming to a stop, the drivetrain is "slapping" from a case where it was dragging to a case where the motor is revving too much for the next lower gear. For coasting and getting back on the throttle, the same effect applies.

But not Randy's S8 ... but anyway, random thoughts to my reasoning -

- With a manual tranny, if shift time is fixed, the harder you brake the less "throttle blip" you need for a smooth heal-and-toe downshift. It's a zen thing. There is an opposite extreme case of braking so hard that the motor, at idle speed, is revving too much. This normally only happens when coming to a stop with a street car.

- If "shift duration" is defined as the point at which the driver notices something is happening to the point when the next gear is "locked", Randy's S8 will always feel like it is
a) shifting smoother
b) completing shifts quicker
This is because at a fixed RPM, there is less MPH jump between gears because of the S8's shorter gearing. The same effect will be noticeable on the torque convertor lock-up. And there will be less slippage.

- With the tip chip in my A6 4.2, downshift duration from 3 to 2 is definitely quicker the harder I brake. However, I still get a thump if I brake hard to a stop and let the TCU decide on it's own how long to take to downshift from 3 to 2.

Sven_S8

to think it's in the electronics. Though it confuses me this still happens with a chipped TCU. Maybe there is a 'glitch' somewhere between MAF, ECU and TCU, the one giving the other an incorrect signal, causing a gearchange or slippage at an odd moment. (This is also noted in the fault description in the manual.)

The procedure to figure this out may be to get a new MAF, and (re)map the ECU and TCM. The first is easy, the (re)map requires some thorough knowledge of the matter... Don't know if there are any chiptuners on board?

But I also wouldn't be surprised if it turned out to be just a MAF (or at least on some occasions - it needn't be the same issue on each and every car). Mine went bust, and at the time I thought the tranny was fecked... (erratic shifting at low speed) MAF replaced, and all was fine again.

Flaw: this *should* give <i>some</i> fault code (mine: "load recognition - implausible value", and "right bank too lean"). However - IIRC - the MAF itself didn't fail the test. It was replaced anyway, as the chief mechanic agreed this was a likely cause, and that cured the problems.

NB: some enthusiastic driving in Tip mode - upshifts at redline, pre-corner downshifts ASAP - made my Tranny shift MUCH better and quicker!

Remember the learning process takes quite a while (~ 250km IIRC).

ryoung

The pads and rotors can remove kinetic energy at perhaps 10x the rate of engine braking. I never measured it, but I can't imagine that you can decelerate at more than ~0.1g with engine braking alone. With the left pedal, you can decelerate at near 1.0g.

Whether in TIP mode or not, normally I can't feel the effect of additional engine braking when downshifting. For better or worse, I brake very hard even on the street and just don't notice at all the additional braking from the engine. At the same time, there's never a thump from the tranny (and also never a thump when someone's behind me, when I do brake "normally").

BTW, ltooz_a6_a8's A8 tranny also seems to be OK. I had the impression from this and earlier discussions that the hunt-seek-thump sometimes developed with time/mileage, and that the symptoms sometimes improved after a ATF/filter change.

And ... who's TIP chip are you using in the A6?

KaMaKaZieP -ALUMIN8-

part #077133471D Price: $373.34