Transmission Thump....do you think we can figure it out?
08-25-2004, 08:29 AM
#11
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Torque. Do you think the computer unlocks the torque converter to facilitate a smooth shift, and
if the transmission is "hunting" the computer that controls the torque converter gets confused and unlocks?
08-25-2004, 08:54 AM
#14
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Normally a torque converter only locks in the highest gear ...
for the reason you said, it makes for smoother shifts. Anything's possible, but I'd be surprised if the torque converter ever locks in 4th or lower.
08-25-2004, 09:14 AM
#15
Mine, thumpless, can lock in 3rd, 4th and 5th above 26 mph
Maybe even second also.
What you say about lockup being limited to top gear is true of the first American implementations.
Your S8 may be programmed differently, but if I'm accelerating calmly in an '01 A8 and have shifted via tip to third before 26 mph, there's a very definite lockup at 26 mph -- the rpm falls and is no longer decoupled from road speed. It is quite adamant about maintaining lockup above 26 mph in tip though it's much more willing to unlock in D.
I still think that even the thumping torque converter clutches are locking and unlocking at about the right time -- that the dropouts at light throttle are in fact normal for economy while coasting -- but that the issue is whether you can feel the transitions or not. Clean fluid, accurate throttle position readings, and other TCU and ECU learning may all help.
Speaking of which, how about cleaning the throttle body then doing whatever throttle body adaptation is appropriate, so that the throttle readings at light throttle are more likely to correspond to expected airflows?
Tom
What you say about lockup being limited to top gear is true of the first American implementations.
Your S8 may be programmed differently, but if I'm accelerating calmly in an '01 A8 and have shifted via tip to third before 26 mph, there's a very definite lockup at 26 mph -- the rpm falls and is no longer decoupled from road speed. It is quite adamant about maintaining lockup above 26 mph in tip though it's much more willing to unlock in D.
I still think that even the thumping torque converter clutches are locking and unlocking at about the right time -- that the dropouts at light throttle are in fact normal for economy while coasting -- but that the issue is whether you can feel the transitions or not. Clean fluid, accurate throttle position readings, and other TCU and ECU learning may all help.
Speaking of which, how about cleaning the throttle body then doing whatever throttle body adaptation is appropriate, so that the throttle readings at light throttle are more likely to correspond to expected airflows?
Tom
08-25-2004, 09:35 AM
#16
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My '73 Saab Sonnet had this feature !!
The Saab had a manual transmission and two clutches, one "normal" but also a centrifugal clutch that would automatically disengage at light or no throttle. The coasting, free-wheeling car would get better fuel economy, but it was a little hard on brakes.
Very quickly, though, the centrifugal clutch would wear and begin engaging with a bang. You could disable this "feature" with a lever on the side of the transmission. The better long term solution was to weld the centrifugal clutch solid at the first opportunity.
If you're right that Audi's tranny has a clutch that also disengages under light or no throttle, perhaps we could convince GIAC to disable this "feature" in their TIP chip. The sales of their tranny chips would probably increase several fold if they'd also cure the thump.
1973 Saab Sonnet III
<img src="http://www.supercars.net/servlets/PW/garagePics/VICIOUS/2car1.jpg">
Very quickly, though, the centrifugal clutch would wear and begin engaging with a bang. You could disable this "feature" with a lever on the side of the transmission. The better long term solution was to weld the centrifugal clutch solid at the first opportunity.
If you're right that Audi's tranny has a clutch that also disengages under light or no throttle, perhaps we could convince GIAC to disable this "feature" in their TIP chip. The sales of their tranny chips would probably increase several fold if they'd also cure the thump.
1973 Saab Sonnet III
<img src="http://www.supercars.net/servlets/PW/garagePics/VICIOUS/2car1.jpg">
08-25-2004, 09:43 AM
#18
AudiWorld Super User
How do I know if mine is thumping or not. I don't hear anything and it does shift smoothly through
all speeds. At what mileage does this normally happen? My odo is 105,800 and the trannie was replaced at 68k? Does this mean the fluid and filter replacement NOT helping?
08-25-2004, 09:48 AM
#19
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Paul, did you read
<a href="https://forums.audiworld.com/a8/threads/15256.phtml#72487">my post on the "Gearbox issue"</a>?
That's from the fact. manual btw. Of course they advise to replace everything (as usual), but there may be a lead there, coinciding with your line of thinking it might be the electronics.
It would indeed be useful to gather data on the affected gearboxes. 4 speed, 5 speed, codes?
BTW... could the recoding possibly have anything to do with this? If so, setting it back to std. code may be a way to see if that changes anything.
I'm still puzzled Bentley gives these codes, whilst the factory manual says it's not allowed to use any other codes.
Factory codes:
<img src="http://www.tyresmoke.net/attachments/214007-Gearboxcodes.gif">
Quote:<i>"<b>Other codings are not permissible</b>
Once the coding operation has been completed the fault memory in the control unit is automatically erased.
If an invalid code number is entered the control unit retains the old coding."</i>
That's from the fact. manual btw. Of course they advise to replace everything (as usual), but there may be a lead there, coinciding with your line of thinking it might be the electronics.
It would indeed be useful to gather data on the affected gearboxes. 4 speed, 5 speed, codes?
BTW... could the recoding possibly have anything to do with this? If so, setting it back to std. code may be a way to see if that changes anything.
I'm still puzzled Bentley gives these codes, whilst the factory manual says it's not allowed to use any other codes.
Factory codes:
<img src="http://www.tyresmoke.net/attachments/214007-Gearboxcodes.gif">
Quote:<i>"<b>Other codings are not permissible</b>
Once the coding operation has been completed the fault memory in the control unit is automatically erased.
If an invalid code number is entered the control unit retains the old coding."</i>