Shift overshoot...trans or tune?

[DrX]

Finally got to the track last weekend to break some parts. The logs show that in Normal shift mode, commanding shifts at 5800 RPM, there was 200 RPM of overshoot. In Performance shift mode, commanding shifts at 6500, I was hitting my 7000 RPM ETC rev limiter. Except for the 2-3 Performance shift, WOT shift MPH was setup so that corresponding RPMs were below the WOT shift RPM values. For Normal mode this difference was 400-500RPM for 1-2 and 2-3. For Performance mode the difference was only 40-50RPM for 1-2, for 2-3 the difference was actually -ve so I've changed that. But both 1-2 and 2-3 hit the rev limiter in Performance mode. Is this a tuning issue or am I about to lose another 80E? Otherwise, the trans did seem to be performing well.

The first screen shot below shows a 1-2 shift when commanded at 5800 RPM. The next screenshot is a 1-2 shift when commanded at 6500 RPM. It appears that in the case of the latter, the shift would not have occurred at all would the rev limiter not have closed down the throttles. I don't see any conflict with the kickdown tables.

The tune is scaled 50%.

In the video linked below there are 3 runs shot with a Go Pro inside the truck. The first of these runs(10.99 ET)was with shifts commanded at 6500 and you can hear the throttle dip at each shift. The final run was with shifts commanded at 5800 and you can hear the quicker shifts with no throttle dip. You can also hear the rear u-joint let go after the 2-3 shift!






https://www.youtube.com/watch?v=Cx9zefG2q2E

[DrX]

Forgot to mention that the D1 transbrake also failed to respond to the switch. I have not used it yet, but the truck just rolled forward when I held the switch and released the footbrake. Shifter was in D1. Wiring/switch tested OK and activated the brake on the previous trans.

[joecar]

Hi DrX,

Great vid, thanks for posting.

Lack of RPM dip (on each upshift) usually indicates something is slipping... even with a 4L80E (closest ratios of the GM transmissions) you should be getting RPM dip on each upshift.

[DrX]

Hi Joe,

Will have to see if I can log when/if the shift is being commanded. I was more concerned about the engine as this was the first time pushing it this hard. The only trans parameter logged was TFT.

Grant

[DrX]

I wonder if this is related to the D0910 - D0965 WOT upshift MPH tables? My tables are modified as stated above, but in stock 80E calibrations the relative RPM values are 1400 - 2300 RPM lower than the corresponding cells in the D0940 - D0971 WOT upshift RPM tables. Probably should have left the MPH tables alone?

[DrX]

I think H0104 was not correct. This would make a difference with the Shift at VSS values set close to the Shift at RPM values. Must have been a leftover form the tune used to build this one. Not that the 04 Avalanche stock tune value matches the OE 31.5" tires either. All of my tires are close to that same height and I am still using a 3.73 gear ratio as per OE. Stock is 1577 rev/km, but I get closer to 1480 rev/km.

[joecar]

Any of the VSS calculation factors would affect the shift MPH... good find DrX.

[DrX]

Either I didn't hit the tow/haul switch after the last restart in the staging lanes yesterday or it shifted early. Don't see how that could occur though if it wasn't at shift RPM yet. Only got one log before my laptop died and wouldn't charge again.

It appears that my third and final run wasn't so good for the trans. Haven't had a chance to test anything as it has been raining all day. http://www.youtube.com/watch?v=p-no-Nz4z7c

edit: just got out for a very brief ride. Any throttle at all and the trans sounds like it's full of trash. Looks like input/output speeds are equal both in 3rd and in 4th.