Allow TCC lock duing shift???
Thread Starter
Drifting
Joined: Jul 2002
Posts: 1,386
Likes: 80
From: NC
Cruise-In IV Veteran
St. Jude Contributor
Allow TCC lock duing shift???
I recently purchased LS1 Edit and I have been comparing many of the stock A4 C5 PCM calibrations between model years. I have noticed that in the older '98 & '99 PCMs the converter is set to lock during shifts, while the '01-'03 PCMs are set not to lock during shifts.
Now can soneone explain to me the reason the older C5s lock the converter during shifts while the newer C5s do not? I am speculating that GM may have changed this due to possible wear and tear issues with the transmission, but I am unsure.
What are the trade-offs for locking vs. unlocking the converter during shifts?
Which option is better for performance?
For those that have LS1 Edit... What setting are you using?
Now can soneone explain to me the reason the older C5s lock the converter during shifts while the newer C5s do not? I am speculating that GM may have changed this due to possible wear and tear issues with the transmission, but I am unsure.
What are the trade-offs for locking vs. unlocking the converter during shifts?
Which option is better for performance?
For those that have LS1 Edit... What setting are you using?
Thread Starter
Drifting
Joined: Jul 2002
Posts: 1,386
Likes: 80
From: NC
Cruise-In IV Veteran
St. Jude Contributor
Re: Allow TCC lock duing shift??? (Doubletap)
I also have a post in the Scan & tune section. However I was hoping to get more visibility here in Tech/Performance. Aside from the actual PCM setting there must be a technical reason for GM to have changed this setting between model years.
My post from a performance point of view is best suited for this section of the forum I believe. Surely someone out here should know enough to provide more insight on this topic. :confused:
My post from a performance point of view is best suited for this section of the forum I believe. Surely someone out here should know enough to provide more insight on this topic. :confused:
Instructor
Joined: Sep 2003
Posts: 104
Likes: 0
Re: Allow TCC lock duing shift??? (bgood)
My '97 doesn't seem to do that. As I understand it, you have to be in "D" to get lockup in 3rd. I'll check to see if then shifting to "OD" results in a 3-4 shift without unlocking. No way have I seen lockup in third with selector in OD. Maybe I'm wrong.
The reason I think it isn't locked during shifts is the shutter or judder or little pulsing you might feel with the TCC locked. The TC is a good shock absorber for engine/transmission torsional vibrations. If I recall, there was a time when some highend GM automatics actually had a very small bit of slippage programmed into a locked up TC; maybe 1/2% or less, just to smooth out engine vibs at cruise. It wasn't enough to generate excessive heat or wear.
As far as transmission loading, TCC only locks during part throttle, right? It's not a factor in WOT shifts unless you are able to change the programming.
I think harsh WOT shifts would easily overload a TCC.
The reason I think it isn't locked during shifts is the shutter or judder or little pulsing you might feel with the TCC locked. The TC is a good shock absorber for engine/transmission torsional vibrations. If I recall, there was a time when some highend GM automatics actually had a very small bit of slippage programmed into a locked up TC; maybe 1/2% or less, just to smooth out engine vibs at cruise. It wasn't enough to generate excessive heat or wear.
As far as transmission loading, TCC only locks during part throttle, right? It's not a factor in WOT shifts unless you are able to change the programming.
I think harsh WOT shifts would easily overload a TCC.
Melting Slicks
Joined: Dec 2003
Posts: 3,315
Likes: 17
From: Near Jacksonville Fl.
Re: Allow TCC lock duing shift??? (OldSStroker)
My '97 doesn't seem to do that. As I understand it, you have to be in "D" to get lockup in 3rd. I'll check to see if then shifting to "OD" results in a 3-4 shift without unlocking. No way have I seen lockup in third with selector in OD. Maybe I'm wrong.
The reason I think it isn't locked during shifts is the shutter or judder or little pulsing you might feel with the TCC locked. The TC is a good shock absorber for engine/transmission torsional vibrations. If I recall, there was a time when some highend GM automatics actually had a very small bit of slippage programmed into a locked up TC; maybe 1/2% or less, just to smooth out engine vibs at cruise. It wasn't enough to generate excessive heat or wear.
As far as transmission loading, TCC only locks during part throttle, right? It's not a factor in WOT shifts unless you are able to change the programming.
I think harsh WOT shifts would easily overload a TCC.
The reason I think it isn't locked during shifts is the shutter or judder or little pulsing you might feel with the TCC locked. The TC is a good shock absorber for engine/transmission torsional vibrations. If I recall, there was a time when some highend GM automatics actually had a very small bit of slippage programmed into a locked up TC; maybe 1/2% or less, just to smooth out engine vibs at cruise. It wasn't enough to generate excessive heat or wear.
As far as transmission loading, TCC only locks during part throttle, right? It's not a factor in WOT shifts unless you are able to change the programming.
I think harsh WOT shifts would easily overload a TCC.
The TCC is a wet clutch roughly 13-14" in dia. and only see's engine torque no matter what gear your in or what your speed. :D
Back in the 80's I did some work with the Corvette Development group at MPG and we found the best 1/4 mile times were obtained by locking the TCC at 3000 rpm in 1st gear! :eek:
The problem with this is after several runs the transmission would fail hard parts, like the input housing or planetary gears, sun gear drive shell etc.
TCC was locked during a shift to minimize the distirbance of the transmission.
As I understand it the A4 will not up shift into 4th at WOT nor will it lock the TCC.
Only Ed Wright programming will provide this feature as far as I know. :D
Thread Starter
Drifting
Joined: Jul 2002
Posts: 1,386
Likes: 80
From: NC
Cruise-In IV Veteran
St. Jude Contributor
Re: Allow TCC lock duing shift??? (corvettebob1)
Now with LS1 Edit I see where the converter is set to lock and unlock under certain situations and gears. Along with those tables there is a separate option to lock the converter just for the actual shift itself. This stand-alone option is what I am curious about.
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