I've been searching for a while trying to figure this out, but I haven't found a definitive answer, so here goes...

Using very light throttle, not towing, no incline:

1-2 13 mph
2-3 22 mph
3-4 31 mph?
converter lock at 40 mph

I feel a "bump" at 31 mph, and the rpm drops by about 100. It doesn't feel like converter lock, because I can still move the tach by feathering the pedal, but it seems very subtle for an upshift. As far as I can tell, the converter isn't locking under 40 mph.

So what's the deal with 31 mph: 3-4 shift or converter lock? If it's a lock, that means that 3-4 isn't happening until 40 mph, right before another lock. Doesn't make sense.

 

Converter lockup can occur in multiple gears on these trannies....depending on throttle position / load...

 

So... are you saying that 31 mph is a converter lock, and 3-4 is at 40 mph along with another lock??

 

I guess it depends upon how you are accelerating. If you maintain speed below which point a 3>4 shift occurs, then the TC will lock up in third. Accelerate some more, the TC unlocks, you drop into 4th when the algorithm determines it's appropriate, and the TC locks again.

 

Where does the 3-4 shift happen at very low throttle, on level ground, with nothing in tow?

 

Dunno - never really paid much attention - and I leave the OD disabled for all my city driving - to me 4th is just a nuisance in town, lol. That info should be in the owner's manual (?).

 

Yeah, you would think, but no. It has tables for manual shifts, but that's it.

 

Crap - need a dude with access to the shift schedules in the stock calibration - they're here ( yo, suzook!)

Or, you could determine it empirically lol!

 

Tried the empirical route.. still can't be sure. Staring at the tach is proving to be a little dangerous. All of a sudden I look up and I'm 100 yards down the street. Scary.

 

A passenger, lol.

When I feel better I can do a quickie datalog on my Xcal2, but by that time, someone will have prolly filled in the blanks

 

Mine is around 35mph and if I'm light on the throttle the RPM gauge doesn't really move I just feel a thump when it shifts into 4th. The TC usually locks up around 40-45.

 

• The 'feathering' you feel is the electronic throttle control.
  
• The TC can be unlocked to a MAX of ~1020RPM
  
• You are more than likely feeling 3rd tc lock schedule.
  
• First gear is the only gear that doesn't lock.
  
• There are also time modifiers to stay unlocked.
  
• In 'cold' mode the tranny doesn't lock as normal as its keeping the TC unlocked longer to heat up the transmission.
  
• The 3-4 shift can be locked to locked or locked to unlocked depending on the pcm.
  
• 4th gear normally comes in around ~42mph and keeps ~1200RPM depending on gear and tire.
  
• You can test this by locking out O/D and seeing if you still get the "bump" you are describing.

 

I didn't think of disabling O/D - great idea! Then if I still get the "bump" at around 31mph, it could only be converter lock. The only reason I'm having a hard time believing it's converter lock is because I can still get the tach to fluctuate about 200 rpm. I shouldn't be able to do that if the TC is locked, right?

 

Get me the computer code for your truck. It should be a 4 digit code like SVB2. I can look at your shift schedules.

Also, the converter lockup is modulated on these. So, yes, it can be lockup you are feeling and when you apply a little throttle it is modulatiing the lockup. They are not an on/off type of lockup.

Darrin

 

Interesting, Darrin.

Can you describe this modulation behaviour more fully?

Thanks!