When in tow haul and the TC s locked up in 3rd gear, Does the TC stay locked when it shifts into 4th/OD ?

 

It has to unlock to shift doesn't it?????

 

That's why I am asking !!! The reason I asked is because when locked up and in 3rd it feels like the tranny just shifts it OD with it locked cause I only feel 1 shift not 2. It doesn't seem like it unlocks between 3rd and 4th/OD.

 

The TC only needs to unlock to downshift, not upshift. If the VB is modified that restriction us removed. If you add a lockup switch to a stock transmission it will lock the TC in 1st gear and shift all the way to OD locked.

Factory programming doe snot allow a locked to locked shift. Thats inherent to save the drive train from the TQ the engine generates. Depending on certain parameters, on the shift from drive to OD the TC lockup clutch is pulsed off with a PWM signal. The TC starts to unlock at the shift point then applys again because the release signal is so fast. What the TC clutch sees is a pressure drop that allows some minimal slippage to minimize the shock of the shift point.

In normal driving the pulse is so fast it feels like the TC never unlocks but it does enough to handle the TQ. The engine is also defueled slightly at the shift point to further mitigate the shock. A stock trans will never EVER shift locked to locked becuase the TQ the engine generates is over 100 ft\lbs beyond the max input rating of the trans (48RE). The 68RFE operates the same way to manage the TQ applied at the shift points and save the parts.

Note this does not apply to triple disk TC's, only singles. Under aggressive throttle a triple disk never unlocks becuase the pulse is too fast to physically release the clutches. An OD shift with a triple disk under heavy throttle defines the term "bang shift".

 

Great post no 6 oh no. Thats what I thought. When I am in 3rd and the TC is locked and the tranny shifts to 4th/OD it felt like the TC doesn't unlock but it does and just enough that you can't feel it. Now, if I install a Mystery Switch or a 4th gear lock up switch will it kill the tranny if i use it properly? Does anyone know if you manually lock the TC will it still down shift? For example if I am locked up in 3rd using the mystery switch will it down shift to 2nd if I get too low in the RPM's or MPH? Also, does anyone know if I use the 4th gear lock switch will the TC stay locked in 4th gear? Thanks Pete

 

Unless you modify the VB, no it will not downshift with the TC locked. Thats designed into the VB function.

If you don't use a lockup switch on the TC it will unlock in OD. If there is a switch on the OD gear to hold it, it won't downshift.

 

Thanks no 6 oh no !!! If I use those 2 switches properly are they hard on a stock tranny ?

 

If you use to hold the gear and lockup where the computer wants to shift it down and unlock, yes. It can be done but its a fine line.

Add a shift kit and those concerns are mostly addressed.

 

What does a shift kit typically run?

 

Cost is small, $60-70, if you do it yourself and don't make a mistake.

 

I can work on an engine but not a transmission !!!!!

 

I have the Mystery Switch installed. Today I was in 3rd gear with OD off and the the switch on so the TC was locked up. I got into the petal a little bit at around 35 mph and it the tranny downshifted. I thought it would downshift with the TC manually locked? Pete

 

Hmm, now that is different. Pretty sure mine won't do that. Could be the 07 trans is different because it has the OD off?