Engine/Transmission (1994 - 1998) Torque converter lockup switch

[Dual EE]

I installed a TC lockup switch following the directions from

TST web page. The directions state that the trans will not shift out of 4th gear once locked. I am experencing a down shift even when the lock up switch has been applied. If I apply the maximum throttle the trans will down shift then go back into lockup. The switch does have to be turned off in order to stop or the truck will stall.



My question is this. Is the trans supposed to still down shift between 3rd and 4th even when the lockup switch has been applied.



Thanks for your help.



Don Vizgaudis

 

[Joe G.]

Is your TC stock? Mine is a DTT and it will down shift with the TCC locked with my switch if I stand on it. When I had a stock TC it would not do that.

 

[Dual EE]

Joe G,

Yes, I believe the TC is stock. I bought the truck used a few years ago and it appeared nothing had ever been touched before me.

 

[BDech]

I have a switch on a 95 and it would not downshift with it on

 

[JKouzez]

yea same here mine wont downshift either, you did get the 94-95 instructions, because i remember i was about to start and i got the instructions for the 96 and up.

 

[JoshPeters]

Mine didn't downshift till I installed an updated valve body. Now even with the lock up switch on, it'll downshift at WOT if the conditions are right.





Josh

 

[Howard Durand]

I don't think shifting in or out of OD with the TC locked is very good for the transmission.

I have never tried a WOT downshift while the TC was manually locked but have caused a downshift by pressing the OD lockout switch. I didn't like the way it shook the truck so I re-designed my switch so that the TC would unlock momentarily when the OD switch was pressed.

 

[Joe G.]

Howard,



I didn't think of modifying the OD button to do that. Pretty neat. I fooled around with shifting in and out of OD with the TCC locked. After a little practice I can use the fuel pedal so that the shifts are pretty smooth. I also have a button to step on if I want to force the TCC to unlock for a while. Stops, shifts with a load, etc, etc, ... I also installed a shift lever from a '99 so the OD button is more handy.

 

[krs]

Seems to me that there are two wires at the PCM that are the colors specified by the TST instruction (orange/black?).

If you hook into the wrong one you'll have normal TC operation including downshift.

I've got a vague memory (all of my memories are vague now) of threads about this.

 

[JEricson]

I am new to the TDR and have also thought about installing the mystery switch. However i'm confused. I have a 1997 with 47re trans. I am told that this trans has torque lockup in 3rd and OD.



what will the switch do that is'nt done automaticaly by the trans?

 

[Joe G.]

The next time you drive it let it lock up and then lift your foot. Watch the tach. It will drop to idle after a few seconds. That's because the TCC (torque convertor clutch) automatically unlocks when the truck is coasting. That is the reason that an exhaust brake will not work with an automatic transmission with no additional control over the TCC. The mystery switch prevents the TCC from unlocking after it has locked until the switch is turned off so you can use an exhaust brake.

 

[JEricson]

Joe G; thanks for unconfusing me. what about lockup in second? if i shift to second and then turn switch on will it lockup in second? i get into a lot of 6 & 7 % downgrades.

 

[Joe G.]

You need an after market VB for that. Most all of them provide 2nd gear lockup that you can hold. The stock VB will allow lockup in 2nd with a mystery switch but you cannot make it hold the lock when you lift.

 

[RedRamer]

Hi Joe

I just installed the mystery switch in my 97, hoping to get 2nd lockup when I put the stick in "2"... but it ain't working out.

To have this, must I get a modified VB? and if so, are their any side effects to this VB that you are aware of?

thanks



btw: I tried with and without the relay bypass and everything seems to wrok the same... should be to leave the relay in?

 

[Joe G.]

You have to have a modified VB to get 2nd gear lockup. You have a 48re trans which is different from my 47rh in the way it does the lockup. I'm a little surprised that your switch works the same way with and without the relay. It must be the way your PCM is programmed. A '96 has problems because with the relay and the switch on it will lockup ok but will not unlock.



In aftermarket VB will give you higher pressures and better shifts. Both are BIG pluses. If you buy one make sure that it has 2nd gear lockup.

 

[RedRamer]

thanks

these modified VB,... . is the pressure so high that you should probably tear it down and replace the front seal?

 

[RedRamer]

thanks

these modified VB,... . is the pressure so high that you should probably tear it down and replace the front seal?

 

[RedRamer]

thanks

these modified VB,... . is the pressure so high that you should probably tear it down and replace the front seal?

 

[Joe G.]

I don't think the front seal would be a problem. Some transmissions have a lip seal problem, but I don't think your '97 would have that. However, the big problem with these transmissions is the torque convertor. The modified VB will certainly help with shifts and stuff like that, but it won't affect the slopply TC.