Engine/Transmission (1994 - 1998) when to turn on mystery switch

[MAleksandrowicz]

i recently installed a mystery switch in my truck. i have been turning it on at about 30 miles per hour and it works great. my 0-60 is 9 seconds with it on and 13 with it off. a friend of mine told me to only turn it on once i have reached 55 mph and it is in od. is this true. will using how i have been hurt anything

 

[Lnwing]

I don't see any transmission upgrades in your profile. If you are pushing the kind of power you are making thru a stock transmission, you're on borrowed time, mystery switch or not, IMO.



I installed mine to allow the use of an exhaust brake, and that's about the only time it's on.

 

[bmoeller]

I'd be careful too, using it (if stock trans). I don't have a switch, but could slip my stock transmission or t/c very easily, if I didn't watch it. Even stock. I still managed to get another 50k out of it, before the BOMBed auto. Can't slip this one.

 

[MAleksandrowicz]

i dont have any transmission upgrades that i know of but i just recently bought the truck and did all the upgrades that it currently has myself. i have had a 10k pound trailer and the transmission never slips even if i get on it. i dont really care if i blow it because i am going to convert to a 5600 when i have the money

 

[Allnew2Me]

Okay I have to ask, what is a mystery switch?

 

[Joe G.]

It's a manual torque convertor clutch lock up control switch. It was called that by TDR member Russell Ward as a joke when he invented it.

 

[Jschafer]

If I remember correctly when he invented it he put the switch next to the OD switch on the 94, at that time the switch next to the OD switch was called the mystery switch, as it had no purpose back then.

If I remember correctly.

I use mine any time I want to make more boost as I loose fuel in the higher RPMs usually after 40 mph or so.

 

[Allnew2Me]

Thanks for the info

Well I guess it isn't a mystery anymore! Thanks for explaining that for me

 

[Howard Durand]

The PCM in my 94 does not normally allow the TC clutch to lock up until the truck is up to speed and has shifted into OD. Theoretically, it does not shift into OD until a reasonable highway speed has been reached. The problem is that my PCM has a hard time deciding what a "reasnonable highway speed" is.

If the truck is unloaded and normal acceleration is used to get up to speed, it will usually shift to OD around 45 mph and the TC locks up shortly after that.

Hang a trailer on the hitch and things change. Mine will usually shift normally if accelerating from a stop up to highway speed.

Where I have run into problems is when traveling on two lane roads in fairly heavy traffic or in changing terrain causing deceleration followed by acceleration trying to keep up with the flow.

This is where it shifts way too early into OD then into TC lockup causing the same thing as shifting a manual into too high a gear. It bucks and shudders and scares the devil out of me. I have found that keeping the TC switch in "unlocked" position takes care of this problem.

The switch should not be used to lock the TC before a reasonable highway speed has been reached. 55 mph is not a bad choice. I try to use manual lockup only when the exhaust brake is being used.