Freezing the Slushbox. Torque Converter on-demand lockup switch.

[orange4boy]

After much frustration with the Previa's slushbox and the inability to P+G properly I have decided to try to bypass the ECT and put in a switch to get lockup in all gears. I live on an island with a low speed limit and steep hills so the TC almost never locks up. Im not sure how much this will help my FE but I'm determined to try it because I suspect it will. The manual transmission gives the Previa 16 mpg over the 15 the auto gets in city driving. That's 6% better and I bet it's more in hilly conditions. So if those losses are mostly the TC losses this should help. Trying to find a stickshift for the Previa is like trying to find something really hard to find: Hard. To find.

I looked into this and asked Christ some nagging questions and have decided to give it a try.

Most of the reasons for the lack of TC lockup at low speeds are about "driveability" and power. It reduces shift shock and at low engine temperatures, increases driveability. Who needs driveability? I have been told that many new Auto transmissions lock up the TC in all gears for better FE.

One question I have is about shift shock: would this damage the transmission or drivetrain? I drive pretty light on the throttle so I'm hoping this would mitigate the shock but I guess I will find out how strong the shock is if I get the bypass to work.

If so I may look at a way to apply lockup unless the transmission is shifting. this may require a skillset beyond my own if it means modifying the ECT.

I plan to set this up so when the brakes are depressed the lock disengages which is one of the ways it's controlled now.

Thoughts? Suggestions? Warnings? Colour commentary?

[Tygen1]

I'd be wary of using the torque converter lock under high torque situations. Many cars are made with as little a TCC lock up clutch as they could and they just can't handle high torque and will fail. Many mustang owners have done the TCC switch and killed thier converter this way, of course they are trying to use it for better 1/4 times etc...

[SVOboy]

Rick has done this before on his integra, I think. So hopefully he can chime in with some thoughts on the experience.

[orange4boy]

they just can't handle high torque and will fail.

Do you know if they fail because they burn out from slippage or is it a structural failure?

If it can't take the torque of the hills then I will have to content myself with low speed cruise.

[orange4boy]

I just found this great post at Toyota nation about how to bypass the ECT and set up a manual shift switch with on demand TC lock up.

The Free Mod Series: Part VIII Electronic Transmission Controller - Toyota Forums :: Toyota Nation

You can set up a 6 position rotary switch that give you the ability to change gears at will which is great for FE because I will be able to shift up sooner.
It's just at the limit of my skill level although I might start with the TC lock up first for simplicity.

[dcb]

There might be a problem with the lockup switch first approach.

If you don't control WHEN the transmission shifts (i.e. with the rotary switch) then it seems probable that you have some gear changes under power without any tc slippage (oops, didn't anticipate that downshift in time). I don't know how big a concern that is though, might just be an occasional hard shift.

[orange4boy]

I'll find out how harsh the shifting is then decide what to do. From the sounds of it, the shifting isn't that hard. Off road guys do this all the time. You can even buy kits to do on demand TC lock up.

If it's too harsh what I will need is a rotary switch that requires me to unlock then shift, like the push button lockout on an auto tranny. Hmmm gets me thinking.

[Big Dave]

Lock up the TC and you cut the flow of ATF to the cooler. Heat builds up and expensive and often spectacular (a trail of parts and fluid scattered down the road) transmission failures follow.

Face it: The automatic was never intended for hypermiling. The manual transmission is far superior.

[jcp123]

I like the idea...the TC in my Mom's Mazda is far, far too skittish...

[orange4boy]

Lock up? Affirmative!

Time to wire? Ten minutes, sir!

Just got it working this morning. This is a temporary set up with no "ghost" resisitor to fool the ECT. I just cut the TC lockup wire, found a 12V+ to power it and put a momentary micro switch in to complete the circuit.

First impressions:

There was a rumbling sound the first time I switched it on. I was in 3rd doing about 30 mph. At first I thought this was the TCC slipping but it turns out it was the engine rumbling from being at too low an rpm for the gear. When I tried it again I downshifted to 2nd and it was great. Solid and smooth. I miss that direct connection you get with a standard tranny, now I has it.

Now I need a tach to learn the shift points because I can't hear the engine.

This will work better with the full control for sure because the gear chosen by the ect is too high for the TC to be locked. I may be able to make it work better by adjusting the downshift cable. Will have to try that out later.

For now it will stay a momentary switch.