V8 5-spd Transmission actually 6 Speeds?

[thirstyturtle]

Help me out here gang. I have a 2006 V8 which has the 5-spd transmission but it sure does feel like I have 6 speeds. Let me explain:

Driving down the highway doing 70mph, tachometer sitting at 2,000 RPM's, start going up a slight hill, give it a littte extra gas and you can feel and hear the transmission kick down a gear, Tachometer rises to 2,300 RPM's, speed stays the same. So I should be in 4th gear right? Well if I then kick the shifter over to "4" then the transmission changes hears and the tachometer jumps to 3,000+ RPM's.

So what's the deal here? Is there a 6th gear overdrive or something?

 

[lddrew]

torque converter locking up kemosabe

 

[thirstyturtle]

Sweet! So is there anyway you could explain what that means exactly?

 

[lddrew]

Sweet! So is there anyway you could explain what that means exactly?

wikipedia knows all!!! i couldn't quite find the words to say it.

important bits in red

A torque converter has three stages of operation:

Stall. The prime mover is applying power to the impeller but the turbine cannot rotate. For example, in an automobile, this stage of operation would occur when the driver has placed the transmission in gear but is preventing the vehicle from moving by continuing to apply the brakes. At stall, the torque converter can produce maximum torque multiplication if sufficient input power is applied (the resulting multiplication is called the stall ratio). The stall phase actually lasts for a brief period when the load (e.g., vehicle) initially starts to move, as there will be a very large difference between pump and turbine speed.

Acceleration. The load is accelerating but there still is a relatively large difference between impeller and turbine speed. Under this condition, the converter will produce torque multiplication that is less than what could be achieved under stall conditions. The amount of multiplication will depend upon the actual difference between pump and turbine speed, as well as various other design factors.

Coupling. The turbine has reached approximately 90 percent of the speed of the impeller. Torque multiplication has essentially ceased and the torque converter is behaving in a manner similar to a simple fluid coupling. In modern automotive applications, it is usually at this stage of operation where the lock-up clutch is applied, a procedure that tends to improve fuel efficiency.

:bigok:

 

[thirstyturtle]

Okay so that makes sense to me!

I'm wondering though, if the lockup clutch improves fuel efficiency then why wasn't it already locked at 70mph? It waited for me to give it more gas and needed more power...

 

[lddrew]

i misread your original post. what I believe to have happened was the torque converter unlocked, giving you the feeling of a downshift and some git up and go. then once you hit cruising speed again it will lock back up.

but yes on a 5 speed trans you will count 6 distinct shifts
like on my Allison i count 7 shifts

 

[thirstyturtle]

Well that's pretty cool. I did not know how torque converters work but it's pretty awesome.

Thanks for the insight and new knowledge!

 

[lddrew]

Not a problem man. automatic tranny's are by no means simple. and the TC is just one element that is diverse as well. it is pretty amazing what they can do.

 

[d2huffman]

I believe that you can also get lock up in 4 when driving in 4 - like towing.

 

[lddrew]

I believe that you can also get lock up in 4 when driving in 4 - like towing.

do you have a tow haul button on these trucks?? sorry i joined today and haven't even sat in the new TR4. just tryin to learn,

but on my allison it locks in 5th gear and 6th when driving normal.

hit the tow haul button and it locks the converter in all but 1st gear for towing heavy and raises the shift points to keep it out of the torque curve. handy feature

 

[DC runner]

On most vehicles that is what the O/D off button does. On the 4runner, you just pop it into 4th. 5th gear is essentially overdrive.