With your foot off the gas, when tcc disengages, engine will idle down some, truck will accelerate a bit, depending on the hill. (more than it would if you didn't do anything anyway.)

 

Be careful. Running with the engine and drivetrain unhooked going down a hill can end badly. Especially on a 1500 whose brakes may not be adequate.

Personally Id rather have that engine braking going downhill when Im towing heavy.

 

I will say something that peeved me off on my trip to KY this past weekend. Bunch of cars and light duty vehicles towing (I40 through TN/NC). I shift up to 5th and put my cruise on at 70, im chugging along up and down the hills with the trailer no problem. These fools going down a hill will pass me like im on jacks, then when we hit a hill not even a big hill, they fall back and I ride on by. My speed never changes, when my truck hits a grade, the boost picks up 3-15 psi depending on the grade and I hold 70, going down a hill, I hold 70. These fools are running 60 up a hill then 80 down it. It got pretty annoying, they pass me then pull over in front of me going down the hill, then when we go back up I have to pass them so I dont have to get on the brakes. /rant

 

^ they're driving dodges. your in a diesel ford.. lol.

no wait, if they were in a dodge it'd be 80 downhill and 45 uphill.

 

So as long as you don't let it downshift while in o/d its fine? I can play the hills and speed right in my area to where I can keep it from downshifting whatsoever. Is it fine then?

 

No. Overdrive is exactly that, overdrive. Something to the tune of .69:1.... trying to pull/haul a significant amount of weight in O/D is going to generate a LOT of heat, heat is what kills your trans.

 

It is my understanding that the clutch pack that holds OD is about half the size of the clutch packs for other gears.... MonteC would have to verify this, but I'm pretty sure I've read this here before.

This smaller clutch pack + the 0.69:1 gear ratio makes it quite easy to slip the clutch pack in OD which can create a lot of heat. If the clutch packs were up to it, towing in OD wouldn't be nearly the problem that it is now (as MonteC so kindly reminded us with his Ford story.. lol).


The transmission should run cooler in OD with the TCC engaged as well:

The engine does 'work' on the fluid in the TC (Work-in) and the fluid gains kinetic energy. The goal is to have all of the kinetic energy in the fluid to be converted into 'work' done on the transmission input shaft (Work-out). All of this takes place in the torque converter.

This would be ideal: (Work-in) = (Work-out)

The problem is that the efficiencies of these devices don't permit a 1 to 1 ratio of (Work-in) to (Work-out), so some of the (Work-in) done by the engine is converted into heat energy in the fluid (Heat-tc). This heat energy gets stored in the fluid, and should be removed by a transmission cooler.

So this is more realistic: (Work-in) = (Work-out) + (Heat-tc)

If you engage the TCC to lock-up the TC, the torque converter functions as a shaft and transmits work directly from the engine to the transmission, thus removing (Heat-tc) from the above equation.

If the truck is in OD and the TCC is disabled, then yes, you'll have excess heat generated in the TC due to a higher (Heat-tc).


Oops.... got myself off on a little tangent.

-JT