I was just wondering about pulling semi heavy loads down the interstate in OD. Lets say your pulling about 6k pounds down the interstate. Is it hard your tranny to stay in OD going up hills and letting converter unlock? Or, is it better to man. hit OD off? I have no transmission temp gauge, so I really don't know what is save and what is preceding an overheated tranny.

Stories?

 

Do what you have to in order to keep the converter LOCKED as much as possible.

 

In general, your trans won't stay in OD once you start on a hill with a load anyway... Once you have to press more on the gas pedal, the trans will shift anyway.

What you don't want it doing is shifting in and out of OD all the time. That's whats 'bad' on the trans. Once it starts doing that, it's just better to lock it out.

If you can hold OD for long periods of time, then run it.. If you have to press the gas pedal more to hold your speed in OD, then you really aren't saving anything anyway, so if it shifts, then just keep in locked out. Only run in OD if you can hold it for long stretches...

Mitch

 

You also don't want the TC unlocking all the time. If it keeps unlocking in OD, even if it doesn't downshift to 3rd, lock out the OD and the TC should stay locked in 3rd a lot more than it would in OD.

You might want to get a Scangauge - this can display your tranny temps.

 

For instance...? I'm in OD, I start going up hill, so I let off the gas a little and loose speed to keep TC locked as much as possible. Now, there is a hill coming up that I know I can't stay in lock up. Is it better to climb the hill with TC unlocked but in OD, or is it better to man. shift into 3rd and climb hill with TC locked?

Thanks for the input fellows, great advise! My birthday is coming up. I might try to con wife into buying that read out gadget!

 

I repeat - keep the TC locked as much as possible.

 

It is very unlikely that you would be able to hold OD, locked or unlocked with a load going up a hill anyway...

In your scenario, you don't want to let off and lose the momentum you already have, so I don't understand why you would let off?? At that point, when you let off is when the TC unlocks anyway, no matter what speed you are going.

What I do is if I'm in OD and coming up on a hill, I give it gas and that usually makes the trans shift into 3rd anyway. Then I give it as much gas as I can without making it downshift to 2nd. Hit the bottom of the hill with as much speed as I can and keep the speed up. If the hill is too steep to hold 3rd, then it'll shift into 2nd, but you have to make sure your TC locks in 2nd as well... I can then pull the hill @ 50-55mph in 2nd gear pulling around 3500 rpms.

During this whole exchange, my trans temp might creep up to 195* on a hot day. On cooler days, it'll get to around 180*.

After you get used to how your truck handles the load and hills, you can start anticipating these things and prepare earlier for the grade. Traffic plays a role too, because it always seems you get that one car in front of you that causes you to lose all your momentum, then you are at the mercy of the entire grade!

In my experience towing, I'm either in locked OD or in 3rd. There is no in between, other then coasting down the other side of the hill, then the TC unlocks, but you are coasting, so there is nothing you can do anyway... Even coasting in 3rd gear, the TC will be unlocked. My trans temps actually go UP while coasting down hill because of this. If you can give it some gas, the TC will lock up and the trans temp will go down.

Having a trans temp gauge makes all of this much easier, then you can see what happens in each case and find your trucks pattern and learn from it how the temps rise and fall accordingly.

Without my aftermarket gauges (water and trans), I wouldn't have a clue as to what the trans or engine is doing.... Other then working hard...

Mitch

 

Cool! That's why I asking. I have no temp reads. I didn't mean that I let off go up hill. I really meant ease back on the gas so it won't down shift, and thus I loose a bit of speed. But since your temp is staying down, I'm not that worried about. What I have sometimes done is go up a hill in OD and let it unlock but not shift into 3rd. I now that is a bad idea

Thanks for the advise

 

Now, about that scan gauge... I'm sure where to post this at...

I was wondering about mounting locations, and if there are other gadgets similar to compare to?

 

Without the aftermarket gauges is there a way to know when the TC unlocks ? I was reading that you might not shift out of OD but the TC still unlocks, is that just when you let off the gas or even gassing it uphill under heavy load ?

 

Watch your tach.

 

Learn some of the vehicle speed/engine speeds in each gear. Say, 2000rpm is 70mph in 4th gear with TC locked. unlocked, it vary more with accelerator pedal, say 2300-2500rpm. 3rd gear TC locked (OD off button) is 3000rpm. Whatever your truck's specific tire size/axle combo is, learn it. Generally, the tachometer will vary more with light variation of accelerator pedal with TC unlocked vs. locked.