Engine/Transmission (1994 - 1998) Transmission O/D off button (when to use)

[PGaither]

I have a 96 Ram 2500 w/Cummins Turbo Diesel, Auto trans. ; sometimes when going on a highway onramp with a grade it seems to go into O/D (4 th gear) to soon even without a load or trailer, is it o. k to shut off the O/D in these situations even though I'm not pulling a trailer? I find myself in this sittuation on a daily basis ussually, is it o. k to shut off the O/D on a daily basis in these sittuations even though I'm not pulling a trailer? I only ask because a guy that works on transmissions told me not to use the button unless I absolutely have to when I'm towing, because the O/d is what ussually goes on these tranies, is that true? Is it better to use, or not to use the overdrive to increase its longevity, life?



Phil

 

[bmoeller]

Welcome to the TDR!



In those situations it is better to turn off the O/D, particularly if you have 3. 54 gears. Best to lock it out 'til around 50-55mph. Doing this will keep the pressure up in the transmission, so the transmission, or lock-up clutch in the torque converter from slipping.

 

[PGaither]

Thanks for the welcome!

Thanks for the welcome, this is a great web site! This is my first Diesel, and I have only had it for about 4 months, and I absolutely love this truck (especially the Cummins Turbo Diesel motor, thats the best part of the truck!), its a 96 2500 SLT (auto) reg cab, long (8 ft. ) bed with only 150,000 miles, I'm going to put a pic. on the website, I picked it up for $8,900 last june.



Phil

 

[krs]

Hi,



To support bmoeller's correct response the transmission depends on internal line pressures to hold it's clutches and bands engaged. When the engine is turning it drives a pump which makes that pressure. The faster the pump turns the higher the pressure (within designed limits).



Too many transmissions are are allowed to run in OD with the pressure low which is the reason for many of the failures mentioned by your guy who works on transmissions. Think he's looking for work?

 

[PGaither]

Thanks

Thanks, so its actually better to use the O/D off button, than to not use it if I understand you correctly? So its good to shut the O/D off arround town when I'm not going over 35-45 mph.....

 

[JohnE]

YES

Absolutely!

Positively!

Canceling the O/D means your TC will lockup in 3rd gear. That is good for city/urban driving. I do it all the time.

 

[Dfuruness]

Welcome to the TDR...



You bet, OD off in urban areas. I run mine off anywhere under 80 Km/hr... eh. . Good old metric. .



Keep on rollin...



Don

 

[shendren]

i turn mine off when i start up in the am. i don't use it or turn it back on unless i am on the interstate or consitently over 55-60mph... ...

 

[RedRamer]

Yep, with the OD off in town it's like cruising with a standard.

When pullin a trailer I always keep it off till I hit 55mph then let her go right into 4th lock up. Best torque range possible.

One more trick you might want to try if your pulling weight.

When on highway uphill and you're slowing down and you know she's going to drop a gear... DON'T LET IT DO IT BY ITSELF.

When you do, by the time that darn transmission figures out where it should be you'll probably have slowed down to about 50mph, still going uphill, and that most time will be too low an rpm to keep the speed up and the pressure on.

I take it out of OD manually at anywhere between 55-60, then she downshifts real quick with good speed and makes most hills that way.

goos luck

 

[Crowhurst]

With my BD Autolock I have opted to change to "overdrive only when selected", so the vehicle starts and runs in drive, unless I select overdrive. This seems much more useful to me, and it's a switchable option on the Autolock. I suspect some of the experts on this site will know an inexpensive way of achieving the same result. It certainly helps to avoid lugging when towing. Nick.

 

[Piersol]

I don't know about all of you, but if I'm not pulling anything I can't get into OD fast enough. On a on ramp I punch it and the tach moves to 2250 rpm and i have very little acceleration (about 15 psi boost). Once it goes into OD it shoots up to 22psi and i take off like a rocket.

 

[Bseg]

I do the same as Piersol. Once my truck hits overdrive at ~ 50 mph it pulls like there is no tomorrow.



I haven't done my trani yet, will have to eventually but I'm going to wait till it starts acting up. I agree with the others when it comes to doing the whole job the first time. It is expensive but when you consider the time and cost to do it a second time it's worth it.