O/D-RPM Question

[SHOOT1SAM]

It seems to be somewhat of a consensus to not have the O/D engaged when towing, until around 2000 RPM.



My question is: Is that 2000 RPM towing and THEN engage it, which drops the RPM's? Or, is it when you engage O/D, 2000 RPM's are maintained?



Thanks in advance.

Sam

 

[FMcClaren]

Sam

I,m new to this CTD myself. But 60 mph works for me. I always

turn OD off as soon as I start the truck and when I hit 60

I turn it on. I drive 65 or a little over. When I drop back to about

60 I cut it off. I never get below 1800 in OD.

HAVE A GOOD ONE

Frank

 

[DHatfield]

My truck is a stick which may make a difference, but any time I am about 55 - 60 MPH my truck stays in overdrive (1600 - 1700 RPM's).

 

[chuck3]

towing in OD

I think it depends on the trailer wts a lot. I tow in OD with my trailer it weights somewhere around 6500 lbs, but try and keep my rpms above 1800 or so as I have heard you can cause slippage if you get below 1500 rpms. It depends on what you feel is right for you.

 

[Ramboy]

I have Bill K's TC & VB and he advises against using O. D. below 60 m. p. h.

Phil

 

[Randy J]

Here's a question for ya'll, I use the O/D to slow down, is that bad? When going to work, I can hit the clover leaf without ever touching my brakes by turning off the overdrive, and letting the truck slow down. Is this bad on the transmission?

 

[illflem]

If it's bad it sure hasn't effected my AT, 142k entirely stock with only fluid changes and adjustment. I use OD off to slow down all the time.

 

[JMorrow]

Ditto

I have a 1993 W250 and have been doing it since the truck was new.

 

[JohnMcIntyre]

I have the Bill K. VB&TC and driving around town, OD is usually off, but when out on the open road, when you can find them , when turning OD on, it will usually kick in around 55+mph and then the RPM is maintained at around a steady 1750, loaded or empty. THis was my preference when Darren & Vinny set up the TC & VB in Abottsford in April.

 

[SHOOT1SAM]

Thanks for the replies, but please forgive my denseness Are the RPM's you guys have stated while towing, or just normal driving? And again, are you engaging the O/D at those RPM's, or engaging it when you can maintain those RPM's? Thanks again,



Sam

 

[Shooter]

while towing you should not let the rpm's drop below 2k unless you are on level terrain. With a stock auto that means about 3k in direct at 75 accelerating or pulling hills or 2k cruising in od. Real nasty gear split. Under load below 2k,tc locked up, your lock up clutch fluid pressure is low and clutch slippage or shudder can / will occur which will require a non warranty overhaul/ DTT upgrade. I tow a lot and that is the reason for my GV overdrive unit. I tow in direct, GV od, about 2200 rpm @75 mph locked up and 2400 rpm unlocked. The GV puts me about 250 rpm higher than in 4th ( od locked up) or the same as 4th unlocked w/ DTT 91% tc. I prefer the direct-GV od as that part of the trans is a little stouter than the collaged afterthought od part of the trans.

MY $. 02

 

[Fireman Dave]

Off for me

I always tow with OD off. My TT weighs around 6,000 lbs. I tow with it off for 3 reasons.



1. It's better for the transmission. 3rd gear is a 1:1 ratio. In OD, the planetary gears are turning, but they aren't with OD off. The transmission is the weak link on the truck, so I like to try to do all I can to keep it from failing.



2. Keeps the RPMs up. It feels like I'm lugging it under 1900. Cruising along at 2000-2300 feels much better.



3. Higher RPMs = Lower EGTs. EGTs are lower in 3rd than in OD.



The only downside to towing with OD off is mileage. But I estimate only about a 2mpg increase with OD engaged. To me, the difference isn't worth the higher possibilty of failure, and I like the responsiveness with the RPMs higher. I averaged 10. 5 mpg on a recent 5600 mile towing trip. I believe wind conditions and the wind resistance of the trailer are the leading causes of lower mileage. My truck has 19,000 miles on it now (13k when I started out on my trip).



Just my opinions!

 

[Extreme1]

2000 is the towing RPM, If you can do it in OD, go ahead...

On OUR recent trip to (The Socialist Republic of) California, I would leave it engaged when I was able to accellerate to a good cruising speed. With the mods I've done and the load I was hauling, I needed to keep above 1700 RPM (60mph) to keep the EGT down unless on level ground. If I came up behind some dolt on good uphill, I would have to drop out of OD and slow down.



Also, if starting out on a really steep hill (not too many after the TC and injectors) I would have to keep it locked out until I could get over the large step between 3rd and OD.



Don't worry about hurting the trans, the OD section has been significantly upgraded. Now the weak link is the TC.



Hi Dave!

 

[dewdo]

I think your rear end ratio will have a lot to do with your RPM in or out of overdrive. I have the 4:10 and tow on the flat and small hills in overdrive all the time. In overdrive 2000 rpm will give me about 64 mph towing or not. On the highway I use overdrive most all the time. When I get into moderate hills or my speed drops to 50, I kick it out of overdrive.



Dewdo in the other Washington