Overdrive

[Patsdeere]

I guess I have a few holes in my knowledge base, but was wondering, why would you turn off over drive? A previous post suggested it so you don't burn up the tranny. My grandfather did it when he was pulling a camper, but never could tell me why.

Wouldn't OD help on the long stretches in terms of mpg?

Thanks.

 

[Dennis Benson]

It's just downshifting a gear to gain engine braking, and prevent riding the brakes. It helps me when going down an icy hill, or on long stretches in the mountains. It also hold me close to the speed limit in town on a particular hill where the police like to set and wait for speeders, just push the button feel it downshift and watch everyone pumping the brakes.

 

[showcrop]

If you are in hilly country it would be constantly shifting up and down which will generate heat and shorten the life. Since I can see ahead down the road and my transmission can't I would sometimes shift up if I knew that it would not need to shift down soon. Heavy trucks with autos are usually formatted to go only to four when you hit D then when you get to open level road you hit the up button to get into five.

 

[rustyfarmall]

If you have several miles of basically flat road, no hills, then leave it in overdrive, but use some common sense also. If the tranny is constantly shifting into and back out of overdrive, then you will get better efficiency by just locking it out.

 

[Patsdeere]

I guess that make sense. I am in basically flat country (a minor rolling hill here and there) so I guess I will leave it in OD when I am cruising the highway and drop it out of OD when I am tootling around town and on hills.

Thanks for the lesson.

 

[JMS/.MN]

Operator manual of the Ford truck recommends it when pulling a trailer.

 

[ScottyHOMeY]

The computer driving your tranny isn't as smart as an educated driver. Letting your pickup's computer allow you to go in overdrive under a heavy load with even the slightest upgrade is gonna overwork your tranny, toast fluid, all the bad outcomes. With a stick in such a situation, an informed driver would downshift long before the computer would drop an auto. Last slushbox I had, I about wore out the floorboard kicking it down to get another gear.

 

[Mike N Mo]

Running in overdrive when towing a trailer depends on a lot of variables, such as trailer weight, engine, axle ratio, and trailer frontal area. With my previous truck, a '90 F150, 351, 3.55 gears and a 6500# trailer, if I let it shift into overdrive on a level stretch of road, then push the button a minute or so later to go back to drive, I'd have to let up on the accelerator to maintain the same speed. I got better mileage in drive than overdrive, because the engine was in it's best powerband. With a light trailer you could run in overdrive with no problems. Mike

 

[camju]

If it's windy you won't want to use OD even on the flats.A ford taurus I had, did 3 mpg better in D than OD in any condition just the way there set up OD don't meen better milage.

 

[kruser]

OK - Got me thinking (kinda).
Occasionally pulling 7500-8000# with a 2002 Chevy 2500 mostly flat but a few hills. I've always used the Tow/Haul in Overdrive - no problems at 125,000 miles. Wrong?

PS: Blind in both eyes so I can't reference owners manual.

 

[mkirsch]

No. It's a COMMON SENSE thing, not a hard-and-fast rule.

Preventing shifting, and keeping the torque converter locked are the important things.

Trucks made in the last 15 years or so have locking torque converters, which drive the transmission directly once the transmission shifts into overdrive.

 

[john_Bud]

(quoted from post at 19:04:21 06/17/10)

The computer driving your tranny [b:4eae2ae9e7]isn't as smart as[/b:4eae2ae9e7] an educated driver.

Actually, with the "Tow/Haul" mode in nearly all 10 year old and newer trucks, the computer is typically [b:4eae2ae9e7]smarter than[/b:4eae2ae9e7] an educated driver. Also, faster to make the needed changes as conditions dictate. They don't change when it's not needed, so they allow the truck to maximize the fuel economy. They don't get distracted.

They also typically put the transmission into a more aggressive mode where they will wind up higher RPM, shift with greater fluid pressure and lock the converter differently.

The old tyme trans controllers would allow the engine to lug down when towing in OD and the OD was much more fragile. So, while it used to be the thing to do, it hasn't been needed in at least 10 years.

 

[johndeerefan]

I always use the tow/haul mode when towing with my 2005 F-250 Powerstroke. The shifting rpm changes and has a built in braking system when using this function. It will kick into overdrive in this mode at about 64 mph. Normal 2 lane road driving, it will stay in drive and run at about 2000-2500 rpm. 2000 rpm in a 6.0L is about the most bang for your buck for fuel mileage when towing. Although, I average about 9 mpg pulling 10K and 16 mpg normal highway driving without a trailer. Not to mention, the turbo typically runs about 10 pnds of boost almost all the time in tow/haul mode unlike the varying boost amount you get in normal mode.

 

[NEBeef]

The Fords changed from an "overdrive off" switch to the tow/haul mode in 2004, I think? As the name implies, the "overdrive off" simply prevented the transmission from going into overdrive. The newer Tow/Haul mode changes shift points and even uses a different gear pattern in some transmissions - overdrive on 2nd gear to produce "third gear" on the 5R110 transmissions, if I remember correctly. Tow/Haul also changes the the downshift points in conjunction with the brakes to provide increase engine braking on deceleration.

 

[R.D.F.]

All the answers have some merit, BUT, the real reason for towing out of overdrive is fluid cooling. In OD the trans may work harder, hense, higher fluid temps, also the engine turns less rpm"s so it pumps less gallons per minute through the trans. cooler, so with warmer fluids and less cooling capacity may lead to premature transmission failure.

 

[Brian Jasper co. Ia]

Older overdrive transmissions typically have fewer clutch plates in the overdrive section. What I noticed last weekend hauling a CA Allis to a show with my 98 Chevy was with the empty trailer it would downshift from 4 to 3 and unlock the converter, then quickly re lock the converter.
As a transmission guy, I would pick a gear that the vehicle can handle without having to downshift on each hill and select tow/haul mode if it has one. The guys driving GM trucks with the Allison trans can just put it in D and go. The LCT 1000 is a medium duty truck trans that was put into a pickup. It wasn't until about 04 or 05 that you can lock overdrive out on them. Ford's Torq-Shift seems to be almost if not as good as the GM Allison. I've built my share of 4L60E and 4L80E trannys, but have never seen anybody tear up an Allison.

 

[souNdguy]

yep.. my 04 f250 has the tow/haul.. and it's nice ( 3.73 rear end ). my 99 f450 has the OD off.. and it never gets used due to the 4.88 rear end.. IE.. with od off I can't even hit 45mph.. .. of course.. the truck doesn't even strain under a load the f250 would so it's a moot issue

soundguy

 

[NEBeef]

4.88 - wow! My 97 F250 had the 4.10 rear end and it would kick into overdrive at about 36 MPH... as you said, the OD-off button didn't get used much at all!

 

[souNdguy]

yep.. the 4.88 rear on that 450 is low.. lower than I would like, as I am at 2750 rpm to make 75 mph down the interstate... but it pulls darn good.

soundguy

 

[ASEguy]

When I worked at Dodge they told us at Chrysler tranny schools the reason you don't do it is "grade hunting" or the constant downshift and upshift which generates more heat and also causes more clutch wear. I suppose that is directly related to engine size and what you are pulling.
Gerard

 

[lloyd in sc]

I was hauling a trailer with a 67 ford with standard transmission & didn't lock out overdrive coming down Lookout mt. in Tn.
No engine break that way & when brakes faded I found a wide spot & put it all in a slide & stopped 3 foot from edge of road .
Still remember how far DOWN looked...

 

[john_Bud]

(quoted from post at 06:51:04 06/28/10) yep.. the 4.88 rear on that 450 is low.. lower than I would like, as I am at 2750 rpm to make 75 mph down the interstate... but it pulls darn good.

soundguy

Probably pulls so good you don't notice the extra weight of having to pull a fuel pump along behind it...


4.88 -- now that's not made for highway cruising!