Towing in overdrive with manual transmission


#1

An F-250, Powerstroke, 6 speed manual overdrive with 300,000 miles needs a transmission. The overdrive gear is “blown out”. In the first 200,000 miles the truck went through three clutches (broken spring, not worn out). Switching to an aftermarket clutch solved that problem. It It pulled a heavy trailer about 5,000 miles. At 285,000 miles it started pulling a 10,000 pound boat most of its miles. When the transmission failed I was told that overdrive should never be used when towing. I thought that overdrive should be switched off when towing uphill with an AUTOMATIC to avoid constant shifting, but there is no reason not to use overdrive with a manual transmission so long as the engine is not lugging. Comments?


#2

I used overdrive with my Pathfinder (5-speed manual). No problem at all. As long as the engine and tranny can handle it I don’t see a reason why NOT to.


#3

No reason not to with a manual. If your truck can pull the load in high gear, feel free to do so.

Most of the time what damages high gear in those 6 speeds is missed shifts.

Skip


#4

I would say it was fine if you were driving a commercial truck, but with a pick-up truck, I feel different.

There is a reason not to use overdrive when towing heavy loads with a manual six speed. It isn’t just about preventing hunting with an automatic transmission. It is about forcing the engine to remain within a certain RPM range that is optimal for towing heavy items. You should never tow using overdrive unless your payload is very light. That goes for manual and automatic, as long as you don’t redline the engine.

The other advantage to not towing with overdrive it that it gives you better control of your vehicle. You don’t have to downshift as often to climb hills and engine compression will help control your speed going down hills.

Overdrive is used to save fuel. If you are towing 10,000 lbs., I doubt there are any fuel savings to be had by using overdrive.


#5

You’ve never driven one of these rigs. They aren’t anything like a car or even a half ton truck. Even in the Automatics, the transmissions in them are heavy duty commercial transmissions. Chevy uses Allison in their trucks, Dodge and Ford both use automatics that are similar to Allisons in theirs. These trannys are made to pull.

An F250 is a 3/4 ton truck. That diesel engine is a variant of the same engine used in a lot of 2 ton trucks (like the Penske Trucks). 10,000 lbs may on a 5% + grade over a long distance require a downshift, but most likely even at that the truck has plenty enough power to pull that weight in high gear no problem.

I don’t know if he’s got the older 7.3L trucks or the newer 6.0 liter trucks. Being as it has 300,000 on it and still runs, I’m kind of guessing a 7.3L. At any rate, depending on the gearing, (3.73 or 4.10) that engine will turn between 2200 and 2800 at 70 mph. You don’t want to drop it to 5th gear and be turning 2600 to 3200 rpms, particularly if it’s a 4:10 axle. Redline on a 7.3 isn’t much more than 3200. The 6.0’s redline is quite a bit higher, but still you want to keep it in the 2400 range on the highway.

The 6 speeds in these trucks are really 5 speeds with a Granny gear.

At 300,000 miles, pulling that kind of load, I would really just kind of write that off as expected wear.

I’m not sure how he drives his, but a good portion of the people with these rigs shift up and sometimes down without mashing the clutch. 6th gear is a little more difficult to hit than the others and frequently gets banged a little pulling it out of gear coming to a stop.

Skip


#6

Towing ANYTHING in Overdrive = Bad idea. unless you are travelling through the barren wasteland of no hills or curves that is known as Iowa. keep the ratio @ 1:1 @ the very very most.


#7

I routinely tow a loaded car trailer with an F-250 6-spd diesel. Skipper is absolutley right about the RPM ranges and what the tranny is designed for. Unless you drive one, you’re not qualified to post on this subject. I seldom need to shift down unless I’m climbing a long steep hill. That’s not often. 70 MPH is a breeze in 6th. The engine is practically loafing. If it will pull in in 6th, pull it in 6th. The OP didn’t ruin 6th by towing with it. He ruined it by putting 300K miles on it. Not bad in my book. The one I drive won’t be there for another year or so. The conventional “wisdom” about not towing in OD is meant for AUTOMATICS, and is not true in this case. In fact it’s not true of automatics in diesels designed for the purpose.


#8

You don’t want to drop it to 5th gear and be turning 2600 to 3200 rpms, particularly if it’s a 4:10 axle.

Uh, Skipper, would you please explain what the axle has to do with anything? If you travel at 70 MPH, whether you travel in 5th gear or 6th gear, the axle moves at the exact same speed. The same goes for the drive shaft. The engine speed will be different, but the driven wheels rotate at a speed equal to the speed of the truck, not the speed of the engine. How does traveling in 5th gear at 2,600 to 3,200 RPMs make a difference with a 4:10 axle?


#9

It has a heck of a lot to do with it as it dictates what RPM the engine is going to have to turn to move the truck at a given speed.

These big trucks aren’t meant to be sports cars however, they can move. A truck with a 3.73 axle in it will probably top out before redline at just over 95 mph with a 7.3L Powerstroke. The 6.0 is a little faster because the redline on the engine is higher. A 7.3 redlines at 3200 rpm’s. 6.0’s I believe go up to about 3800 rpms. With a 4:10 axle, you engine is going to turn more RPM’s at the same speed, so if redline is 95 mph with a 3.73, it’s probably something like 85 mph for a 4:10 axled truck. If you drop a 6 speed back into 5th gear with a 4:10 axle, I would guess redline to be somewhere along the lines of 60 to 63 mph. My Dodge’s tranny is geared a bit slower than the Fords, and the Cummins redlines at 3000. If I’m above 60 mph, I’m going to be running in high gear.

These engines aren’t meant to run at or near the redline rather well below that. Remember, we are talking about heavy duty diesel engines not gas motors or some 4 cylinder sewing machine diesel in a VW. My Cummins likes to run right at 1800 rpms for maximum efficiency, and it’ll do it all day with a heavy load behind it. Those powerstrokes like to turn around 2200 to 2300. Much more than that and you are floating the lifters on them and burning much more fuel for very very little gain in power or torque.

The RPM’s I gave you are pretty close for 5th gear in a Ford Powerstroke for both a 3.73 and 4.10 in 5th gear at 70 mph. The 3.73 rear is the lower RPM obviously, you can see that the 4.10 at that speed is redlined out, and that’s not good for the engine.

The thing about these rigs that people don’t understand that don’t drive them and haven’t driven them very long is, the transmission is set to work with the engine to keep it in the torque band at given speeds. That’s why they quit putting 4 speed manuals in these trucks 20 years ago. You want to keep the engine in it’s power band for maximum efficiency. On a 7.3, that’s between 1700 and 2300 rpms. My Cummins’ band is between 1600 and 2100 rpms. Above or below that and you need another cog to pull.

Tranny lifes on these things isn’t near as good as it probably should be and a lot of it depends on what they are doing with the truck. There’s not a tranny made that can tame the power of a 5.9 Cummins or 7.3 Ford. 100,000 miles is pretty good for a clutch on these trucks and 300,000 on a tranny is a pipe dream, particularly if it’s been towing 10,000 lbs around. The whole point is, you aren’t going to help things gearing down when the RPM’s do not dictate doing so. Trannys are much much cheaper than one of these engines. The injectors alone on that Ford cost $2700 for the parts alone let alone labor and miscellaneous gaskets and the like. The injector pump on my Cummins is a $4500 item. These engines cost around $12,000. Use the tranny to keep the engine purring like it’s meant to, if it wears out, it wears out.

Skip


#10

Skipper didn’t explain it directly, but when he says a “4.10 axle” he means a rear differential with a gear ratio of 4.10 to 1 (4.10:1), which means for every turn of the rear axle the drive shaft turns 4.1 times. Since the rear differential is built into the rear axle folks refer to it as a 4.10 axle. As an aside the rear diff ratio is never a whole number, so different teeth mesh with each revolution, for even wear.