I just bought a ‘99 Ford F350 Crew Cab dually diesel 4x4 to be used mainly for pulling my 20’ 4-horse gooseneck trailer and various other heavy towing jobs, both on and off road. The truck has the 7.3L Powerstroke turbo diesel engine, 6-speed manual overdrive transmission, and a 4.10 rear end. The problem is the gearing ratio of the tranny & rear end. The way this truck is geared out, at about 50 MPH in 4th gear it’s turning 2500 RPM and needs to be shifted up to 5th gear, which is labeled as overdrive. But I’ve always been told never pull a trailer in overdrive.
I didn’t have this problem with either of the other tow vehicles I’ve used that were equipped with overdrive transmissions. The '92 F150 I used to pull a 2-horse bumper-pull trailer had a 5.0L V-8 and an automatic overdrive. I could activate the overdrive lockout and still cruise at 65-70 MPH without putting any undue strain on the drive train. And the '87 F250 with 6.9L diesel and 5-speed manual that I’m now retiring will also run 65-70 MPH in 4th without redlining the engine, but it won’t pull the kinds of loads I’m needing to pull now.
So, back to this new truck. I can wind it out in 4th gear, but at 60 MPH it’s turning better than 3000 RPM and really wants to be up shifted. It redlines at 3600 RPM which might get me up to around 65 MPH, but I really don’t want to push it that hard. The owner’s manual says “Never exceed 55 MPH when towing a trailer”, but it can be down right dangerous to go that slow on the Interstate Highways these days. Without a trailer in tow, it seems to have plenty of reserve horsepower and torque when running in overdrive at normal highway speeds and will easily accelerate from 65 to 70 MPH while climbing a 3% to 4% grade without downshifting. So, it seems to me it would be capable of towing a trailer at 65 to 70 MPH on a fairly level grade without overtaxing anything. For an uphill grade, I would most likely have to slow down a bit and downshift to 4th.
So, after all that, here’s my question: Exactly what damage would I be risking by shifting this truck into overdrive while towing a trailer?
As this is a manual transmission, there is nothing “magical” about overdrive. It is just another gear.
If the truck has the power to pull it, use the extra gear.
Also, this truck is pretty much designed with trailer pulling in mind. Did you notice anything in the manual that says you should not use 5th (or 6th) gear while pulling a trailer? They would surely mention it if there was a reason to avoid them.
I’m not sure I understand why you would not want to pull a trailer in overdrive. Assuming, of course, that you’re keeping the engine in the correct operating rpm range (not bogging it), I don’t see any difference.
Might this be wisdom that was valid some time ago and passed down, but that doesn’t apply anymore?
I’ve done my share of towing, nothing quite as substantial as the OP, but still never had any problems using overdrive.
I’ve got a Ford E-350 with the full towing package, 3-speed auto with overdrive. It’s got an overdrive-lockout button on the shifter; the manual said to use that if I was towing something and it kept shifting back and forth from 3rd to overdrive when going up and down hills, so I’d hazard a guess that the problem isn’t being in overdrive, it’s jumping back and forth under a heavy load.
The general reason for not pulling a trailer in overdrive comes from pulling trailers with cars that have automatic transmissions that were not designed to pull trailers.
Generally there were issues with locking torque converters and such that weren’t designed to deal with the extra load of the trailer.
In this instance, that “rule of thumb” should not be applicable at all.
Pretty much, with a manual transmission, you can use any gear that works.
Thanks all for the feedback. I have read that with automatic overdrive transmissions the biggest problem is heat buildup from the extra strain, which in turn causes viscosity breakdown of the transmission fluid, which can then lead to mechanical failure. But that is with automatics, not manuals.
And yes, scotth, the owners manual does say to not use overdrive when pulling a trailer right about where it says to not exceed 55 MPH. That (plus the previous warnings) was what made me wonder about the specifics of the situation. I agree with your supposition that the manual overdrive is simply another gear with the distinction that the output:input ratio is greater than 1:1, but I did want to check for errors in my thinking.
Looks like we’re all in agreement here, so as soon as I get my hitches installed I’m going to hook up a trailer and see if this bad boy is as bad as I think it is.
Many automatic overdrive trannies have an internal construction such that they are “sturdier” in drive than in overdrive. Towing in overdrive can overstress the tranny, whereas it could handle the load in drive.
I’m not aware of any similar consideration with manual trannies, although I guess it’s possible. I’m not familiar with the internal details of 6-speed manuals. I would have no qualms towing in overdrive with the 4- & 5-speed overdrive manuals that I am familiar with.
I can’t help but wonder if the “don’t tow in overdrive” warning was meant only for automatics, but wasn’t made clear. If that’s a possibility, you might want to check with a knowledgeable mechanic at a dealership or a tranny specialty shop.
FWIW, the 6th speed in this particular transmission is the stump-pulling ultra-low granny gear that when used in conjunction with the Low-range 4WD generates a creepy-crawly speed around 1 MPH or less. The gear selections are R-L-1-2-3-4-O for a total of 6 forward speeds. Of course, since this truck does have a high/low transfer case, I guess technically it should be listed as a 12 speed, but it’s not. Sorry for any confusion caused by Ford’s choice of gear names.
I would be hesitant about towing a heavy load in 5[sup]th[/sup] gear (overdrive) with the 5-speed transmission that was in the 85 Toyota pickup I had.
The 5[sup]th[/sup] gear looked like an afterthought grafted onto a 4-speed transmission. The driving gear was at a catilevered overhang at the end of the layshaft that extended past the rear bulkhead. The whole thing just looked Rube Goldbergish.
Well, I usually use the hydraulic lift on my tractor for pulling up stumps. But if I had any stumps to pull right now, I wouldn’t have any qualms about using this truck to do it.
So, how do YOU remove those pesky stumps from your pastures and/or potential construction sites?
I use to tow a 36 foot gooseneck trailer behind a Chevy C3500 (one ton dually) and I used overdrive all the time. The truck was an '88 and had the 454 with a 4 speed manual with overdrive. Truck and a loaded trailer were well over 15,000 pounds and I never had a problem. I could drive with the cruise control set at between 65 and 70 and only have to downshift on moderately steep grades.
first of all when people say your not supposed to pull a trailer in o/d that only applies to an automatic trany! the reason being is when you pull a trailer with an o/d automatic transmission when going up hills or upgrades it shifts in and out of o/d a lot thus causing a lot of heat to the transmission and its fluids thus causing the fluid to break down and over a period of time (sometimes being very short) will cause the transmission to over heat/ware down! if you are pulling a farely lght trailer and on farely flat ground it may not hurt to shift your automatic trany into o/d after exceding 60-65 mph, now if you do shift into o/d and you notice the rpm of your motor keep rising and falling quite often you will need to shift back into drive or most comenly 3rd to prevent the trany from over working/building excess heat!
Agree completely. Regardless of all other factors, the only thing that matters is that the engine be operating at an appropriate RPM for the desired MPH and weight being pulled. If the engine is happy (not lugging or over revving) it doesn’t matter in which gear the tranmission is operating.
In the latest manual for your truck, there’s no mention of overdrive for trailering, other than in the automatic transmission section. So, there you go.
Its been a few years since it was explained to me (by a very experienced tranny rebuilder), but the issue is the frequent shifting from OD to the more powerful lower gear(s), leading to heating probs and faster wear/tear on smooth-shifting trannies. The slipping of the plates is what makes for smoother shifts (iirc), and going between gears constantly is bad over the long haul. Innards of trannies may be a bit different nowadays, but friction is what makes 'em work, and keeping friction/heat to a minimum leads to longer lives of parts within a tranny.
I remember Neil writing out a lengthy post on this on a different (Mopar/Charger) Forum years ago, but that site is dead now unfortunately. There were some OEM trannies built that could reliably handle the stresses of using OD with added weight of trailering, but it was still recommended by manufacturer not to do so (of course). Monitoring temp of tranny fluid, by a gauge, is best way to know if the tranny is being abused beyond its abilities, IMHO.
