I have a '97 F 250, 5.4, 3.73, with trailer towing pkg. I am towing an 8000 lb. trailer in a frequent moderate hilly area. I have started to tow in overdrive after I have gotten to 60mph. The truck will stay in od until about 1600 rpm and down shift. I'll switch to 3rd untill I reach 60 and then back into od. With a run I can climb the hills in that gear until the rpm slows to 1500 rpm, or so, when , I again, turn off the od. I do not experience trans hunting with this method, and to my understanding of the owners manual, this should be ok. Is there anything weak about 4th gear that I shouldbe concerned with? Again, the trans is not gear hunting, and the engine temp is in the lower 1/3 of operating temp. Anyone with a suggestion or info on this, please reply. thank you, gdblake

[This message has been edited by gdblake (edited 08-10-1999).]

[This message has been edited by gdblake (edited 08-10-1999).]

 

My Owner's Manual tells me to turn off OD if it shifts up and down frequently (towing or not). It's OK to tow with OD as long as it's not shifting in and out frequently.
I turn mine off when it's hilly and back on when it's flat.
Hope this helps.

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1999 F-250 XLT Super Duty Crew Cab Long Bed
V-10, Automatic 4R100, 4.30 Limited Slip.
GVW = 6700# Towing Capacity = 13,300#
4 Wheel ABS disks + Reese 15K hitch
Dark Hunter Green. Ford Running Boards.
Grey Rhino-Liner. Captain's Chairs. CD+Tape
Polished Stainless Steel Wheel-well Molding http://members.home.net/jchartier/jnctrk.html

 

J-C has the right idea. I would also add that the time to turn OD off is when you find yourself mashing the gas pedal down and the truck isn't accelerating. At this point, the tranny will drop out of OD and downshift, sometimes abruptly. To my way of thinking, that's too late. As soon as I notice the truck slowing even with increased pressure on the gas, that's the cue for me to turn OD off.

Lugging the engine is not only bad, but will decrease your mpg.

[This message has been edited by Dennis (edited 08-12-1999).]

 

nomo,J-C,@ Dennis--thanx for the reply. I was concerned about 7.5 mpg towing in 3rd during my first 2 trips, I'd like to use od when possible-but as you say--gas is less expensive than transmissions. I would appreciate any other thougths on this. Shifting into 3rd upon first feel of sluggishness upon acceleration is a great idea! I'll do it.--thanks again.

 

It sounds like you are simply delaying the upshift to OD once the tranny hunts 3rd. If so, then not only is the tranny slipping, but the engine is "lugging". Neither of these things are good for longevity. The heat build-up occurs in the tranny, not the engine. So, without a temp guage on the trans., you won't see the effect of towing in OD.

I prefer to tow with OD off. The cost of a new transmission and the associated "down time" can buy a lot of gasoline.

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1997 4x4 Expedition- 4.6L, true dual exhaust w/glass-packs, K&N air filter, SuperChip, airbox mods, Edelbrock shocks, 285/75R16 BFG ATs, Optima "T-Bone" wheels, and Clarion In-dash CD player.

1993 4x2 F150 Reg. Cab LWB- 5.0L, cat-back dual exhaust w/glass-packs, K&N air filter, Superchip, fresh paint, and Line-X bedliner.
http://members.visualcities.com/NoMo

 

gdblake,

It looks like you have the wrong diffrential ratio to properly match the load you are towing. A 3.55 would probably be a better choice and keep the OD off. The 3.73 is a little too many rpms for the job and in OD not enough rpms to do the job. And with the 3.55 while not towing you would get a little better fuel economy in OD.

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97 4.6 F150, 1/4 = 17.48 @ 82.2 mph, 88 5.0 Mustang 1/8 = 7.409 @ 93.72 mph

 

Thanks for the reply--LarryS--The only other choice for the ld F250 was a 3.31 and that was not available with the tr tow pkg.

 

You would have to get the 3.55 installed at a performance shop or I am sure your dealer could do it. You might go through the calculations and see if the 3.31 would do it also if you know what rpms it takes at the speed you drive to achieve the torque then the formula for rpm is mph x transmission ratio x diffrential ratio x 336.14 divided by tire diameter. For example, with your 3.73 gear at 60 mph in OD (.7 ratio) your rpms would be: 60 x .7 x 3.73 x 336.14 divided by 28 = 1880 rpm. This is assuming you have the 235 70 16" tires which are 28" tall. With the 3.31 in 3rd you rpms would be 2384. This might be just right for your load and not near as high as the 3.73 in 3rd. If the 3.31 is offered from the factory then I know the dealer could reprorgram for the 3.31 and make your speedometer correct. Good luck.

[This message has been edited by LarryS (edited 08-19-1999).]

 

LarryS--Thank you for the reply and the math on calc rpm's

 

Your welcome. And let me know what you decide to do.

 

I agree with the 3.55 and O/D off pulling. I have a '98 F150 4x4 Off Road 5.4 Regular Cab, Short bed, and frequently pull a relatively light trailer of around 3,000# and in O/D at 60 m.p.h or up it will hold it but not accelerate very strong. After my cousin told me all about replacing his tranny and not to pull in O/D I've just decided to give a few m.p.g up and pull in 3rd. It's at about 2400-2800 from 60 to 70+, accelerates very strong without shifting and holds speed easily over bridges, etc.

 

Thanks for the reply, LarryS and PNUTFISN. I very much appreciate your responses.