Maxtar wrote: I'm new to the 5th wheel scene and need to know the proper way to use the tranny when towing. I've got a F-350 dually diesel and pulling a rather heavy trailer with a tri-axle set up. When starting out, should the overdrive be off and should I continue driving with it off all the time even at highway speeds? Or, should I start with the OD off and then when I reach cruising speed can I turn it on? I would appreciate some comments as regards this issue. Thanks in advance.
Your question can normally be answered in you owners manual.
RVUSA wrote: The tranny fluid temps rise rapidly when you leave OD off
I found the opposite to be true.
When I was towing 10,000# I let the tranny shift into OD. It did not hunt and temps were OK. When I jumped to 14,000# the tranny would hold OD on the flats, but the transmission temp would creep up. When I locked out OD and force the downshift the trans temp dropped - so I would normally lock out OD towing heavy.
I have had the 4r100 in 2 rv's and now an f350. All 3 have done the exact same thing (not implying yours didnt do as you said). Tranny temps rise when OD is off, tranny temps drop when OD is engaged. It would skyrocket if the OD was off and the torque converter was unlocked.
On the last RV when the temps went over 200 the front seal would leak, and the world was convinced it was on fire. The only way to keep the temps under 200 was to run it in OD and when on grades, stop a lot to let it idle and cool back down.
AZ T&T wrote: I had a 2000 F350 (Fantastic truck!) and had to have the tranny replaced at 35,000 miles. I was told that towing with the overdrive on was the main reason. I was over a 100,000 miles on the 2nd tranny when I sold the truck and never had any problems with it.
I would definitely tow with it off.
I bought the truck used, it has 125,000 on it. The guy had all the maintenancce records and I didn't see anywhere where the tranny had any problems. It runs good and shifts good too. Sounds like I should probably leave the OD off when towing, especially on hilly terrain. I still wonder though, if at highway speed and on flat ground if that might cause any problems with OD on. Did you ever operate like that, with OD off on the hills and OD on on the flats and at highway speed?
* This post was
edited 05/05/12 09:37pm by Maxtar *
I really appreciate all the responses here. Got some sound info about the tranny and towing with it. I just need to get out on the road and see how it all goes.
I will let the Ford guys tell you whether or not to use overdrive, but I'll explain what overdrive is since many people really don't understand what it is.
The old transmissions used to have 1,2,D as gears, with D being "drive". In reality, D was just 3rd gear. The trans would shift from 1, to 2, to 3 as you sped up. D )or 3rd) was always a 1:1 ratio. If the engine was spinning 2000 RPM, so was the driveshaft to the rear wheels.
Nowadays, we have 4, 5, 6, or even 8 speed automatic transmissions in trucks, and several of them can be "overdrives".
The term "overdrive" simply means a ratio above 1:1.
Example is my 48RE in my truck, which has one overdrive ratio.
This means that in 4th (aka overdrive), the engine has to turn only 69% as fast as the driveshaft turns, thereby saving fuel. The new 68RFE that is used in the newer Cummins powered trucks has two "overdrive" ratios: 5th is 0.82:1 and 6th is 0.63:1.
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About the OD or no OD. The fact of the matter is a non locked up converter is slipping plain and simple. A slipping converter will heat up the fluid; a lot. A locked up converter is just that; locked up with no slippage.
That being said it's best to follow the manufactures instructions in almost every case. Sometimes the lockup band is not big enough to hold the load and the manufacture does not recomend you to tow in OD. 700R4 is an example of this.
Above all please do the 6.0 to 7.3 mod. It is a great mod to do and will give your tranny more of an edge to saving it. DO IT.
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About the OD or no OD. The fact of the matter is a non locked up converter is slipping plain and simple. A slipping converter will heat up the fluid; a lot. A locked up converter is just that; locked up with no slippage.
That being said it's best to follow the manufactures instructions in almost every case. Sometimes the lockup band is not big enough to hold the load and the manufacture does not recomend you to tow in OD. 700R4 is an example of this.
Above all please do the 6.0 to 7.3 mod. It is a great mod to do and will give your tranny more of an edge to saving it. DO IT.
Just to clarify. If you turn off OD on the 4R100 transmission, the torque converter still locks up in 3rd gear. OD and a locking torque converter are not one of the same.
RVUSA wrote: The tranny fluid temps rise rapidly when you leave OD off
I found the opposite to be true.
so I would normally lock out OD towing heavy.
Tranny temps rise when OD is off, tranny temps drop when OD is engaged. It would skyrocket if the OD was off and the torque converter was unlocked.
On the last RV when the temps went over 200 the front seal would leak
When the TC is unlocked for sure temps go up. Transmission are different too I guess, since mine will run up to 200 degrees not towing anything. There could be differences in what a switch does too. For mine it just locks out the highest gear - so operating at the lower gears is identical.
I have a 99 Ford F250 diesel. The dealer told me to leave in OD when cruising down the highway and only turn it off when the tranny changes gears often like climbing hills. I also leave it on when going down hills because I have an exhaust brake. When I use the exhaust brake with OD off, it's hard on my tranny. My 5er is about 9000 lbs when loaded.
After a few minutes on the highway, you will KNOW whether you can leave OD on or off. It's not rocket science.
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