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Old 07-25-2007, 08:25 PM   #1
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Ford 150 Over Drive

This year when I purchased my Airstream,the Airstream dealer advised me to always use OD on my Ford 150 when pulling the AS. Is this the proper procedure? It does appear to tow better when in OD.
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Old 07-25-2007, 08:37 PM   #2
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Ah, I'd strongly advise you to get out the owners manual for your model of the truck and to read it carefully! (Our 2000 model F150 manual advises against towing any kind of load in OD.)

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Old 07-25-2007, 08:40 PM   #3
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Quote:
Originally Posted by eubank
Ah, I'd strongly advise you to get out the owners manual for your model of the truck and to read it carefully! (Our 2000 model F150 manual advises against towing any kind of load in OD.)

Lynn
Our F250 has the same advice. In fact, with the manual transmission, it is recommended to tow in 4th gear, rather than 5th. This is even found on the sunvisor of the truck.
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Old 07-25-2007, 09:58 PM   #4
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The only caution in my owner's manual is don't use cruise control.
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Old 07-25-2007, 10:21 PM   #5
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Quote:
Originally Posted by eubank
Ah, I'd strongly advise you to get out the owners manual for your model of the truck and to read it carefully! (Our 2000 model F150 manual advises against towing any kind of load in OD.)

Lynn
I agree, especially if towing in hilly terrain. The only time I used OD on my '01 while towing was on totally flat freeways.
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Old 07-25-2007, 10:28 PM   #6
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We use OD on our E150 unless we are going up a hill and the engine cannot maintain speed.

I have always wondered WHY you are not supposed to tow in OD? Can anyone explain the theory to me?
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Old 07-25-2007, 10:35 PM   #7
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I don't know if the dealer knows anything about towing. Using the OD all the time while towing just doesn't sound right.
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Old 07-25-2007, 10:40 PM   #8
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After towing for a few years using overdrive we had to have our transmission rebuilt in our 1996 Ford Bronco. The transmission shop advised that when towing with the Ford you should always desengage OD.
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Old 07-25-2007, 11:02 PM   #9
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Bit of a hijack here....

Hello all -

Reading all these towing threads, as always!, with great interest. I do however have a chevy (apples and oranges?) - it is a 2500 with all the HD stuff.

Having just completed a LONG 2100 mile cross-country move with SilverToy ('92 34'er) in tow. I can say that I DID tow with OD ON most of the time (cause it lower trans temps according to the gauge) and only used 3rd gear when on REALLY hilly terrain or on the onramps that were uphill. Did use Tow/Haul (Ford has something similar) in a few spots. Again, most were aggressive terrain and at relatively lower speeds. Whenever I did use 3, as opposed to OD, I did see higher RPM's and higher trans temps as a result.

I did a quick calculation, and according to my math I got 10.678MPG accross 2100 miles. ABQ to IAD (Washington DC). Not bad.

I second the question about why OD can't be used more liberally - with the gudicious eye on the temp gauge/ speedo to monitor the constantly crossing/intersecting lines of "best for all situations" situation. Not sure if that last part was clear, but what I guess I am trying to ask is, if I am NOT a dummy following the herd, but am actually monitoring my gauges, am I not doing AT LEAST as well as just using 3 for everything? Will my trans really suffer from my 'abuse' of not using 3 all the way?

Apologise, if I am hijacking, but this question seems to come up again and again, and am looking for perhaps a more clear understanding of the OD question.

Thanks in advance for all thoughts!

Axel
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Old 07-26-2007, 12:17 AM   #10
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That's what I don't understand. It seems to me that OD is just another gear in the tranny, and when selected the tranny will be spinning that driveshaft at the same speed, but the engine will be running lower RPMs. That's the main reason we use OD while towing on the flat, because I don't want the engine running higher RPMs unnecessarily.

Of course, Ford automatics are prone to failure without the added stress of towing, so we might be pushing our luck. In fact, it's going into the shop tomorrow because it's been acting a little weird. Maybe they'll be scolding me for towing in OD!
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Old 07-26-2007, 12:18 AM   #11
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Quote:
Originally Posted by Stefrobrts
I have always wondered WHY you are not supposed to tow in OD? Can anyone explain the theory to me?
let me offer an explanation that others can correct or improve...

i'm not related to or dating an auto mechanic.

assumptions: 4 speed auto/od, electronically controlled, locking torque converter.

3rd gear is a 'direct drive gear' with a 1-1 ratio...

4th gear is a ratio of 1-0.6 or 1-0.7, which means the gearing is 'overdriven' and

allows the drive shaft to spin faster than the engine....

for example in 3rd, if the engine is at 2000 rpms so is the driveshaft,

while in overdrive if the engine 2000 rpms the driveshaft might be spinning at 2800 or 3000 rpms...

(of course final rear axle ratios determine how fast the axles/wheels/tires spin...)

so overdrive allows one to drive at higher speeds, while allowing the engine to operate at lower/idea rpms for fuel economy or torque...

in an automatic transmission there are 'clutch packs' between gears.

these are alternating layers of clutch "disks" and "plates" covered with a film of tranny fluid.

as the transmission shifts through the range of gears, these clutch packs spin, heat up and lock together.

so when shifting up/down between 3rd/overdrive the clutch pack is slipping/locking up...

with each shift up or down this heats up the plates/discs and fluid.

the clutch pack between 3rd and overdrive is usually the smallest in the tranny.

my assumption is that most of the "work" was done moving the load from zero up through 3 gears and beefier clutch packs are needed for these gears.

for example there may only be 5-6 layers in the overdrive clutch pack while the lower gears packs have 8-9 layers.

fewer, smaller discs/plates means more work/heat is generated at the clutch pac when in action.

cruising vs towing or hauling a big load...

normally while driving with minimal cargo the torque converter locks up at 45 mph or so,

and the drivetrain quickly shifts to overdrive as acceration peaks/levels off.

maintain a contstant high speed without bursts of accel/decel and the tranny stays in overdrive....

so the small clutch pack only heated up once or twice on the way to constant overdrive.

with towing, or hauling a heavy load the transmission may start shifting up/down from 3rd to 4th 'seeking' the ideal gear/rpms/torque/power band...

this constand shifting up/down will heat the overdrive clutch pack and burn either the plates/discs themselves or the tranny fluid.

burnt fluid loses lubricity. burnt plates/discs don't engage properly so slipping may result.

modern electronically controlled trannys 'learn' from 100-200 miles of driving behaviors,
so up shifts and downshifts MAY stop after towing a bit into the wind or over hills...

someone please correct my clumsy description of things....

_______________

so back to the 'yes/no use overdrive while towing question...


-read the owners manual
-IF alot of up/down shifts happen while towing, turn OFF o/d.
-if the total mass towed/hauled is close to the gcwr or max towing figure, turn OFF o/d
-if the total mass towed/hauled is small, use o/d...
-if driving alot at higher speeds (while towing) use o/d
-if the hills or HEADWINDS lead to lots of accel/decel, turn OFF o/d...
-if tranny temp gauge shows much temp change with o/d off or o/d on, do the opposite.

one caveat is that most factory tranny temp gauges aren't very accurate...

so if you are serious about this add an accurate/sensitive aftermarket gauge set for tranny, exhaust and oil.

last issue....

even with good gauges, and fresh fluid and minimal signs of temps climbing....

the clutch pack (disc/plates) can overheat/burn up....

since the over drive clutch is smaller,

it must get hotter and go through more heat cycles to heat up the several quarts/gallons of tranny fluid.

so a region could be cooking without the entire mass overheating enough to bump the sensor...

change the tranny fluid more frequently when towing and ask to smell it, for signs of burnt bits....

use a syn tranny fluid, unless the owners manual forbids doing so.

cheers
2air'
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Old 07-26-2007, 06:29 AM   #12
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Od

I would like to tweak on 2airishuman's answer a little bit.
1. The clutches in an automatic transmission are lock clutches, not slip clutches. They must lock up completely in less than 1 revolution. The shock of the sudden lockup is taken up by the torque converter.
If they slip more than that you have critical problems and will be burning the surface material off the clutch plates very quickly.
2. The torque converter in the automatic transmission is the heat producing module. When it locks 95% or so of the heat production ceases. That is why the TH700R4 (4L60 and 4L60E and probally 4L80 series as well) has a temperature switch that will automaticlaay lock up the torque converter if the transmission fluid get too hot(even though by that time the fluid is heat damaged).
3. If your tow vehicle runs hotter with the overdrive locked out check to see it the torque converter is actually locking up, also have a mechanic check the engine for things like proper timing etc. Late ingition timing or lack of advance will cause overheating at higher RPMs.
4. I have two friends that own transmission shops. According to them no overdrive should be engaged while towing. They have hardheaded customers that insist on towing in overdrive (GM, Dodge, Ford, jury still out on Nissan and Toyota) and they end up with a rebuilt transmission about every two years (OD unit replaced entirely every rebuild).
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Old 07-26-2007, 06:30 AM   #13
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In a shop I worked in, we got about 3 trucks a month in with burned up (a couple literally) transmissions. The common denominator in these cases was carrying heavy loads, or towing a heavy trailer in Overdrive. I still have the remains of one O/D clitch pack on my desk, it is a blueish fused hunk of metal and friction material. Not only, as 2 air says, is the overdrive clutch pack the smallest in the transmission, it also has the smallets bearings keeping everything moving.
Back in the good old days when I was in the R/D end of things, it was decided that if the load carried/towed was more than 1/2 the rated load for the truck, Overdrive should not be used. There is just not enough surface area in the overdrive mechanism to radiate the heat generated by overloading it, plus the overdrive assembly is furthest away from the cool, "fresh" transmission fluid entering from the cooling lines.
I have also found very little difference in fuel consumption towing with overdrive on or off, the engine revs higher in 3rd, but works harder, albeit slower, in 4th (or 5th, if equipped). With the cost of a transmission rebuild fast approaching $3,000, it is best to heed the vehicle manufacturer's recommendations.
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Old 07-26-2007, 07:49 AM   #14
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I have a chev. duramax diesel with the Alison transmision. I have 4 gears and one overdrive. I cant control when it goes from 4th to O/D but sometimes I wish I could. The computer controls it. If I manualy drop to third its way to high of RPM. Are the new transmisions just a diferent beast than what you guys are talking about?
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