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  1. #1
    Fleet Admiral jtexas's Avatar
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    Default Towing in overdrive

    I noticed in another thread several posts advising to never tow in overdrive. I know it's been covered before but if we could just clarify:I been led to believe that:* The OD gear is a mechanical link to the engine, vs a hydraulic link in the lower gears, and therefore easier on the tranny and the fluid.* Shifting is what builds heat and * as long as the car shifts into OD & stays there, towing in OD is better for the trans than towing in Drive.In town, in heavy highway traffic, and in hilly country I always turn OD off, but I ordinarily cruise in overdrive.Agree? Disagree?thanks,jtw
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  2. #2
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    Default Re: Towing in overdrive

    Just my opinion here, but the manual on my 1994 K1500 says to not use OD while towing. Fast foward 11 years and 142,000 miles and the original transmission is still with me and going strong [knock on wood].I don't have the mechanical expertise to know whether it would be OK to use OD. I simply do what the book says and it has so far worked out. How's that for a non-answer?

  3. #3
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    Default Re: Towing in overdrive

    Follow manufacturers guidelines. That being said, I tow in OD as long as the tranny isn't shifting in and out alot. In stop and go traffic OD is off.

  4. #4
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    Default Re: Towing in overdrive

    jtexas, I agree with you. 142,000 on an auto that tows is very good, so you must be doing it right. We won't even get into gear ratios, RPM's, speed limits, terrain, etc.
    Lake Shasta with Mt. Shasta in the background, June 2011


  5. #5
    Moderator JB's Avatar
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    Default Re: Towing in overdrive

    Good point, JTex.In some (not all) automatic OD transmissions the converter is locked in OD. On others it may lock in any gear or only the top 2 or 3 gears. You are correct that IF you have this transmission the tranny runs cooler when the converter is locked. These vehicle manuals usually don't tell you not to tow in OD.Then there is torque loading the engine at less than peak-torque RPM. That can be bad for the engine with a heavy tow. If you are anywhere near the tow rating lock it out.With manual trannys the OD gear ratio assumes highway speed with no tow. Towing anything near the rating will overload the drive train and engine in OD. Mfgs almost always say don't tow with a manual tranny in OD.Good luck.

  6. #6

    Default Re: Towing in overdrive

    I was told by a mach. that even if you are OD and it is not shifting you still should take it out. He said that the plates and gears are still slipping and causing damage just not enough slip to shift out of OD. I had a friend who toad alot and had to replace trans. @ 80,000 and they said it was because he used OD while towing @ high speed even though he did shut OD off in ctiy driveing. I fill pay extra in gas and take out of OD and save the trans

  7. #7
    Supreme Mariner Silvertip's Avatar
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    Default Re: Towing in overdrive

    SCS - if the mechanic you talked to said gears and plates are slipping in OD, don't let him near your tranny. There is considerable misinformation here. The only time an automatic transmission slips is during the shifting process. All other times slippage only goes on in the torque converter (just like it does when you sit at a stop lite) and even that is eliminated when the converter locks up. Nearly every automatic transmission already has a cooler built into the radiator and its there to make sure the fluid stays at a uniform temperature -- in northern climates you can overcool. Addition of an external cooler is only required if you are pulling extremely heavy loads with lots of starting and stopping and/or city/hilly terrain where shifting has to occur. Towing in or out of overdrive depends on a number of factors and is not a "must always" situation. The most important is knowing what the axle ratio is and secondly what load you are towing and how the transmission behaves. Towing too heavy a load with too low an axle ratio causes frequent shifting and can cause engine overheating whether or not OD is used. There are simply too many mismatched tow vehicles out there. That's why various ratios are offered. Deeper gears (higher ratios) are better for towning -- period. For those that are math challenged 3.0:1 is a lower numerical ratio than 4.1:1 so don't confuse low ratio with lower gear. If the transmission does not hunt (repeatedly downshift or require the converter to repeatedly lock & unlock) it is ok to tow in overdrive assuming engine temperatures stay normal. Even if the converter unlocks periodically that's not a problem so long as its not unlocked for a prolonged period. Few people can tell when this happens unless they have a tach and even then they often mistake that action as a transmission shift. Overdrive shifts result in approximately 18% RPM change whereas a torque converter unlock will see about 800 RPM change. You can check this by maintaining a steady speed (55 - 60 MPH) and then just barely touch the brake pedal. You will see the tach rise as the converter unlocks. There is absolutely no difference in towing in overdrive than there would be towing in fifth overdrive or fourth direct in a standard transmission. Nothing is slipping except as pointed out above and that's what the tranny is designed to do. At age 65 I've probably logged more tow miles than most folks on this board and I've never lost a tranny -- but the key is know when its ok to tow in OD and when its not. I routinely run all of my tow vehicles in excess of 100,000 miles and never have a problem (all GM if that matters).

  8. #8
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    Default Re: Towing in overdrive

    Upinsmoke, Good Job explaining it.
    Lake Shasta with Mt. Shasta in the background, June 2011


  9. #9
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    Default Re: Towing in overdrive

    Yes thanks, I have a 03 F150 with OD and have been locking it out when "when I remember" must of my towing is on the freeway and level so not much shifting going on. RPM are much lower and the motor is not lugging so I don't worrie too much about OD or no OD.

  10. #10
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    Default Re: Towing in overdrive

    Did one 50 mile trip w/ OD on the Mountaineer w/ trailer. Actually lost 0.7 MPG as without OD. Hated the accel on mild grades too.

  11. #11
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    Default Re: Towing in overdrive

    Follow your owner's manual. In my "modern" (newer than say, 1994) cars, it specifically says to tow in OD. My belief is that these are computer operated transmissions and are best served by putting the tranny in OD and letting the computer decide when to shift. My older (86) chevy P/U, I believe says to tow in drive (or 3rd?), not OD. My newest Suburban has a "tow/haul" switch which makes everything very easy! (if I remember to use it). It changes the shift points and also makes the shifts more abrupt/hard. Keeps the revs up and avoids much of the slippage in the smoother, normal shifting.

  12. #12
    Lieutenant rwidman's Avatar
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    Default Re: Towing in overdrive

    My vehicle's manual advises to disable overdrive while towing. Now if I were towing a couple thousand pounds on level ground I might decide to ignore this advice. Since I am towing at the limit of my rated towing capacity (7,000 lb), I disable overdrive for towing.I suggest following the advice in the tow vehicle owner's manual.
    Ron

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  13. #13
    Supreme Mariner Silvertip's Avatar
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    Default Re: Towing in overdrive

    The key to OD or not OD is to know what your vehicle is doing. If the torque converter continually unlocks and locks, or the tranny shifts from OD to D frequently, those are signs you better pop it into D.

  14. #14
    Fleet Admiral Mark42's Avatar
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    Default Re: Towing in overdrive

    I tow in O/D in my 97 Mountianeer 5.0 AWD with no problems. But I probably tow a much smaller boat than most of you folks. In the Mountianeer, you hardly notice the 1200lbs behind you. I am very aware of the shifting and locking behaviour of that trans and it seems to not be affected by the trailer. I just accelerate slowly, and let the truck make its own shift decisions. On long trips I find my speed creaps up to 70 - 75 before I catch myself and coast back down to 60 - 65. I do think it uses more gas towing but I have not checked. We have 150K plus miles on that truck. Its a truly great machine.
    1985 Bayliner 1600 Capri Cuddy, 1965 MFG Niagara Custom. >> MFG Video<<. >> MFG Project<< >>Bayliner Hard Top Project<< >>Bayliner Repower Project<<


  15. #15
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    Default Re: Towing in overdrive

    Give this a try next time you tow. Find a long flat stretch and set your cruise control at 55 with your tranny in OD. Now put your foot lightly on the accelerator. Now shut off the OD. You will find the accelerator actually backs off just a little even though you're still running 55. Less pedal...better economy.'96 F150 351W 3.55 rear E4OD tranny pulling Monterey 256 8080 lbs

  16. #16
    Supreme Mariner Silvertip's Avatar
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    Default Re: Towing in overdrive

    If you are towing 8080# at 55 MPH in overdrive with 3.55 gears you should not be in OD period. At that speed the engine is way off its torque peak. In OD that 3.55 ratio becomes 18% less so you are at an effective ratio of 2.93:1 which is hardly conducive to effective towing. When we talk about towing in OD we are talking about much less weight (up to about 4,500#) and freeway speeds. Vehicles set up for towing generally have a minimum of 3.73 gears or deeper. It takes alot of horsepower to compensate for a poorly chosen rear axle ratio. That's one of the biggest mistakes people make when buying a tow vehicle. Trust your sales person and you will certainly be disappointed because he/she has probably never towed a trailer in their life.

  17. #17
    Fleet Admiral Mark42's Avatar
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    Default Re: Towing in overdrive

    The Mountianeer has 3.73 gears, and in od 60 mph is 2000 rpm. Does that sound too low an rpm?
    1985 Bayliner 1600 Capri Cuddy, 1965 MFG Niagara Custom. >> MFG Video<<. >> MFG Project<< >>Bayliner Hard Top Project<< >>Bayliner Repower Project<<


  18. #18
    Supreme Mariner Silvertip's Avatar
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    Default Re: Towing in overdrive

    Depends on what load you are towing but you are probably ok. Again, as long as the tranny doesn't continually unlock the converter or drop out of OD, you are ok. My boat and trailer with all the gear is crowding 3000# and my S10 crew cab with 3.73 gears handles OD just fine. I can cruise effortlessly at freeway speed and there is only one long hill on my usual route that the tranny will come out of overdrive on. On a hilly road with a 55 MPH speed limit, I'll pop it out of OD.

  19. #19
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    Default Re: Towing in overdrive

    Originally posted by Mark42: The Mountianeer has 3.73 gears, and in od 60 mph is 2000 rpm. Does that sound too low an rpm?
    That combo won't even know 1200 lbs is back there. Your 5.0 should be making good torque at 2000 rpm. Your boat is also probably pretty small and doesn't add much aero drag.

  20. #20
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    Default Re: Towing in overdrive

    There is so much malarkey being thrown about here. I am a professional mechanic, and even though I'm not a tranny guy, I know enough to ask someone who is. No tranny shop with a good reputation will tell you to tow in OD unless you have the Tow/Haul option. If your owner’s manual say it's ok, then it's ok. Otherwise kill the OD, or kill the tranny. Best bet is to ask around and get the name of two or three REPUTABLE tranny shops. One that specializes in trannys. Ask them and then follow their advice. If you get contradicting advice, question why. A local rebuilder who is state, and ASE certified and who teaches at the local University Center tells me DON'T TOW IN OVERDRIVE, EVER!!!!! Except with TOW?/HAUL turned on, and then it's questionable.Ask the experts, the reputable experts. They see the inside of trannys that failed, and can know why. Who else on here has seen the planetary gear set? Or a smoked clutch pack? A warped case? A valve body? How 'bout an auto trans clutch pack? If your heart doctor said "Don't lift or pull more than 25#'s,", who would you listen to? Him/her or posts on hee telling you it's ok, as long as you fell ok. Who's the educated one? The expert?And Upinsmoke's long post was almost scary to read. I am sorry UIS. Whereas it was technically/theoretically correct, it was in actuality WRONG! Yes, the clutch packs lock up and the torque converter clutch locks up too. But since there is only a friction connection between the clutch's, when you over-torque those clutches, there will be slippage. That is what happens when you tow. You are severely torquing those clutch packs, sometime to their limits, sometimes over their limits. Will you know when you've exceeded the clutches' friction limits? The heat created is mostly from the torque converter slippage. But the fluid still flows though the rest of the engine and is what is used to engage the clutch packs. So there is heat generated elsewhere as well. Again UIS I'm sorry to slight you. You are correct about how a trans works properly, but when it is stressed, all bets are off. The difference between book learnin' and the real world.

  21. #21
    Master Chief Petty Officer
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    Default Re: Towing in overdrive

    Originally posted by Mark42: I tow in O/D in my 97 Mountianeer 5.0 AWD with no problems. But I probably tow a much smaller boat than most of you folks. In the Mountianeer, you hardly notice the 1200lbs behind you. I am very aware of the shifting and locking behaviour of that trans and it seems to not be affected by the trailer. I just accelerate slowly, and let the truck make its own shift decisions. On long trips I find my speed creaps up to 70 - 75 before I catch myself and coast back down to 60 - 65. I do think it uses more gas towing but I have not checked. We have 150K plus miles on that truck. Its a truly great machine.
    You are very aware of what that 5-spd auto is doing? Good for you. Every time I've ever test driven one, it's been hard to tell when it shifted. A good charactersitic. And you obviously pay attention to your vehicle. GOOD FOR YOU!

  22. #22
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    Default Re: Towing in overdrive

    Ah,10-4 DLM, good to have another OD expert aboard
    Lake Shasta with Mt. Shasta in the background, June 2011


  23. #23
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    Default Re: Towing in overdrive

    As someone that pays warranty claims, I'll add this.1. Follow the owners manual. The people that designed it know more about it than you do.2. The real test, if the manual says it's OK, is: If the transmission does not "hunt" (shifts in and out of OD with light throttle pressure) it's OK.Most transmissions develop far more heat in the non OD mode than they do in OD. Why? The torque converter is designed to slip (torque amplification). Slippage creates heat in the fluid. In the OD mode, the torque converter is locked and power flows directly through the transmission, not unlike a manual trans.Most "tow/haul" modes do nothing but increase line pressures and change shift points. The transmission works exactly as it does in the normal drive mode except for the properties mentioned above. Ratios are the same, torque converter lock up is the same, just applied later. Tow/hual modes are for increased acceleration and offer engine braking in all ranges.

  24. #24
    Vice Admiral snapperbait's Avatar
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    Default Re: Towing in overdrive

    Speaking from experience (i've blown up a few of em'), the 4th gear clutch pack in a GM 700R4/4L60 transmission is the smallest clutch pack both in diameter and in the number of plates and steels in the transmission... Lock the converter or don't lock it, it does not matter because the 4th/OD clutch pack does not have the holding capacity for any significant extra weight.. Load it in OD, eventually it is going to slip, period....Best bet on a 700R4/4L60, lock the converter in third...
    I don't give interviews, and I'm no longer a public figure..

  25. #25
    Supreme Mariner Silvertip's Avatar
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    Default Re: Towing in overdrive

    Weight has nothing to do with it. Its the engine torque that clutch pack has to handle and it doesn't which gear you are in. If it can't handle maximum engine torque, then there is a design flaw. The engine and transmission management systems determine when shifting is necessary. If that system continuously tells the transmission to lock/unlock, or pop in and out of OD, then its best to be in third. It's the heat created by the constant up and down shifting that destroys clutch packs.

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