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Old 06-17-2019, 05:45 PM   #21
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My Chevy does not have an overdrive button - instead gears 5 & 6 are overdrives. The only choices are whether or not to turn on tow/haul - or when going down hills, to manually downshift.
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Old 06-24-2019, 05:33 AM   #22
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I have always towed with overdrive on. I have a scan guage to monitor transmission temperatures, if it starts to get to hot or shifts to much then I will lock out overdrive. JMHO
Heat kills transmissions. Agree with the scan gauge and monitoring.
From what I heard from a seasoned transmission guy of 40 years is that you should judge how you tow with the particular transmission you have and not a general statement. I had our old Trailblazer transmission rebuilt at 250,000 by him. He asked me all about how and what I was towing and then told me to use O/D in future as that particular transmission was better that way.No issues after that until the Trailblazer rotted around a great performing transmission
Nothing wrong with an additional tranny cooler as well in my opinion.
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Old 06-24-2019, 05:45 AM   #23
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Out on the flats on Hwy or Interstate, I'm running with Cruise ON and OD..(tow/haul mode) not locked....(OFF) Goes into 6th gear and rarely downshifts unless on a longer hill. Lower RPM = Higher MPG.
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Old 06-24-2019, 06:30 PM   #24
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I trashed one transmission towing in OD. Not gonna do that again. While I agree that on a level run, stress on the OD would be minimal, those would be the exceptions.
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Old 06-25-2019, 09:37 AM   #25
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With a 4 speed OD transmission, the transmission will run cooler and be far less prone to slip, if you do not use overdrive. My last TV was a 4 speed chevrolet, I always towed in D3, never had a transmission problem.
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Old 06-25-2019, 09:42 AM   #26
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With a 4 speed OD transmission, the transmission will run cooler and be far less prone to slip, if you do not use overdrive. My last TV was a 4 speed chevrolet, I always towed in D3, never had a transmission problem.
My last TV was a 4-spd GMC. I always towed in Drive (allowed OD) and I never had a transmission problem.


Maybe our experimental data cancels each other out.
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Old 06-25-2019, 09:56 AM   #27
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The tow/haul button is on there for a reason. If a mechanic tells you you don't need it get it in writing so they can replace the tranny for free. Heat kills and it kills very quickly!
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Old 06-25-2019, 10:00 AM   #28
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The tow/haul button is on there for a reason. If a mechanic tells you you don't need it get it in writing so they can replace the tranny for free. Heat kills and it kills very quickly!
You may be speaking to someone's intermediary question but the original post asked about overdrive, not tow/haul. My tow/haul does not lock out overdrive (the top 2 in my 6-spd) although for some trucks, it does.
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Old 06-25-2019, 10:44 AM   #29
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In the past the od switch simply looked up the torque converter for better mileage. The torque converter is in a sense a clutch.

By disengaging, it prevented the transmission from hunting. Shifting in and out of overdrive often. Damaging to,the transmission.

Modern transmissions have computers to control that. In the old days it was up to you.

So if pulling a not max load on flat ground, the od is great. If the trans is hunting, then it needs to be locked out.

On a diesel truck pulling a big load the tow haul mode locks out sixth for better operation. Lower temps. Less hunting.

Watch the transmission temp gage. Try it out both ways.

Transmission repair is north of $3000. Improving mileage saves a few bucks.
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Old 06-25-2019, 10:52 AM   #30
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You may be speaking to someone's intermediary question but the original post asked about overdrive, not tow/haul. My tow/haul does not lock out overdrive (the top 2 in my 6-spd) although for some trucks, it does.
Yep... I'll reiterate again for those not following along...

A modern tow/haul button and the older O/D on-off button are two horses of a different color.

You cannot compare apples to oranges and give generic advice about both.
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Old 06-25-2019, 11:00 AM   #31
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Yep... I'll reiterate again for those not following along...

A modern tow/haul button and the older O/D on-off button are two horses of a different color.

You cannot compare apples to oranges and give generic advice about both.
This is correct!
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Old 06-25-2019, 12:01 PM   #32
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I have an 08 F150 and pull a 4000lb loaded camper. I always pull with OD off. RPM are a bit higher but it is still reasonable at 2500 RPM at 60-65 mph. I'm not an expert, but the shifting and OD slippage can not be good with a load. We have towed at least 15,000 miles and through the Rockies OK. 150K on truck as of today.
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Old 06-25-2019, 12:15 PM   #33
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Originally Posted by Mr. Dan View Post
My last TV was a 4-spd GMC. I always towed in Drive (allowed OD) and I never had a transmission problem.


Maybe our experimental data cancels each other out.
Hi, Mr Dan.
I'm certainly glad that you never had a problem, but I've got more than experimental data. I was a transmission technician at a GM dealer for many years, after which I provided technical assistance to GM dealer mechanics, as a GM contract employee. While I was in the dealership, we advised, on the recommendation of GM engineers, that customers did not tow heavy loads in OD. I repaired or replaced some number of them due to towing in OD.
Any time power flow goes through a gearset, heat is generated. In third, D3, power flow in is power flow out. There are no working gears. In overdrive, the overdrive ratio is generated by using one of the planetary gear sets, so operating in overdrive inherently creates more heat. Additionally, every time there is a shift, there is a certain amount of slip. The overdrive band releases, some slip there, and the one way roller has to take the power, again, slight slip. Anything slipping creates heat. The real issue is that torque capacity in 4th (OD) is not as great as in D3. When in D3, there are 2 clutches applied, the 3-4 clutch and the overrunning clutch, both holding the same parts. In OD, the 3-4 holds one part, the 2-4 band holds a different part, torque capacity is reduced. If there is slight slip under load, it is not likely to be noticed until you see the fluid and the smoke coming out the back. At that point the transmission needs major repair.
OK, enough technical babble, but it does inherently have higher torque capacity, and runs cooler, in D3.
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Old 06-29-2019, 04:44 PM   #34
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I towed a 5500 lb camper with a 2006 F150 5.4L with 3.73 gears. I found the 5.4L was a very capable towing engine. I never saw over 3500 rpms (a couple of "surprise" downshifts), with about 3000 rpms the norm in 2nd gear pulling bigger hills at 55 mph. I could have gone faster, but I saw no need to rev the engine just to get to the top a bit faster. I just sat back and enjoyed the scenery with the big trucks. I read where so many people make their engine scream just to go fast.

On level road, the 5.4L did a great job of pulling in OD (4th gear) unless there was a heck of head wind. In rolling hills, if the tranny downshifted, I turned off OD.

Concerning the comment that torque converter locks up just in OD, I saw the torque converter lock up in 2nd, 3rd, and 4th monitoring a ScanGauge II. Usually the 1st downshift felt was actually the torque converter unlocking.

I think the 2006 F150 owners manual stated something like: "Tow in OD unless the is transmission is downshifting frequently"........or something like that.

1 thing I did not do is engage cruise control in OD after a few pulls trying that. The cruise control would call for too much gas, causing the tranny to downshift, where I could feather the right peddle so that would not happen. If I wanted to use cruise, then I would lock out OD.

Hope this helps.
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Old 06-29-2019, 05:02 PM   #35
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Not sure if this is responsive or relevant, but with our 2018 Chevy 6.0 w/4:10 I believe the upper 2 gears of the 6 spd transmission are OD ratios. Except for downhills or >= 6% grades, we just engage tow/haul and let the computer figure it out. For the exceptions, we do things manually.
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