Yes, very good posts. I like Terry's 50% rule, that make's it pretty much a binary decision for me--OD off.
I have experimented with OD on and off and find that were only talking about one mpg difference on a flat wind free highway. I'd have to drive a lot of miles to save enough from that one mpg to cover a $3,000 transmission rebuild.
Towing my 23' makes my truck downshift from OD to third on as little a grade as an interstate overpass here in FL. So, even if I wanted to tow in OD, I'd always be switching it off before the overpasses. It's easier to just leave it off.
Randy
__________________ Randy and Pat Godfrey
2nd VP Florida Unit WBCCI# 7591 - AIR# 17017
2007 Safari SE 23' - Daisy
2006 Lincoln Mark LT - Hoke
My van's problem turned out to not be tranny, it was a bad u-joint - so that's a relief!
So using Terrys 50% rule, I guess I'm probably still ok. I have a 2800# trailer fully loaded, and a 6600# towing capacity. Because of the big truck/small load, I guess I'm ok. I still switch OD off when necessary, but I think on the flat it's ok to leave it on. I'm not worried about milage (it's the same towing or not), just that it's annoying to hear the engine running higher than it needs to.
I have almost the same Question. We are just now lookinf for our first AS .We have 2001 F350/7.3liter /Harvester Diesel/Allision Tranny. This is a monster tranny.What about this setup, Are we in danger of loosing a tranny if we tow in OD?
Your monster truck would probably pull any Airstream and not notice. However, I would think the same advice applies. If it's downshifting out of OD to pull hills and bridges, it's generating heat. If it's doing that a lot or hunting for the right gear, I would switch off OD.
Randy
__________________ Randy and Pat Godfrey
2nd VP Florida Unit WBCCI# 7591 - AIR# 17017
2007 Safari SE 23' - Daisy
2006 Lincoln Mark LT - Hoke
Randy Thank You
Kinda figured that would be the answer. Its good advise for everyone("If the tranny is searching for the correct gear ("TURN OF THE OD")I do listen to that Power Plant Randy,seems Ive driven desiels all my adult life(45 yrs OTR) from the 2cycle Detroit Desiel to CAT 855 CI Monsters.
We continue our search for just the rite AS. ,the truck is ready with brake controller mounted and the equilizing hitch in the warehouse,now to find the correct AS to go with this combo.
Thanks Randy
Roger
I'll make a couple of points that relate to the overdrive issue:
1. If you ride a pedal cycle with gears up a hill, and you are in too high a gear, you will feel a huge strain in your legs. Change down, pedal faster and you will feel less strain. That is a rough and non-scientific analogy which shows the extra strain you are putting on a transmission by risking using the overdrive.
2.By definition, in overdrive, the output drive from the gearbox is turning faster than the engine. If you strip down and dismantle a simple manual gear box, you will see that in top gear (not overdrive), the engine is coupled solidly and directly to the prop shaft connected to the back of the gearbox. There are no intermediate toothed gears which can break, or whose bearings can fail. When overdrive is engaged, the power is transferred across to a parallel shaft in the gearbox. The receiving gear has less teeth than the transmitting gear, so it rotates more quickly, and at the other end of this shaft, the drive is transferred back to the output shaft by another pair of meshed gears. You can see that in top gear, there is far less to fail. Overdrive units are inherently weaker because they introduce a complex path for the power, and this path is weaker than the direct physical connection in top gear. That has been the case in the simple manual gearboxes I have overhauled.
Those two reasons cause me to avoid towing in overdrive.
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
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