O/D off switch

[PORCHDOG]

I have a W24 and I guess a 6 speed Allison transmission. My question is how do I best use the O/D off switch? I have read the manual and I am now confused. I have been driving in the #3 position (top pushed in). Will that give me the best gas economy?

[edgray]

If you have a 6 speed, then the switch should be a three position rocker. When in the "midlle" position you are preventing the tranny from going to 6th gear which will permit the lowest rpm at hwy speeds, and should yield best MPG. When you have the switch in the lowest position (4th gear max) you should see a light on IP showing "O/D OFF". The simplest thing to do is put it in the highest position (6th gear) and forgitaboutit. Ed

["007"]

We have same engine different chassis. I drive in Cruise Control mode most of the time with OD switch on. Runs around 2000 RPM and shifts very little even on low hills.
Only time I take it off is on down grades and shifting gears down for braking.
Would think yours would run the same only with a extra gear and maybe a grade brake system on your engine.

[Gotta_P]

I leave mine in the O/D On Position (Enables 6th gear) all the time and let the tranny do it's thing... It will select the optimal gear for the given circumstance. I only engage the Grade brack whn in hilly terrain, otherwise, I leave it off...

[DriVer]

Quote:

Originally Posted by Gotta_P I only engage the Grade Brake (TGB) when in hilly terrain, otherwise, I leave it off...

Paul, You can leave the TGB engaged 24/7. It only works when it needs to unlike a Jake brake when you take you foot off the throttle is calls for the engine to retard. When you tap or step on the brake when the vehicle is fairly straight and level the TGB won't function.

I turned on my AUGB (aftermarket) and I have not turned it off since day 1 unless I was just checking something.

Slowing your vehicle at all times is possible by turning the O/D OFF however it does not usually bring in enough compression via the gearing to slow the vehicle significantly. One is better served when exiting the Interstate at speed to just grab a lower gear via the select shift method. Leaving the O/D switch alone will assure that you will always be in O/D when the schedule calls for you to upshift back to cruising speed and you have up-shifted back to 4th from the lower gear.

[Gotta_P]

Quote:

Originally Posted by DriVer Paul, You can leave the TGB engaged 24/7. It only works when it needs to unlike a Jake brake when you take you foot off the throttle is calls for the engine to retard. When you tap or step on the brake when the vehicle is fairly straight and level the TGB won't function. I turned on my AUGB (aftermarket) and I have not turned it off since day 1 unless I was just checking something. Slowing your vehicle at all times is possible by turning the O/D OFF however it does not usually bring in enough compression via the gearing to slow the vehicle significantly. One is better served when exiting the Interstate at speed to just grab a lower gear via the select shift method. Leaving the O/D switch alone will assure that you will always be in O/D when the schedule calls for you to upshift back to cruising speed and you have up-shifted back to 4th from the lower gear.

Mike,

Thanks for the tip! I was leaving it on 24/7, but it seems to downshift even if I am on level ground and just tapping the brake a bit to slow down a couple of mph's. I would like to leave it on all the time because with the white lettering against the tan upolstery, I can never remember which switch is the grade brake, and don't feel comfortable sticking my head down below dash level to read it!

Maybe the aftermarket GB works slightly different from the factory model, I don't know, but I do know it will down shift every time I tap the brakes, and many times I don't want it to!

I also noticed the tranny will automatically downshift and apply some engine braking as I slow down for a traffic light, almost like it knows to downshift as the speed lowers. This is with the Grade Brake off and even pressure on the brake pedal. I think this is pretty cool!

[ron55]

So I don't have to turn off my Over Drive when down shifting? I have always down shifted manually at every stop and going downhill to save my brakes.

[DriVer]

Quote:

Originally Posted by ron55 So I don't have to turn off my Over Drive when down shifting? I have always down shifted manually at every stop and going downhill to save my brakes.

ron55, using the OD OFF technique to slow down IS effective when you need to scrub a little speed perhaps when you are closing in on some traffic ahead of you on the Interstate OR other non demanding situations.

When and IF you need to "Whoa!" Grab a gear there driver and make something happen. Going from .71 to 1.0 isn't at all very much compression. Now go from .71 to 1.41 or 1.81 and now you're talking some slow down.

I'll tell you what "MY" biggest problem is sometimes, I forget to toggle the OD back ON and I sit there and watch my RPM hover wonderin' what's wrong!

So now if I need to slow a lot, I grab a gear and leave the OD where it is.

[edgray]

Quote:

Originally Posted by ron55 So I don't have to turn off my Over Drive when down shifting? I have always down shifted manually at every stop and going downhill to save my brakes.

RON:
Think of it this way... the OD switch ONLY prevents upshifts (beyond 4th gear) but has no effect on the tranny regarding downshifts. Ed

[Mr JP]

Paul, How you describe how your GB works is just how mine works. If i leave it on (GB) it will down shift when I would prefer not to down shift. I turn the GB on when I start down a grade. Mine is a stock unit also. I do like the GB and use it. Good luck !!

[Paul T]

It's great in mountain driving and can let you lead the brake pedal by a large margin. Unfortunately, the Allison transmission can't see what's coming up next in regard to downgrades and upgrades. U can!