Engine/Transmission (1998.5 - 2002) Over Drive, when to use

[johnharris]

I own a new Cummings 3/4 ton with auto trans and 4:10 ratio gears. When pulling my boat (3,400 lb), light load, I'm unsure when to take it out of OD. I heard that the OD gear is the weakest gear in the Tannie and was wandering if on gradual grades I could leave it in OD since with my high gears if I shift into 3 the revs are very high forcing me to have low MPH.

 

[phoekema]

OD use

You should be able to keep it in overdrive 99% of the time with that low a weight and with the higher (numerically) axle ratio. I have the 3. 54 and pull close to 14,000 lbs and use overdrive all the time on the highway unless I drop below 50 mph. A good test is if you can pick up speed fairly easily in OD you are not 'lugging' the engine.

Even with your setup, you may want to seriously consider a transmission upgrade some time in the future. Check into ATS, DTT, Goerend, Suncoast... ... ... . there are other good ones, but in my opinion the above mentioned are the leaders in the field at present. You won't believe the improvement a transmission upgrade will make!

With your situation, there is probably no particular rush for an upgrade - you are not even getting the truck to breathe hard yet.

 

[work2muchplay2little]

There are basically two issues, and only one to really be concerned with at stock power levels and that is avoiding lugging the engine, which basically boils down to being able to accelerate and increase engine RPM in the gear your in. One of the reasons to avoid lugging is the inevitable rise in EGT - even stock engines can get close to exceeding the generally accepted limit of 1300 degrees for sustained driving. This is basically a long-winded way of encouraging you to get some gauges - EGT/boost and fuel pressure. Oh, BTW, your Cummins probably doesn't even know you own a boat at 3400lbs. Now maybe if you took the wheels off...

 

[RCone]

My thinking on this issue is this: Depends on your RPM's. You are towing a very light load and you have 4:10's. You should have no problem towing in overdrive. I, on the other hand, tow about a 10,000# 5ver with 3:54's. I NEVER tow in overdrive, with my modifications, as OD IS the weakest link. My engine likes it better at 2400 RPM's than it does at 1800 in OD. I guess if I was traveling 65-70MPH I would be in OD, but I don't because that is my preference with that kinda of a load. Gotta be able to stop you know.



Regards,



Roger