I understand that it is unwise to pull any kind of weight in overdrive except downhill, but I have noticed that my rpm's get pretty high (within a few hundred rpm of redline) at freeway speeds when I leave it in fifth (6 speed). What Rpm should I consider to high for extended periods or is it safe to rev that close to redline often? Thanks in advance

 

You can pull in OD, what kind of wt you talking? I pull my 7k lb trailer in OD all the time except up the steepest ( 5 to 6 % ) grades.

 

I pull a trailer with 6 horses and tack. Im not sure of the weight but I would guess its around 10,000-12,000.I just dont want to kill the tranny, but then again a tranny is alot cheaper than the cummins motor. Im leaving to go deer hunting tomorrow and wanted to get some feedback before pulling out.<br><br>I noticed you live in west jordan, im not that far away in american fork. Nice state to live in eh.

 

The following from the August 1999 Power Booster News (A Cummins Publication) tells me you won't break the engine at high RPM's:
And from the same publication:
The only concerns that I have heard about with a 24-valve Cummins and overdrive on a manual transmission have to do with the five-speed transmission. Five-speed owners have an issue with the 5th gear nut loosening. Five-speed owners are told to avoid running in 5th gear (overdrive) below 1800 RPM.

If I owned a six-speed transmission rather than the five-speed I have, I would run the highway in overdrive, loaded or not, anytime I could without lugging the engine.

 

Thomas, that answers my question perfectly. Thanks a bunch, that takes a load of stress off.

 

Over the last few months I have slowly gone to using OD all the time on the five speed. I do keep it above 2000 or so. I now have near 150,000 on it and all is well. It runs 2200 at 75 in OD. I drop it out at 68 to 70, pulls better anyhow.

 

Haulin in dixie is right you can pull in o/d as long as your above 2000 rpm. This was confirmed to me by the service manager at my dealer when i was having 5th gear problems.

 

The 5-speed is the only concern because OD is on the tailshaft accompanied by the nut. The 6-speeds OD is on a counter-shaft so it is perfectly okay to pull heavy loads in OD with-in reason.

 

After reading this thread, I guess I've been running a little low on the RPMs. I went for a 90 mile trip today and kept the RPMs 1800-2500. I seems to run better now (at all RPMs).<br>

 

On average I tow 20,255 lbs in OD on a 6 speed. Ask member J.R. Adkins he will vouch on the 75-85 mph rescue runs.