How much time in overdrive???

[thisoldhippy]

I have an Isuzu 6bd1t diesel that I have been thinking on putting in my 1979 Elandan 2 440 loadflite. Was wondering about putting the loadflite behind it! Not sure I need the overdrive. I tow a lot out here in Oregon. Lots of hills and pretty heavy 24,000lbs. Guess what I'm wondering is how much I will actually use the overdrive transmission? Thanks for your thoughts.

[bluebird]

If you already have an overdrive trans that'll mate to the engine you want to use, use it. Most will have a lower 1st gear ratio so the rig will move easier. Plus most also have a lock up converter, so even if you run it in 3rd at least you will benefit from the locked up converter. That alone will help save some fuel, and IF you ever are able to use the OD it'll be available.

[Froggy1936]

 On my 4L80E trans 4 speed W OD & lock up TQ  On trip from Pittsburgh to Philidelphia on the Turnpike it was in OD quite a bit traveling @ 59 MPH With Cruise control on .On any grade It would Drop to 4th then to 3rd but stay in lock up speed would drop also So i would give it gas and it would drop out of lock up and start rebuilding speed For some reason my cruise will not try to hold speed going up small grades , A problem i have not looked at yet As i watch for drop off and help it along . I am still gathering info as it is all new to me this last trip was its first & full of mishaps  Frank

[bluebird]

My buddy and I both have 30 ft coachs, 454, with the 4l80E trans. We both pull 18 ft car trailers in OD most of the time. Mine don't seem to kick down or out of OD as much as his, but his coach is about 10" taller and 3"  wider than mine. I have driven coachs when I was shopping, that dropped out of OD on almost any type of incline. When traveling without pulling, I have to be on a pretty steep grade before mine kicks out. I don't flog it though, just leave the cruise set at 65.

[Wantawinnie]

What is your rear end gear ratio? If the Isuzu diesel operating range is at all like a Cummins 6bt you will not be able to run at highway speeds without an overdrive. My rig has the Cummins swap with 4.56 gears, 19.5 tires, and the A518/Gear Vendor overdrive combo. It's all done at about 45-50mph floored without overdrive. Find an online rpm calculator and put in your setup. I don't think you would be very happy without overdrive. A gear vendor behind the 727 and 3.73 gears would be nice combo.