Installation of Ranger III Overdrive unit

Like many guys before me, I was unhappy with the rpm's my engine was turning when at cruising speed on the hwy. Fuel mileage was poor and the noise was very tedious. I thought of dropping my rear axle ratio from the 3.55 to 3.08, but was unable to find anyone with that gear ratio for my front diff, a Dana50. So I kept my eyes open for an Overdrive unit. I finally found one on E-bay and bought it, a Ranger III unit made by Advance adapters, designed and adapted to be used on the t-19 4speed transmission.
Click here to go to their webpage

Many of the overdrive units out there bolt onto the rear of the existing transmission or transfer case. This is fine on a 2wd truck, but for a 4wd, it means then that the overdrive can only be used in 2wd, and if by some mistake it would be activated while in 4wd, well something would have to break. The Ranger unit is uniqe in that it bolts in front of the 4 speed transmission so it can be used both in 2wd and 4wd.

Installation wasn't technically difficult, although the t-19 transmission is made of cast iron, and his very heavy, so a big transmission jack, and lots of strong hands were definately helpful. One has to remove the existing transfer case and transmission. The rear driveshaft has to be shortened 7 1/2" and the front one lengthened the same. The transmission crossmember support has to be moved back on the frame the same distance, and the transmission hump on the floor has to be modified to allow the 4 speed trannsmission to move back, requiring a bit of sheet metal work. The input shaft of the overdrive unit is an exact copy of the 4speed transmission, and bolts directly into the bellhousing. The transmission then bolts onto the back of the overdrive unit with minor modifications of the input shaft sleeve(has to be shortened), and the transfer case goes back on.

Here's a few pictures...some of them may be a bit large
Overdrive unit coupled to t-19 prior to installation
Overdrive unit mounted in the truck as seen through the floorboards
Overdrive as seen from below, between the bellhousing and transmission
Minor floor mods required!
Final floor mods done

You can see that the ranger is a manual shift unit, which means you now have another stick to deal with. It doesn't seem like too much of a problem initially, but becomes a bit of a pain when shifting from 2nd-over to 3rd-direct, or 3rd-over to 4th -direct, because you have to shift both levers. Even worse than that, is the gear whine associated with overdrive trannys, which vibrated up the new stick. It was very loud, and even set up a noise in the original 4 speed stick.I decided to rig up something to get rid of the second stick and still be able to somehow remotely shift the O/D unit.

I thought of using the electrical solenoids from a couple old starter motors, but they aren't strong enough, I thought of an electrically triggered vacumn booster on a cable like the cruise module, but it too doesn't have enough "pull" and is quite slow. Finally I came up with an air(you have to have onboard air) driven piston. I used one that came from a dump truck. It originally is used to lift the latches which hold the tailgate closed, and is operated remotely from the cab with an air valve switch. I rigged up a mounting bracket, which provides good leverage for the piston. a cable(an old manual choke cable) comes up the 4 speed stick and acts in push/pull fashion to activate the air valve switch, and the whole thing mounts down under the truck, on the side of the Overdrive unit, doing away with the second stick, and all the associated vibrations. Now, when I want to shift the Overdrive, I just pull up on the button to go into O/D and push down to go back into Direct.
Here's a few more pics....
Air valve and cable prior to installation
Piston in the closed(direct) position
Piston in the open(overdrive) position

Before installation of the overdrive, on the hwy cruising at 60mph(still slower than the average traffic) my engine used to run just under 2500rpm. I averaged about 18mpg(Canadian-about 15U.S.) and the noise was terrible. Since installation of the overdrive, I now see around 1900rpm at 60mph, and my mileage has increased to about 22mpg, and the difference in engine noise is incredible. I don't have it yet, but next summer we are getting a 23ft r/v trailer, and I'm very much looking forward to pulling it with the O/D unit.

Overall, I see this as a big project. I have a good shop in my basement with lots of neat tools, and a small arcwelder, and those things made it do-able. I'm not sure I'd have tackled this one without those kind of facilities. It makes the truck way nicer in terms of driveability and comfort, and I know I will always wonder how I managed so long without it.

Just a little update to the original article. I found that the air driven shifter would sometimes not push the linkages far enough to fully engage the transmission and when I let out the clutch, it often would jump out of gear with a big bang, or worse, grind the gears terribly. I didn't feel secure enough when I made the shifts like this, so I went back to the original second stick configuration mounting the stick on a large piece of rubber to get rid of the vibrations it made. I still plan on having the air driven shifter in there one day, but it'll have to be one which moves the linkages both ways by air rather than one which shifts via air one way, and using a return spring the other way such that the air piston is having to push against the return spring.

Zigg