Has anyone ever used a overdrive on a motorhome(i.e. gear vender or other brands) I talked to Bill h and he likes his. I would like to know more about how they work. Is it like an extra top gear? What are the pros and cons.
Ken

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Here's a little more detail:

The GearVendors unit is a modification of the old Laycock de Normanville overdrive unit found in such British cars as the Triumph, Austin-Healey, etc. It uses a planetary gear arrangement to provide the overdrive function. As such, it can be shifted under power and will work best with an automatic transmission. The downside (which doesn't apply here) is that this unit is designed to transmit power only in one direction - that being from the engine to the rear axle or transfer case. This means that the clutch mechanism will slip and eventually burn up if used with an exhaust brake on a diesel engine (where power is transmitted from the wheels to the engine) if the GearVendors unit is engaged. The other downside is that, since the GearVendors unit shifts with internally-generated hydraulic pressure, it usually isn't functional until about 20 or 25 MPH.

The U.S. Gear unit is a modification of the Doug Nash overdrive that is a modification of the Ford top-loader 4-speed transmission. It provides overdrive or underdrive through electrically actuated/spring assisted shifts within the "auxiliary transmission". This is why throttle pressure (actually, drive torque) must be removed before the actuator/spring can make the physical shift. This shift can be pretty noisy - a noticeable clunk. The U.S. Gear unit works best with manual transmissions and can be used with exhaust brakes on diesel engines.

The GearVendors is an overdrive unit that replaces the tailshaft housing on the the back of your transmission. It requires that your driveshaft be shortened. Installation is very straightforward. It is like any other overdrive, in that it allows a 30% drop in engine speed for the same road speed. 3rd overdrive is good for cruising and letting the engine loaf, and maybe saving some gas. 2nd overdrive is where it comes into its own. For the hills where high is too high, and 2nd buzzes the engine too much, 2nd overdrive is just right. There is, I guess, a first overdrive, but have never used it. It comes with a control of some sort, but I just use a simple switch.

http://gearvendors.com/mh3speed.html

GearVendor in my Barth has an automatic shift at 45mph and manual shift, done with a foot shift switch

I've wondered myself about the reduction of engine wear and the higher engine temp when traveling over 60 mph, with a 4th gear. But when I looked at the price of one WOW! I would almost think it would be cheaper in the long run to replace the transmition with a factory 4 speed. My Barth is a 1980 35ft. It has a 454 with a 3 speed hydromatic transmition. Im new to all this. Bought my Barth about 4 months ago.

I've looked into the new Allison 1000 5 or 6 speed. It's the one hooked up to the 502 ci on the new Workhorse chassis. It's a 5 speed with the 6th gear locked out because they are used in lighter duty box trucks. This tranny from a salvage yard runs $4500 with the computer.

I like the simplicity and easy availability of parts and repair with the TH400. Any tranny shop can fix a TH400. Heck, even I rebuilt one once. Even an exchange unit would be simple. I wonder how the electronics would interface with a P30. With my luck the darn computer would fail if I did the allison thing. But they are really nice.