Wants To Build A Plug-In Unimog
Question: I am considering an electric-powered off-road vehicle. I would like to convert a Unimog 411 hardtop to electric power using a DC system. My concern is creating the effect of compression braking. Any experiences or ideas?
Eric Pringle
Cerritos, CA
Answer: I don't think that the world is quite ready for an electric-driven off-highway vehicle due to the many complications involved. However, with that being said, an electric off-highway vehicle would be very cool.
First off, the amount of battery capacity to handle the loads would have to be quite high. Keep in mind that most battery-powered cars available are small and lightweight, and have a very limited mileage range. With current technology, the battery design for something used off the highway ... well, it just isn't going to happen overnight. What could be worse than having your battery go dead miles off the highway without a plug-in site? Plus, electric DC motors usually have a limit of around 2,200 rpm. So without going through a transmission with an overdrive unit, overall speed would have to be limited to electric-motor rpm.
There are a couple of ways to tackle this project, and both would require a motor/generator along with a battery pack. The simplest would be to have a motor/generator somehow incorporated within the driveline of the vehicle, with the vehicle's original motor also providing power. The electric motor would have to be mounted just behind the gas/diesel engine and in front of the transmission. That way, it would be like one of the current hybrid cars. Naturally, there would have to be some kind of specialized control unit that would decide when to use the electric motor. All this would add weight and a very complicated system to the vehicle.
The second and most ideal method, while perhaps not practical and overall speed-limiting, would be to ditch the transfer case as well as the driveshafts and somehow mount a motor at each wheel, right next to the portal section of the axle. This way, you would be able to control the amount of power to each wheel as necessary. Just imagine being able to apply total power to a wheel with traction and just let the others roll along. For this to operate properly, it would take a highly sophisticated computer feedback system to be able to distinguish between wheel slippage, such as when going around a corner and/or when extra traction is needed, plus the necessary program to change the field load to each motor when using it as a braking system.
So what it comes down to is, you had better have a team of electrical and mechanical engineers as well as mega-dollars to tackle a project like this.
Scout II Axle-Swap Sources
Question: In response to "Scout Dana Swap for CJ-7," (Mar. '08), here are some links and info that may prove helpful.
Several companies offer reverse shackle kits that allow for full-width Scout, GM, fullsize Jeep, and Dodge axles to be installed under later CJs. A few are Poison Spyder Customs (www.spydercustoms.com), Expert Off Road (www.expertoffroad.com), and Mountain Off Road Enterprises (www.mountainoffroad.com). Also, according to FAQs on the Binder Bulletin site (www.binderbulletin.org), '80 Scout II front axles have 2 degrees of caster built into them. Caster correction bushings can also be purchased that allow for up to 1.5 degrees in caster for earlier Scout front axles from Super Scout Specialists (www.superscoutspecialists.com). Hope this info helps!
Brett Henderson
Conifer, CO
Answer: You're right-these companies do have full-width axle kits for CJs, and I am well aware of their existence and perhaps should have included them. I didn't for a couple of reasons. One, they are shackle reversal systems. Not that I'm against that, as I am a real supporter of rear shackle solid front mounts. They take a lot of stress off the spring and spring mounts, and do improve ride quality. The serious rockcrawlers don't like them because they allow the axle to move rearward when it's up against a solid obstacle. By contrast, with the shackle in front, it forces the axle forward and into an obstacle for better traction.
Here is where I see the problem, and I did mention it in my initial answer. The steering box has to be moved forward to accommodate the longer pitman arm when using the Scout axle. This makes for more fabrication work to make a correct steering-box mount. I think that it would be impossible to move the box forward using the kit from Expert Off Road due to the design of their kit that utilizes a new front bumper (which, by the way, I think is really cool).
Shackle reversal kits also move the axle about 1.5 inches forward, which makes it mandatory to move the steering box even further forward. Not that someone with some good fabrication skills couldn't do this, but then again, if he had the skills in the first place, he wouldn't need to buy the kit, would he?
Shackle reversals also require a driveshaft with about twice as much travel as a standard shaft. So when you factor in the cost of the new long-travel slip-yoke front driveshaft and an outboard spring mount kit ($400 to $500), new steering knuckles for the Scout axle, and all the miscellaneous parts to make it happen, the Scout axle doesn't look all that inviting.
And that, again, brings up the subject of caster angle. My reference book shows the '80 Scout at 1 degree caster and all the earlier years at 0. Even if the '80 model year had 2 degrees (and how many '80 Scout axles are you going to be able to locate?), and even if you used some offset caster bushings that offer 1.5 degrees of increase, that is not nearly enough caster angle for good handling. (I like to see 5-7 degrees.) Not to mention the fact that the pinion angle will totally suck. The only real way to correct the pinion angle/caster angle is to cut the weld holding the steering knuckles to the axletube, rotate them, and reweld.
Anyway, thanks for your insight on this and I really do appreciate readers setting me straight on issues and offering alternate solutions to problems.