Here's our situation. We've bought an RV (actually a bookmobile that we're converting) so my wife can do some travel nursing. We need to bring another vehicle along, but can't drive it separate (else one of us would be left alone with one or two screaming kids, if we're all in the RV then I can drive and she can take care of them). We have a 2002 E320 RWD Wagon, and a 1985 300D (which is RWD too of course).
After much thought, we've decided the 300D will most likely be the car to be towed behind the RV. It's older, not worth as much (so if it fell off, transmission is destroyed, etc. we're not out as much $$$), and of course it's my car (the wagon is my wife's, of course she's more willing to risk my car).
Anyways...things aren't completely straightforward with this car. It's an automatic transmission, so can't just tow it 4-down and leave it in neutral. It's also a RWD so can't just use a car dolly and drive the front up on it. I could use a dolly and drive the rear up on it, but that's not optimal. For one, the steering wheel would have to be tied (can't rely just on the steering lock), plus it'd put more stress on the front wheels/suspension/etc. (I had the stabilizer bar break on one side, used a torsion bar saver, the way it's designed it only puts pressure on the welds when the front wheel is being pushed forward, which only happens when the car is traveling backwards...).
What I think I can do, is to tow it 4-down, in neutral, with the engine idling. I mean, it's a diesel, those can idle all day and night long right? It'd take a lot of gallons of diesel to pay for an alternative (transmission pumps, quick disconnects for the driveshaft, etc.). I can just put a wireless cam setup in the driver's seat so I can keep an eye on the RPM gauge. If the engine dies, I'll know in time to pull over and get it started back up.
I know someone will want to know what the owner's manual says. It states:
The vehicle may be towed with all of the wheels on the ground and the selector lever in position "N" for distances up to 120 km / 75 miles and at a speed not to exceed 50km/h/ 30mph.
To positively avoid a possibility of damage to the transmission, however, we recommend to disconnect the drive shaft at the rear axle drive flange on any towing beyond a short tow to a nearby garage.
So, the manual does state that it could be towed a decent bit at low speeds. Am I correct in assuming that with the car idling it should be able to be towed at highway speeds (55-60mph) for much longer stretches (say, 300-400 miles at a stretch)? Am I also correct that letting the engine idle for extended periods of time won't be too bad for it?
Last question. I've been unable to find any towbars that will fit this specific car, or our other car for that matter. Does anyone have a towbar that connects to their W123 and if so, what did you use? Did you have to have the base plates custom made? Any help would be useful.
BTW, I know that ideally you'd just use a trailer. Problem with that is where do you store the trailer at the campground (or even in the hospital parking lot, as some do have RV hook-ups)? Towing 4-down is the next preferred method, followed by the car dolly (which you still have to store somewhere, plus your car isn't secured as well to it as to a towbar). Even if the only solution is to use a car dolly, I'll still probably want to tow it with the rear wheels on the ground, and thus need to know about just letting it idle the whole time.