Doesn't towing damage the transmission?

Frequently when I am driving down the highway I will notice an RV towing a passenger vehicle of somekind. In the vast majority of cases all four wheels of the car are on the road while being towed. Also, I imagine most of them have automatic transmissions. Isn't this damaging to the trans? What happens to these cars after driving two or three hundred miles?

Thanks, Al Kondo

Reply to
Al Kondo
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"Al Kondo" wrote

Yes, it's potentially damaging. Because the autotrans does not pump the oil while towing, the oil pump only runs with the engine. So it may become too hot, first the ATF oil will get damaged and then the transmission itself. A manual trans runs in air with only drops of oil spread by the teeth of the gear wheels. Much less friction than in an oil bath.

Thomas

Reply to
Thomas Schäfer

Al Kondo wrote in article ...

There are devices available that can be installed on RWD automatic transmission vehicles to disconnect the rear axle from the drive train while towing. A switch on the dash engages and dis-engages the device.

Front-wheel drive automatic transmission cars that are dollied by the front wheels are no concern since the drive train is not rotating, and the rear wheels are mounted with tapered or roller wheel bearings.

On standard transmissions, since the countershaft in a transmission is in constant mesh with the output shaft, and the synchronized gears, the gears in a standard transmission sling lubricant around while being towed - much the same as when being driven.

Bob Paulin - R.A.C.E. Chassis Analysis Services

Reply to
Bob Paulin

In an automatic, yes, it can (not neccesarily "will", just "can") damage the tranny, which is why those folks that do more than minimal towing do one of two things: Drop the driveline and plug the rear end of the tranny, or have a "cutout" installed. Dropping the driveline is pretty self-explanatory, and is obviously the cheaper, more "DIY" method. The "cutout" accomplishes the same thing (disconnecting the rear end of the tranny from the rear axle) but accomplishes it using any of several methods that all boil down to "disconnect the driveline". When activated, the cutout isolates the rear axle from the tranmission, leaving only the axle shafts and the differential (which, in every case I know anything about, is oiled like a manual - see below) spinning when the vehicle is in motion. In the deactivated position, it locks the driveline and axle together.

For front-wheel drive cars, similar cutouts are available, despite "drop the driveline" not being an option. Or just put the car on a dolly and tow it that way, and the problem becomes nonexistent.

For vehicles with a manual tranny, it's a total non-issue - Hook 'em up, put 'em in neutral, and go. You just plain can't hurt the tranny by towing 'em.

I hear you already... "Why not???"

Well, oh seeker of wisdom, it's really pretty simple (but not particularly obvious until you've been inside one of the beasts) and boils down to "lubrication".

An automatic relys on input revs from the engine to spin the various pumps and impellers that move fluid around.

When an automatic is turned by being towed, the output shaft is spinning, but the pumps aren't. Which means that all the fluid just kinda lays there in the pan and torque converter doing absolutely nothing, which in turn means that the whole thing is effectively spinning without lube. No matter how experienced or green you are, I'm sure you can easily understand that "gears spinning without lube" equals "Something's gonna break" - the only questions that apply are "how long before it does?" and "how much is it going to cost to fix afterwards?"

A manual transmission (or at least, every one I've ever had anything to do with) on the other hand, is either put together in such a way that the largest gear on the countershaft is "dunked" in the oil bath provided by the pan so that it's spinning "through" the oil and spewing it everywhere, or it has a device of some kind (possibly fancy - some sort of mechanical pump, perhaps - or possibly dead-simple, like one or more strips of metal or plastic that are long enough to hit the oil) attached to or driven by the countershaft, which performs the same function: Getting the oil out of the pan and onto/into the parts/places that need it.

Since the countershaft is always coupled to the output shaft, regardless of whether the vehicle is in gear or not, whatever method of oiling is used (whether "big gear", pump, or flinger) is active anytime the output shaft is turning. Because of this, towing a vehicle with a manual transmission is a complete and total "So what?" situation that presents exactly zero risk of damage to the tranny. (other than the usual "everything wears out eventually" risk that can't be escaped in any way other than not letting it spin at all, which of course defeats the whole purpose of having a car with a transmission to begin with...)

Reply to
Don Bruder

Of course, if you're towing a 1965 or earlier Chrysler product, that's not a problem since those transmissions have TWO pumps that operate in parallel- one driven by the engine and the other driven (voila!) by the driveshaft. The other cool thing is that you can PUSH START those cars too, because the rear pump develops enough pressure to put the transmission in gear, spin the torque convertor, and (if pushed fast enough) turn the engine.

Aside from that, I think the actual failure mechanism in an autmatic that is towed too far is that the clutch packs overheat, not the gears. The planetary gears still dip in fluid as they rotate and should get some lubrication. But the clutch packs are above the fluid level, and even if they have fluid in them it isn't circulated out of them, and the residual drag in the clutch packs (even in neutral) can generate a LOT of heat.

Reply to
Steve

Others have said good points.

I own a couple Jeep 4x4's and if they are towed, you are supposed to stop every 200 miles and run the engine in gear with the t-case in neutral to spin it up and lube the t-case where the driveshaft hooks up.

Most folks I hear of just unhook the rear driveshaft in them if they are towing for a long way so as not to take any chances.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Al K>

Reply to
Mike Romain

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