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Automatic transmission question.

F

Fritz Maurer

Well-known Member
I see cars being towed behind campers all the time.
Why does this not damage the transmission?
Without the pump turning there is no lube pressure,
and the rotating parts are above the oil level. I dont
know about front wheel drive, but the trans in
question is a 89 AOD in a town car. I had told my
son to take the drive shaft out and just flat tow it
home with his Burb. With the shaft out it would at
least give a little bit more range between fill-ups, as
he is pulling it 2300 miles, but I was just wondering
about the lubrication issue. Will it fry the output
shaft bushings or not? Thanks, Fritz
 
Ford AOD is not flat towable more than a few miles at low speed. Most rear wheel drive automatics are this way. There are drive line disconnects available in the RV industry to disconnect the transmission. A lot of 4WD vehicles have a neutral in the transfer case that serves the same purpose.

RWD manual transmissions are not flat towable, either. No lube to the mainshaft when towed because the counter shaft is not spinning, so the speed gears will seize to the mainshaft. FWD manuals can usually be flat towed because the final drive provides oil splash.

There are exceptions to the automatics, though. The GM 4T40 and 4T45E can be flat towed, they were designed with this in mind. They have a final drive driven lube pump. These transmissions were was the HHR was so popular behind RVs. It also came in some Cavaliers/Sunfires, Malibu/Grand Am/G6, and Cobalt/G5.

There also electric lube pumps available in the RV world to provide lube pressure, making normally not towable transmission towable.
 
I used to think it was ok to tow a manual but I got to thinking the cluster gear would not be turning in neutral. The input shaft is locked to the front gear on the cluster gear so the engine would have to be running or the clutch held down and in gear for it to turn when towing. The clutch would fly apart. The cluster gear(counter gear) is what slings the oil up to lube everything on the main shaft.
 
Used to see a lot of farm pickups with hitches on the front, to tow them around. But maybe behind an older tractor it doesn't do any damage. I have towed my 1984 manual 2wd Mazda pickup behind a tractor many times, mostly 20 miles, but times close to 50. No damage yet.
 
Many of these are set up with a drive shaft disconnect - when you look at the $200,000 motor home - spending a few dollars on a disconnect is a drop in the bucket.
 
There are driveshaft couplers for this which is probably the best way to go albeit a little expensive.

https://www.youtube.com/watch?v=qhQukbD8JV4
 
I have read that a towed vehicle should not be pulled for more than 500 miles without starting them and getting the transmission fluid recirculated before continuing with the tow.
 
When I was working at a RV dealership the way it was done was by adding a electric pump to the trans or by using 4wd that you could put the transfer case in neutral.
 
These days, most vehicle manufacturers publish recommendations about which of their products can be towed with all four wheels on the ground. In the case of GM, they put this in their trailering guides under 'Dinghy Towing'. ('Dinghy' is the RVer term for a towed vehicle. Like a yacht's dinghy, which is often towed behind the yacht.)

Check out page 54 in the towing guide at the link below.
2022 Chevy Towing Guide
 
I towed my ford Edge a couple years. I think doing the 500 mile start up was recommended. The edge turned out to be a little too heavy. I have a Chevy Tracker now. Hardly know it's behind me. The tracker is a Suzuki with a chevy name. Stan
 
What gets damaged in old 3 speed is the tailshaft bushing. But, in some of them lube level can be high enough that the second gear will pick up enough to keep the only parts moving oiled up.
The only parts moving in neutral will be the second gear, because it is attached to the mainshaft which is rotated by the driveshaft. That and the bearings in the back of the main drivegear all that needs lube.

Full lube, or overfill if possible will keep those parts lubed OK.
 
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