Moss Motors, Ltd

Calling all manual transmission experts!  There's discussion on another thread about towing a MG Midget, with comments about disconnecting the driveshaft to avoid damaging the manual transmission.

Drawing on my limited mechanical knowledge and some towing experience in my mispent youth, I'm wondering how one could tear up a MG transmission when towing.  Given the assuption that it's placed into the neutral shift position, that would mean the two "striking dogs" are not locked on to any gear.  The mainshaft is spinning, of course, along with the sliding hubs.  Since the engine is stopped, the first motion shaft, the cluster gear, and the meshed gear assemblies on the mainshaft would not be turning.  Correct so far?

Unlike an automatic transmission, these old MG trannies are not cooled from engine coolant, so overheating by towing is not an issue.  Is there enough lubricant in the casing to lube the gear hub roller bearings if the cluster gear in the bottom of the case isn't turning and slinging the lube around?  Is that the failure path?

Just curious!  

Mr. Mason-

Having destroyed a tranny by towing it a long distance I can give you a description of the symptoms that resulted.

ALL the syncros were COMPLETELY shot. (It had a four speed syncro tranny that was a lot of work to install in a 67 MGBGT.)

You had to FIRMLY hold it in every gear or it would pop out.

When I drained the oil a lot of rather large pieces of metal came out.

You could still drive the car but you had to very accurately double clutch on up and downshifts.

I would say that your idea about the oil not getting where it needed to is accurate.

If you think about it, when a car is typically in neutral , the input shaft is spinning and the output shaft is not.

When towing , the opposite occurs. Not good.

Also, on a long trip I wonder if the shift lever bounces around a lot and the gears try to engage.

Additionally, all the oil is tilted to the back of the tranny due to the nose up aspect of the car. This cannot help the situation.

Anyway, I can tell you it was a hard lesson to learn .

 

LCJUTILA




 

Hi folks, I think Dick M put his finger on the debateable topic. We are talking about splash lubrication and there's not much splashing going on during a tow.If you combine that with a gearbox that has not been turned over in an age, has dubious oil in it and oil seals that need waking up gently, then I believe you have potential for serious damage on a sudden, high-speed, long-distance, tow. Those of us that have suffered are probably shouting the loudest here!

Contrast that to a car that gets regularly driven has good oil in the box,  together with maybe an additive like moly, and good? oil seals then maybe its a different story . Im  still not sure I would not take some extra precaution like overfilling the box [and subsequently draining] before a long distance tow even on a well-used runner.But hey, we all have our own little personal habits!!       cheers    - - -   steve

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To a man equipped with only a hammer, most problems look like nails

If the car is to be towed in a nose-up position, such as when a dolly is used, removal of the driveshaft is wise indeed. Some folks have gotten away with not removing the shaft, but I assure you that if they've gone any great distance, they have shortened the life of the gearbox. I once had a customer bring me a TR6 that had been towed from Maryland to Colorado on a dolly without removing the driveshaft. He claimed that everything was fine when he hitched up, but when I disassembled the 'box, there wasn't much left that was useful. Most components had burned to a crisp as a result of the oil just laying in the bottom of the transmission where it did NOTHING.

It's not quite as clear when flat towing. In fact, it depends on the specific gearbox. I might tow twenty miles that way with a B, but not a thousand. That begs trouble, though many have gotten away with it. My luck doesn't run that way! Take out that driveshaft!! How long does it take to do it?

Better yet, rent, or purchase, or borrow, a trailer. That's the best way to go by FAR!

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

So, to summarize everyone's imput ...

Dolley use:  In town, short mileage - OK.  If used for a long-distance tow, the drive shaft MUST be disconnected from the transmission.

Flat tow:  Be aware that normal transmission internal lubrication is not occuring.  Ensure the transmission fluid is topped off on the high side if possible.  Some transmission designs handle this better than others.

Long distance tows should use a trailer.

Additions?  Corrections? Comments?

It would certainly look goofy, but I suppose one could use a dolley on a long tow with the rear axle on the dolley.  I believe the front tires will self-center as you go.  Possible?

Only 1 addemdum...

U-Haul will not rent a trailer for out-of-state hauling. When they ask, "where are you hauling?", keep that Tid bit to yourself!

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

'68 Sprite 1275
'76 Midget 1500