Towing Allison w/ Driveshaft - What Can Happen?

[rkinga2]

Info from Allison on truck transmissions says to not tow w/o disconnecting driveshaft.

What's the problem w/ towing w/ driveshaft? Could I do it if I leave the engine running to drive lube pump? (I'm specifically thinking of a cement truck where you would want to leave the engine running to rotate the mixer, anyway).

What's the worst that could happen? Does the fluid overheat - pop into gear - bearing fail - could something overspeed???

Allison also says not to coast in neutral - Is this a similar situation?

Thanks for your time & expertise.

 

[GregLocock]

That's right. Most modern transmissions take their oil pump drive from the front of the gearbox, so if you tow them in neutral with the engine off the back half of the box is spinning with no oil pressure.

The worst that could happen is very expensive.

Coasting in neutral is discouraged by all sorts of people, for all sorts of reasons. Works for me, on a car.



Cheers

Greg Locock

 

[evelrod]

Why would you need/want to tow a cement truck with the engine running in the first place? Many of the bigger trucks around here run the hydraulic pump for the drum from an auxilliary engine instead of a PTO, anyway. Am I to assume that you mean to tow it on the motorway and not just short distances aroung the jobsite?
If, for whatever reason, towing is a necessity---Gear Vendors of San Diego

http://www.gearvendors.com

might be a good place to start.

Rod

 

[rkinga2]

Rod,
An APU would be nice.
I'm stuck with a PTO-driven pump.

 

[icrman]

The out put shaft bearings, governor and the bearings it runs in, and anything else that is attached to the output shaft that requires lubrication could be ruined if it is towed with the engine off. A short distance is okay. Automatic transmission fluid is very low viscosity and the oil film won't last too long.
Even in the old days of rear pumps, it was not recomended to tow the vehicle.
The not coasting in neutral is something that doesn't make sense to me.
Unless it is the slower input speed of an idling engine thus lower pump volume. As far as the clutches go some are not applied during normal hiway speeds anyway. So they are skating on the oil film. <---- another reason for not towing with engine off.

 

[carnage1]

earlyish torqueflight tran's don't run the pump while in park, maybe the allison shuts off the pump in neutral?

depending on the control mechanisim when shifting from neutral to drive it may force it to shift through all the gears. even if it happened quickly engaging first for just a second at high speeds destruction would be instant.

or are you refering to a stick?
I have always been told not to coast in neutral with a stick because you might not be able to get it back in gear at the botom of the hill without stopping. it makes absolutly no sense to me because either you have synchro's or you know how to rev match, or your never going to make it to second.

also some manual gearboxes and transfer cases use a front mounted pump (internaly) others just drag the lower gearset through the oil and sling it arround.

 

[evelrod]

...or are you refering to a stick?
I have always been told not to coast in neutral with a stick because you might not be able to get it back in gear at the botom of the hill without stopping. it makes absolutly no sense to me because either you have synchro's or you know how to rev match, or your never going to make it to second.

It's a generational thing, carnage1. Since I was tought to drive in pre 1940 cars that did not all have synchro gearboxes or hydraulic brakes, I was always admonished (threatened with extinction) by my dad to never coast down long hills in neutral (Oklahoma overdrive, as I learned it being from Texas as I am)! In the event that the engine died and would not re start, you would be "in deep ****".

A great many auto "truisims" come from the Model A Ford era. Many of them, more than one would expect, have survived into the 21st Century intact and with their origins forgotten.

Merry Christmas (I like that, even if it is not PC)

Rod

 

[icrman]

Most all modern large class 8 manual truck transmissions are also Non syncronized.
carnage1, what Torqueflight was that?
And if the pump is not running, then what would lubricate the transmission? How did they disconnect the pump from the drive lugs on the converter. The ones that I worked on out of middle 50's era, put out line pressure in park. And they can't do that if the pump isn't running.
Allison would have to disconnect the torque converter from the flex plate to operate the transmission with out a pump at idle speeds in park. Because with out oil sooner or later the bearings would be gone.

 

[NormPeterson]

Early Torqueflites, in both cast iron and aluminum case models, had both front and rear pumps. An occasionally useful consequence of that arrangement was that you could pop-start cars equipped with it off a push.

Norm

 

[icrman]

Back to
""earlyish torqueflight tran's don't run the pump while in park, maybe the allison shuts off the pump in neutral?
""

Not only would there be a lubrication issue with out the pump running, while the engine is running and rotating the torque converter.
There is the issue of there not being any pressures available for band or clutch application. ie. with out the pump running there is no way to put the transmission into gear.
I have never seen an older torqueflite transmission that has that feature. If there was I would like to see the information.

 

[NormPeterson]

What the early Torqueflites won't run while in 'park' is the rear pump (though it will be running if you're coasting in neutral with the parking sprag not applied).

As you note, it's apparent is that the front pump must be running whenever the engine is turning over; else you'd never be able to engage any of the ranges without a 'push' or a roll downhill to get the rear pump working.

Incidentally, most years that used the early TF had pushbutton range selection. At least in the 1964 versions, the park position was activated separately by its own lever (which also drove the selector cable such that the transmission was put into 'N' and the selector button for 'N' was pulled into the depressed position if you didn't specifically hit the 'N' button first). Somewhere between the 1964 and 1967 model years, the TF's separate 'park' activation and the pushbuttons were discarded for the 'PRND21' lever arrangement, probably under bureaucratic pressure for industry-wide standardization of controls.

Maybe still having a wet-process copy of the Torqueflite section of the official service manual in my possession does qualify me as a pack-rat . . .

Norm

 

[icrman]

I was quoting a post above. Norm I know about rear pumps.
"Parking Sprag" I think you mean Parking Pawl.