Can I tow.........

[Power Wagon]

Originally posted by mark93

In the exploded view of the NP 205 transfer case I see no oil pump.



Some aluminum case units, like the 208, 231 and 241, do have an oil pump.



The 205 would suffer the same as a manual trans because there are no gears turning in neutral.



Before 1966 they used to put rear pumps in auto transmissions so you could push start the car and tow without restictions when the trans was in neutral. I read somewhere the rear pump was eliminated for "safety reasons" (it's safe to say profit was increased). Speaking of increased profit, it reminds me of the 6 speed second gens getting a 13" clutch the Mickey Mouse way-all those baloney modifications to the starter mount, flywheel and clutch cover to get a clutch inferior the first gens!

No, there is no "pump" if you're looking for an engine oil pump type pump. What happens, is that the rotation of the front gears and the design of the case lifts oil out of the bottom of the transmission and spreads it across the upper gear shafts, lubricating the bearings. IN all probability (I haven't seen the innards of a Getrag or NV 4500 ), the oil is flung up, and some small "catcher" will direct it into a bearing and through the shaft to lubricate the rest of the inner bearings.



In a transfer case, there is a large gear attached to the output shaft that does the same thing. By the operation of this gear, and passages and blocks built into the housing and shafts, the output shaft functions as the "oil pump" in the same way, by tranferring oil into the inner bearings when the vehicle moves.



Even transmission guys refer to it as "the pump" because it's action is to move oil up and funnel it into the critical bearings.

 

[mark93]

Hey guys.



I've double checked the NP 205 diagram.



The input shaft/gear has a pilot bearing in the output shaft much like a manual trans.



According to the diagram, all of the gears are constant mesh, so if the input shaft does not turn none of the gears turn-the same as in a manual trans.



When towing with the NP 205 in neutral there is relative motion of the spinning output shaft to the stationary input shaft, causing the pilot bearing rollers to spin, and relative motion of spinning output shaft to the stationary low range gear, which has a sleeve bearing that rides on the output shaft. Oil is needed at the pilot bearing rollers and the low range gear sleeve to prevent damage. The dog (clutch) teeth on the output shaft appear to be only thing could possibly slash oil but they are too far above the oil level for that. Even if they were in oil they are relatively small and would not splash much oil. The residual gear lube would allow some time before failure-more so than the 5-30 in the trans.



It appears the only way to safely tow a first gen is is either with the engine idling AND Transfer case in 2H OR after disconnecting the drive shaft.



For the NP 241, which uses a planetaty gear set and a chain, there is an oil pick-up screen so the above may not apply.

 

[ShortB]

I know... an old thread.



BUT, I have a new question. One that, from what I can tell, has not yet been covered.



What about towing a '91 250 2WD 5-spd (Getrag) with only the front wheels on a tow dolly AND with the truck idling in neutral? As long as it wasn't towed over about 50 mph and not for more than 20 miles or so, does anyone know of any damage this could do to the truck?

 

[mysteryman]

towing

As long the trans is in good condition and full of oil ... You should not have any problem... slower is better !

I have towed many many trucks across the country... I have a pair of old axle shafts that I cut the flanges off of. . When I tow long haul . I pull the axle shafts and replace the with the cut off flanges to keep the oil in... I also prefer to use a tow bar instead of a tow dolly. . I remove the front bumper and bolt the tow bar directly to the frame... It is a lot easier to back up with a tow bar!!! If you must use a tow dolly be sure it has room for at least an 80 inch wide axle... Good luck with your tow

I know... an old thread.



BUT, I have a new question. One that, from what I can tell, has not yet been covered.



What about towing a '91 250 2WD 5-spd (Getrag) with only the front wheels on a tow dolly AND with the truck idling in neutral? As long as it wasn't towed over about 50 mph and not for more than 20 miles or so, does anyone know of any damage this could do to the truck?