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Towing vehicle(tow truck) With single speed transfer case

Brizzo Jenkins
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Brizzo Jenkins Enthusiast

Brizzo Jenkins

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So the Chevrolet owners manual says to not tow a 4 x 4 vehicle with a single speed transfer case with “any“ wheels on the ground. It says to use a flatbed tow truck only. I will always do what Chevy says, as to not void my warranty. But, I can’t conceptually understand in my brain why I can’t tow my truck in 2-wheel drive with the rear wheels lifted off the ground and the front wheels on the pavement rolling. As long as my four-wheel-drive is not engaged, why would my front wheels do any damage to the vehicle? From my understanding, when the vehicle is in 2 Wheel Dr., the front differential is disconnected from the transfer case and front drive train. Why would this cause damage? 
 

inversely, couldn’t I  disconnect the rear drive shaft and tow it with the rear wheels only on the ground?

 

just seems weird that Chevy says “no“ to absolutely any options with towing with wheels on the ground. I mean, how the hell do they expect me to get it on a flatbed tow truck without “pulling it with wheels on the ground”. Just a thought. Maybe someone with more knowledge of the Single speed  transfer case linkage/ 4-wheel drive system can advise.  

davester Senior Enthusiast

davester

Posted
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It's fine for the 10-20 feet the vehicle moves to get it on the flatbed or on dollies

 

I don't know the specifics of your vehicle, but it likely has to do with lubrication in the transfer case.  It may be something that your front diff always spins the front driveshaft, and the transfer case doesn't get lubricated in that mode.

Brizzo Jenkins Enthusiast

Brizzo Jenkins

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So I got curious and put the cell phone camera underneath the truck and focused on the front driveshaft. In four-wheel-drive its spins, in 2 Wheel drive, it does not.  This leaves me even further confused as to Chevrolets towing restrictions. if the front wheel drive shaft is not connected to the transfer case, why can’t it be towed with the front wheels on the ground.  Chevrolet specifically states that a two speed transfer case with the active “neutral“ switch, can be towed with wheels on the ground, but that a single speed transfer case with no “neutral“ cannot. Still not understanding the mechanics as to why. If the 2 Wheel Dr. mode “disconnects“ the front axle from the driveshaft, what’s the problem?

Edited by Brizzo Jenkins
davester Senior Enthusiast

davester

Posted
Posted

Well, then, perhaps there's something about the front diff that doesn't like being towed.  Maybe you can phone up gm and get a more definitive answer?

 

Does it really matter?

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Brizzo Jenkins Enthusiast

Brizzo Jenkins

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Posted (edited)

Just sitting here bored and letting my brain wander. If I’m going to ask a tow truck company to make sure they “send a flatbed tow truck“, I was just wanting to know why I was asking for such, mechanically speaking.  
 

also curious if it is something with the front differential, why does Chevrolet allow dinghy towing for a two speed  transfer case

Edited by Brizzo Jenkins
newdude Senior Enthusiast

newdude

Posted
Posted (edited)

Can't dolly tow with either transfer case.  So no hook tow truck.

 

Can't dinghy/flat tow the single speed case because there is no neutral position on that transfer case.  2HI, 4HI and AUTO.  That's it. 

 

The 2 speed case has 2HI, 4HI, 4LO and most importantly NEUTRAL.  The case has to be put in NEUTRAL before flat/dinghy towing.  Can't do that with the single speed case.   

Edited by newdude
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davester Senior Enthusiast

davester

Posted
Posted

I was referring to dolly tow with a regular tow truck (so all 4 wheels are off the ground).

 

The thing with the 2-speed transfer case (at least with the GMT800 ones), is that when the transfer case is in neutral:

 

-the front diff is unlocked, so if you tow with the front wheels down, it's no problem (to the front diff, it's just like driving around normally, and the front driveshaft doesn't spin, so the rest of the drivetrain is fine)

-if you tow with the rear wheels down, the rear driveshaft spins the output shaft of the transfer case.  This is ok, because the oil pump in the transfer case is driven off the output shaft, so oil is pumped through the TC, so everything stays lubed while in motion, and (also important) the output shaft of the transmission isn't being rotated

 

For 2wd vehicles, the problem with towing with the rear wheels down and the transmission in neutral, is that the oil pump in the transmission is driven off the transmissions input shaft (so the transmission works with the engine running regardless of what speed you are going).  But, with the engine off (typical for when you are towing), and the rear wheels on the ground, bits in the transmission are spinning without the oil pump going to lube them, which is "a bad thing".

 

I don't know the internals of the 1-speed TCs or the front diff used with them, but most likely, they don't work the same way, and will be damaged if towed for any significant distance.

Brizzo Jenkins Enthusiast

Brizzo Jenkins

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I wonder if it is possible for the vehicle to be dolly towed with the real wheels on the ground if the drivetrain is disconnected. Chevy doesn’t mention it in the owners manual. However, I have seen many of tow truck drivers do this on other 4 Wheel Dr. trucks with automatic transmissions. I know Chevy says no “dolly towing“, irregardless to drive type/transfer case type (single/2-speed) But just wondering if it’s possible if the driveshaft is disconnected, and the front wheels are up  

Edited by Brizzo Jenkins
redwngr Senior Enthusiast

redwngr

Posted
Posted (edited)

The dolly the tow truck brings runs on the ground and carries one set of the trucks wheels.

The tow truck lifts the other end of the vehicle, so the other set of wheels is not on the ground.

 

Flat deck is not required.  

 

Pic is not a pickup, but demonstrates 'dolly towing'image.jpeg.23d04a82ed378861681ae7adb0b4ab87.jpeg

 

 

 

The two wheel dolly type that is sometimes used behind a pickup or rv puts us back in the don't do it discussion. 

Edited by redwngr
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Thomcat Senior Enthusiast

Thomcat

Posted
Posted

As I read it you can dinghy tow a 4WD in neutral  but can't dolly tow with either a two or four wheel drive with one axle on the ground. Could be because it has nothing to do with rotation of either the tranny or transfer case but the angle of towing.

 

 

My .02 guess:

The output bearings on the axles may depend upon splash lubrication from the oil in the sump....towing front axle up on 2WD or 4WD might oil starve the output bearing on the rear axle, maybe even the wheel bearings. Towing rear axle up on either 2WD or 4WD might screw up the rack and pinion or worse throw vehicle out of control on a turn......I'm assuming this gen. is fly by wire and there is no longer a solid connection between the steering wheel and the wheels on the front axle which is driven by an electric motor integrated into the computer controlled rack (so no more power steering pump either) and no longer way for the tow truck driver to strap the steering wheel or use a locking steering wheel to secure front wheels without possible damage.

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  • 1 month later...
htoooh New Member

htoooh

Posted
Posted (edited)
On 4/9/2020 at 3:21 PM, Brizzo Jenkins said:

So I got curious and put the cell phone camera underneath the truck and focused on the front driveshaft. In four-wheel-drive its spins, in 2 Wheel drive, it does not.  This leaves me even further confused as to Chevrolets towing restrictions. if the front wheel drive shaft is not connected to the transfer case, why can’t it be towed with the front wheels on the ground.  Chevrolet specifically states that a two speed transfer case with the active “neutral“ switch, can be towed with wheels on the ground, but that a single speed transfer case with no “neutral“ cannot. Still not understanding the mechanics as to why. If the 2 Wheel Dr. mode “disconnects“ the front axle from the driveshaft, what’s the problem?

This is a great response for me.  I was trying to figure out if the axles were indeed turning in 2H on the single speed transfer case.  I had to edit this, I put the truck into gear, forward and reverse, with the single speed transfer case in 2H and the axles do, indeed, turn.  So, I'm hoping that there will be sufficient lubrication as I plan to flat tow a single speed transfer case in a 2019 GMC Sierra with the drive shaft disconnected.  I will be installing a drive shaft disconnect that I can control from the driver's seat.  The disconnect will stop the drive shaft from turning and the folks who will install it say that I can tow with the vehicle in Park.  Since the front axles are not turning I'm assuming that the front wheels will get the proper lubrication as long as the transfer case stays in 2H.  Any thoughts?  The manufacturer of the disconnect switch says that they have installed these parts on single speed transfer cases with no problems and no returns.  I don't think I'm going to worry about it but I am interested in what others think.

Edited by htoooh
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swathdiver Senior Enthusiast

swathdiver

Posted
Posted
1 hour ago, htoooh said:

This is a great response for me.  I was trying to figure out if the axles were indeed turning in 2H on the single speed transfer case.  I had to edit this, I put the truck into gear, forward and reverse, with the single speed transfer case in 2H and the axles do, indeed, turn.  So, I'm hoping that there will be sufficient lubrication as I plan to flat tow a single speed transfer case in a 2019 GMC Sierra with the drive shaft disconnected.  I will be installing a drive shaft disconnect that I can control from the driver's seat.  The disconnect will stop the drive shaft from turning and the folks who will install it say that I can tow with the vehicle in Park.  Since the front axles are not turning I'm assuming that the front wheels will get the proper lubrication as long as the transfer case stays in 2H.  Any thoughts?  The manufacturer of the disconnect switch says that they have installed these parts on single speed transfer cases with no problems and no returns.  I don't think I'm going to worry about it but I am interested in what others think.

Never heard of a driveshaft disconnect, let alone an automated one; how does that work?  In my generation truck and the next, swapping in a 2-speed transfer case with the switch and module was a plug and play affair.

 

Are the T1s using the MP3010 transfer case?

AlaskaErik Enthusiast

AlaskaErik

Posted
Posted
On 4/9/2020 at 1:22 PM, newdude said:

Can't dolly tow with either transfer case.  So no hook tow truck.

 

Can't dinghy/flat tow the single speed case because there is no neutral position on that transfer case.  2HI, 4HI and AUTO.  That's it. 

 

The 2 speed case has 2HI, 4HI, 4LO and most importantly NEUTRAL.  The case has to be put in NEUTRAL before flat/dinghy towing.  Can't do that with the single speed case.   

My 2 speed case also has an Auto position for full-time 4WD operation

N55_6MT Enthusiast

N55_6MT

Posted
Posted

This was explained to me as such: GM no longer uses a traditional transfer case, so even when in 2WD the only thing separating the front driveshaft from the rear is a clutch pack. The clutch pack won't transmit a meaningful amount of torque when disengaged, but if the speed differential between the front and rear driveshafts is to great, there may be increased wear on the clutches.

Brizzo Jenkins Enthusiast

Brizzo Jenkins

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Posted (edited)

I would say if you absolutely MUST tow it on a dolly, there is only one “safe” way to do it. Disassemble the rear driveshaft and put the front wheels on dollies. Even then, it’s not approved by the manufacturer, and could possibly void your warranty if anything goes wrong.  Safest bet is to put it on a trailer. 

Edit...

my only concern at this point would be If the rear differential and bearings are receiving proper lubrication.  I would think that it would not be an issue, but GM does some weird stuff in their engineering department. I have not had the chance to study if the lubrication system to those rear parts are independent, or pump driven. Maybe someone with further knowledge can advise us?

 

Edited by Brizzo Jenkins
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