Motorhome towing an 80

[landtank]

I don't think you need to add a pump for the tranny as long as the t-case is in neutral.

The driveshafts turn at different speeds all the time except for when you are travelling a perfectly straight line on a perfectly flat road and all the tires are exactly the same size.

 

[Capt. Jim]

If you go the route of dropping the drive shafts, you can unbolt at the diffs and leave them connected at the TC. This saves you from undoing 2 flanges (8 bolts) and having to store the greasy shafts somewhere in your rig. Just need to secure them to the frame so they won't drag or separate at the slip joint.

 

[Tuner]

Any 4x4 jeep can be flat towed from the factory as can any full size 4wd chevy and the trailblazer/envoys. I considered a GC but really like landcruisers.

Landtank...that makes sense. So by selecting N from HNL, the transmission is not turning and no pump is required....but the xfer case has these mysterious spider gears and a viscous coupler connected to the driveshafts that spin...at somewhat similar speeds due to the rotation of the tires...causing what problem?

I will post what I find out from the toyota transmission guys tomorrow.

 

[firetruck41]

I actually have seen a LX470 being towed behind a 1/2 million dollar motorhome. Don't know anything about it though.

 

[Capt. Jim]

As mentioned above, locking hubs at all 4 wheels would be the easiest solution, as the '96 has a full-floater rear axle.

 

[IdahoDoug]

I honestly cannot think of a reason why the 80 cannot be flat towed with the tranny in Park and the transfer case in N. The tranny would be out of the equation with zero turning (Park keeps even any residual hydraulic spinning from happening). The F/R shafts would spin at about the same speed, so the hydraulic coupling (aka viscous coupling which it is not) should be happy.

The center diff has its own static oil bath just like the F/R diffs - ie there's no oil pump when the truck is running.

Something bugs me though. What disconnects in the center diff to provide the neutral position? Could there be a bushing there that's simply not designed for a spinning F/R drive shaft during towing while the input shaft from the tranny is stopped? Simply not enough gear oil flow at that spot? In normal operation, there would be zero difference between the F/R shafts and the input shaft from the tranny, so that bothers me. I don't know how a pump could be configured to ensure there's moving oil at that location as there's no pump in this gear case to begin with.

If someone could come up with exactly how that disconnect occurs, it would shed some light, but that would be my area of concern - not the tranny.

DougM

 

[firetruck41]

So, what would the difference be between leaving it in Hi and the tranny in neutral? vs tcase/center diff in neutral?

EDIT: I would guess just the fact that the tranny fluid is not being pumped through the cooler, and the input shaft will be turning, possibly causing a heat related problem?

 

[IdahoDoug]

Ben,

This would have a physical shaft connection between the center diff (spinning while being towed) and the tranny's output shaft. So a shaft within the tranny would be spinning, but with the engine off the tranny pump would be not circulating fluid, and a bearing in the tranny could overheat. In the old days, the tranny pump was on/part of the output shaft, so when it spun fluid circulated. I don't know if this is true on the 80's tranny and the downside of being wrong is a horrendous expense.

DougM

 

[landtank]

Doug, according to the FSM the T-Case layout of my 96 has an oil pump that is mechanically driven within it.

Ben, I'm not 100% sure but I think that the pump in the tranny is up in front, so unless the torque converter is turning there is no fluid being pumped through the system.

Turner, the VC works by locking up when sensing the rotating differences between the front and rear shafts. Some have damaged theirs by excessive engagement such as running tires of different sizes. My recomendation for using locking hubs on the front was just being cautious of the unknown as well as the truck might tow better and create less heat in the drive line.

 

[Tuner]

Like I said, there is some serious talent on this board.

It is sounding more and more like a heat related problem within the xfer case...which was the proposed problem with the 4runner as well. The bearing surface for the driveshaft was the primary worry. I overfilled the xfer case with 75-140 synthetic and did some test runs gradually increasing the speed and distance. It never got too hot to leave my hand on it and 4700 miles later is no worse for wear. I'm aware there are big differences between the two xfer cases in question.

The folks at Remco sell a rear shaft disconnect kit ($1000) and a set of manual hubs ($600) that make it bulletproof but I hate to waste money.

I think that manual hubs on the front disconnect the wheels from the axle whcih sounds like a good idea. This LC has OEM diff locks. With the locks engaged, does it turn the front axle into a limited slip arrangement?

I'm looking for other credible advice as well and will post my findings so we all have a better understanding to the ramifications of flat towing without mods.

 

[woody]

I think that manual hubs on the front disconnect the wheels from the axle whcih sounds like a good idea. This LC has OEM diff locks. With the locks engaged, does it turn the front axle into a limited slip arrangement?

OEM diff locks are either locked/spooled "solid" or unlocked/completely open. No limited slip characteristics whatsoever.

 

[Tuner]

OEM diff locks are either locked/spooled "solid" or unlocked/completely open. No limited slip characteristics whatsoever.

On the surface that looks like good news because if they are left open/unlocked, the front tire rotation should not cause any driveshaft rotation. However if the VC does not like differing input shaft speeds...we have a problem. This is strictly supposition on my part becasue I KNOW nothing.

I appreciate you guys letting me ask questions, my background is engineering and I like to know how stuff works.

 

[landtank]

On the surface that looks like good news because if they are left open/unlocked, the front tire rotation should not cause any driveshaft rotation.

Being open the diff compensates for different rotation but the drive shaft still rotates. The only way to stop the driveshaft from rotating is to disconnect the wheels.

 

[cruiserdan]

The folks at Remco sell a rear shaft disconnect kit ($1000) and a set of manual hubs ($600) that make it bulletproof but I hate to waste money.

Let's do a bit of math..........

1600 bucks, plus labor, to fit the bits to the vehicle. Gotta be at least 2 grand and probably more. In the end you have a modified vehicle with extra aftermarket specialty bits to break. Only that particular vehicle will be suitable for "dingy" towing.


Buy a trailer, for about the same money, and tow anything you please .


D-

 

[e9999]

I don't get the locking hubs up front part. With these disconnected, if the rear wheels are spinning, then the VC has to spin the front driveshaft. Whereas if you keep all 4 wheels going and both driveshafts going, the VC should see no difference and do no work. Wouldn't that be better than with front hubs unlocked?
(and yes, of course, disconnecting both shafts would be best)

 

[Tools R Us]

Let's do a bit of math..........

1600 bucks, plus labor, to fit the bits to the vehicle. Gotta be at least 2 grand and probably more. In the end you have a modified vehicle with extra aftermarket specialty bits to break. Only that particular vehicle will be suitable for "dingy" towing.


Buy a trailer, for about the same money, and tow anything you please .


D-

And trailer bearings are much cheaper than Cruiser bearings, birfs, etc.

 

[landtank]

I don't get the locking hubs up front part. With these disconnected, if the rear wheels are spinning, then the VC has to spin the front driveshaft. Whereas if you keep all 4 wheels going and both driveshafts going, the VC should see no difference and do no work. Wouldn't that be better than with front hubs unlocked?
(and yes, of course, disconnecting both shafts would be best)

My thinking is that with the front hubs unlocked the VC would see minimal differences as the front bits turn freely and not hampered by differences in tire rotation. I think the heat in the VC comes from trying to over come rotational differences that it can't for an extended period of time.

And if I was going to do something with the rear shaft it wouldn't be a $1000 mod either, more like just unbolting and hanging it somewhere.

 

[e9999]

My thinking is that with the front hubs unlocked the VC would see minimal differences as the front bits turn freely and not hampered by differences in tire rotation. I think the heat in the VC comes from trying to over come rotational differences that it can't for an extended period of time.

And if I was going to do something with the rear shaft it wouldn't be a $1000 mod either, more like just unbolting and hanging it somewhere.

don't know...
if you were to disconnect the front wheels and have the rear ones still connected, the VC would have to spin the front driveshaft, diff parts, axles etc. If the truck were to be slowed down suddenly, all these front parts would keep spinning and the VC would see a big rpm difference and get hot. If you have both front and rear connected to the wheels, the VC would not see much difference. Not true?

anyway, best to drop the shafts...

 

[Tuner]

Let's do a bit of math..........

1600 bucks, plus labor, to fit the bits to the vehicle. Gotta be at least 2 grand and probably more. In the end you have a modified vehicle with extra aftermarket specialty bits to break. Only that particular vehicle will be suitable for "dingy" towing.


Buy a trailer, for about the same money, and tow anything you please .


D-

You are absolutely right, a trailer avoids any potential problems with flat towing but it also kills what I thought was an interesting discussion because there seem to be differing opinions.

The simple truth is I don't want to use a trailer. They are extraordinarily inconvenient for my purposes. That's not to say a trailer is not a great solution and will work for many people.

I've found a great deal on a '96 LC and I bought it. I sold my 4runner. I have other vehicles but would love to flat tow this awesome truck. I do not mind spending money, just hate wasting it.

I am a deeply superficial person who just likes to understand why things work the way they do and freely admit I like to challenge conventional wisdom not supported by facts. I think I'm trying your patience and apologize.

When I find the definitive answer, I will post it.

 

[cruiserdan]

No need to apologize for anything you have said or done. I wish I could tell you that at 52 miles the viscous coupler will go up in flames or some such other definitive answer about what would happen to the vehicle. I can only relay what the factory says is the way to tow the 80. I can tell you that the FSM (Factory Service Manual) defines the 4th method I detailed (the flat tow) as the "emergency method". The manual does not state the specific repercussions of towing by other means other than a specific caution about towing with the front wheels on a dolly and the rear wheels on the ground.

Logic dictates that flat towing is discouraged because something could get damaged.


D-