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Restrictions when towing a Jimny - technical explanations

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12 Dec 2017 13:24 - 12 Dec 2017 13:26 #187369 by Bosanek
Suzuki's Owner's manual for Jimnys has a section 7 about loading and towing a vehicle.

That chapter contains several severe warnings on how not to tow a Jimny, promising critical damage to the transmission if done the wrong way.

In short, it says that the rear wheels must not have contact with the ground when a Jimny is being towed no matter what.

It also says that the front wheels can have contact with the ground when a Jimny is being towed (from behind), but only if the gear box is in neutral and if both front wheel hub heads are unlocked.


I wrote a corresponding subchapter in the BigJimny wiki article " DO's and DONT's with Jimnys " based on that official Suzuki chapter.


Now,

I can understand why the front wheel hub heads have to be unlocked, in order to prevent transmission wind up during motion.
I am just not certain if having a front propeller shaft connected to the transfer box mechanisms (with the front hub heads being unlocked) would pose an issue here. In theory, any motion of the front propeller shaft during vehicle's motion should be "soaked" by the front differential in this case with much issues.


However, what I definitely don't understand is why is it strictly prohibited to have the rear wheels on the ground when the vehicle is being towed, even if the front wheels are not in contact with the ground?
Last edit: 12 Dec 2017 13:26 by Bosanek. Reason: Some tzpos

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12 Dec 2017 15:13 #187374 by Lambert
Ok . So if you tow a Jimny with the front suspended ie rear wheels down it causes amongst other things a lack of lubrication of the gear boxes especially as the vehicle is not level there's only minimal splash lubrication because the transmission is in neutral and the input shaft is not being turned so the oil pump isn't working. . On the front having the propshaft connected makes no difference if the hubs are disengaged.

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12 Dec 2017 19:37 #187390 by mickt
It is a bit misleading in that towing the car with a rigid towbar system with all wheels on the road is OK as long as the front hubs are unlocked.

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15 Dec 2017 09:06 - 15 Dec 2017 09:09 #187473 by Bosanek
11/60,
thank you for a proper explanation.
But it still leaves some questions non-addressed for me.


So the only issue is the lubrication of the gears in the gear box?
I suppose that the lubrication of the transfer box would not be an issue in this situation, would it?

Regarding the oil pump, I suppose that you refer to engine's oil pump. But I do not see what is an issue if that oil pump is not working, since the engine is turned off anyway and the gear box is in neutral, meaning that nothing turns in the engine during towing anyway.

As far as I know, during normal operation, the oil in a manual gear box circulates only by the splashing effects of the gears, not by the operation of any oil pump. Or am I wrong? If I am correct, then I do not see much difference (regarding lubicration of the gears in the gear box) between running a gearbox by engine's throttle or running it in neutral mode with the vehicle cruising in "freewheeling" mode. The gears are turning anyway, its just the source of the force which turns them that changes (engine or the wheels).


If I am correct, shifting the gearbox in neutral while the engine is running and the vehicle being in motion, and then freewheeling on a flat road or downhill would essentially be the same situation as towing that vehicle with its engine being turned off, gearbox in neutral and (at least) its rear wheels on the ground.

If the latter is bad for the gear box, then so should be the first too (freewheeling with the engine on and gearbox in neutral), as some people have a habit of doing?



mickt,

Suzuki did not write that towing a Jimny with all wheels on the road and front wheel hub heads disconnected is allowed, and neither did I in the above mentioned wiki article.
It is clearly stated that the rear wheels must not have contact with the ground during towing no matter what, implying then that all four wheels on the ground is also prohibited.

What is officially allowed though, is to have ONLY the front wheels on the ground, but only after making certain that both front wheel hub heads are disconnected.
Last edit: 15 Dec 2017 09:09 by Bosanek.

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15 Dec 2017 09:20 #187475 by Lambert
I was under the impression that the gearbox has a separate oil pump driven by the input shaft. I could be wrong.

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15 Dec 2017 19:34 #187502 by Wychall
I'm not an expert on Suzuki but in general automotive terms a manual gearbox is splash lubricated whilst an auto box relies on the input shaft oil pump. An auto should never be towed, or even bump started as it will not be lubricated. I don't understand why Suzuki say not to tow a manual, unless it risks damage to the transfer box.

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16 Dec 2017 12:58 #187534 by facade
With the engine stopped, and the gearbox in neutral, all the gears are standing still, so there is nothing (except the synchro hubs, which are smooth) to throw oil around inside the gearbox.
The output shaft (main shaft) is turning though, through the centre of the stationary gears (and is above the level of the oil) so the tiny needle rollers and plain bushes around the output shaft will eventually run dry and fail.

The transfer box will be fine, as it is all rotating and flinging oil around as nature intended, although the chain slack will be on the other side.

Also Suzuki have to deal with numpties towing the car with dogs, and small children inside, who may knock it into gear, or engage 4x4, or who may have left it in 4x4 when it broke down, so they suggest removing the propshaft so nothing can happen, and the Ambulance chasers can't help sue them for millions because they "never told me not to tow it at 90mph with my foot on the clutch in 4wd and 1st gear" :pinch:

If it suddenly breaks, go back to the last thing that you did before it broke and start looking there :)
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16 Dec 2017 16:19 #187543 by 1066Boy
So in short, simple terms that I understand, its ok to tow it in a normal fashion with another vehicle as long as its only a short distance?

Jimny JLX Facelift model 2005.
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2" lift with Procomp Es1000 shocks.
Diff and transfer box guards from Jimnybits.
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16 Dec 2017 17:57 #187546 by facade
I'd have thought a couple of miles once in 10 years would be ok. I'd drop the rear propshaft off if it was going any distance.

(Basically, if it would take longer to remove the propshaft than to tow it home, I'd just tow it with it on)

In The Olden Days we used to just tow cars as far as we had to and never took any notice.

When the front pulley came apart on mine, the Nice AA man suspended towed it with the front wheels on the floor about 20 miles.

If it suddenly breaks, go back to the last thing that you did before it broke and start looking there :)
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19 Jan 2018 10:21 - 19 Jan 2018 10:38 #188559 by Ronstan

facade wrote: With the engine stopped, and the gearbox in neutral, all the gears are standing still, so there is nothing (except the synchro hubs, which are smooth) to throw oil around inside the gearbox.
The output shaft (main shaft) is turning though, through the centre of the stationary gears (and is above the level of the oil) so the tiny needle rollers and plain bushes around the output shaft will eventually run dry and fail." :pinch:


But the same applies to regular cars with manual gearbox. Why than there are no warnings in manuals?
And what if we leave engine idling? The input and counter shafts will be turning so there is a splash lubrication. Would it be a solution?

Ronstan
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Last edit: 19 Jan 2018 10:38 by Ronstan. Reason: Another thought

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19 Jan 2018 19:05 #188589 by 1066Boy
Ronstan, just seen your signature. Nice to have another ex-Niva owner on here. :)

Jimny JLX Facelift model 2005.
Kashmir Blue Pearl Metallic.
2" lift with Procomp Es1000 shocks.
Diff and transfer box guards from Jimnybits.
215/75/15 General Grabber x3's
and a driver called Allan (1066Boy)

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20 Jan 2018 01:43 #188601 by Ronstan
Haha, mixed fillings related with Niva ;)

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