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Why shouldn't you tow a RWD car?
smart51 - 7/9/11 at 07:26 PM

I've been asked why you shouldn't tow a RWD car with its rear wheels on the ground. I know that it is said that you shouldn't and have even seen it in a hand book. I can't think what harm it would do. What do you think?

rf900rush - 7/9/11 at 07:32 PM

I think that mainly applies to autos.

ReMan - 7/9/11 at 07:33 PM

I Think it's auto's that would be affected.
the wrong bits being turned and pumping backwards (borrocs i'm sure) but that sort of thing

jba falcon - 7/9/11 at 07:39 PM

If you tow a rear wheel drive you stand the chance of knacking the main shaft bearings in the gearbox. When the engine is running the input shaft and layshaft are turning even when in neutral, this spash lubricates the upper bearings on the mainshaft. without the engine running and the mainshaft being turned from the wrong end ie by the prop there is no splash lubrication for the upper bearings on tn the mainshaft. You can tow for short distances and at lowish speeds without too much risk, but a long journey at motorway speeds will cost you!
D

jba falcon - 7/9/11 at 07:41 PM

I should have said that is for manual gearboxs, especially ones with oil pumps that run of the 1st motion shaft. Auto box's are a complet no go other than towing to the side of the road.
D

britishtrident - 7/9/11 at 07:56 PM

quote:
Originally posted by jba falcon
If you tow a rear wheel drive you stand the chance of knacking the main shaft bearings in the gearbox. When the engine is running the input shaft and layshaft are turning even when in neutral, this spash lubricates the upper bearings on the mainshaft. without the engine running and the mainshaft being turned from the wrong end ie by the prop there is no splash lubrication for the upper bearings on tn the mainshaft. You can tow for short distances and at lowish speeds without too much risk, but a long journey at motorway speeds will cost you!
D




Nonsense

The rule is don't tow automatic (except very early BW and Ford US boxes with two oil pumps) for any distance, modern Jatco auto boxes are so fragile they shouldn't be towed at all.

mangogrooveworkshop - 7/9/11 at 08:09 PM

Oh well we must have knackered a thousand gearboxes
we have dragged stacks of breakdowns....... never had to do autos.

r1_pete - 7/9/11 at 08:22 PM

Some manual boxes have an oil pump driven from the input shaft (Rover SD1 for one) which doesnt work when being towed in neutral, the workshop manual and handbook has a warning to this effect. The Getrag in my E Type is from a BMW and that is the same.

smart51 - 7/9/11 at 08:23 PM

OK thanks guys. I'll pass your remarks on with suitable caveats.

owelly - 7/9/11 at 08:58 PM

Just to add....I wouldn't be towing a BEC engined, RWD car too far either!

Liam - 7/9/11 at 10:50 PM

quote:
Originally posted by jba falcon
Auto box's are a complet no go other than towing to the side of the road.
D


Not always true - manual of my Omega, for example, gives you 60 miles at 50 mph reccommended max, but I know many who've towed longer without damage.

morcus - 8/9/11 at 01:59 AM

I was under the impression is was bad to tow any car with the driven wheels on the ground because of risk to the driveline, you deffintily shouldn't tow and auto with it's driven wheels on the ground, and the dualogic manual for the fiat has very strong warnings about towing it full stop.

rusty nuts - 8/9/11 at 06:54 PM

Some , mainly American, autos have a rear pump in the gearbox which enables them to be tow or bump started . I must have towed hundreds of manual cars in the last 40 years with no problems but some modern cars I wouldn't tow

britishtrident - 8/9/11 at 07:06 PM

quote:
Originally posted by rusty nuts
Some , mainly American, autos have a rear pump in the gearbox which enables them to be tow or bump started . I must have towed hundreds of manual cars in the last 40 years with no problems but some modern cars I wouldn't tow


Early BW and Ford boxes (early US Ford boxes were made by BW who then started producing under own brand) had the rear pump last I encountered was in a Ford Zodiac Mk2, because of the rear pump it could be push started.

britishtrident - 8/9/11 at 07:19 PM

quote:
Originally posted by morcus
I was under the impression is was bad to tow any car with the driven wheels on the ground because of risk to the driveline, you deffintily shouldn't tow and auto with it's driven wheels on the ground, and the dualogic manual for the fiat has very strong warnings about towing it full stop.



The needle roller bearings aren't under any appreciable load when being towed so need very little lubrication, the situation is a bit like the spigot bearing in the end of the crankshaft which has no oil supply.

Most Old fashioned (1960 to about 1990) planetary autos should only be towed for short distances, slightly longer distances can be covered if it is overfilled with transmission fluid. CVTs s should never be towed, and modern conventional planetary automatics such as the JATCO have internal friction parts that are so easy to burn out towing is definite no-no.