I'm sure theres a good reason, but why can't you tow an automatic car for any real distance, or bump start one
dominic
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According to an AA man, theoretically you could bump start an auto, but you'd have to get it up to 40 - 50mph in order to do so...
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I'm sure you can tow an auto, but obviously in neutral. However there may be some wind up in the box. Put an auto on a ramp, in neutral with the engine running and the driving wheels still rotate slowly.
There's always some drag in the torque converter that reduces economy and causes this effect.
GK
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Towing an auto.
Ford Sierra manual says
Auto in N and stay in N
Max speed 30 MPH
Max distance 30 miles
else drive shafts removed or driven wheels lifted
Do not know what other manufacturers state or what happens with modern cars
Tow starting - says manual boxes only.
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Some manual cars cannot be towed with the driven wheels on the ground I.e Rover Sd1. This is because the oil pump in the gearbox is not being driven so a lot of damage can be done.
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Most autobox pumps are driven off the input shaft and hence if the engine is not running there is no lubrication. Towing the car obviously turns the output side of the gearbox and without the pump running all lubrication breaks down and you wreck the 'box.
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Should add to the above that this applies even in N.
Can't bump start because there is no direct coupling to the engine (its a torque convertor). TQ coupling efficiency is propn. to cube of speed differential between impeller and turbine - hence at very low rpm (pushing car along at couple of mph) there is virtually no coupling and engine will not be turned over.
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I once had a Capri auto on which the hexagonal oil pump drive shaft failed at speed, I kept trying to kill the engine to stop it seizing by flicking ignition off and on (very quickly for obvious steering lock reasons!) but it kept restarting when the ignition was turned back on!
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A perfectly correct answer again from Aprilia (why won't you let us have your profile? -- I'm sure it would be interesting).
Some autoboxes, I'm thinking of the very early BW35s, had an auxiliary pump driven by the output shaft to enable the car to be towed. On the BW35 this auxiliary pump was deleted in about 1965 as a cost saving.
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Aprilia -- my apologies -- I have just spotted your newly-posted profile! Excellent!
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Dizzy, my profile is there - I just haven't put the "P" onto my user name yet.
You are right about the old BW with the pump on the output. There were a few of the older boxes with this auxilliary pump, but they were gradually omitted for cost and reliability reasons.
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I'm sure that on a car I owned that it could be if an extra litre of oil was added to the box, however this had to be drained back to normal levels before driving the car.
Steve.
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Perhaps I ought to start worrying then. When my son rather carelessly wrapped my MG (rear wheel drive) round a kerb the AA towed it to a garage, and I thought you couldn?t tow an automatic either. When I said as much to my son, he said the AA hadn?t said it was a problem. And I assume the AA know what they?re doing.
You don?t want to know how much damage was done!
Carole
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Another aside to this, with AWD SUBARUs, you cannot tow a manual
as it has a fixed ratio drive with 50/50 power to front and rear and a centre diff, but the automatic version with a variable front to rear drive ratio can be towed but a link in the fuse box must be removed to make the control system think it is working in front wheel drive only (1998 legacy model for my information)
Ian L.
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Steve
I can't see how adding a litre of ATF would make a difference. At autobox has an oil pump (usually a 'crescent' type) driven off the input shaft. It draws ATF up from the oil pan and pressurises it to feed to the various bearings within the box. This high pressure (line pressure) is also regulated down in proportion to other parameters (engine load, road speed) to provide control pressures for the spool valves in the valve body. Depending on which pressure is greater, the line pressure is directed to the appropriate clutches/bands to engage the appropriate gear. Of course these days much of the work of these spool valves is done by solenoids controlled by an ECU.
If the oil pump is not running (engine not running) then oil is not being pumped to the bearings, gears, clutches and bands. You can tow the car a few miles (say 20 miles) at low speed and the residual oil on the internal parts will keep the 'box lubricated. If you tow the vehicle further or faster then the oil film will be removed and you will have a lot of (expensive) friction.
Adding extra oil to the oil pan will not help, because there is no pump to get it round the gearbox.
I run an auto and I would not tow it more than a mile with the engine off. If your auto breaks down then get the driven wheels off the ground before it is towed, no matter what the AA/RAC etc. say.
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Dizzy,
That makes me remember the BW35 on my 1.3 Mk1 Escort....one winter it was so cold that first thing in the morning the torque converter fluid was so viscous the poor starter motor was trying to turn the gear box. No problems moving the car on the starter that day!
Waited until the afternoon and car started first time with no problems!
Ian L.
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People used to say you could only tow an automatic for a limited distance and at a limited speed, unless you removed the propshaft. With virtually everything today being front wheel drive this wouldn't be very easy! You could, I suppose, obtain the same effect by removing the front drive shafts; second thoughts, don't think I'll bother!
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My Grand Cherokee says it can be towed with both gear selector and ratio selector in neutral. Well, the manual say that, not the car....:o)
Terry
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Aprilia,
What you say sounds right but I'm sure I've read what I posted in the owners manual. I'll see if I can find it, could even be the 405.
Steve.
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405 would have the 4HP14 box and it can't be right for that (I know those boxes quite well, having rebuilt a few). It could of course be that the manufacturer gave wrong info in the manual (wouldn't be the first time!)
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Aprilia,
According to the owners handbook (page 122) -
The automatic transmission is topped up with an additional 2 litres of oil. This will ensure adeuate lubrication.
The vehicle is towed at a maximum speed of 30 mph (50 kp/h) and not for more than 30 miles (50km) with the selector at N.
After the operation; do not forget to drain the excess oil to the correct level.
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I was short by a litre of oil.
Don't think I'd risk towing it though!
Steve.
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Hmm, strange.
That towing advice would be correct with or without the extra oil. I think maybe the extra oil is for the diff. (which is part of the 'box on these).
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Possible that the book is wrong as you said. I think I'll leave it at that!
Steve.
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