17

Is it possible to push start a car with automatic transmission?

Use case: Let's say the battery is dead or you have a bad starter. I know this can be done on manual cars by putting the car in to gear after the car starts moving.

Can you do the same with an automatic transmission?

Does the automatic transmission type matter? (traditional torque converter, CVT, DCT, etc.)

  • You cannot do it with a traditional torque converter, but I really don't know with the other auto tranny types. With the standard, you have to have fluid flow through the TC and that occurs at the front of the tranny, not the rear wear the drive line or axles would be spinning. – Pᴀᴜʟsᴛᴇʀ2 Aug 12 '15 at 1:01
  • If the tranny in question has a rear pump driven by the output shaft (most don't), then you can push start the vehicle. Dual Clutch and Constantly Variable trannies don't operate like regular automatic trannies in that they don't (to my knowledge) operate by redirecting tranny fluid to lock and unlock planetary carriers; they don't even have planetary gears. Since they do not rely on pressurized fluid to operate, it is my guess these may be push started, provided or course, that there is enough juice in the battery to provide a spark and operate the fuel injectors. – BillDOe Aug 12 '15 at 1:27
  • Good question!! – Shobin P Aug 12 '15 at 9:31
4

I believe you can do it with a traditional torque converter. I've done it. It's not smart.

Push by your buddy, no. Push with another vehicle, yes - but as the other Steve M suggests you'll need the high side of 25-35mph to maybe make this happen.

Without the tranny fluid pump driven, you won't get TC proper fill, BUT there's usually enough residual fluid left in the TC to attempt this unwise stunt. It;s the difference between a really good transmission fluid service and the ones we all actually did... How many of us oldtimers removed the shield (back when you could) and rotated the TC, pulled the plug, and drained the converter? No flame here; I'm as guilty as any.

On edit: I should qualify that as I'm talking old-school. C5 or 727 era, early totally hydraulic systems, where you will always have some reverse power path back to the TC. Modern TCM solenoid valve systems I doubt it, and I simply don't even know. I think I remember working on something that was stuck in an "emergency tow mode" that purposely uncoupled the power flow path to prevent damage (likely dry pump burnout) during flat towing.

  • 1
    If you cannot get line pressure (even in old transmissions) you cannot start an automatic transmission via pushing it (no matter how fast you push it). The only auto trannies which you could do this with are really old, in fact some of the first automatics which had the pump at the rear of the transmission. I'm talking back in the 1940's era transmissions. – Pᴀᴜʟsᴛᴇʀ2 May 29 '16 at 20:26
6

From experience, my old Mazda 323-C Auto could be bump started at a speed of around 34mph (which is far too fast to push!). This was a traditional type auto box so I don't know how it would differ for something with a CVT / DSG gearbox.

I used to carry jump leads in the boot of this car as the most effective way to starting any car but certainly an automatic with a flat battery is to jump the car using another car or a jumper pack.

If your started motor is dead, check that the exciter cable is alright and without breaks as this can stop the starter spinning over. Is this a real world problem? If so, what is the make and model of the vehicle and what are the symptoms?

5

Automatic transmissions originally had a feature that allowed push starting, a rear pump in addition to the front pump. If the car was rolling the rear pump would provide pressure even if the engine was not running. Some speed was required 15 to as much 30mph recommended for some makes to transmit enough torque through the torque converter to turn the engine for starting. All automatic cars through 1958 and some into the mid 1960s were push startable, some examples are GM's hydramatic through 1958, Chevrolet's powerglide through 1966, Fordomatic/Cruseomatic through 1963 and some Fords through early 1968, Chrysler's Torqueflite through 1965. Reference "how to push and tow automatic drive cars" inside back cover of MOTOR AUTO REPAIR MANUAL.

-2

I believe that the possibility to push-start a modern car with a completely dead battery is a myth. I tried it once with a manual transmission car along with several workmates that helped to push the car. Even despite achieving significant speed, no gear would start the car. I even tried to turn the key at the same time I released the clutch pedal, just in case the car was designed not to be push started!

The problem is that typically, if the battery has no charge, it is close to zero volts. How do you excite the alternator's coils if the battery has close to zero volts? The alternator in modern cars is electrically excited and has no permanent magnets.

I ended up fetching my jumper cords, which helped to start the car.

If push-starting is practically impossible with manual cars, no amount of pushing will start an automatic transmission car. Of course, all of this applies only if the battery is completely out of charge. If there is some charge left, but not just enough to start the engine, the charge may be enough to excite the alternator's coils and therefore start the engine.

  • 1
    To push start a manual - and this is well-documented elsewhere - the key has to be in the "run" position. When you release the clutch, the engine turns, which turns the alternator, producing more than enough current to activate all the electrical bits. The idea is that you're replacing the function of the starter by getting the engine spinning yourself, which is all the starter does, anyway. I've push-started late model Porsches, among other "modern" cars. It still works. The battery runs the starter. The alternator runs the car, and charges the battery. – 3Dave Jul 20 '18 at 21:30
  • @3Dave and how did you deduce the key wasn't in the "run" position? Of course it was, and in one of the tests I even turned the key to the position that engages the starter motor! – juhist Jul 21 '18 at 8:27

Not the answer you're looking for? Browse other questions tagged or ask your own question.