A good triend of mine told, and I quote “An automatic transmission will never “reverse drive” an engine.” I did not want to insult his inteligence so I tried it in my 1996 Dodge 2500 van, V8, 46RE 4 speed automatic. I tried it on 4 hills. As I started down the hill, I turned OFF the ignition as I slowed down near the bottom of the hill, I turned the ignitin ON and the engine fired up and I went on. On one hill I waited 24 seconds before I turned it ON. Mu friend says “it can’t be done”. Can anyone give me an educated answer to my question.
An automatic transmission will reverse drive an engine. You can push start a vehicle with an automatic transmission. I’ve done it many times. Only with an automatic transmission the vehicle has be going 30-35 MPH in order for it to work.
Simpler test - go down a hill in N, then in D with no gas. Big difference = engine braking = engine being spun by the torque converter.
Would the engine be spun by the converter if the trans was in N? I went down the hill in D with the engine being spun by the converter.
Sorry, I misread what you said. You are right.
You cannot push start a modern vehicle, as the transmission has no rear pump to generate fluid pressure and engage the transmission’s clutches. On some older vehicles <1965, you can.
However, the transmission will ‘drive’ the engine. If it couldn’t, then you couldn’t use a lower gear for engine braking, such as when descending a hill.
So long as you left it in gear and were going fast enough, turning the key off does not stop the engine from spinning…no matter the type of auto. If the engine spins, the front pump spins and the clutch packs remain pressureized. Your transmission probably defaults to 3rd or 1:1 when power is removed from the shift solenoids. The EPC solenoid most likely defaults to full line pressure when power is removed. Both of these defaults would protect the transmission when someone does the “exceptional” (as in exception to normal operation) thing that you’re doing. If the engine did stop spinning, the transmission will not spin the engine even if you were going 100mph. The only thing that would happen then is that you’d be spinning planetaries and one-ways without any lubrication at all. After that, you’d have a transmission that likely wouldn’t work at all.
so your answer IS? Yes or NO?
The answer is YES if the transmission is already engaged, you don’t put it into neutral and you don’t slow down to the point that the so-called “reverse drive” causes the engine to stall…yes the literal use of the word stall…stop spinning regardless of cause. I’m betting that would occur somewhere between 10 to 20 mph. Go ahead, give it a try.
I just have never waited until it stalled. Thanks for your complete answer. I will tell my friend when I talk to him again, probably soon.
This thing seems to have stalled yesterday but I would still like to hear more facts about the matter.
You’re conversing here with someone (me) that knows exactly how that transmission works…there is no magic or mystery or any more real “facts” to offer. It is not a majic box–just a piece of machinery.
So, you are saying that a converter does indeed reverse drive an engine?
Some food for thought about a purely direct mechanical connection between the rear wheels and the engine.
Assume an engine or transmission is removed and installed on an auto trans car. Next step is installation of the converter bolts which hold the engine flexplate to the converter.
This means lining up the flexplate and converter holes for those bolts. Depending on the car model I use a fingertip or the tip of a small scredriver to rotate the converter so as to align the converter holes with the ones in the flexplate.
If there as a direct mechanical connection in the driveline I could not rotate the converter with either a fingertip or a screwdriver.
This leads to the following points.
To align the holes would one shift the transmision into DRIVE and rotate a rear tire while having someone watch to see if the converter rotates?
If the converter bolts are installed and tight does this mean that one could place the transmission into DRIVE, rotate the wheel rear by hand, and have the engine rotate OR the rear wheel lock up due to the inability to overcome the human power losses through the drivetrain?
I’ve got my opinion; just curious about others.
Tranny needs a rear pump for this to work…But lots of older cars HAD rear pumps just for this reason…Torque converters, fluid couplers with a stator, will indeed reverse drive to a certain extent…not very efficient but they WILL transmit torque in either direction…
“If there as a direct mechanical connection in the driveline I could not rotate the converter with either a fingertip or a screwdriver.” There is none
This leads to the following points.
To align the holes would one shift the transmision into DRIVE and rotate a rear tire while having someone watch to see if the converter rotates?" NO
“If the converter bolts are installed and tight does this mean that one could place the transmission into DRIVE, rotate the wheel rear by hand, and have the engine rotate OR the rear wheel lock up due to the inability to overcome the human power losses through the drivetrain?” NO
Where do you come up with such rediculious stuff!!!
From actually doing it countless times maybe?
Well. I have at least 6 yeses and no nos, I guess that means a torque converter can and does reverse drive an engine!! I will tell my friend the next time I hear from him.
Are you saying that you have done this countless times?
What part are you saying is impossible? The only thing I claimed to have ever done is rotate the converter with a fingertip or a small screwdriver, all depending upon access.
Are you saying that it’s impossible to rotate a converter this way?
YOU are wrong. And OK4450 is absolutely correct (as he is 95% of the time in general). Countless numbers of mechanics can prove You wrong. The only way it could be impossible would be, if the lock-up function in the converter was still engaged (not possible) or you have a defect in the transmission.
The give You a little credit - that lock-up function is what still keeps Your (and others) engine spinning with the ign. off.
Not all transmissions was born with electronically controlled lock-up. If my memory serves me right, Volvo, Opel (GM) and Mercedes was the first to come with that function back in the late 70’s and that’s before any computer, pms, sos, ecm and what have you was installed in cars. They were controlled by hydraulic pressure in the transmission and the kick-down cable and a few of them also through a valve activated by the speedo-drive in the transmission.
The converter CAN reverse drive - to a certain degree. If you coast down a hill in - say - D, lock-up disengaged - and notice the rpms and then touch the throttle so you have a slight pull from the engine then the rpms will be higher. That’s because there is a slip in the converter. That is what the lock-up function prevents by locking the 2 halves of the converter together. If you floor the throttle from a standstill, it will (should) not engage before you reach a very high speed, at steady speed it will probably engage at around 35-40 mph. If you are coasting, loosing speed, it will disengage at a lower speed, maybe around 20-25 mph.
Sorry for this long input.