The terminology is terrible. It should be can the transmission drive the engine and vise versa…no hyphonized “reverse-drive”. The two entities are either going to spin or be spun…backwards or forwards…who cares? Anyhow, I’m absolutley correct and I’m going to have to agree with myself on this issue.
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?
At the risk of inciting some of the more irritating posters on this board, I feel compelled to reply. I’ll use an example to illustrate my point. Imagine two electric fans placed close enough together and facing in the same normal airflow direction that when the rear fan is turned on, it pushes enough air to spin the front fan even though it is not energized. Not so unlike the TC, the air is the viscous coupling rather than a hydraulic fluid. With both fans off, turn the rear fan with your finger. Does the front fan spin? Of course not, you’re not spinning the rear fan fast enough to engage the coupling action. In the car example, if we ignore the transmission hydraulics for now, you’d have to spin those rear tires very fast to emulate the normal speeds needed for converter coupling.
In addition, the fan blades are designed to be most efficient with the front blade pushing the rear blade. If you reverse the order, they will still affect each other but it will be far less efficient. Back to the fan example, if I turn on the front fan, it will suck air past the rear fan blades and if there is enough energy to over come the losses, the rear fan blade will spin too.
Can a reverse driven TC spin the engine? I would say that is dependent on a whole bunch of assumptions. If it’s not locked up mechanically, it can still happen but the engine’s resistance to rotation has to be overcome with enough rotational speed on the backside of the TC. For example, it’s going to be a lot harder to spin an 11:1 compression motor than say an 8:1. At some point it’s not going to work because the TC is designed to drive the other way. It’s only needing to overcome the driveline resistance, not overcome the inefficiency of reverse driving and the compression of the motor to boot.
I agree with you, as much as I understand what you are saying. I know the driving force is greater from the engine thru the converter, than it is from the transmissio thru the converter, but it will still work. I was thinking of the 2 fan situation myself, but figured if I mentioned it, I would get shot down.
puting the car in drive and rotating the engine by rotating a rear wheel Won’t work
And there is no direct mechanical connection fron the engine to the transmission.
I only use the terminology “reverse Drive” because one of the best transmission man on here used it.
TwinTurbo has made a great analogy about the 2 fans. This analogy came to my mind the other day but I figured it was pointless to even mention it.
Why is it I get no answer to the simplest of questions, as per the rolling the converter with a fingertip one?
So if anyone other than Elly wants to explain then answer me this.
I’ve tried this test on 3 vehicles at my house (4R70W, non-electronic AOD, and a 4L60E.
There is no engine rotation or engine restart after allowing the car to coast in DRIVE for more than a few seconds.
Transman performed this test on a 46RE equipped Dodge pickup and got the same result.
So, why do the above examples have no engine braking and no engine restart after more than a few seconds?
Transman tested it on a 518 tranny, I don’t know if they are different.
“Why is it I get no answer to the simplest of questions, as per the rolling the converter with a fingertip one?” Of course you can rotate the converter with a finger, as long as it is not bolted to the engine.
But I am almost positive that you cannot rotate the converter by turning a rear wheel.
Now here is a testimony of someone who didn’t even know he was testifying.
All 3 of our cars have automatic transmissions and tachometers. When traveling (say) 55 mph and I see a light turn red up ahead I immediately take my foot off the gas and start to coast. I notice that the rpm’s continue to hover around 2000 even tho’ my foots off the gas
Well, I count 9 “yeses” and one crazy one so I guess the answer is YES!!
HET TRABSMAN, I guess I am not the only one who doesn’t know what I am talking about.
Um, I believe you’re incorrect. I’ve had many vehicles over the years that didn’t even HAVE a lockup TC, and you could still initiate engine braking by downshifting the automatic to a lower gear. (or just watch the tach rise momentarily on each downshift)
If the TC could not transmit torque both ways, engine braking would be impossible. It may be more efficient transmitting torque from the engine to the transmission, instead of the other way, due to the turbine design, but it still transmits torque.
Also, since the lockup function is initiated by a solenoid, it would likely ‘unlock’ as soon as you turned off the ignition and the solenoid lost power.
A bit more testing over the weekend. First, a more thorough test of my Lincoln. (4R70W)
Three tests at 3 different speeds.
45 MPH - key off and instantly back on - engine restarts (likely due to converter inertia)
key off and a 4 second delay - no engine start - no engine braking.
55 MPH same as above
65 MPH also same as above.
Daughter’s '05 Mustang (5R55S I think is the transmission model) Two tests.
55 MPH - key off - instant back on - engine start.
key off - 5 second delay - engine start.
key off - 15 second delay - no start.
Second test at 65 MPH. Results same as above.
Son’s '95 Toyota Camry. Two tests and keep in mind this is a FWD car.
55 MPH - key off - instant back on - engine start.
key off - 5 second delay - engine start.
key off - approx 15 second delay - no start.
Second test at 65 MPH same as above.
So what I would like to hear from someone who has residual grease under their nails and an assortment of scars on their knuckles (Elly excluded) are some opinions about the above tests.
(Keep in mind that these tests were also performed previously on a non-electronic AOD Ford and a GM 4L60E with results similar to the 4R70W in my Lincoln. At this point I feel my testing encompasses more than what Elly has referred to as “some late model Fords”. To be honest, the entire point of all of this testing is beyond ludicrous.)
Oblivion, I don’t know who you say is incorrect. But I agree with every thing you just said.
I have never said that all transmissions wpuld work in the way mine does. I only know that mine does, up to 24 seconds, at least. I may have said that some late model Fords would not either, I should have said ALL late model Fords.
Now you did these tests with the ignitin OFF, as I did also. How about if you left the ign ON? Transman said a Torque Converter would never "reverse drive an engine. That should mean with the ign ON or OFF.
You probably should not use words like “ludicrous”, some of us ignorant farm boys might not know what it means!! Especially if we have clean habds.
Didn’t we already determine (in a suspiciously similar post) that Fords seem to give up early for some reason when doing this test?
Yes, it seems that Fords give up early with the ign OFF, I suspect they will “hold back” with the ign ON.
The tests were done with the key in the OFF position. The engine was killed and the key then turned back to the RUN position after varying amounts of time to determine at what point (how many seconds) the engine would restart on its own.
What’s the fixation on Fords? The GM 4L60E I tested did the same thing.
My daughter’s Mustang (built by Ford far as I know) required a lengthy key OFF delay before the engine would restart so this one varied a bit.
The same applies to the Toyota Camry.
As to Fords holding back with the ignition ON that is not true. Coasting in DRIVE with the engine running or with the engine off/key in RUN does nothing more than allow the car to coast freely.
(The old Mercury Sable I had (FWD and vastly different) would do the same thing.
OK, I have already conceded that Ford-built would not keep running with the key off. Now I guess that I need to concede about GM cars. However, I know that my Dodge will keep turning the engine for at least 24 seconds and I’ll bet for longer or until the speed reachhes a slow figure. Remember, my Dodge is 15 years old.
Come on guys, help me out, these guys are ganging up on me!!
What is the default hydraulic circuit of the transmission specific valve body with power to the shift solenoids, EPC and coast clutch solenoids turned off when operating in a particular gear? Many trasmissions have overdrive over-running (usually a sprag type) clutches that are bypassed via a clutch when in reverse or in any “overdrve-off” condition. This is the reason the Ford “gives-up.” I still wonder why this is of such fascination? Any answer to that one?
Well, I guess I’ll give up! I just hate to be told by transman that i know nothing about what I’m talking aboit and have ok4450 to agree with him, when I KNOW Positively that my Van will push the engine with the ignition OFF or ON. Plus there have been several others who have had the same experience as I.
I just have to add that transman said that “engine Braking” was done by the transmissiion, not the engine or torque converter. Of course, it is done by the engine thru the converter. Or from the transmission thru the converter to the engine.
Well, I guess I will give up!! I just hate to be told by transman that I know nothing about what I am talking, and have ok4450 to agree with him. I know Positively that my van will “reverse drive” or "turn the engine with the key OFF or ON. And several on here have had the same experience as I have. Also he, transman, said that a transmission did the work, not the converter. anyone should know that if the converter did not “reverse drive” there would be no “engine braking” at any time. Downshifting going down a hill would be futile. My van holds back some in Drive but it really holds back in 2nd.