Turning off your car at 55 mph


#101

Still not convinced and I’m still digging a bit on the Mopar transmissions. I did find a blurb where Chrysler had admitted to a programming fault with the TCM and this fault involves the converter lockup. Whether it has anything to do with the symptom being discussed I have no idea at this point.

While it’s true the lockup is a mechanical affair, it’s also true that it takes hydraulic pressure to make it work.
The pressure to activate the lockup is applied through the converter solenoid which releases the pressure at the appropriate time to disengage it. (assuming it’s working as it’s supposed to)

It’s also dependent upon temperature and speed. The various Chrysler transmission specs I’ve looked at refer to the lockup being inactive under 43 MPH, 22 MPH, etc. all depending upon the model.

Maybe there’s a hitch with Chrysler transmissions and the lockup solenoid is remaining closed when the key is turned off. I’m still looking at that angle of it.


#102

ok4450, “I don’t get fuel pump operation having anything to do with converter lockup.
If a car is coasting at 60 MPH with the key in RUN and engine off then where does the ignition pulse come from to cause the ECM to trigger the pump relay?”

If a car was coasting at 60 mph with the key in the RUN position, why would the engine be off?

“where does the ignition pulse come from to cause the ECM to trigger the pump relay?”

It’s coming from the ignition being ON.


#103

I am almost sure that the converter unlocks when the key is turned off. I know we got far from the OPs question, but it’s been interesting!!

Hey, I put a backup camera on my Van today. It’s interesting to see 120 degrees behind you.


#104

I know very little about automatic transmissions (except that I got very upset when they took the drain plug out of the torque converters) but I can tell you that my 2004 PT Cruiser will re-fire without the starter at highway speeds and down to 20 mph. I have not trier it slower.

I discovered this because of an oil pressure light problem. The oil light would come on and stay on until I shut off the car and restarted it but it didn’t dound like an engine with no pressure. I discovered if I shut the key off for a few seconds and then back on the engine would fire up without the started and the oil light would stay off for the rest of the trip.

I have had a new sending unit riding in the glovebox for a couple of years now but I can’t reach the sending unit without a lift and it just doesnt seem urgent.


#105

So does this mean that a Chrysler product can have a tow bar attached to it and the vehicle can be dragged clean across the country with the wheels on the ground without damage to the transmission?


#106

I have NO idea But I doubt it VERY MUCH


#107

If logic that is used is that the engine is rotating and the converter is locked then this means that one should be able to tow a vehicle clean across the country because the pump in the transmission is providing fluid pressure due to engine rotation and there should be no problem with frying the transmission due to fluid starvation.
What does the Chrysler owners manual say about this?

Of course, this brings up the fact that the engine itself will be rotating against compression for that entire 2000 mile trip or whatever it may be along with providing one heck of a drag on the vehicle doing the towing.


#108

I should think that anyone would have sense enough to put it in neutral!! I doubt it would be a good idea (toeing it for any distance0.


#109

That’s beside the point though. In neutral or not, transmission internals are still rotating. Few automatics use bearings, they use bushings and bushings do not take well to no lubrication.

If the transmission is in neutral then (here we go again) what is driving the transmission oil pump?

Just for hoots, I’ll pose this scenario on this thread to a good friend of mine who has been a transmission guy for about 40 years. (mostly domestic and he knows these things blindfolded)
You know of course that I’m tweaking you a bit. :wink:


#110

I think what’s happening is that the engine and transmission keep spinning and somewhat keep each other ‘alive’ until the speed gets very low.

You could not push start the car, but when the drivetrain is running at highway speeds, the engine coasts, running the front pump on the transmission, the transmission since it still has fluid pressure, keeps the engine engaged and turning, and they both keep turning until the speed is too low and the honeymoon is over.

If you’re still not convinced, why not rent a Chrysler vehicle and try it? I can say that my 94 does it for sure. I haven’t tried it with my 2006. Maybe I should. This is a Mercedes transmission on my 300… so now I’m curious. I seem to remember that I could do this with my ancient Newport with a V8 and a 727 tranny, but I don’t think it kept going as far before disengaging.


#111

Where is your mind? If the transmission was in neutral, then the engine would not be turning, as you said 2 post back. Good greif, can’t you get the drift? Read my lips: While going down 4 different hills, I turned off the ignition, left the vehicle in drive and just before I reached the bottom of the hill, I turned the key ON and the engine started up. I did not use the starter. ON one hill it coasted 24 seconds.


#112

Oblivion, you are correct. I think we have established 2 things:

  1. Some Chrysler transmissions will push the engines.
  2. Late model Fords will not!

#113

At best, you’d have a very hard time keeping the car under control.

When learning to drive, I had to turn off (key to ACC, not to LOCK) the engine at low speed (~15mph) in a vacent parkinglot to get a feel of what happens if the engine stalled. The only thing I really noticed the steering and brakes took a lot of force, and when I pushed them hard enough to really slow down, the wheels locked up because the ABS can’t work like that.

When our starter motor died recently, I was reminded how much we take power-everything for granted. I had to “drive” while the towtruck driver pushed the car out of the garage. It took all my strength to turn the steering wheel fast enough to stay on the driveway and then almost all my strength to stop rolling downhill before hitting a brick wall.


#114

Now here’s someone with an OFF-The-Wall comment. In my experiment. the engine never stopped turning, the brakes and steering never failed and the engine fired up when I turned the key ON.


#115

The issue I have, as all along, is that I’d like to hear at least a fairly technical explanation of why come. It requires fluid pressure to maintain the converter lockup and the clutch packs and I don’t understand where this fluid pressure is coming from if the key is turned off and the converter lock is released.

I am at best lukewarm on automatic transmission rebuilding although I have done a lot of partial repairs and replacements of automatics. Most of my experience has been with manuals.

The reason for this is the methodogy of dealers. As an import tech we work with what is assigned to us; from a simple oil change to suspension work to electrical and engine repair. A single mechanic will cover all phases of car repair.

If one gets into the GM or Ford realm for instance you will find that in their shops they have a dedicated transmission guy (Transman for one), maybe several driveability guys, a heavy line guy (engine repairs), electrical, etc, and in some cases even a squeak and rattle guy whose job it is to track down those annoying irritants and who also appear to be masochists of some sort.


#116

ok4450, 1 2 3 4 5
"The issue I have, as all along, is that I’d like to hear at least a fairly technical explanation of why come. It requires fluid pressure to maintain the converter lockup and the clutch packs and I don’t understand where this fluid pressure is coming from if the key is turned off and the converter lock is released."

In the above post, you asked where is the fluid pressure coming from? A. as long as the converter and engine and tranny are still moving, the pressure is still there. But at some point as things slow down, the the engine will stall and it;s over. I am talking about my own Van a 96 Dodge 2500, 5.2 liter V8, automatic transmission. I tried bump starting it today after I had turned off the ignition and put it in neutral, after a few seconds turned it ON and put it in Drive, but it did not start up.
I used to have a '99 S-10 that would go into free wheeling if you let up on the gas. I am sure it would not bump start. Now guys, don’t agque about this (the S-10) I know what it was doing!! It had a tach and a glass packed muffler I could see the tach fall and hear the engine slow down.


#117

ok,

Since I know that you understand torque converters I know you will understand this. You know that inside the torque converter the input shaft of the transmission is turned by fluid flow. There is no hard connection between the crankshaft of the engine and the input shaft of the transmission except for the applied converter clutch. (Only when its applied) The engine is turning faster than the transmission input shaft creating the fluid flow (force) to turn the input shaft of the trans, the veins in the converter cause the fluid to change direction (called vortex flow). The fluid flow is the only driving force to the input shaft. When this flow is lost, lubrication to the transmission and line pressure to the transmission is also lost. Converter lockup and line pressure will not hold for long after the engine fails.

transman


#118

If the engine could not be turned by the transmission, instead of just driving the transmission, then it would be impossible on an automatic to downshift and use engine compression for braking. And clearly you can, on every automatic. Some seem to lose pressure sooner than others with the engine not supplying any power, as the car slows down, as we’ve established.


#119

"The fluid flow is the only driving force to the input shaft. When this flow is lost, lubrication to the transmission and line pressure to the transmission is also lost. Converter lockup and line pressure will not hold for long after the engine fails."
True, BUT in my van, this flow is not lost until the speed reaches some low figure, I do not know what that figure is. And I only know that it will hold for 24 seconds. I haven’t tried it longer. I am convinced that speed not time is the factor.


#120

Engine braking is done inside the transmission by way of overrunning clutches for example. Not by converter operation.

transman