2015 JK Rolls when in gear and engine is off!

H20JNKY

H20JNKY

Member
Automatic transmission: Can someone give me some insight if this is normal or not? I tried it at home yesterday in the drive way at an incline. Put it in drive, turned the car off, rolled. Put it in reverse, turned car off, rolled, put it 4 low, drive, turned car off rolled. Every scenario I drove at least 15' before turning the ignition off. I find it very odd that this would be normal. Other then this the jeep drives like a dream and 4x4s great.
 
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H20JNKY said:
Automatic transmission: Can someone give me some insight if this is normal or not? I tried it at home yesterday in the drive way at an incline. Put it in drive, turned the car off, rolled. Put it in reverse, turned car off, rolled, put it 4 low, drive, turned car off rolled. Every scenario I drove at least 15' before turning the ignition off. I find it very odd that this would be normal. Other then this the jeep drives like a dream and 4x4s great.
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Please clarify what you mean by "rolled". Rolling a foot is a whole lot different than consistently rolling while in gear. A little clarification will go a long ways on this thread.
 
Speedy_RCW said:
Please clarify what you mean by "rolled". Rolling a foot is a whole lot different than consistently rolling while in gear. A little clarification will go a long ways on this thread.
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Rolling until I step on the brake. Rolled about 10' until I stopped it. This is an automatic transmission.
 
Coop said:
Agree. The only resistance is the torque converter vanes and transmission fluid.
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Well, I have a manual yj and it doesn't roll, so I wanted to test the automatic JK to see if it would stay put. My thought was, what if I lost power on a hill for one reason or another while in gear? Obviously I have my brakes, e-brake and park. Anyway, just wanted to know if this was normal and that I wasn't going insane and to learn why it's like that.
 
The torque converter doesn't lock you into gear like a clutch would. It is meant to slip at low rpm (or no rpm) think of it like if you depressed the clutch on a manual. There is nothing holding the trans to the stopped engine. The park gear has a pawl in the transmission that locks it up. This is also why even with an automatic park brakes are helpful for increasing the life of your transmission. It helps spread the stress that the pawl has to hold.
 
H20JNKY said:
Well, I have a manual yj and it doesn't roll, so I wanted to test the automatic JK to see if it would stay put. My thought was, what if I lost power on a hill for one reason or another while in gear? Obviously I have my brakes, e-brake and park. Anyway, just wanted to know if this was normal and that I wasn't going insane and to learn why it's like that.
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As others have mentioned, this is normal with an auto trans. I can't speak as to your mental health though. [emoji6]
 
H20JNKY said:
Well, I have a manual yj and it doesn't roll, so I wanted to test the automatic JK to see if it would stay put. My thought was, what if I lost power on a hill for one reason or another while in gear? Obviously I have my brakes, e-brake and park. Anyway, just wanted to know if this was normal and that I wasn't going insane and to learn why it's like that.
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For an automatic, when you shift into park, you engage a metal pawl into the shaft to lock the transmission. With the weight of a JK, you want to set the parking break, especially on a hill or incline, so the full weight of the JK isn't on the tiny pawl.
 
Coop said:
For an automatic, when you shift into park, you engage a metal pawl into the shaft to lock the transmission. With the weight of a JK, you want to set the parking break, especially on a hill or incline, so the full weight of the JK isn't on the tiny pawl.
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Never thought of this and never set my e-brake in the driveway (however slight the decline may be)... guess I better start using it. Thanks for the info!
 
QuicksilverJK said:
The torque converter doesn't lock you into gear like a clutch would. It is meant to slip at low rpm (or no rpm) think of it like if you depressed the clutch on a manual. There is nothing holding the trans to the stopped engine. The park gear has a pawl in the transmission that locks it up. This is also why even with an automatic park brakes are helpful for increasing the life of your transmission. It helps spread the stress that the pawl has to hold.
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Thank you for the explanation! I feel a lot better knowing how the automatic works now vs the manual.
 
A torque converter is a pump, a pump that couples the engine to the transmission using fluid pressure while the engine is turning faster than the transmission input (I am not talking about lockup clutches because they don't engage if shut down or not moving fast enough). If you keep your engine running and do not rev the engine, depending on the stall speed of your TC you can (and most likely will) roll backwards when you put the transmission in a forward gear, same for rolling forward in reverse. The vehicle will roll both directions in either gearing, but rolling forward probably isn't noticeable in drive or rolling backwards in reverse because a person is expecting that type of motion. This is why you hear people say you can't push/bump start a vehicle with an automatic transmission.

With the engine off it is the same, no fluid pressure between them so nothing to couple the engine to the transmission. Unless something is in place in the transmission (the small parking lock pin) or after (parking/emergency brake) the vehicle will move when a force is applied (either through gravity or pushing), engine compression will not help.

Sorry :( , poor joke, Anton Yelchin just passed away after being crushed between his house and his (here's the irony) Jeep when it wasn't put properly into park and he was caught between it and his garage when it rolled. He had a newer Grand Cherokee with some odd quirk that made it hard to properly place the transmission in park - which is why a parking/emergency brake should always be used,one should never rely on the parking lock pin to hold a vehicle, especially on an incline.
 
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