Car sways back and forth during start up [ Video ]

[JAM486HP]

I think a trip to the dreaded dealer might be unavoidable, though maybe you guys could point me in a direction as to what might be causing this or it's normal.

First video at startup on a level surface, vehicle in Park, without the brakes applied, it rocks back and forth as soon as the engine turns. Been doing this since day 1.

Second video this time in Neutral without the brakes applied, the car rocks about 6 seconds after startup. This I only just discovered by starting in different scenarios, parking brake on, no brake, remote start etc..

A10, no strange noises, no lights or codes and the car runs great

Startup in Neutral no brakes applied​

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[Ciulster]

I know what the problem is! Your car came with the wrong transmission! Joking aside, that looks like it might have something to do with parasitic forces moving through the driveline. I once jacked up the rear end of my truck and even though the transmission was in neutral it was able to spin the rear wheels up to about 10mph at idle, I was able to stop it by hand though.

These cars are fairly high horsepower but even still there shouldn't be THAT much power being sent to the wheels while out of gear. If indeed the startup flare is enough to move a 4000 pound car a bit through parasitic transmission forces alone I'd be concerned my transmission was built with some tolerance out of spec and it's dragging power out of it to the rear wheels somehow. Might want to at least get the dealers opinion on that and see if it's normal. Not worth it to keep driving it if the trans is assembled wrong and will eventually burn up.

 

[JAM486HP]

I know what the problem is! Your car came with the wrong transmission! Joking aside, that looks like it might have something to do with parasitic forces moving through the driveline. I once jacked up the rear end of my truck and even though the transmission was in neutral it was able to spin the rear wheels up to about 10mph at idle, I was able to stop it by hand though.

These cars are fairly high horsepower but even still there shouldn't be THAT much power being sent to the wheels while out of gear. If indeed the startup flare is enough to move a 4000 pound car a bit through parasitic transmission forces alone I'd be concerned my transmission was built with some tolerance out of spec and it's dragging power out of it to the rear wheels somehow. Might want to at least get the dealers opinion on that and see if it's normal. Not worth it to keep driving it if the trans is assembled wrong and will eventually burn up.

My initial order was manual, then my old wrecked knees talked me out of it.

Yeah I try to avoid dealerships like the plague. Probably should get it on record. The initial startup movement in Park I figure was just a lot of horsepower fired up would make the car move a little. It's been doing that from day 1.

The one that really puzzles me is startup in neutral and the car moves 6 seconds later.

 

[Ciulster]

One thing to note too is modern automatic transmissions do do a lot of weird things behind the scenes. Might be something like the transmission doing a start up self diagnostic check and after 6 seconds it's engaging a clutch pack or a valve body solenoid or something and even though it's in P or neutral that's enough to let enough power through to move the car without brakes on. Every electronic solenoid Dodge transmission I have ever seen from about 1993 and up when you put it in reverse, like clockwork, wait 3 seconds, it buzzes for 2 seconds in a way that sounds like someone running their nail along a metal file. Something to do with solenoids or something. Just the way they operate.

 

[Ciulster]

Another thing to note too is maybe ask the dealer to verify your park brake is setting correctly. If I understand the owners manual correctly the park brake should automatically set and stay set with the car running and should not disengage until shifted into a moving gear. Same how the hills start assist and hill hold is supposed to hold the park brake on until it detects the clutch being let out and a little throttle being applied. This might be a normal running condition of the car that is normally masked by the parking brake being engaged by the computer for startup

 

[JAM486HP]

Another thing to note too is maybe ask the dealer to verify your park brake is setting correctly. If I understand the owners manual correctly the park brake should automatically set and stay set with the car running and should not disengage until shifted into a moving gear. Same how the hills start assist and hill hold is supposed to hold the park brake on until it detects the clutch being let out and a little throttle being applied. This might be a normal running condition of the car that is normally masked by the parking brake being engaged by the computer for startup

This is all great information. I wondered about the auto hold feature, I have it disabled though sometimes on a cold start it will be activated until I accelerate

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