Car Jerks Forward When Starting - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
Problems and Service Talk about any mechanical problems you are having

Closed Thread
 
LinkBack Thread Tools Display Modes
post #1 of 27 (permalink) Old 09-23-2013, 05:28 PM Thread Starter
Prospect
 
Join Date: Sep 2013
Location: Richfield, WI
Posts: 12
Question Car Jerks Forward When Starting

A few months ago I bought a used 2008 Cobalt LT with 31,000 miles & automatic transmission. Just a couple weeks ago I noticed that right after starting the engine the car will jerk forward and make a "thunk" sound even through it's still in park. It only does it after the car has been sitting for at least a few hours; never having been just shut off. Any ideas?
Bry1105 is offline  
Sponsored Links
Advertisement
 
post #2 of 27 (permalink) Old 09-23-2013, 05:59 PM
Contributor
 
Join Date: Nov 2008
Location: Clovis, NM.
Posts: 360
Garage
this "thunk" is how loud ?

when I start mine without foot on the brake, it will roll forward and make a noise,
but I would not even come close to call it a thunk.
I'll look at work cause I believe there was a tsb, something like,
customer complains that vehicle rolls forward when starting the car.
said something of this is considered normal operation for starting without
brakes applied.
just throwing that out there.

07 G5 GT

Cherry's Tree


Randy
Now serving Boost
272whp 276wtq @10psi
Cherry GT is offline  
post #3 of 27 (permalink) Old 09-23-2013, 06:58 PM Thread Starter
Prospect
 
Join Date: Sep 2013
Location: Richfield, WI
Posts: 12
The "thunk" & movement is different every time. Sometimes barely noticeable; just a slight "click" and little to no movement. Other times the car actually rocks forward and the "thunk" sounds like a REALLY hard shift. It's like the car is trying to move forward put can't b/c it's still in park.

Last edited by Bry1105; 09-24-2013 at 07:20 AM.
Bry1105 is offline  
 
post #4 of 27 (permalink) Old 09-23-2013, 07:41 PM
Super Moderator


 
Plain Jane's Avatar
 
Join Date: Mar 2013
Location: Montreal, Quebec
Posts: 3,860
Garage
Are you on an incline/decline? Do you use the handbrake?

'07 Eclipse GT build thread - 280whp, 254wtq
Plain Jane is offline  
post #5 of 27 (permalink) Old 09-23-2013, 08:17 PM Thread Starter
Prospect
 
Join Date: Sep 2013
Location: Richfield, WI
Posts: 12
My driveway is perfectly flat. I do sometimes use the e-brake when parking, especially if parking on an incline.

After searching the entire internet I've got a couple thoughts:
- clutch/transmission plates are sticking
- transmission control module

Any other thoughts?

Last edited by Bry1105; 09-24-2013 at 07:22 AM.
Bry1105 is offline  
post #6 of 27 (permalink) Old 09-24-2013, 03:06 AM
Super Moderator
YourCobalt.com Premium Member


 
Coby7's Avatar
 
Join Date: Oct 2011
Location: Magnetic Hill, New-Brunswick
Posts: 11,820
Garage
Maybe you have a broken motor mount.

Every minute spent angry is a happy minute lost for ever and ever!!!
Drives 2016 Cocoa Buick Encore 1.4L Turbo auto KL4CJDSB2GB652675
Drives 2016 Sunset Orange Trax LT1 1.4L Turbo auto 3GNCJPSB8GL142716

Never drive faster than your guardian angel can fly
Coby7 is offline  
post #7 of 27 (permalink) Old 09-24-2013, 08:06 AM Thread Starter
Prospect
 
Join Date: Sep 2013
Location: Richfield, WI
Posts: 12
Combined with the above problem, I've noticed is that the car seems to shift weird. There are times where I'll think "why did it shift there. I wouldn't have." When casually crusing down the road at 35-40-ish, it'll upshift again (when I wouldn't) and cause the rpms to go really low, like 1800. As soon as I give it a tiny bit of gas just to maintain speed it'll downshift. As soon as I lift off the gas to coast it'll upshift again... like it doesn't know which gear it wants to be in. It also seems sluggish to accelerate; I really have to stomp on the gas for it to downshift and accelerate.

Between the issue I first posted and the one described here, I really wonder if it could be the TCM? Is the TCM making the trans act goofy?

Last edited by Bry1105; 09-24-2013 at 08:34 AM.
Bry1105 is offline  
post #8 of 27 (permalink) Old 09-24-2013, 08:11 AM
YourCobalt of the Quarter Winner
YourCobalt of the Month Winner


 
BankerBalt's Avatar
 
Join Date: Oct 2010
Location: Eagan MN
Posts: 4,647
Garage
Motor/trans mount. Do you have any codes for the trans shifting at different points?

Sent from AutoGuide.com Free App

Forged L61 BW S252 Turbocharged Showoff Thread
BankerBalt is offline  
post #9 of 27 (permalink) Old 09-24-2013, 08:13 AM Thread Starter
Prospect
 
Join Date: Sep 2013
Location: Richfield, WI
Posts: 12
The check engine light has never been on. Could there still be codes?
Bry1105 is offline  
post #10 of 27 (permalink) Old 09-24-2013, 08:14 AM
Chevy Customer Service
YourCobalt.com Premium MemberExpert
 
ChevyCustSvc's Avatar
 
Join Date: Nov 2010
Location: Detroit, Michigan USA
Posts: 794
Bry1105,

Do you plan on having your local GM dealership look into this concern? Depending on when your Cobalt was originally purchased, you may still be under your powertrain warranty. We can look into this further for you. If you are interested, please private message us your name, VIN, phone number, and the name of your GM dealership.

Erica Tiffany
Chevrolet Customer Care

Have you checked into Chevrolet Owner Center? You can maintain service history, check on warranty or recall information, and more. Visit my.chevrolet.com!
ChevyCustSvc is offline  
Sponsored Links
Advertisement
 
Closed Thread

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome