Surge on start up

**pajeff02** · 09-21-2009, 01:47 PM

Kind of an odd thing our car does on cold start up. Approximately 20-30% of the time when we first start our car it will surge forward the slightest bit. It's just enough movement to give you a scare. No noise or any other accompanying symptoms.

I understand how the parking pawl works and the transmission is definitely in "park". The transmission was serviced - fluid, filter and tailshaft seal, back in March and everything looked good. It shifts great and we have no other issues. It is the only automatic I have ever experienced this in. Anything to be concerned about?

**JaycenK** · 09-22-2009, 04:09 AM

odd, almost like something in the sprag assembly is not disengaging all the way or a clutch is not releasing all the way. I'm guessing you pull up to were ever in drive and then go to park? Does it always move forward when you have the problem or does it move backwards?

**pajeff02** · 09-22-2009, 04:32 AM

Originally Posted by JaycenK

odd, almost like something in the sprag assembly is not disengaging all the way or a clutch is not releasing all the way. I'm guessing you pull up to were ever in drive and then go to park? Does it always move forward when you have the problem or does it move backwards?

Pull up, come to a complete stop, place the shifter in "Park", and I always let the car idle for just a bit before shutting it off. It only surges forward, never backward. Also, I have never heard it click or make any noise that would lead me to believe that the parking pawl is not fully enagaged in the transmission.

**Smittro** · 09-22-2009, 04:42 AM

My 01 6er does this too. Almost feels like it's still in gear for like a split second then releases. I put mine in neutral for a sec., set the parking break first then go to park and shut down. That way only the brake is holding the car not the trany. Keeps torque off the drive line when not running (meaning the weight of the car is off the drive train). Took the surge right out of it on fire up..

I do the same with a standard transmission too. Pull it out of gear, set the brake, shut motor down, then put in first gear. Same thing! Puts the weight of the car on the brakes not the trany. That way it's still in gear to catch it if something happens and the parking break lets go.

**pajeff02** · 09-22-2009, 04:45 AM

Originally Posted by Smittro

My 01 6er does this too. Almost feels like it's still in gear for like a split second then releases. I put mine in neutral for a sec., set the parking break first then go to park and shut down. That way only the brake is holding the car not the trany. Keeps torque off the drive line when not running (meaning the weight of the car is off the drive train). Took the surge right out of it on fire up..

I do the same with a standard transmission too. Pull it out of gear, set the brake, shut motor down, then put in first gear. Same thing puts the weight of the car on the brakes not the trany. That way it's still in gear to catch it if something happens and the parking break lets go.

I agree, best practice is to set the parking brake. We park on the level though and quite honestly I have yet to check the parking brake to make sure that it completely disengages if set. Although our car is essentially rust free, I have no idea if it has ever been used. Good to hear I am not the only one with this issue.

**Smittro** · 09-22-2009, 04:51 AM

Originally Posted by pajeff02

I agree, best practice is to set the parking brake. We park on the level though and quite honestly I have yet to check the parking brake to make sure that it completely disengages if set. Although our car is essentially rust free, I have no idea if it has ever been used. Good to hear I am not the only one with this issue.

Haha, yeah mines spotless underneath too. I take very, good (maybe too good) care of my 01 6er. She does'nt get her feet wet except maybe the stray puddle. Rust free here too, came in handy when I changed the fuel pump the hard way (no cutting holes) lol...

**pajeff02** · 09-22-2009, 04:57 AM

Originally Posted by Smittro

Haha, yeah mines spotless underneath too. I take very, good (maybe too good) care of my 01 6er. She does'nt get her feet wet except maybe the stray puddle. Rust free here too, came in handy when I changed the fuel pump the hard way (no cutting holes) lol...

Rust free is a wonderful thing. My exhaust unbolted real easy when I installed my catback. Looks like the rest of the system should come apart the same if I get the balls up to order LT's and a catted Y this winter.

**Smittro** · 09-22-2009, 05:04 AM

Originally Posted by pajeff02

Rust free is a wonderful thing. My exhaust unbolted real easy when I installed my catback. Looks like the rest of the system should come apart the same if I get the balls up to order LT's and a catted Y this winter.

Yeah mine goes to climate controlled storage this year. Next year she may not see the road. Starting over groung up rebuild nose to tail and ls1 package.
I did'nt get time this summer to start cuz of the other project I got going. lol

**Cutlass** · 09-22-2009, 05:49 PM

Its completely normal. No worries. There is a GM Service Bulletin describing it. Here it is.

Originally Posted by GM

#PIP3763A: Slight Vehicle Movement In Park At Start Up After Cold Soak - keywords 3T40 4L60 4L60E 4L65E 4L80E 4L85E 4T40E 4T45E 4T60 4T60E 4T65E 4T80E 5L40E 5L50E 6L50 6L80 6L90 6T70 6T75 AF225 AF235 aisan - (Jan 5, 2007)

Subject: Slight Vehicle Movement In Park At Start Up After Cold Soak

Models: 2007 and Prior Passenger Cars and Light Duty Trucks
Equipped with Automatic Transmission

Condition/Concern:

Some vehicles may rock or move slightly forward or rearward while in park at start up after cold soak. This condition may be accompanied by a clunk noise. This is a slight movement that is more often seen visually, rather than felt, when viewed from the outside and using the auto-start feature, if equipped.
Recommendation/Instructions:

This slight movement is due to the residual transmission fluid in the clutch packs that creates a partial apply on start up. This movement is stopped by the parking pawl and/or transmission fluid exhausting completely from the clutch packs.

This slight movement has no adverse affects on the transmission and no repair should be attempted. This condition is normal. This can be verified by comparing with another identically built vehicle under the same cold conditions.

To prevent this condition from occurring, the parking brake should be utilized as per Owner's Manual recommendations anytime the vehicle is parked.