: Transmission lurch



realhighpockets
09-19-04, 06:13 PM
Iíve noticed something unusual with my 98 Concours w/80K. When it has sat in the garage for at least 24 hrs, and is started, the car lurches forward until it engages the parking lock in the transmission. Is this unusual? Iíve looked through the service manual and donít see a troubleshooting table. There are no codes, the fluid level is normal, and the color looks and smells normal. There are no driving problems. Should I worry?

JimD
09-19-04, 06:55 PM
My Seville has done that from day one although I would describe it as a "creep", or a torque reaction. Normal.

Eldyfig
09-19-04, 11:26 PM
Every once in a while, if I pay attention, mine will do that also. I am not sure what the deal is. Everything with the trans works like a charm.

realhighpockets
09-20-04, 10:21 PM
Thanks for the replies. I've never owned an autotmaic transmissioned car that has done this.

Pjs
09-22-04, 06:24 AM
My 95 SLS does the same thing, although it doesn't do it all the time...3-4 times a week

dretwenty5
09-27-04, 03:22 PM
My 96 Eldorado does the same thing, has been doing it for at least 6 months. Just set the parking brake.

96 STS
11-05-04, 02:19 PM
Hi all! As the name implies, I've got a '96 Seville & I've recently noticed my car doing the exact same thing when I start it up sometimes. I doesn't really seem bad, just very unusual.

The car quickly "creeps" forward about 3-4 inches when it's started. I've NEVER experienced this in ANY other auto car that I've owned in the past. Just wondering how common this is & if anyone figured out what causes it.

96 STS

blb
11-05-04, 03:21 PM
'94 STS does the same thing........usually worse after the first start after it it has set a couple of weeks or more without running.

BeelzeBob
11-05-04, 11:11 PM
What you notice is perfectly normal with the 4T80E transmissions. It is just the clutch packs knocking themselves loose the first time with cold fluid in the clutch pack. Every 4T80E will do this on coldstarts. It is just more obvious in some situations where the floor is very flat in the parking space and/or the tires are aired up for low rolling resistance. There is nothing wrong...just the nature of the beast. It only rocks on the intial rotation of the start. It wont actually move the car...just rock it slightly against the parking pawl. This movement is a little more obvious in a transverse front wheel drive transaxle arrangement due to the rotational movement of the engine allowed by the mouting system. If you open the hood and watch the engine/trans assembly while you idle and shift from park into drive and then reverse you can see the engine move fore and aft considerable. TFWD mounting requires "looser" mounts for isolation and that allows the engine to rock a little more. Since the torque reaction from the parking pawl will rock the engine the initial movement at startup is magnified on the TFWD cars by the rock of the engine mounting. Just the way TFWD cars are...

96 STS
11-06-04, 01:24 PM
Thanks Bbob!! Now I feel better. I've had my STS for almost 1 year now & just now noticed this. But, I also noticed this at about the same time that car was put in the garage. It was in the back yard before, on a slight incline. So your explanation involving flat parking surface fits my situation.

Thanks again for the detailed explanation. I will now ignore it & enjoy my ride.

Thanks,
96 STS

BeelzeBob
11-07-04, 04:30 AM
Yea, the startup "lurch" is simply a fact of life with clutch packs like automatic transmissions use.

If you ride a motorcycle you should be familiar with this also. Ever notice when you start a motorcycle and put it into gear the first time how much of a CLUNK you get and/or that the trans seems balky to engage and that the first engagement is a bit harsh...??? Same deal...the multiplate clutch has to shear a lot of oil that is holding all the plates together so that first engagement into gear that forces the clutch plates to slip is always harsher than the next ones. I work around this by starting the engine and letting it warm up a bit and then killing it with the kill switch, putting the trans into gear and then re-starting the engine with the trans in gear and the clutch disengaged while cranking. You can always feel the bike lurch forward a bit as the starter breaks the clutch plates loose for the first time. After that initial "sticktion" is broken the engine idles fine in gear with no creep or anything and it doesn't clunck so badly when putting it into gear on subsequent shifts after it has broken the clutch plates loose the first time.

This is always more promenent on the first cold start of the day due to the length of the over-night cold soak. The oil viscosity at start up is dependent on two things...the temperature and the length of the soak. The oil viscosity increased as the temperature gets lower (as the engine cold soaks until it cools to ambient temperature) and then continues to increase once the engine temp stabilizes with time. Parafin formation in the oil takes time and continues for up to aoubt 48 hours usually depending on the oil blend and brand. The parafin formation with time is what causes the viscosity to keep increasing with time even though the temperature has stabilized. That is why the creep during crank is more obvious on the first start in the morning and not again during the day even though the car may cold soak to the same temperture sitting during the day.....

96 STS
11-07-04, 11:37 AM
Bbob.............You know too much!! :)

But don't stop. We love, respect, & appreciate you for it. Keep it coming.

Cheers,
96 STS