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-   -   lunge at startup (http://www.ramforumz.com/showthread.php?t=168205)

Bill2010Hemi 02-23-2014 08:11 PM

lunge at startup
 
Hello, can anyone tell me why my 2010 ram lunges forward momentarily in cold weather when I start it?

RogerRamJet 02-23-2014 09:47 PM

It lunges forward while it's in park?

TransEngineer 02-24-2014 09:30 AM

I presume you mean it lunges forward once you put it in Drive. This is usually associated with torque converter drainback. Typical cause is a bad spin-on filter in the transmission. Did you recently have the transmission serviced (filters replaced)?

Step 1 would be to check the fluid level. If OK, then next step would be to drop the trans oil pan and check both filters. Look for a loose (or completely fallen out) spin-on filter, or a main sump (flat) filter that is cracked at the base of the plastic snout, split open along the side seam, or has the plastic snout dislodged from (or not pushed up through) the seal in the pump housing. If everything looks OK, then replace the spin-on filter with a Mopar filter (current filter likely has a bad anti-drainback diaphragm in it).

SShadow1974 02-24-2014 09:55 AM

Or you can wait until your RPM drop below 1000... I have the same situation, but it only happens if I don't let the RPMs settle down after starting the truck.

Bill2010Hemi 02-24-2014 05:37 PM

Quote:

Originally Posted by RogerRamJet (Post 1339625)
It lunges forward while it's in park?

Yes, while it is in park. On cold mornings (below freezing) I will open my door, start the truck without getting in and it will lunge forward...it doesn't take off or anything but it will rock the tires back and forth for a second.

RogerRamJet 02-24-2014 06:09 PM

Quote:

Originally Posted by Bill2010Hemi (Post 1340513)
Yes, while it is in park. On cold mornings (below freezing) I will open my door, start the truck without getting in and it will lunge forward...it doesn't take off or anything but it will rock the tires back and forth for a second.

That's interesting. Know a good Catholic priest? :LOL:

Maybe Mark (TransEngineer) will get back on and shed some of his brilliant insight and knowledge. :smileup:

TransEngineer 02-25-2014 09:33 AM

Quote:

Originally Posted by Bill2010Hemi (Post 1340513)
Yes, while it is in park. On cold mornings (below freezing) I will open my door, start the truck without getting in and it will lunge forward...it doesn't take off or anything but it will rock the tires back and forth for a second.

Well, who'da thunk it? (Not me, that's for sure)

I guess it won't actually go anywhere if it's in Park, but if it does jerk it could be due to clutch drag in Neutral due to the cold fluid. Or maybe you have a damaged UD clutch pack that is passing some torque even when released.

Will it drive forward when it's in Neutral (hot or cold)? If so, then you definitely have a damaged (or welded) UD clutch. Next time, try starting it in Neutral instead of Park (make sure you are INSIDE the truck!!) and see what happens. If it does start to move, is that only for an instant, or does it keep going?

Bill2010Hemi 02-25-2014 05:51 PM

No, it starts in Neutral but doesn't move at all, even when I give it gas. I will start it in neutral in the morning. It only did it on mornings when the outside temp was in single digits or low teens...lately it has been upper 20's lower 30's in the mornings and it hasn't done it. I doubt we get anymore temps that cold til next winter.

Bill2010Hemi 02-26-2014 07:40 AM

Started up in Neutral this morning..it lunged forward just enough to rock the tires back and forth and quit. Don't know the temp this morning but its pretty cold.

TransEngineer 02-26-2014 08:57 AM

Well, trans fluid thickens as it gets colder, so I'm guessing the residual fluid in your clutch packs (in particular, the UD clutch) is causing some drag (even though the clutch is released) and therefore tries to move the truck. But as soon as things start spinning, the fluid in the clutch (which would be laying in a puddle in the bottom of the clutch retainer) gets spread out around the clutch, giving just a thin layer of fluid on the discs (rather than a solid slug of fluid completely filling up all the space between the discs), so the drag force disappears (or at least, drops off enough that it's unnoticeable).

So bottom line, I wouldn't worry about it.


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