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Feels like someone rear ends me when I am stoped

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My 1996 legacy lsi automatic, has a problem. When I am stopped waiting at a light I will feel a tud for a second (kind like someone rear ended me) it does this after I have been stoped for a minute or so. It is strange, the idle seams fine and it doesn’t make a noise. It does it when the car is in drive or park. Does anyone have any idea what this could be???

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Is the tranny fluid full, and good fluid? Only thing I can think of is that sitting stopped in drive is heating the fluid up after a minute, and causing it to do something.... not sure what though....

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That's bizzare. I don't know what would be causing the issue if you have the vehicle in park.

 

I guess one thing you could try is jacking the car up off all four wheels. Run the car, and then come to a stop, and put it into park. See if you notice the wheels moving.

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My 1996 legacy lsi automatic, has a problem. When I am stopped waiting at a light I will feel a tud for a second (kind like someone rear ended me) it does this after I have been stoped for a minute or so. It is strange, the idle seams fine and it doesn’t make a noise. It does it when the car is in drive or park. Does anyone have any idea what this could be???
A couple of years ago, a woman who was driving a Ford product pulled off the road in front of me, then followed me home, accusing me of having rear-ended her while we were stopped in a line of traffic. Of course, I hadn't done so! It took a cop and the obviously undisturbed road-salt residue (it was winter) on both my front bumper and her rear one to sort of convince her that our cars hadn't "kissed". I suspect that the car, which she said was new to her (although not itself new), was doing something similar to what you're describing.

 

I'm not sure, but you could be having a problem with the torque converter not locking/unlocking correctly. The symptom isn't unique. Does it do it when cold, or only after the trans is warm? When stopped in drive, the idle doesn't change at all when the thud occurs?

 

EDIT: Here are some things that might help in understanding trans operation:

http://endwrench.com/pdf/feb2004pdf/4EAT.pdf

http://endwrench.com/images/pdfs/4EAatPh2Win04.pdf

http://endwrench.com/images/pdfs/4EAT.pdf

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Ya i was thinking that It could be the torque converter. This is the first automatic that I have owned so not sure what to expect.

 

It does it when it is warm, it usaly does it in Drive but I have to be stoped. I put it in Park to see what happens and it does the same thing. Dosn't do it right away it takes about a minute to happen. Usally only happens once but sometimes twice.

 

As for the rps, they dont seam to change. But it is hard to tell beacause I dont know when my car will lurch.

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does it have rear drum brakes? I've seen some weird movement from some kinda torque held in place by warped drums when brakes are released. It was on a '90 maxima though.

 

I dunno

 

weird

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It does it when it is warm, it usaly does it in Drive but I have to be stoped. I put it in Park to see what happens and it does the same thing. Dosn't do it right away it takes about a minute to happen. Usally only happens once but sometimes twice.
Hmmm, this happening more than once per stop makes it "interesting". Make sure the trans not only is sufficiently filled, but also not overfilled; be sure to check it with engine running, warm, on level ground, after going through all gears, etc. Since you don't know how old the fluid is, even if it looks fairly clear and red (and especially if the fluid is dark or smells wrong), and the level is correct, perhaps it's time for a full flush with new fluid. That will sometimes get rid of varnish, etc that may be causing a valve or solenoid to stick. Make sure the correct type gets used; the wrong one can cause strange problems due to different frictional characteristics.

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Yes I will flush the system. Is that someting that I can do myself of should I take it in???

Oh ya and what kind of fluid do you recomend?

I don't know what you feel comfortable doing. Here are some previous threads worth reading that discuss the issue and related things:

http://www.ultimatesubaru.org/forum/showthread.php?t=50129

http://www.ultimatesubaru.org/forum/showthread.php?t=49761

http://www.ultimatesubaru.org/forum/showthread.php?t=51084

http://www.ultimatesubaru.org/forum/showthread.php?t=47978

http://www.ultimatesubaru.org/forum/showthread.php?t=38872

 

My '99 uses Dexron III, but you should verify what yours needs. Some people think a synthetic is better, others don't find an advantage to it.

 

I'd also suggest that you consider that the problem may be sensor-related. Even a bad ground connection can cause strange symptoms in an electronically-controlled trans. Some of the threads listed above go into that (although torque-bind is the main concern touched on). Are there any dash lamps flashing, especially for a while after the engine is started? Maybe a trouble code has been set; you could get a scan done and see if anything comes up. Some of the auto parts suppliers will do that for no charge.

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Could it be the duty solenoid/ rear clutch pack, releasing ? and or are your tyres the same size front to rear ? maybe there is alittle windup that lets go when stopped?

 

my edumacated guesses :rolleyes:

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My 1996 legacy lsi automatic, has a problem. When I am stopped waiting at a light I will feel a tud for a second (kind like someone rear ended me) it does this after I have been stoped for a minute or so. It is strange, the idle seams fine and it doesn’t make a noise. It does it when the car is in drive or park. Does anyone have any idea what this could be???

 

When I worked at a GM dealer about 5 years ago, every so often a customer with a full-size Chevrolet pickup, Suburban, or Tahoe would come in complaining about a "thump" that was felt after the vehicle had been brought to a complete stop and was sitting there for 15-30 seconds with the brakes applied. Technicians used to lubricate the rear driveshaft splines (where the driveshaft enters the transmission) to solve the problem. They referred to it as "driveshaft bind"

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