: Thud, Clunk, Bang When shifting from Drive to Reverse or From Reverse to Drive



maydog
06-08-05, 12:25 AM
Howdy,

I recently purchased a 2000 SLS on ebay and I am in the process of making sure it is road worthy. One of the issues I am dealing with is a tactile shudder and an audible clunk sound when the trans is shifted between reverse and drive.

I can also feel a slight clunk from accelerating from a complete stop. It feels and sound similar to the problems I had on my 97 STS when the mechanic fubar'd my driveaxle. I have jacked up the front end on each side at a time and I can rotate the tires some, it does appear that the Axles and joints are rotating with the tire, so I suspect the axles are good. Am is missing something, is there something within the trans (such as the differential) that could cause this?

When I park on an incline, the vehicle rolls back slightly after releasing the brakes.

Is this normal? What other steps can I take to isolate the problem?

danbuc
06-08-05, 01:08 AM
Sounds to me like the front engine mount has gone bad. With the hood open and someone watching, shift from reverse to drive and look to see how much the engine moves. If it rocks back and forth as you describe, than it's most likely the front mount. The kick you feel from a dead stop, is the engine itself moving, before it actually begins to turn the wheels. When it get worse like mine, you'll get the same feeling when hitting the gas after coasting for a while, especially on a hill. My advice is to check the front mount, and make sure it's still good (which it probably isn't from what you desribe). If indeed it has gone bad, get it replaced. From what I've heard, the newer style Sevilles are more prone to killing front engine mounts for some reason (not sure why though).

The slight rolling action after removing your foot from the brake pedal when in park on a hill, is just the drive train, taking up the slack between the various gears in the tranny. I would strongly recommend using the E-brake especially on a hill, to prevent any trouble shifting out of park, after excess stress from rolling forward or backward. This motion can sometimes cause the little pin that "locks" the tranny, to get wedged in there, and make it difficult to get into gear. The E-brake really isn't necessary, but it's a good thing to use just in case.

maydog
06-08-05, 01:31 AM
Thanks,

I will check the mount, but I doubt that that is the problem. With one wheel of the car jacked up I can rotate the tire a 10-20 degrees forward and back again by hand. I can hear a clunk deeper inside the car when it engages at the end of rotation and will not turn anymore in that direction. This is done with the engine off.

Both my 97 STS and 96 aurora do not roll back like this in park. I think I will do a more thourough inspection of the axles tomorrow - until then I am looking for other things to check out while I am underneath.

Jack Ammann
06-08-05, 04:05 AM
Maydog...it's almost a certainty that it's motor mounts some kind of way. Also check the torque straps at the top-front of the engine compartment. When you find the problem, post back and tell us what it was and what it took to fix it. :yup:

maydog
06-08-05, 10:13 PM
The front mount does appear to be shot. I will snap a photo of it shortly. I will attempt replacing it this weekend and see if the issue clears up.

The axles are good, There is a little rotational play inside the trans, but maybe that is normal.

maydog
06-08-05, 10:34 PM
I used one jack near the driver wheel to get the car up. The second was used to jack up the engine and trans, I used the metal "bridge" between the trans and engine as a jackpoint. There was not a lot of room to manuver. When I actually replace the mount I will jack up both sides and use jackstands.

Motormount 1 (http://maydog.dyndns.org/www/catcon/motormount%20001.jpg)

Here is a photo of the mount, at first I thought it looked ok. After I jacked it up and used the mirror I could see where the separation occurrs.

Motormount 2 (http://maydog.dyndns.org/www/catcon/motormount%20003.jpg)

The car is so different (better) than my 97 - my wife is falling in love with it.

Jack Ammann
06-09-05, 02:35 AM
[QUOTE=maydog]I used one jack near the driver wheel to get the car up. The second was used to jack up the engine and trans, I used the metal "bridge" between the trans and engine as a jackpoint. There was not a lot of room to manuver. When I actually replace the mount I will jack up both sides and use jackstands.

I think you're exactly on the right track. While you're at it, I'd replace both motor mounts and the torque straps. I was gonna suggest gettin' a BIG pry bar to work with, but maybe you can do without it. Good luck. Keep us posted. :cheers: