Reverse clunk

[Erik Sears]

So I’ve search, unsuccessfully looking for a clunk in my 99’s drivetrain. I don’t think it’s the cobra clunk since it only does it in reverse. So the symptoms are backing up, at idle, when I let the the clutch out I can feel a clunk in the floor that sounds like a hard contact, or someone gently whacking the floor with a small hammer. Nothing going forward. This made me think it was the tranny mount letting something ride up into the tunnel. I put it on the lift, nothing. The mount seems soft, but it’s in tact. I can’t see any hard rubs, shiny spots, sloppy u-joints, etc. I have no idea what else to look for. I pulled the 2 cross member bolts out of the tranny so I could feel how stiff the rubber is. Should I be able to flex the transmission mount by hand? Should it be that soft?

 

[01yellercobra]

There will be some movement with the stock rubber bushings. I'd check the diff mounts as well. It might be moving around.

 

[me32]

Also check the drive shaft U joints.

 

[olympic]

The stock trans mount is very soft so as long as it's intact it's good. What you are experiencing is probably the Cobra clunk. Mine does the same thing and usually I only hear it in reverse. It became really noticeable after installing solid diff bushings and sounds like a hammer hitting the floor of the car, as you described. It's caused by "play" in the differential. You can check for it by rotating the driveshaft by hand with the trans in neutral. Here's a vid of mine: