94twincam trans/shift problem w reversing

Hello!

My car has been exceptionally well-behaved for over a year (knocking on head). I just had the oil changed a while back and my mechanics didn't seem to think anything was amiss.

However, a couple times in the last few months, it has hesitated when I shifted to reverse, and shaken heavily once, and made a "thunk" sound, before it would go into reverse.

This is very startling and I don't know what to make of it. It hasn't ever done this right when I turn it on, if that means anything. Also, it could be that I don't have the brake down hard enough? Or that I am on a slight tilt (this seems to happen when I am turning around in a driveway... but it's only been about 3 times so I haven't kept total track of it.)

I haven't noticed any other transmission problems, but then again, it has never been particularly smooth either, imho. (But I am not a car person, so I can't really say.)

No lights go on or anything like that (unless I am not noticing, if it just blinks. I am usually looking behind me when this happens, or just sitting there hoping it won't happen.)

Does this sound like anything to anyone? Any suggestions?

I looked at these threads but wasn't sure anything sounded identical:

http://www.automotiveforums.com/vbulletin/showthread.php?t=147489&highlight=trouble+shifting+reverse

http://www.automotiveforums.com/vbulletin/showthread.php?t=140082&highlight=trouble+shifting+reverse

and this one, which may as well have been in French:
http://www.automotiveforums.com/vbulletin/showthread.php?t=359210

All suggestions welcomed!!!

Thanks so much for your help. I am really hoping to not have anything catastrophic happen to this car. (Which my nephew says is almost "vintage." ; > ) I am really grateful it's driving so well.

This is a common issue with the TAAT automatic transmission in the S-Series known as the "reverse slam".

The most common cause is a loose input shaft nut, but the valve body may also need to be replaced.

You may be surprised to hear that performing these repairs will not be as expensive and difficult as it sounds. All of the work can be done without removing the transmission. If you can do the work yourself the Input/Output shaft nut service kit is $80 on ebay and a new valve body can be had for around $200.

Most people do the Input/Output shaft nut fix first. If that doesn't fix it then they go ahead and also replace the valve body. There are some videos on youtube that do a good job of walking you through the work. The Saturns they are working on may not be the exact same year or model as yours, but the info is still applicable to your car.

Ruley73: thank you sooooooooooooo much!!! I will print this out and take it with me to the mechanic.