clunking noise when in reverse

[jim97gst]

I have a strange problem with my 97 GST. I'm not sure if this belongs in problem diagnosis or here. Anyway, when I first start my car and go into reverse, after I've backed up about 5 feet or so, I hear a single clunking sound. I don't really know how to describe the sound. It's not super loud. Other than this, the transmission seems to be fine. Any ideas of what could be wrong?

A few months ago, I changed the tranny gear oil to Mobil 1. At first, it was kinda hard to shift when it was pretty hot. I bought some Penzoil Synchromesh and intended to try that, as I'd read so many good things about it. I haven't gotten around to changing it yet, but the transmission seems to be shifting fine now. The reverse clunking thing started sometime after I changed the tranny fluid, but I don't think it was right after.

TIA
Jim

 

[RedAllWheel]

The clunking could be your transfer case or driveshaft or many other things, I would have someone listen from outside the car while you move it to try and pinpoint where the noise is coming from. As far as the Mobil 1, I would change it ASAP. My theory is synthetic fluid, instead of adding friction like syncromesh, or syncroshift, it does the opposite and reduces the friction inside the trans which doesn't allow the syncros to do their job. You might be ok now, but high rpm shifts in a race situation... Grindozo!