I have a 2000 Z28 with some mild mods. One mod is a hypertech programmer have tuning installed,shift points,and shift firmness. When the car shifts from 1-2 at part throttle i hear a clunk. Could this be a problem with the tranny,u-joints,or rear end? It shifts good and strong under full throttle. I dont know if this is normal or not. Please reply if you know.

 

Do you have your shift firmness increased? If so set it back to normal and see if the noise goes away.

 

I am having the same problem with my 98 SS M6. I haven't done anything to it mod wise. But I was getting the same thing, a clunck. I have no idea what it is, I was told it was the clutchs in the posi unit, I'm still not sure if that is it. I was told to replace the fluid in the rear end. You may wanna try that, it seemed to make mine some better. My u-joints are fine, also my ring and pinion are wearing fine, bearings are fine, springs on the posi unit are fine also. Only thing left is the clutchs in the posi unit or the spider gears. I think I'm gonna replace the posi unit. Its only a hundered bucks for a brand new one.

But, I'd say check your u-joints first, then if that doesn't help change the fluid. Mines been doing it for about 2 months and nothing has broken or anything, and I don't go to easy on her. Mine has changed sounds though, its now like 3 or 4 clunks in a row, that aren't as loud. I don't understand it! I've had 4 very good mechanics listen to it and they don't know either. Although the next step is to start lookin in the transmission, my syncros are going that my have something to do with it. Anybody else got any suggestions, would be very appericated!

 

Its not the u-joints. a clunking noise when putting it into gear (m6 or auto) is oftens times the sign of a bad trans mount. the gm mounts theyve been usung ffor the last 500 yerars suck ***. go spend 20 bucks on a nice poly trans mount and i think your problem will be fixed. let me know how it turned out.

Scott

 

OH yeah, had the transmission mount check it was fine also. It doesn't happen when putting it into gear it happens when giving gas, about mid throttel, not as bad when getting on it though. It also does it sometimes when I'm breaking. Now that I've changed out the fluid it seems to start happening after the rear end heats up. Doesn't do it when im just starting off.

David S