deja Posted December 5, 2007 Share Posted December 5, 2007 I finally got around to investigating the clunking sound coming from the right rear of my 280Z. This only happens in reverse. It sounds like something is hitting something that is revolving, pretty much at the driveshaft speed. I recently did an LT1/4L60E conversion and at the same time installed lowering springs and struts with a lot help from Nullbound. I never had this problem before the conversion. On my initial test run I noticed what sounded like a clicking the first time I put the car in reverse. The second time it was louder and the third time it turned into the clunking sound I hear now. I have checked the wheels and adapters and they are tight. There is no sound if I rotate the wheels or the driveshaft by hand. I have crawled under and checked for loose bolts and anything that is close to rubbing. The only thing I see is the u-joint is only about 1/16" from the sway bar with the suspension loaded or unloaded. But I see no wear marks on either, its tough to see it very well though. I started the car while it was on stands and put it in reverse, the noise is still there, maybe not as loud but its there. I'm thinking the sway bar is hitting when the car is under reverse load, does this make any sense? If so I thought I would remove the sway bar to see if that fixes it. I seem to remember I can't just unbolt the bar and take it off. Is there a process, like loading or unloading the suspension I need to do to remove the bar? Any other ideas on the cause of this would be greatly appreciated. Like I said it only does this in reverse, going forward there is no clunking noise at all. Oh yeah one more thing. When I had the car up on stands and in reverse the diver's side wheel turned like I thought it would, the passenger side was moving but very slowly, I grabbed it and it stopped turning. Is that normal? I do not have LSD so I know only one wheel is driven. Is the fact the passenger side wheel is turning at all because it has no load on it or is that a clue of something wrong? Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted December 5, 2007 Administrators Share Posted December 5, 2007 Do you have the stock 280-Z rear sway bar in place? In reverse, the nose of the diff wants to come “down” and with rubber diff bushing, the nose of the diff will come down a little and with the larger diameter GM driveshaft and U-joints, the clicking/clunking sound you are hearing could be the diff input shaft/driveline U-joint rubbing on the sway bar. Just a thought. Quote Link to comment Share on other sites More sharing options...
Dragonfly Posted December 5, 2007 Share Posted December 5, 2007 I might just be thinking negative here but to me it sounds a lot like the rear differential "death knock" which is caused by the shaft in the carrier coming loose and wallowing out the hole (it sits in) in the carrier. All three of my diffs that died from this ailment started out making a knocking sound when putting the car into reverse, then when backing up and finaly under deceleration. This could be a good time for you to go ahead and drain the rear diff, pop the cover off and take a look at things on the inside, if all is healthy put some new gear oil in and start hunting for something much less major. Good luck on this one. Take a look at Jons sticky on differentials to learn more of what I am talking about. Dragonfly Quote Link to comment Share on other sites More sharing options...
deja Posted December 5, 2007 Author Share Posted December 5, 2007 Do you have the stock 280-Z rear sway bar in place? In reverse, the nose of the diff wants to come “down” and with rubber diff bushing, the nose of the diff will come down a little and with the larger diameter GM driveshaft and U-joints, the clicking/clunking sound you are hearing could be the diff input shaft/driveline U-joint rubbing on the sway bar. Just a thought. Yep, stock bar. That's what I was thinking. Quote Link to comment Share on other sites More sharing options...
deja Posted December 5, 2007 Author Share Posted December 5, 2007 I might just be thinking negative here but to me it sounds a lot like the rear differential "death knock" which is caused by the shaft in the carrier coming loose and wallowing out the hole (it sits in) in the carrier. All three of my diffs that died from this ailment started out making a knocking sound when putting the car into reverse, then when backing up and finaly under deceleration. This could be a good time for you to go ahead and drain the rear diff, pop the cover off and take a look at things on the inside, if all is healthy put some new gear oil in and start hunting for something much less major. Good luck on this one. Take a look at Jons sticky on differentials to learn more of what I am talking about. Dragonfly That's possible for sure but it didn't do this before I swapped engines and lowered the car. I haven't really driven the car other than that one test run so I doubt it just decided to die now. Well there is that famous Boyd luck, LOL. The car had a SBC in it when I got it but the PO used a stock Datsun driveshaft, U-joint and flange which is much smaller than whats in there now, amazing it all held up. It did however have the usual clunk when you firsr take off, but that seems to be gone now. Quote Link to comment Share on other sites More sharing options...
The Chiropractor Posted December 5, 2007 Share Posted December 5, 2007 Something else just occured to me Dale. You may wish to replace the front diff insulator. Once they get fatigued they can make the clunking noise. I believe that you mentioned that you hear the "usual clunk" when you take off. That is definitely a sign. (Others, please correct me if I am wrong.) When I get into doing any suspension work on the cars I have owned, (5 S30's so far) I always just replace the front diff mount. It removes slop, vibration and the "usual" clunking noise. Quote Link to comment Share on other sites More sharing options...
The Chiropractor Posted December 5, 2007 Share Posted December 5, 2007 BRAAP made reference to this in his post as well... SOGGY DIFF MOUNT = POSSIBLE U-JOINTS SLAPPING Quote Link to comment Share on other sites More sharing options...
datman Posted December 5, 2007 Share Posted December 5, 2007 Check the 2 nuts where the diff bolts to the moustache bar are very tight...this is where my "clunk" was coming from. I changed just about everything before I found it! Quote Link to comment Share on other sites More sharing options...
deja Posted December 5, 2007 Author Share Posted December 5, 2007 Something else just occured to me Dale. You may wish to replace the front diff insulator. Once they get fatigued they can make the clunking noise. I believe that you mentioned that you hear the "usual clunk" when you take off. That is definitely a sign. (Others, please correct me if I am wrong.) When I get into doing any suspension work on the cars I have owned, (5 S30's so far) I always just replace the front diff mount. It removes slop, vibration and the "usual" clunking noise. It probably wouldn't hurt to change that anyway. But that start off clunk that was there with my old setup is gone now. I think that was the u-joint in the old setup. Quote Link to comment Share on other sites More sharing options...
deja Posted December 5, 2007 Author Share Posted December 5, 2007 Check the 2 nuts where the diff bolts to the moustache bar are very tight...this is where my "clunk" was coming from. I changed just about everything before I found it! Thanks, I will check them again tonight. Quote Link to comment Share on other sites More sharing options...
deja Posted December 5, 2007 Author Share Posted December 5, 2007 BRAAP, you and I were right. Oh, yeah we had rubbing. It was the u-joint hitting on the swap bar. I unbolted the sway bar, pulled it out of its frame mount and tye-wraped it so it wouldn't drop and ran the car forward and backward several times. Of course I am totally deaf now from the open headers but there is no clunking! Yahoo. Now the question is how do I fix this. The obvious but most expensive one is to get a rear mounted sway bar. Or I could just take the thing off and see how it handles without one at all. Or somehow figure out how to lower the frame mount which looks tough since the bracket is welded on and at this stage I don't want to attempt welding in that area. At The Chiropractor's suggestion I will pick up a new diff isolator anyway just because its a good idea. Who know maybe that will raise the diff enough to fix it. For now I have pulled the bar out completely. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted December 5, 2007 Administrators Share Posted December 5, 2007 Or I could just take the thing off and see how it handles without one at all. In my LT1Z I ran without a rear bar most of the time. I prefer it gone in most conditions. Corner exit bite and compliance is improved more than the 'rotate-ability' is reduced. Quote Link to comment Share on other sites More sharing options...
deja Posted December 6, 2007 Author Share Posted December 6, 2007 In my LT1Z I ran without a rear bar most of the time. I prefer it gone in most conditions. Corner exit bite and compliance is improved more than the 'rotate-ability' is reduced. I was searching around today about sway bars and saw a lot of posts including yours that said that very thing. I did notice most of the people that said the took it off were road racers, not drag racers. I am building a daily driver but being an old road racer myself I want it to handle well too. Thanks for the post, we'll see how it goes. Quote Link to comment Share on other sites More sharing options...
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