pete280z Posted July 26, 2007 Share Posted July 26, 2007 I've got a 1975 280Z with AFAIK the stock R200. All bushings and front diff mount have been replaced within the last 300 miles. Every nut and bolt was double checked for correct torque. With the car on the ground and transmission out of gear, I can grab the driveshaft and freely rotate it about 15 degrees. When I do there is a thunking/clunking sound coming from the diff. I don't see any visible play in any of the u joints and the half shafts stay perfectly still. Is this time for a new differential? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 27, 2007 Share Posted July 27, 2007 You need backlash in your ring and pinion gears. Backlash is one of those settings that doesn't really change unless something REALLY bad happens to the differential. Backlash might be .005 to .007" when you measure it at the ring gear. When you measure it at the pinion it gets magnified. 15 degrees sounds totally fine to me. If you got another differential it would also need to have backlash as well so it probably would not help. If you think I'm wrong you could pull the diff, take off the rear cover and measure the backlash to be sure its within spec, but I'd bet that it is. One other thing to check for clunking is the splines on the stub axles. As they wear the stubs can rotate a bit causing a clunk. Solution is to replace the stub axles and companion flanges. Quote Link to comment Share on other sites More sharing options...
pete280z Posted July 27, 2007 Author Share Posted July 27, 2007 I can't imagine anything terrible happening to this diff. The drivetrain was basically 100% stock when I got the car (still is) and it's seen < 1000 miles since then. The stub axles were out to change wheel bearings when the bushings were done and everything looked OK to me. I'll go over everything one more time before I run out to the yard to get another differential. Something's definitely not right though. I'm getting a distinct clunk on every shift unless I'm _very_ delicate with the clutch. "Aggressive" shifting makes a really horrible noise. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted July 27, 2007 Share Posted July 27, 2007 Have you checked the front differential mount? That's a common thing to fail, and it fits your description of the noise. When the mount fails, the nose of the diff lifts and moves around when you shift and apply the throttle. It's much easier and cheaper to fix than the diff itself. Quote Link to comment Share on other sites More sharing options...
pete280z Posted July 27, 2007 Author Share Posted July 27, 2007 Front diff mount is brand new. The strap is in place, but seems pretty loose. If I wind up pulling everything out again I'm going to do Clifton's mod to the front diff mount just in case. I haven't done the transmission mounts so I guess while I'm checking everything out I'll replace those too. Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 27, 2007 Share Posted July 27, 2007 Front diff mount is brand new. The strap is in place, but seems pretty loose. If I wind up pulling everything out again I'm going to do Clifton's mod to the front diff mount just in case. I haven't done the transmission mounts so I guess while I'm checking everything out I'll replace those too. When the diff mount was replaced, how were the bolts that fasten the mount to the diff oriented? As I recall, if you install the bolt from the top such that the nuts are installed at the mount (i.e. bolts pointing down), then there isn't enough clearance to keep the bolt from hitting the crossmember on decel. It's a bigger pain in the arse to install this way but the diff bolts need to be pointing "up" (so the bolt head is between the mount and the crossmember) for clearance. Quote Link to comment Share on other sites More sharing options...
Adam Posted July 27, 2007 Share Posted July 27, 2007 Mine does the samething however I have a r180 it maybe different. Quote Link to comment Share on other sites More sharing options...
pete280z Posted July 27, 2007 Author Share Posted July 27, 2007 When the diff mount was replaced, how were the bolts that fasten the mount to the diff oriented? As I recall, if you install the bolt from the top such that the nuts are installed at the mount (i.e. bolts pointing down), then there isn't enough clearance to keep the bolt from hitting the crossmember on decel. It's a bigger pain in the arse to install this way but the diff bolts need to be pointing "up" (so the bolt head is between the mount and the crossmember) for clearance. I'm 90% sure I have them installed "up," but that's another thing I'll check when I go over it again. Quote Link to comment Share on other sites More sharing options...
pete280z Posted July 29, 2007 Author Share Posted July 29, 2007 Just when you think you've been thorough... Went back and checked everything again. I found one nut on the inboard side of each half shaft that could be tightened about another 1/4 turn and one bolt on the driveshaft that could use the same. Then I checked the transmission mount. Everything looked fine with that, but an exhaust hanger on the transmission seemed wrong. The bolt on the hanger had about .75" of vertical play. I'm guessing that a chunk of rubber was missing. Anyway, tightened it down and all is good. Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 30, 2007 Share Posted July 30, 2007 Just when you think you've been thorough... Went back and checked everything again. I found one nut on the inboard side of each half shaft that could be tightened about another 1/4 turn and one bolt on the driveshaft that could use the same. Then I checked the transmission mount. Everything looked fine with that, but an exhaust hanger on the transmission seemed wrong. The bolt on the hanger had about .75" of vertical play. I'm guessing that a chunk of rubber was missing. Anyway, tightened it down and all is good. Okay, well I'll take credit for making you take another look under there. Glad it was that easy to fix. Quote Link to comment Share on other sites More sharing options...
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