mtnickel Posted May 14, 2015 Share Posted May 14, 2015 Well, this thread is just a warning to those doing diff work to probably have it setup from a diff shop. If nothing more than to remove the liability if something doesn't go right. Perhaps the stock Clutch units are machined near identically and can be swapped out by a DIYer, but for all else, I'd say definitely get it setup at a diff shop! Story is: I bought a Helical centre for my excellent condition 3.90 R200 that i had to search for. Was from a low mile 280zx and felt nice and tight and smooth when I got it. LSD Centre was a japan made NOS unit from a company called XEBEC. I know a little sketchy buying a diff from a non-recognizable name, but everything I could find online from OLD posts said they were quality units. The japanese writing on the box and made in japan left me worry free. Price was pretty good too (about on par with OBX, but looks much better). Came with new bearings assembled as well. Well, I swapped out the open centre for the unit. Everything SEEMED to measure out. Backlash was between .004 and .007. That backlash variance (.003 difference from tight to loose) around different points perhaps was my problem, not sure. Runout was .001, maybe .0015. Didn't think much could be done to correct it, and figured was probably close enough considering was within spec. Bought an inch pound torque wrench to check preload. Diff slipped in with a decent amount of pressure and felt nice and tight but not ridiculously tight. Ended up not having adapter to use the wrench but figured it felt like it was going in with about as much force as the open one did. Anyways, on to install. Diff ran just fine for the first 100 miles. Then I got my car tuned a bit better and started to do a few harder launches. After the first 3-4 launches i started to hear just a slight whine. Did some reading and many said theirs just get noisy when the fluid thins out after harder runs. Didn't think much of it. The whine was still fairly mild, about the same volume as my walbro fuel pump (and similar sound too). Well, diff ran same way for another 100 miles or so and then I got a little adventurous with pushing the car. After another few hard launches I noticed a distinct increase in whine. Thought maybe since it was really hot it got louder. Decided to look into it when I got it home and looks like the diff is done for . Excessive slop, and fine metal shavings in the oil (along with the drain plug covered in about a 1/8" thick film of fine oil shavings). There was no whirring sounds and the stub axles are nice and tight. So I'm fairly sure carrier bearings are just fine. the pinion flange is also right tight up and down. But spinning the pinion flange is stiff and notchy. Grabs and binds with lots of free play to moving the output. If i had to guess, the inner pinion bearing is toast. Other background info. Car developed a fairly significant vibration above 80mph. And only other work I did on diff was to swap the pinion flange and change the seals. Tough to hold the output shafts so I just used an impact set on low setting (which usually gets me to about 100 - 140ft lbs. Used a touch of thread lock too, to be sure. My hypothesis (and perhaps others can chime in). 1) the Backlash variance was too great. .003 difference around the gear should have been warning sign? Also, the .004 end is .001 tighter than factory spec of .005. 2) By using the impact to install nut, I possibly could have overtightened? I know the r200 uses a spacer and not a crush sleeve and have read of other users doing the same, but it could have put too much torque on the pinion bearing. 3) The driveline vibration I had could have been imbalanced driveshaft and put a whack load of stress on the pinion. If it got hammered a little too much, once there was play it would only get worse from there. Not sure which of the above is the culprit, but just a warning to those to be extra particular about setting these things up. I should have pictures sometime next week. Luckily I have a spare 3.545:1. I'm keeping my fingers crossed that the centre was not destroyed by the metal particle filled oil. Best case it's all fine, next best case, just the carrier bearings need to be replaced. Worse case, it's a write off. It wasn't driven very far at all since the whine got worse, and it was still driving just fine but with a little more free play (clunk) and louder whine. Will be taking it in to have setup and inspected and report back. Thanks for reading!Mark ps. Car is 260z with RB25DET and Rb25 trans. Probably putting out somewhere between 275 and 300hp. It hooked up amazingly while it lasted with the LSD and RE-11A's. Too bad it was only for a few days . Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 14, 2015 Share Posted May 14, 2015 1) the Backlash variance was too great. .003 difference around the gear should have been warning sign? Also, the .004 end is .001 tighter than factory spec of .005. This is your problem. On most diffs, the ring gear has to be hammered onto the carrier. On the Nissan carriers they fall right off, but maybe your aftermarket had a tighter fitting pilot. Something is DEFINITELY wrong if you have .003 difference in backlash around the ring gear. Good news is that you can probably swap that LSD into a new housing, just disassemble and clean it up. Might want to check that the surface the ring gear sits on is flat. Could have been dropped or something at one time. Could mill the flange flat again if needed and then adjust backlash. Quote Link to comment Share on other sites More sharing options...
mtnickel Posted May 14, 2015 Author Share Posted May 14, 2015 (edited) This is your problem. On most diffs, the ring gear has to be hammered onto the carrier. On the Nissan carriers they fall right off, but maybe your aftermarket had a tighter fitting pilot. Something is DEFINITELY wrong if you have .003 difference in backlash around the ring gear. Good news is that you can probably swap that LSD into a new housing, just disassemble and clean it up. Might want to check that the surface the ring gear sits on is flat. Could have been dropped or something at one time. Could mill the flange flat again if needed and then adjust backlash. Many thanks for taking the time to read my post Jon. The center unit was really old stock (probably 20 years old at least) and looked really well packaged in factory box, so I thought fairly rare that it would be out flat. I do recall scratching my head a few times about why it had a tiny bit of runout (.0015) in the axial direction (radial was fine). That was probably the problem though. I was a little over eager however and thought I could get away with it since backlash around the gear was in spec (albeit varied). I followed the FSM as well which said to apply loctite to the ring gear matting surfaces; Maybe possible it was over applied and film thickness was too great in one area causing more runout. The Ring gear fit the center diff I'd say perfectly. more or less had to be tapped on with a rubber mallet. Any slight angle difference and it bound going on. Once both faces were matted you could spin the two (independently) with a little effort to line up the ring gear holes. Most machine shops would be able to true the carrier? Wonder what they use as a reference for clamping it in the same way the carrier bearings do. Could use my old diff case in the jig i suppose. Regards, Mark Edited May 14, 2015 by mtnickel Quote Link to comment Share on other sites More sharing options...
mtnickel Posted May 19, 2015 Author Share Posted May 19, 2015 (edited) This is your problem. On most diffs, the ring gear has to be hammered onto the carrier. On the Nissan carriers they fall right off, but maybe your aftermarket had a tighter fitting pilot. Something is DEFINITELY wrong if you have .003 difference in backlash around the ring gear. Good news is that you can probably swap that LSD into a new housing, just disassemble and clean it up. Might want to check that the surface the ring gear sits on is flat. Could have been dropped or something at one time. Could mill the flange flat again if needed and then adjust backlash. Confirmed run-out. Radial (ring centering machined edge) looked to be out about 1.8-2thou. The axial runout (flatness of ring gear surface) surely was out .002". Guess this is what grenaded the diff. http://vid1116.photobucket.com/albums/k569/mtnickel/datsun/5E470516-F6AE-44A5-87FC-5FA5617A31A4.mp4 http://vid1116.photobucket.com/albums/k569/mtnickel/datsun/42A92ED1-78D8-4C2A-82B9-F838074FED40.mp4 Lots of metal in the diff from the gears wearing so much. One side carrier bearing looks not too bad, the other has some slight slight knick/fine scratch type marks. Similar looking to this, but shinier (lower bearing race). Edited May 19, 2015 by mtnickel Quote Link to comment Share on other sites More sharing options...
mtnickel Posted June 11, 2015 Author Share Posted June 11, 2015 Here's my actual bearings. Anyone have thoughts on if they are usable? Here's the worse one. Was going to hit them down with an emery cloth Quote Link to comment Share on other sites More sharing options...
mtnickel Posted June 11, 2015 Author Share Posted June 11, 2015 well, looks like i can source some new bearings for not too much. likely worth it. Instead of looking for OEM, you can search for 30209 bearings 45x85x20.75mm tapered roller bearing. Ideally something made in Japan. SKF, KOYO, etc. Shouldn't be too much more than $40/pr if you find a good bargain (ebay store closeout or something). Quote Link to comment Share on other sites More sharing options...
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