johnc Posted February 5, 2001 Share Posted February 5, 2001 I've been queried twice today on this topic, so I'll post it here for those that are interested: Nissan Motorsports recommends 70 ft. lbs. I normally ran mine at 85-90 ft. lbs. for autocross. It falls off from there after a few events. If the breakaway torque gets down to 35-40 ft. lbs. its essentially an open diff. If the breakaway is 110 ft. lbs. or over its essentially a locked diff. You will need to check it at least once per year and expect to replace the clutches every 12 to 18 months. Autocross is especially hard on clutch type diffs. ------------------ John Coffey johnc@betamotorsports.com Quote Link to comment Share on other sites More sharing options...
Rob Posted February 16, 2001 Share Posted February 16, 2001 Thanks a ton for the information John. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted February 16, 2001 Share Posted February 16, 2001 In my opinion, the correct amount of breakaway torque for an LSD is the LEAST amount that will prevent inside wheelspin. On my car, the 23 lb-ft the '87 300ZX turbo diff had when I installed it 4+ years ago was enough when running on good street tires. Now, running Hoosiers, it's not, but I'll be installing rear camber bushings to eliminate excessive rear toe and re-evaluate (less rear toe should allow me to soften the rear anti-roll bar, which could give me back the inside rear traction I need). The spec numbers I remember for a stock 300 turbo diff were 18-30 lb-ft. The breakaway for a NISMO unit is listed at 45 lb-ft in the catalog. I suppose with gobs of hp more breakaway might be needed, but I can't imagine you'd need more for a naturally aspirated L28 in a well set-up car. Higher breakaway torque => more understeer + greater frictional losses. Dan Baldwin '71 240Z 3.1 COMSCC #7 SPB Quote Link to comment Share on other sites More sharing options...
johnc Posted February 16, 2001 Author Share Posted February 16, 2001 Dan, You're correct. But autocross is a different animal than road race and is really hard on clutch-pack LSDs. Autocross has tighter corners, lower speeds, and you never get into 4th gear (and rarely into third). A higher preload is definately needed. If I was setting up a Z for track events only than I would go with the 70 ft. lbs. that Nissan Motorsports (Ron Johnson) recommends for an ITS car running 225/50-14 Hoosiers. I also think that 45 ft. lb. number is an old recommendation - tires have improved a lot since the mid-1970s. ------------------ John Coffey johnc@betamotorsports.com Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted February 16, 2001 Share Posted February 16, 2001 Good point about autoX vs. road race. No first gear corners at any of the tracks I've been to. 70 still seems like a lot, though. Mine's probably at ~18 - 20 lb.-ft and does do a little, I can feel the clutch pack grab and release during corner exit. I'll see how it does with a softer rear bar setting. How tricky is it to shim a clutch pack? I'm picturing myself on the garage floor surrounded by shims of various thicknesses scratching my head. Dan Quote Link to comment Share on other sites More sharing options...
johnc Posted February 16, 2001 Author Share Posted February 16, 2001 The best description of the process I've come across: http://www.gordon-glasgow.org/lsd1.asp Its not difficult (I can do it), just tedious. FYI... if you can feel the diff grab and release then its too loose. BTW... I don't run a clutch pack diff anymore. A Quaife is absolutely the way to go and its worth every penny. ------------------ John Coffey johnc@betamotorsports.com Quote Link to comment Share on other sites More sharing options...
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