THSCC Forums

Hello all, maybe someone has experence that might be helpful. Last track event at VIR south my rear wheel drive car started misbehaving coming out of cornors during the time trail. It was fine all day long before the last session. Suddenly, I could feel the rear tires spining coming out of turns. This has never happened before and I think my overall driving has been relativley constant. I don't think I changed my power on point very much. I thought it might be tire or suspension issue, after close inspection everything looked fine. Sunday morning with cool tires same thing- all day long. I was able to get a bit more traction by setting the shocks dead soft and the body roll put some weight on the tires. Still slipped but not quite as bad. I assumed the limited slip had finally worn out (140 K miles). I disassembled the unit and it appears there is no wear what so ever. The clutch disks are 1.98 mm thick (New ones are 2.0 mm). Preload springs are right on spec as are the thrust washers. The magnetic drain plug was clean as a pin and all clearences seem to fine. I allways use the correct oil. I hate to take something apart and then put it right back but I'm stumped. Has anyone ever experenced anything similar?
Thanks
Mark

Car brand and model and year???

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Dick Rasmussen

FS 50 2018 Mustang GT

Both tires spinning, or just the inside tire?

Scott

FYI and AFAIK Street type clutch type limited slips with individual clutch disks (such as oem Ford units) get the majority of their clamping force from the diff gears being forced against the clutch pack by side gear thrust loads. If the unit isn't broken, I doubt that a little more use after 140,000 miles would suddenly make it significantly less effective. However, based on specs in my Ford shop manuals, it appears that a couple of thousands of wear per clutch disk could add up to be significant. Another potential factor would be if a different gear lube brand was used recently or if too much friction modifier was added (if relevant for your car). Note that Redline sells NS (for non slip) gear lube specifically without the normally included (in Redline diff lube) friction modifier. You might try using it. It can make a noticeable difference. Otherwise, if the setup and/or driving and/or track conditions were right on the edge of wheel spin previously you may have just gone "over" the edge.

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Dick Rasmussen

FS 50 2018 Mustang GT

Perhaps the tires were heat cycled a few to many times and just weren't getting traction. But I have noticed that my car with a carb does seem to have more power later in the day. just a few thoughts for you to ponder on

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beware of EV powered Ford EXP's they are quiet and come for you when you least expect it... hide behind an aluminum light pole...... ya that will help