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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain. |
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02-25-2021, 08:31 PM | #1 |
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Pinion preload breakaway vs rolling torque difference
I'm working on replacing my FD gear with the Autofactory 4.88 and a solid spacer, reusing all the bearings, and I chose spacer shims by just eyeballing the height with the original crush spacer (yes, I can get calipers if necessary). The breakaway torque I have is a lot bigger than the rolling torque (~60 vs ~12 in-lb). Everything I've read seems to say the rolling torque is really what matters, but the FSM says to measure the "starting torque" which I take to mean the breakaway torque. Should the torque difference be this big, and am I doing something wrong? Do I even go with the torque spec in the FSM (15.67-18.32 in-lb)? The Autofactory instructions didn't include any preload torque specs.
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02-25-2021, 10:38 PM | #2 |
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Static coefficient of friction versus dynamic. It's much easier to accurately measure the torque required to overcome static friction than to measure the dynamic combined with viscous effects of lubricant in play.
It sounds like you got it a bit too tight.
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02-26-2021, 12:15 AM | #3 |
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02-27-2021, 11:24 PM | #4 |
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I don’t think I got a direct answer to my question but I think it gave me inspiration to figure it out- I was pressing the pinion head too hard onto the rear bearing race. Instead, I stopped the press just before contact and let contact happen by screwing the pinion nut on. Now the breakaway torque is just a little higher than the rotating torque. Thanks!
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The Following 2 Users Say Thank You to Rx FR-S For This Useful Post: | jcw99 (02-28-2021), Ultramaroon (02-27-2021) |
02-28-2021, 12:28 PM | #5 |
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Something to keep in mind on the carrier bearing preload, for every 10 pounds of pressure applied to the thrust of the bearings equals 1 pound of preload of the carrier to rotate. Used bearing can be preloaded to adjust for wear. Fwiw, 100-140 of preload has the benefit of keeping the ring gear from deviating as much from the bearing axis line. If I am not explains this right, look up Zuk at gearinstall.com. The diff in the 86s is an 8” Toyota
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