Pinion preload breakaway vs rolling torque difference - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Rx FR-S · 02-25-2021, 08:31 PM

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.

Ultramaroon · 02-25-2021, 10:38 PM

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.

EndlessAzure · 02-26-2021, 12:15 AM

Rx FR-S · 02-27-2021, 11:24 PM

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!

Locost7 · 02-28-2021, 12:28 PM

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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02-25-2021, 08:31 PM	#1
Rx FR-S Member Join Date: Aug 2019 Drives: 2013 FR-S MT, 2023 Acura Integra Location: WA Posts: 16 Thanks: 6 Thanked 15 Times in 7 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	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.

02-25-2021, 10:38 PM	#2
Ultramaroon 義理チョコ Join Date: Sep 2014 Drives: a 13 e8h frs Location: vantucky, wa Posts: 31,867 Thanks: 52,126 Thanked 36,517 Times in 18,919 Posts Mentioned: 1106 Post(s) Tagged: 9 Thread(s)	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. __________________ service manuals

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02-27-2021, 11:24 PM	#4
Rx FR-S Member Join Date: Aug 2019 Drives: 2013 FR-S MT, 2023 Acura Integra Location: WA Posts: 16 Thanks: 6 Thanked 15 Times in 7 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	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!

02-28-2021, 12:28 PM	#5
Locost7 Member Join Date: Jul 2020 Drives: 15 86 Location: al Posts: 45 Thanks: 2 Thanked 5 Times in 4 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	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 Sent from my iPhone using Tapatalk

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