T56 Durability?
Pro
Joined: Aug 2010
Posts: 748
Likes: 3
Transmissions are rated based on fatigue strength and 1st gear is the "weakest link" based on that analysis. While 6th gear is probably used more than 1st from a time-in-gear perspective, 6th gear typically sees no more than 75 lb-ft during 99% of its life span. Contrast that to the many times 1st gear is exposed to full throttle max engine torque (470 lb-ft in the Z06). With steel, as long as you stay below the endurance limit (EL), you'll never have a fatigue failure. The EL is typically 50% of the ulimate tensile strength (UTS) for fully-reversing bending fatigue. For high strength steel like 9310, the EL can be as low as 35% of the UTS but the since the UTS is much higher, the EL is still above lower strength steel. It should be noted the stresses inside the gear teeth are actually zero-max-zero as each pair of gear teeth mesh and unmesh and the EL will be higher. At the gear tooth interface (surface of the gear teeth) where there is compression loading, EL values for hertzian (contact) stress can be substantially higher.
An interesting side note is the maximum input torque at which catastrophic/immediate gear tooth failure occurs can be approximated using a few conservative assumptions. For the ZR1 gearbox with a 9310 steel gear and using the fully-reversing bending fatigue factor of 35% with the 600 lb-ft torque rating, the max engine torque the gear tooth will sustain is 600/.35= 1714 lb-ft. Using the zero-max-zero fatigue factor will yield a higher number and that calculation does not apply to the shock loading that would occur from dumping the clutch.
For your case, you can see from above your transmission will handle upper 500's LB-FT easily without catastrophic failure. The torque capacity GM assigns to a transmission is for infinite fatigue life of the gears/shafting (but not the bearings, synchros, or seals). As you exceed that rating, the clock starts ticking on the fatigue life...the more you exceed it, the faster the clock ticks.
An interesting side note is the maximum input torque at which catastrophic/immediate gear tooth failure occurs can be approximated using a few conservative assumptions. For the ZR1 gearbox with a 9310 steel gear and using the fully-reversing bending fatigue factor of 35% with the 600 lb-ft torque rating, the max engine torque the gear tooth will sustain is 600/.35= 1714 lb-ft. Using the zero-max-zero fatigue factor will yield a higher number and that calculation does not apply to the shock loading that would occur from dumping the clutch.
For your case, you can see from above your transmission will handle upper 500's LB-FT easily without catastrophic failure. The torque capacity GM assigns to a transmission is for infinite fatigue life of the gears/shafting (but not the bearings, synchros, or seals). As you exceed that rating, the clock starts ticking on the fatigue life...the more you exceed it, the faster the clock ticks.
I, as well as many others on the s2000 forums with a lot of HP, shredded 2nd gear by just hitting the gas in gear. not many of the transmission failures on there were 1st gear, the most common was 2nd because of its spacing on the shaft in respect to the supports.
btw are you an M.E.?
Le Mans Master
Joined: Dec 2009
Posts: 5,709
Likes: 6
From: Midwest
So that is a gear tooth analysis only and doesn't take in to account shaft bending. I have never seen the inside of the t56 trans, but are the shaft supports equally spaced?
I, as well as many others on the s2000 forums with a lot of HP, shredded 2nd gear by just hitting the gas in gear. not many of the transmission failures on there were 1st gear, the most common was 2nd because of its spacing on the shaft in respect to the supports.
btw are you an M.E.?
I, as well as many others on the s2000 forums with a lot of HP, shredded 2nd gear by just hitting the gas in gear. not many of the transmission failures on there were 1st gear, the most common was 2nd because of its spacing on the shaft in respect to the supports.
btw are you an M.E.?
