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Old 11-02-2008, 06:18 PM   #81
BAC5.2
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Member#: 43996
Join Date: Sep 2003
Chapter/Region: MAIC
Location: Broketown
Vehicle:
The Aggressive (tm)
You don't know about it..

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Quote:
Originally Posted by jhargis View Post
...I measured changes of dimension at 7 different spots on the case. One data set was recorded at 230ft/lbs, and a second data set at 300ft/lbs. At stock torque (230ft. lbs continuous load) with 3rd gear engaged, I measured a peak dimensional change of .003" at one spot of the case in relation to the bellhousing. That doesn't sound like much, but the 5mt's gear lash spec is .006" with a tolerance of +/-.001". What this means is that the gears are potentially moving beyond their recommended clearance range even at stock power, they're most certainly wildly beyond the recommended tolerance during a launch or hard shift. I stopped at 300 ft/lbs... The input shaft was twisting so much that I feared for my spare transmission's safety. Remember that this data was recorded with the output shafts completely bound up.

Another interesting tidbit that confirms input shaft flex... At 230 ft/lbs, the shaft twists at least 5 degrees at the clutch in relation to 3rd gear... In other words, with the gear locked in place, the clutch disc is about 5 degrees of rotation ahead of the gear... Think of the swirl pattern on a candy cane. At 300 ft/lbs of input torque the input shaft had moved to about 10 degrees of twist... scary.
Doesn't the fact that the output shafts are bound impact your readings? I mean, when you drive the car, the wheels move... You cant get accurate readings without taking this into consideration, can you? I can remember back to Mechanics of Materials, and axial strain, and you have to compensate for the fact that the shaft is rotating in the same direction as the load you are applying to it, in the real world. 300ft/lbs in this configuration doesn't equal the axial deflection with the trans actually in the car...

It would be nice if this helps to stop launching of the front diff from wheel-hop.

Metrology huh? That sounds like it was a fun major. What kind of stuff were you testing to destruction? I'm doing now what Tom did, but for implantable biomaterials.
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