Norm Peterson
corner barstool sitter
I'm pretty sure that the diff temperature sensor was a running production change and that at least the first-year S550s didn't get one.I'm surprised the rear differential even has a sensor. That's almost indicative of a potential issue.
How the heck does the trans get up to 250 F (and eng up to 230F).... in just 3 laps ??
Keep in mind that the S550's differential is inherently less capable of shedding the heat that is generated internally than the S197 or most any other stick-axle design. No axle tubes to act as radiators, tucked up out of the airflow in a cradle (vs hanging out there in the open like the S197's stick-axle diff with only the driveshaft and the UCA in the way). The S550's airflow in the region of the diff is pretty warm to begin with, with those exhaust pipes in close proximity to the diff. Even if the pipes don't add any heat to the diff, they reduce the heat flow out of the diff by reducing the metal surface vs air temperature difference.
This is a known track-day issue with every S550 trim from the GT, through its PP1 and PP2 iterations, up to and including the early year non-R GT350, and has been discussed fairly heavily elsewhere.
There's a lot going on inside an automatic transmission, especially one with 10 forward ratios. In this case, there's four planetary gearsets, four clutches, and two brakes. Some of the intermediate ratios have some of the transmission internal components rotating at higher than engine rpms. and there can be large rpm differences across friction elements that are not engaged (think viscous friction causing heat here).
https://www.thetruthaboutcars.com/2014/12/saturation-dive-ford-10-speed-transmission-power-flow/
Norm
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