Automatic transmissions are an invention of black magic to many of us, just a series of fluid passages and clutches. And at some point they all seem to give up the ghost. For Project Magneto, a combination of high mileage and boost did-in its 10R80. Unfortunately, there are but a small handful of reputable builders of the 10R80, one of which we were most familiar from the NMRA (RIP) – SunCoast Performance – from sponsoring the 8.60 class, which appropriately was inhabited by many of its customers.
With aspirations of running a second or so slower, we felt in good hands enlisting SunCoast for help on our 2018 Mustang GT’s 10R80. After pulling the stock trans after our first dyno test at Pro Dyno, SunCoast had the trans turned around in about a week with shipping time – pretty impressive! The damage was, thankfully, not too bad. We never had a catastrophic failure, but it did slip and flair up on the dyno. Testing has its benefits in catching this early.
SunCoast is one of the few transmission builders that can also tackle your tow rig as well as your racecar, having a large diesel division. That experience comes in handy with these modern 6-, 8-, and 10-speed transmissions that have been adopted in the gasoline world as well. The 10R80 uses three overdrive gears, with a wide split that limits RPM drop to 20 percent between gears. It’s ideal for peakier engines, but it’s not without its faults. From the factory, it is notoriously clunky and susceptible to failure with boost and track use. Though its overall design is beefy, there are weak points that SunCoast has – thankfully for us – figured out how to dial in. Follow along as Montana Cherry from SunCoast gives us the full breakdown of the build.
Clutch and Grab
The OEM clutch packs are typically one of the top offenders when it comes to power-holding capacity. When the transmission is slipping, this is most often the culprit.
“Starting at the front of the transmission, the first clutch pack is actually the ‘B’ clutch. It works along side the one-way clutch — aka Sprag — to hold our P1 sungear. The factory clutch has its hands full with this one as it is used for Reverse as well as first and second, depending on the command from TCM. This clutch will see heat on cars that frequent the drag strip or have owners that like running hard red-light to red-light. We are solely replacing the soft shifting, lackluster factory clutches in favor of the more aggressive GPZ…
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