When it comes to modern transmissions, most owners view them as pure mechanical sorcery. It’s a rarity for a 10R80 to be rebuilt by the DIY mechanic. While the ability to make big power comes easily on a Coyote-equipped S550 Mustang or F-150, the ability to hold that power begins to diminish when forced induction is applied. We sat down with Johnny Brady of Brady Performance to gain some insight into the magical 10R80, where its boundaries are, and what you can do to make your 10-speed transmission last.

All laid out and ready to play. New clutches are setup to enter their new 10R80 home.

Ford Muscle (FM): The 10R80 transmission has been touted as the ultimate transmission by modern Mustang lovers, but what parts do you see failing?

Johnnie Brady (JB): The parts that fail the most on the 10R80 are the E and F clutches. The E and F clutches are the overdrive ones and have the least amount of torque multiplication, and this makes them inherently the weakest.

FM: Is there anyone that makes a better clutch pack to resolve this issue?

JB: I like the way Suncoast Performance does its rebuild kit using Raybestos Powertrain GPZ frictions. Instead of thinning the steels, Suncoast Performance is machining the drum to allow you to run its thicker-than-OEM steels, and still have room for one additional friction and steel. This process allows the clutch pack to be stronger and last longer. Whereas, if you thin the steels to create room for more, it won’t hold up to the heat and will eventually warp.

FM: At what power levels do you start to see these clutches fail?

JB: Stock clutches are holding up to around 700 horsepower. Once you approach the 750 horsepower mark or higher, then I would upgrade the clutch count and rebuild the transmission.

FM: What products are you using to rebuild the 10R80?

JB: We use a Ford factory seal kit, Suncoast Performance steels, Raybestos Powertrain GPZ frictions, and Ford Mercon ULV fluid. I always use the Raybestos Powertrain GPZ frictions, as they’re the best for holding the most power. I’ve seen cars between 1,200-1,400 horsepower running them at the dragstrip with no issues.

I always use the Raybestos Powertrain GPZ frictions. They’re the best for holding the most power. I’ve seen cars between 1,200-1,400 horsepower running them at the dragstrip with no issues.” -Johnnie Brady, Brady Performance

FM: How much does heat play a part in the 10R80’s longevity?

JB: Cooling is a huge part of keeping the 10R80 alive and working well. I run a transmission cooler on anything above 700 horsepower. For a more intense transmission cooler, I run the Derale external transmission cooler mounted underneath the trunk with a fan. In most cases, I wire the fan to run continuously, regardless of whether I’m racing or just riding around town.

I also take out the thermal bypass, which lets the transmission fluid get to a certain temperature. The 10R80 works best at 150-160 degrees –anything cooler and the transmission gets finicky. With the thermal bypass removed, the fluid is allowed to flow all the time and is essentially creating a cooling process.

FM: Is there anything else you remove or replace?

JB: I would also look into replacing the valve body. The valve body is a big problem on the 10R80 because solenoids in the valve body are magnetic. The magnetized components get metallic friction material stuck to them when the plates are wearing down. This starts to cause issues and the solenoids stop working like they should, as it affects pressure, which in turn can burn up a clutch.

I run a Raybestos Powertrain inline magnetic filter with a rare earth magnet that catches any kind of clutch material that would cause issues with the valve body.

FM: Do you have any advice for the naturally-aspirated crowd?

JB: I would stick with the stock clutch count and perform the thermal bypass removal (aka Cooling Mod). When you get into forced induction, then you upgrade the clutch count.

No basket case here. This work bench is strictly for business.

FM: What is your break-in procedure?

JB: I tell everyone to drive the car 500 miles with stop and go driving added in the mix to get the proper heat cycles in. You don’t want to install the new clutches and immediately make your way to the dragstrip. Before the test drive, I perform a transmission relearn and recalibration; this allows the transmission to learn itself again. At first it will shift rough, but will smooth out as it relearns.

Johnnie Brady’s S550 Mustang is where he learned how to rebuild the 10R80 transmission. His car frequently sees hard launches and drag racing.

As you can tell, the 10R80 is a solid transmission, but can be a lot stronger with the right modifications. Replacing the clutch pack, performing cooling modifications, and properly breaking it in can lead to a long life, even with high horsepower.

We wanted to dive a little deeper into why the GPZ frictions come so highly recommended from transmission builders and aftermarket manufacturers. So we went directly to the source to gather more intel. We reached out to Raybestos Powertrain Marketing Manager, Nick Truncone to further fill us in on its GPZ frictions and its capabilities.

FM: It’s becoming obvious that the GPZ frictions seem to be well trusted in the automotive industry. Product supplies use them for its kits and transmission builders make them a must have for install. What can you tell us about the origins of the Raybestos Powertrain GPZ frictions and why they handle high-horsepower builds so well?

Nick Truncone (NT): The GPZ frictions have been proven for years in other transmissions, it’s not something that was created just for the 10R80. We’ve seen it more on the towing side of things, as it was originally intended for the diesel truck applications that had high torque, horsepower, and heat. We moved onto the racing side and have had great success with that, as well.

FM: Have you seen the horsepower limit of the GPZ frictions?

NT: We’ve had clutches back from a transmission that had over 40 passes on it in a car that made 1,543-horsepower on the dyno, and 1,100-horsepower on the track.  We know it can handle the abuse. However, most of the feedback from our transmission builders is that the standard clutch count using the RGPZ-268 kit can hold around 1,000 horsepower. After that is when everyone wants to start adding extra clutches and machining steels to increase holding capacity.

FM: What is the recommended fluid to be used after a rebuild and any thoughts on proper break-in procedure?

NT: We recommend only using the OE fluid. We design the GPZ frictions around the fluid that came in the transmission. We also recommend the relearn procedure to make sure there are no shift issues occurring.

If someone you know or love is suffering from clutch slippage, Raybestos Powertrain GPZ frictions may be the right answer. Ask your transmission builder today if Raybestos Powertrain GPZ frictions are right for your combination. Common side effects include increase holding capacity, less torched overdrive clutches, decreased quarter-mile times, and a lot more smiles. In all seriousness, as high horsepower builds continue to dominate the race track, your clutches need the ability to keep up. Instead of hoping the clutches will sustain the abuse of drag racing, think of Raybestos Powertrain as preventive maintenance saving you from a tow truck off the strip.