Back in March 2020, team Diesel Army headed south to Diesel’s On The Beach for the season opener at Emerald Coast Dragway. As promised, there were a ton of trucks racing and a row full of vendors with their latest and greatest parts on display. One of those vendors was SunCoast Diesel with both gas and diesel parts and projects displayed including one of their shop trucks. What intrigued me most was that they allowed me to test (ahem… abuse) one of their trucks with a SunCoast-built 68RFE transmission.
I spotted Montana Cherry’s truck on social media and have been talking with him about it for a while. Cherry is a transmission specialist down at the SunCoast Diesel, Fort Walton Beach, Florida location. He explained to me that this truck was equipped with one of their 68RFE transmissions with all of their revisions.
Bringing up the boost, letting it eat, and it’s still taking the beating.
Why the need to redo the 68RFE transmission? Because in a stock application, they are okay at best. Add some power to the Cummins and it needs help. To stay up to date with customer demand, perfecting this sometimes less-than-stellar transmission is a top priority for the SunCoast team. With that being said, Cherry was willing to have us put their 68RFE to the test for the day and let us beat it on the race track.
Common 68RFE Issues / Fixes
- Weak Sprag
- Weak Thrust Washer
- Vulnerable 2C Clutch
- Factory 4C Return Spring Is Cheap
- Flimsy Underdrive/Overdrive Drum
- Poor Lower Valve Body Structure
Cherry explains that these are the main issues they see with the 68RFE transmissions, but how do they fix it? Let’s dig in.
Starting from back to front, the factory sprag is up first. “The factory unit is very weak and often flips, as it’s referred to in the industry, rendering them useless and usually leaves the customer with no forward movement,” Cherry said. “Suncoast has cured this issue with an upgraded sprag that features a true roller-style one-way bearing.”
With these larger wheels and tires, I could see how a factory transmission wouldn’t like this abuse.
Moving on, the factory thrust washer is very weak as mentioned above. It is constructed of a plastic/fiber composite, and under extreme shock loads, such as boosted launches, hard shifts, or harsh lockup in racing conditions, this part will break. “We manufacture a billet aluminum thrust washer that retains factory oil flow for cooling and will never break under pressure,” explained Cherry.
Up next are the 2C Clutch issues. “The stock 2C clutch is inadequate at best with its three double-sided clutch design. All of our transmissions feature a proven, billet 2C piston that allows us to add clutch with more aggressive Kolene coated steels.” In this case, more is better. With more clutches and material, that is more power held.
The next bullet point is the factory 4C piston return spring. According to Cherry, “The factory 4C piston return spring setup is a simple, cheap stamped-steel retainer with a thin snap ring sitting on top. This snap ring has a tendency to blow out, even at stock or mildly increased pressures. Suncoast has engineered the solution by machining a billet snap ring retainer that takes the place of the weak factory-stamped steel upper retainer. This billet piece secures the 4C snap ring in a pocket, ensuring it has nowhere to move or blow out.”
Still chugging. Like a boss, this thing never skipped a beat.
One of the most important items that need to be addressed is the underdrive and overdrive drum. The OEM drums will flex under stock line pressure. That is before any modifications and stock power. If you were to add pressure, you make it worse, and clutch wear will show a pattern where the inner radius of the clutch blackens from the heat on apply due to the uneven apply area.
“On top of the flexing, the factory clutch count is only 12 single-sided frictions with a small apply area providing inadequate clamping force for some modified trucks,” Cherry said. “Suncoast has their billet V2 drum. This drum adds over 30 percent more apply area, meaning greater clamping force along with a much-needed thicker outer drum that reduces the overall flex to a minimum. “Our patented drum allows us to run a total of 16 friction surfaces which helps dissipate heat and reduce the chance for slippage. Topping off the V2 drum is another billet snap ring retainer that keeps the underdrive-piston retaining snap ring in place under extreme duty situations.”
Lastly, the pump and valvebody in the 68RFE need to be addressed. In factory form, the stock pump and valvebody combo will achieve a maximum of 160 psi of line pressure. While that may not seem like a lot, even at that pressure the valvebody’s lower casting plate flexes and causes cross leaks resulting in burnt-up transmissions. The 68RFE from SunCoast features Suncoast’s zero-tune valvebody and pump combo which allows line pressures to reach 200 psi without the aid of any additional tuning.
“This is huge for our customers who don’t want invasive tuning for an otherwise stock truck. With upgraded accumulators, accumulator plates, TCC apply valves, and switch valves, this valvebody is ready for the long haul. Topping it off is a DNJ components billet channel plate ensuring the stock valvebody cross leak issues due to flex is corrected,” Cherry said.
Closing Thoughts
Knowing how costly it can be to rebuild a 68RFE, why not step up to a SunCoast unit and not worry about it again? If it can handle the abuse on the race track with wide-open four-wheel-drive shifts with larger tires and wheels, and not skip a beat, I feel comfortable with calling this a solid unit. They’ve hit all of the hot spots on these units and trying it out first hand was great.
For more information about this SunCoast Performance transmission, head on over to their website. Thanks to Montana for the opportunity over the weekend and we hope this gives you guys some information that you may have needed moving forward with your build. For more part testing, truck features, and event coverage, stay tuned right here at Diesel Army.
