2018 F150 Transmission Problem
Thread Starter
Junior Member
Joined: Apr 2026
Posts: 5
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From: New York
2018 F150 Transmission Problem
Hey guys,
Apologize for the lengthy post in advance but it may be important for context. I have a 2018 Ford F-150 Lariat with the 3.5 EcoBoost. It has the notorious 10R80 transmission and a 3.55 rear. The truck is leveled with the BDS Fox 2.0 Kit. I recently had the transmission rebuilt because it was floating out of 3rd and falling on its face for a second or two until it shifted into 4th or 5th, it would intermittently violently upshift or downshift into 5th, and intermittently violently downshift into 8th from 10th. The tranny was rebuilt with new converter, valve body, clutches, CDF drum, outer shell, etc. I brought the truck back to the shop two to three weeks later because I was experiencing the same symptoms but just less often and less dramatic. The solution was apparently a Sonnax "zip kit" they installed in the valve body was making the transmission shift "rough" when not driving aggressively. They removed said zip kit, and it's been fantastic for the most part. Then today happened. While driving I put it into tow haul mode because I had some steep grades to climb. It downshifted harshly from 7th to 6th. I was humming along up a steep grade at about 48mph in 7th gear somewhere between 2500-3000 RPM when all of the sudden the gear indicator on the display dropped to 1st gear and the truck revved to the moon. I let off immediately and the gear indicator went back to 7th and then sequentially downshifted quickly. I stopped and pulled off thinking I just blew it up but didn't see, smell, or hear anything concerning. Temps were good across the board. I got back in the truck and pulled off slowly and it didn't miss a beat. Like nothing ever happened. Apparently, the truck "neutralized" itself. Has anyone ever experienced this? If so, why did it do this? Any pointers on how to solve my plaguing problem I'm happy to listen. I can provide more details if necessary. Thanks in advance!
Apologize for the lengthy post in advance but it may be important for context. I have a 2018 Ford F-150 Lariat with the 3.5 EcoBoost. It has the notorious 10R80 transmission and a 3.55 rear. The truck is leveled with the BDS Fox 2.0 Kit. I recently had the transmission rebuilt because it was floating out of 3rd and falling on its face for a second or two until it shifted into 4th or 5th, it would intermittently violently upshift or downshift into 5th, and intermittently violently downshift into 8th from 10th. The tranny was rebuilt with new converter, valve body, clutches, CDF drum, outer shell, etc. I brought the truck back to the shop two to three weeks later because I was experiencing the same symptoms but just less often and less dramatic. The solution was apparently a Sonnax "zip kit" they installed in the valve body was making the transmission shift "rough" when not driving aggressively. They removed said zip kit, and it's been fantastic for the most part. Then today happened. While driving I put it into tow haul mode because I had some steep grades to climb. It downshifted harshly from 7th to 6th. I was humming along up a steep grade at about 48mph in 7th gear somewhere between 2500-3000 RPM when all of the sudden the gear indicator on the display dropped to 1st gear and the truck revved to the moon. I let off immediately and the gear indicator went back to 7th and then sequentially downshifted quickly. I stopped and pulled off thinking I just blew it up but didn't see, smell, or hear anything concerning. Temps were good across the board. I got back in the truck and pulled off slowly and it didn't miss a beat. Like nothing ever happened. Apparently, the truck "neutralized" itself. Has anyone ever experienced this? If so, why did it do this? Any pointers on how to solve my plaguing problem I'm happy to listen. I can provide more details if necessary. Thanks in advance!
5 Year Member
Joined: Mar 2009
Posts: 1,321
Likes: 532
From: The Great Midwest, aka, Flyover Country
An overly aggressive downshift--from 7th to 1st--certainly doesn't sound normal or good for the drivetrain! My 2018 3.5EB/10R80 has never dropped more than 2 gears when in T/H.
