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Discussion Starter · #1 ·
I recently bought a 2011 F150 FX4 with the 3.5 Ecoboost. It had 125,000 when I bought it. There is something weird going on with the transmission or drive train though. The biggest thing is a clunk or slam when I start to accelerate after cruising speed. Say I'm cruising down the road at about 40 mph and have the foot off the accelerator coasting and i'm in 4th gear. I decide to give light gas to accelerate and then for a split second the RPMs go up and then the clunk/slam. It feels like a slip and then jamming into gear hard. Or like someone lightly rear ended me. It doesn't do it all of the time though. Just off and on. The transmission seems tight and good though when accelerating normally and shifting through the gears. No slipping or revving or mushy shifts.
It seems like the issue is between gears meaning right between the gear shift points or downshifts. It happens as well when I start accelerating for a rolling stop or when i'm not completely stopped. I accelerate and noting for about a second then bam it slams and I start going. Other strangeness that happens that might be related is that when I am stopped and let off the brake (no gas applied), or stopping and almost at a complete stop the truck shakes back and forth. Almost like a bad engine miss, but it's not. It shakes me back and forth quite a bit until i'm stopped or going. Also when completely stopped and after about 5 seconds the truck lurches forward a bit, almost like it downshifted well after stopping. But I see it is in first gear. That happens almost every stop. Last thing is that say I'm coasting in 2nd gear every time I give it light gas is lightly clunks. I can keep clunking that when it's in 2nd and tap the gas.
What could this be? It is very perplexing. I was thinking (hoping) that this might be the issue with the slip yoke not being greased up good enough. Also I was thinking maybe a transmission re flash to learn the shifts might help? Any ideas on what this might be or if I'm on the right track with this? Any help troubleshooting this would be appreciated.

Thanks
 

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2022 Powergrid KingRanch in Sparkle White
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Torque Converter?

You also might have the slip-yoke driveshaft. Notorious for needing lubed. But your symptoms seem to include that, AND something beyond.

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Discussion Starter · #3 ·
Torque Converter?

You also might have the slip-yoke driveshaft. Notorious for needing lubed. But your symptoms seem to include that, AND something beyond.

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That's what I was kind of thinking was that it might not be just the slip yoke stuff. Doesn't quite fit the exact issues of that. But yeah I think my first step will be to get that slip yoke greased. Torque converter makes sense as well.
 

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I recently bought a 2011 F150 FX4 with the 3.5 Ecoboost. It had 125,000 when I bought it. There is something weird going on with the transmission or drive train though. The biggest thing is a clunk or slam when I start to accelerate after cruising speed. Say I'm cruising down the road at about 40 mph and have the foot off the accelerator coasting and i'm in 4th gear. I decide to give light gas to accelerate and then for a split second the RPMs go up and then the clunk/slam. It feels like a slip and then jamming into gear hard. Or like someone lightly rear ended me. It doesn't do it all of the time though. Just off and on. The transmission seems tight and good though when accelerating normally and shifting through the gears. No slipping or revving or mushy shifts.
It seems like the issue is between gears meaning right between the gear shift points or downshifts. It happens as well when I start accelerating for a rolling stop or when i'm not completely stopped. I accelerate and noting for about a second then bam it slams and I start going. Other strangeness that happens that might be related is that when I am stopped and let off the brake (no gas applied), or stopping and almost at a complete stop the truck shakes back and forth. Almost like a bad engine miss, but it's not. It shakes me back and forth quite a bit until i'm stopped or going. Also when completely stopped and after about 5 seconds the truck lurches forward a bit, almost like it downshifted well after stopping. But I see it is in first gear. That happens almost every stop. Last thing is that say I'm coasting in 2nd gear every time I give it light gas is lightly clunks. I can keep clunking that when it's in 2nd and tap the gas.
What could this be? It is very perplexing. I was thinking (hoping) that this might be the issue with the slip yoke not being greased up good enough. Also I was thinking maybe a transmission re flash to learn the shifts might help? Any ideas on what this might be or if I'm on the right track with this? Any help troubleshooting this would be appreciated.

Thanks
I recently bought a 2011 F150 FX4 with the 3.5 Ecoboost. It had 125,000 when I bought it. There is something weird going on with the transmission or drive train though. The biggest thing is a clunk or slam when I start to accelerate after cruising speed. Say I'm cruising down the road at about 40 mph and have the foot off the accelerator coasting and i'm in 4th gear. I decide to give light gas to accelerate and then for a split second the RPMs go up and then the clunk/slam. It feels like a slip and then jamming into gear hard. Or like someone lightly rear ended me. It doesn't do it all of the time though. Just off and on. The transmission seems tight and good though when accelerating normally and shifting through the gears. No slipping or revving or mushy shifts.
It seems like the issue is between gears meaning right between the gear shift points or downshifts. It happens as well when I start accelerating for a rolling stop or when i'm not completely stopped. I accelerate and noting for about a second then bam it slams and I start going. Other strangeness that happens that might be related is that when I am stopped and let off the brake (no gas applied), or stopping and almost at a complete stop the truck shakes back and forth. Almost like a bad engine miss, but it's not. It shakes me back and forth quite a bit until i'm stopped or going. Also when completely stopped and after about 5 seconds the truck lurches forward a bit, almost like it downshifted well after stopping. But I see it is in first gear. That happens almost every stop. Last thing is that say I'm coasting in 2nd gear every time I give it light gas is lightly clunks. I can keep clunking that when it's in 2nd and tap the gas.
What could this be? It is very perplexing. I was thinking (hoping) that this might be the issue with the slip yoke not being greased up good enough. Also I was thinking maybe a transmission re flash to learn the shifts might help? Any ideas on what this might be or if I'm on the right track with this? Any help troubleshooting this would be appreciated.

Thanks
Did you end up resolving the issue? My 2014 has the exact problem and it's driving me mental. I've grease the slip yoke multiple times. I installed a brand new yoke, It failed to resolve the issue.
 

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2020 F-150 STX 4x4 Supercab
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Have you checked the transmission mounts and engine mounts? Shaking reminds me of my old Buick with broken motor mounts…engine just jumped around on acceleration
 

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Do you have air bags in the rear?
 

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I recently bought a 2011 F150 FX4 with the 3.5 Ecoboost. It had 125,000 when I bought it. There is something weird going on with the transmission or drive train though. The biggest thing is a clunk or slam when I start to accelerate after cruising speed. Say I'm cruising down the road at about 40 mph and have the foot off the accelerator coasting and i'm in 4th gear. I decide to give light gas to accelerate and then for a split second the RPMs go up and then the clunk/slam. It feels like a slip and then jamming into gear hard. Or like someone lightly rear ended me. It doesn't do it all of the time though. Just off and on. The transmission seems tight and good though when accelerating normally and shifting through the gears. No slipping or revving or mushy shifts.
It seems like the issue is between gears meaning right between the gear shift points or downshifts. It happens as well when I start accelerating for a rolling stop or when i'm not completely stopped. I accelerate and noting for about a second then bam it slams and I start going. Other strangeness that happens that might be related is that when I am stopped and let off the brake (no gas applied), or stopping and almost at a complete stop the truck shakes back and forth. Almost like a bad engine miss, but it's not. It shakes me back and forth quite a bit until i'm stopped or going. Also when completely stopped and after about 5 seconds the truck lurches forward a bit, almost like it downshifted well after stopping. But I see it is in first gear. That happens almost every stop. Last thing is that say I'm coasting in 2nd gear every time I give it light gas is lightly clunks. I can keep clunking that when it's in 2nd and tap the gas.
What could this be? It is very perplexing. I was thinking (hoping) that this might be the issue with the slip yoke not being greased up good enough. Also I was thinking maybe a transmission re flash to learn the shifts might help? Any ideas on what this might be or if I'm on the right track with this? Any help troubleshooting this would be appreciated.

Thanks
Any resolution?
 

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Barcode hasn't checked in over the past 3 years. You may do well to start a thread stating your issues.
Barcode hasn't checked in over the past 3 years. You may do well to start a thread stating your issues.
Gotcha. I’m a ford tech and will be looking further into mine here soon when I have time to get it in the shop- will drop the answer if I find anything.
 
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