Rythmic thump after hard acceleration
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FTE Chapter Leader
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From: Henderson, NV
Rythmic thump after hard acceleration
Right after I got on the go pedal hard to merge onto the freeway today, the truck developed a rythmic thump with about a 2Hz frequency when on the gas. I foind this thread that suggested that something may be loose underneath and hitting the frame: https://www.ford-trucks.com/forums/1...eleration.html
I have tightened eveything and cannot see any points of contact between the drivetrain and the frame. It only happens when the engine is applying torque to either accelerate or maintain speed. Freguency of the thump does not change with speed or engine RPM. Revving the engine in Park or Neutral does not cause any thumping. Any ideas?
Edit: I am beginning to suspect blown engine mounts.
I have tightened eveything and cannot see any points of contact between the drivetrain and the frame. It only happens when the engine is applying torque to either accelerate or maintain speed. Freguency of the thump does not change with speed or engine RPM. Revving the engine in Park or Neutral does not cause any thumping. Any ideas?
Edit: I am beginning to suspect blown engine mounts.
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From: Colorado Springs
I’d be looking at the engine mounts, leaf spring bushings, transmission mounts...come to think of it wasn’t it you that showed everyone what the internals of the transfer case look like? 
. Maybe check those mounts/bolts too.
. Maybe check those mounts/bolts too.
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FTE Chapter Leader
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From: Henderson, NV
Originally Posted by Colorado350
come to think of it wasn’t it you that showed everyone what the internals of the transfer case look like? .
.
. Thanks for the suggestions.
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FTE Chapter Leader
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From: Henderson, NV
Both engine mounts and transmission mount replaced. Problem was still there. Removed rear driveshaft and drove around gently with tcase in 4x4 and front hubs locked (FWD basically). Problem went away. I'm now thinking my rear driveshaft needs a new ball seat and u-joints.
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FTE Chapter Leader
Joined: Jan 2005
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From: Henderson, NV
Nope. That was the front driveshaft. The rear driveshaft has been on the truck since I bought it. It's about due I guess.
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I know you said you tightened and inspected everything you could.
What about things you may have over looked like spare tire, shock mounts, spring shackles, etc?
Does the thump appear to be rigid metal on rigid metal like or like something hitting the underside of the cab? The fact that it does not change frequency with RPM or MPH is strange and almost sounds like something is loose and thumps until the pendulum effect is gone.
Of course, I am not there in person to hear it, so I might be way off...
What about things you may have over looked like spare tire, shock mounts, spring shackles, etc?
Does the thump appear to be rigid metal on rigid metal like or like something hitting the underside of the cab? The fact that it does not change frequency with RPM or MPH is strange and almost sounds like something is loose and thumps until the pendulum effect is gone.
Of course, I am not there in person to hear it, so I might be way off...
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FTE Chapter Leader
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From: Henderson, NV
Sous, the thump sounds like somebody is pounding on the frame with a mallet. It is then quickly followed by a twang like a heatshield or brake backing plate got plucked. The overall effect is a thump-twang that I can get to come on consistently starting at 30mph, and only when the engine is applying torque to the rear wheels. I could have sworn the sound was coming from the front of the truck when it began but now I have no clue. I've been tightening every fastener in sight each trip under the truck too. It's the weirdest thing the truck has ever done to me.
Bonanza35, you and me both.
Bonanza35, you and me both.
