Jackhammer/thumping noise when accelerating at high speeds


I’m driving a 95 honda accord ex, manual transmission.

I’m getting a thumping noise when I am accelerating at high speeds, 60+ mph. It feels like I am running over lots of little speed bumps, and the frequency increases as the speeed increases. It only happens when I accelerate and the intensity of the thump increases when there is a heavier load on the engine (i.e., when I am accelerating uphill, or depressing the gas pedal further). If I stop accelerating, the car coasts very smoothly. There is no steering wheel wobble, but I can feel the impact of the thumping throughout the car, through the gas pedal & steering wheel.

The CV boots are intact, and there’s no clicking sounds when I turn that would indicate joint failure.

Today the problem started appearing at lower speeds, at around 40 mph. Its starting to feel like a sledgehammer hitting the wheel.

Could this be a wheel bearing or transmission problem? Or most likely front axles?

Better drive it carefully to the shop. You could have broken engine mount(s).

I can check it again, but i’m pretty sure the frequency of the sound is related to the speed of the car, rather than the rpm of the engine… Also, when I am out of gear and rev the engine its still smooth. Reverse gear is also smooth. Does the broken engine mount cause thumping only when the engine is in gear under load? Or is there another way to test this?

I’m going to try a shop tomorrow.

I agree to check motor mounts. The motor mounts get the largest workout during acceleration. As the engine sends power to the wheels, the motor mounts keep the engine from jumping out of the car. The harder you accelerate, the more the motor mounts hold back the engine. As force is applied to the wheels, an equal and opposite force is required to keep the engine in place. Just revving the engine in neutral doesn’t require hardly any hold-back for the motor mounts.

Also, have the suspension checked. For the exact same reason. These suspension parts are also required to hold the wheels in check.

Motor mounts are certainly a prime suspect.

But I’d also put inner CV joints up there as well. The clicking on turns is an outer CV joint thing. Bad inner joints can present as vibration & noise on acceleration.

Turns out that it is the engine mount; both front and side ones are worn out. I’m going to get a replacement tomorrow, but they’re also suspicious that it might be something else. They’ll take it for another test drive tomorrow to see if the shaking will stop after they switch out the mount part.