Hard thumping under light throttle

[oakback]

It's not constant, it comes and goes. It doesn't happen, or isn't noticeable, at highway speeds or under acceleration. When it starts, if I let off the throttle, it stops. I can't feel any direction it's coming from. I rotated the tires and notice no change, and still can't tell where it's coming from. It's pronounced though, like a rubber mallet smacking rhythmically. It's speed dependent, not RPM dependent.

The frequency seems faster than tire speed. Could this be a u-joint?

 

[oakback]

Double checked the lug nuts just in case, they're all tight.

 

[ramangain]

Same if the CDL is activated? Do you have the ability to remove the front driveshaft to the differential to eliminate from the transfer case forward?

 

[OEMGUY0720]

I’ll start with rotating components (wheels, rotors, driveshafts) and then move on to pivoting components (ball joints, suspension links.

 

[oakback]

Same if the CDL is activated? Do you have the ability to remove the front driveshaft to the differential to eliminate from the transfer case forward?

Driving on pavement around 30-35 mph, when it started thumping (last night), engaging CDL stopped it, while still in light throttle. I didn't leave CDL on long since I was on pavement, but I tried it 3 different times, each time it stopped.

Assuming the front driveshaft attaches like any other, I can remove it.

 

[2001LC]

2 most common:
Spare tire is loose. Most often due to loss of air pressure.
Propeller shaft (AKA drive shaft) slide yokes forward & aft under lubed.

The OFFICIAL clunk/thunk driveshaft thread

forum.ih8mud.com

 

[oakback]

Spare tire is plenty tight and aired up (did that when rotated tires, and double-checked). I thoroughly greased all the u-joints and both slip joints, and it's still happening.

I'm familiar with the driveshaft clunk, my Bronco would do the same thing. This doesn't sound like, it's not a single "clunk", it's rapid.

It ONLY happens between 30-40 mph, I can't get it to occur at any other speed. To be more specific with the sound, it's almost exactly like running over the raised reflectors on the center line of a road, but does not feel like it's coming from any certain corner or side.

I'll disconnect the driveshaft and try to replicate it soon.

 

[mdcoa]

If disconnecting the driveshaft results in no change, pull the drive flanges at the front hubs to stop all diff/CV rotation and take her for a spin.

 

[abuck99]

Please when asking for service advice- give mileage, how long you owned it, any applicable service history and any other relevant details that might help diagnose the issue.

Has the driveline ever been serviced or joint's replaced, how often do you grease u joints, what is the condition of the driveshaft splines, original CV axles?, OEM or aftermarket CV axles?, wheel bearings been serviced or replaced?, lifted (how much and for how long) or stock? OEM shocks- original or have they been replaced?, do you offroad it or pavement only? Do you feel anything in the floorboard or gas pedal?

Read this post:#101

Pulsing/droning vibration at highway speeds

forum.ih8mud.com

 

[oakback]

241k miles. I've owned it ~5 years. No idea if anything in the driveline has been replaced before my ownership, I don't have any prior service records or documentation. I've replaced 1 CV axle and the associated flange with an aftermarket CV axle, I don't remember the brand. Wheel bearings were served <1 year ago by me. No lift. Front and rear shocks have been replaced during my ownership. I offroad it, but it's Florida offroad, which mean dirt, gravel, and sandy roads. I don't feel anything in the floorboard, pedal, or steering wheel that coincides with the thumping.

 

[abuck99]

241k miles. I've owned it ~5 years. No idea if anything in the driveline has been replaced before my ownership, I don't have any prior service records or documentation. I've replaced 1 CV axle and the associated flange with an aftermarket CV axle, I don't remember the brand. Wheel bearings were served <1 year ago by me. No lift. Front and rear shocks have been replaced during my ownership. I offroad it, but it's Florida offroad, which mean dirt, gravel, and sandy roads. I don't feel anything in the floorboard, pedal, or steering wheel that coincides with the thumping.

I updated the post with a link to vibration analysis post #101. Check "Speed Sensitive Vibration" What is the condition of the tires?

 

[waitdontshoot]

If disconnecting the driveshaft results in no change, pull the drive flanges at the front hubs to stop all diff/CV rotation and take her for a spin.

Yeah i had the problem with the axles spinning inside the axle flange so this is worth checking out.

 

[oakback]

I also had a misfire. I assumed it was completely unrelated. I had a bad coil which I replaced, fixed the misfire. Now I can't get the thumping to happen. That's weird. I wonder if at a certain speed and rpm, the misfire somehow lined up timing perfectly with something else, creating that feeling in the drivetrain. I haven't driven it much though, so I'll keep trying to replicate.

 

[Retep]

I also had a misfire. I assumed it was completely unrelated. I had a bad coil which I replaced, fixed the misfire. Now I can't get the thumping to happen. That's weird. I wonder if at a certain speed and rpm, the misfire somehow lined up timing perfectly with something else, creating that feeling in the drivetrain. I haven't driven it much though, so I'll keep trying to replicate.

Has it happened again for you since replacing the bad coil? I've been battling this same issue. Only happens around 30-40 mph with light throttle. Once vibration occurs, I let off the accelerator to stop it and then can accelerate like normal again (usually). I'm not sure I can put a percentage on how often it occurs under similar circumstances, but unfortunately its been a challenge for a mechanic to replicate.

 

[oakback]

It hasn't happened since then.