When accelerating, I hear a loud knock/pop noise coming from the drivetrain?

MBERRY0614

MEMBER
1999 FORD EXPLORER
4.0L
6 CYL
4WD
230,000 MILES

It's very loud, sounds like someone is hitting the floorboard with a sledgehammer. I pulled the rear diff cover off and didn't see any metal shavings or any broken gears. The ring and pinion looked good, but some of the spider gears looked pitted. I dropped the front driveshaft, and the noise was still present. It only happens under load, and occurs when driving straight, not necessarily when turning. I engaged 4x4 and the noise was still there in 4HI, but not in 4LO. It's the vehicle listed above with 4:10 limited slip rear end.

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1 Reply

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

If it is loud enough to record, please do so and upload it for me to hear.

Have you checked things such as exhaust hangers and the engine/transmission mounts? If you feel it on the floor, there is a good chance one of the two things I mentioned is the cause.

Check to make all exhaust components are tight and unable to move. If they are good, then do the following.

1) Have a helper open the hood and start the engine.

2) Have the helper apply the park brake, hold heavily on the brake, and place the transmission in drive first as you watch the engine's movement.

3) With you to the side of the vehicle, have the helper slowly apply throttle to the engine to see if the engine moves excessively up or down,

4) Do the same in reverse.

Let me know what you find.

Take care,

Joe