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Engine knocking noise that subsides when clutch pedal is engaged

28K views 15 replies 8 participants last post by  Bad Cornflakes 
#1 ·
Any clue what may be causing this? when I'm driving it's too noisy to know if this knocking sound is happening, but I suspect it is. But when I'm sitting in neutral, I can hear it. And pressing in the clutch pedal (no gear-change necessary) makes the noise go away. Any thoughts?? Does this mean I have a bum clutch?
 
#2 ·
While a "knocking" noise would certainly be considered unusual, a whirring sound that goes away when you step on the clutch is not unusual. When the transmission is in Neutral with the clutch pedal up, the engine spins the transmission's input shaft which spins the transmission and its bearings audibly. Stepping down on the clutch pedal stops the transmission from spinning which quiets things up.

Could that be what you're hearing? Jeeps aren't cars so they use truck transmissions which are noisier plus there is not much sound insulation between the passenger compartment and the drivetrain. Those add up to louder noises new Jeep owners are not used to. :)
 
#9 ·
There's a good chance it's the input shaft bearing on your transmission if:
The noise is both in gear and in neutral, and
The noise goes away when the clutch is depressed, and
The noise gets louder after being driven for a while.

Transmission input shaft is spinning until clutch is pushed in both in gear and in neutral. Gear oil warms up and looses viscosity as jeep is driven.
 
#11 ·
Im new here, and don't want to just jump in, but I just went through this. My tj, would sound like a dollar 2.98 in change when in gear, push the clutch in, and it went away. The sound would change with the throttle, when going down the road. My issue was the input bearing in my 5spd was gone, that and I had 4 teeth missing from the balance shaft. The odd thing, mine only made noise in 1st through 3rd, 4th and 5th made no noise.
 
#14 ·
Water Dog is correct, Im doing a complete rebuild, new bearings, balance shaft, syncros. I will be doing this once, and only once, if it fails again,,, in the near future, I will be doing a transplant. But at the moment, it was the most cost effective. A salvage trans would run 400 to 600, depending on where I pick it up. The rebuild , even with the balance shaft, is going to come in at just under 700. so it just made since to go all the way.
 
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