Mystery knocking sound...

[Thero]

Ok guys, I have a real head scratcher here!

Symptoms:

• Loud knocking noise coming from engine compartment ONLY when accelerating
• No knocking sound when revving the engine in neutral
• No knocking sound when traveling at any speed while in neutral or clutch engaged

So basically, the only time it'll knock is when I'm accelerating in gear, whether it's a 5mph, or 30mph. But as soon as I let off the accelerator it goes quiet.

Possible cause:

• Bent / bad pushrod - but it rev's and idles just fine at all times as long as I'm not moving
• Bad injector - possible, but doesn't really seem to fit
• Bad U-joint - My steering was acting VERY weird earlier in the evening prior to the knocking - but still doesn't make sense that I can go down the road at 30mph and it'll ONLY knock if I'm accelerating. Lay off the gas and the knocking stops.
• Tranny - shifts smooth as ever with no noticeable decline in performance

Any ideas? These symptoms just don't make any sense to me, but something is definitely very wrong under the hood!

[kanuck15]

just cause your trans is shifting ok doesnt mean your TC isnt on its way out

[alberta 7.3]

Stick or auto? You mention clutch, Joe say torque converter.
What is the frequency of the knock? Does it match the RPMs?
Does it sound mechanical like a rod bearing knock, or something in the body like the downpipe hitting the firewall or engine rocking on loose/broken mounts and bumping things?

[kanuck15]

didnt even catch he said clutch, good eye.

[Thero]

Well I figured it out, had someone listen to it from the outside and he thought it was coming from the rear end. Popped the cover off the rear differential and all the grease pour out filled with a bunch of busted teeth off the ring and pinion. Fun times. Trailered it off to the shop yesterday as this is beyond my capabilities.

[kanuck15]

Ah well that isnt cool. Sorry to hear about that. Coulda been worse