Clunking sound coming from front end on acceleration

I get a clunking sound coming from my front end when I accelerate hard from a complete stop.
Any suggestions as to what it could be?

I have a 99 XJ with 4WD, command trac.

I have installed 1.5 -2 inch spacers on the front coils and shackles on rear, otherwise it's the factory suspension. It didn't come with the Up Country package.
I also have replaced the stock exhaust manifold with a Borla header so the dent in the pipe exiting the manifold isn't there anymore.

Any ideas as to what this could be? It only occurs on hard acceleration from a complete stop.
I think that maybe the small suspension lift may have done something to the driveshaft angle. My guess is that when I accelerate hard, the angle from the driveshaft to front differential may become too steep. My only fear is damaging that front driveshaft.

Could it be possible that the shaft could hit the exhaust manifold?

I'll take a look to see if I see any rubbing anywhere.

Any ideas?

Thanks,
MAP

Just for clarification, the clunk isn't just one clunk....

It's more like a clack, clack, clack, clack, clack..... more cyclical in nature which is why I suspect something that is turning...i.e. the driveshaft...

The sound goes away once I speed up... when the XJ levels off from the initial acceleration.

Manuel[/FONT]

mine does the same thing i thought it was the tranny mt but it wasnt its driving me nots it feels like it is commin apart whan i start of hard i am starting to wonder if its the motor mts :banghead:


if you figure it out let me know

I've got the same thing going as well. Mine also did it after the lift. Never noticed before that, but only had it for a month or so before the lift. I have also noticed it more when turning and accelerating hard at the same time, like trying to get out in traffic and there is only a small gap to get in. Anyone out there have any ideas?

Sounds like when my cv jiont on the front driveshaft was going out. Pull your front driveshaft and see if it still does it.

Also,
Check your exhaust manifold for a crack. Mine cracked, and then allowed just enough play in the exhaust for it to move and hit against various parts. Did it mostly on acceleration, and starting up.

The 4.0's are notorious for this apparently, and Jeep has upgraded the design with a newer design, to prevent it.

Check your motor mounts ... particularly the one on the drivers side.

Les

you may also want to check where the pipe passes by the trans crossmember . my trans mount was bad and the pipe would hit when i was hard on the gas drove me nuts . the mount looked good but was almost 3/4 inch compressed .

Thanks for the suggestions guys.

Mine seems to make the sound when I'm accelerating, whether turning or going straight from a stop.

I tried doing it once with 4WD high engaged and it didn't do it which tells me it's related to the front shaft.

One of these days when I change the oil I'll take a good look down there.

Thanks,
MAP

Another spot to look might be the control arm bushings. I ran my trail rig w/o caster adjusters in the LCA frame mounts...the self-adjusting wheelbase noises were "clunks" IIRC.