what you initially described sounds similar to our disco. we do have Active Cornering Enhancement which makes noise at random intervals and sounds "clunky". i think, not sure, but think its got a compressor that constantly resets itself so it can kick in when needing the ACE.

 

ok, been driving the truck the last couple days. The clunk is still there. I also have the ACE system.

Am I supposed to feel the ACE thumping in the floor?

This makes sense, I have duplicated this by coasting in neutral. I do not have the noise when cornering and the ACE system seems to operate normally.

Jax: I think you may be onto something here....I'll slide under the truck and check the sway-bar links/equipment.

Thanks!

 

lets just say for my wife and i, before we knew we had it on the truck (we bought it used) both of us thought there was something wrong as it is a major clunk and thump under your feet. lol. its always cycling at random intervals. you'd think they would have made system that wouldn't make so much noise. good luck bro, keep us posted as i hope this helps.

**i think the ACE system is supposed to make this noise as part of its operation vs. something being wrong with it.

 

I too had the thump. '99 DII 126k. Rebuilt the drivelines/cardan jnt. replaced lubes to see if chunks of gears would drain out. Checked to see if the brakes were somehow randomly kicking in or sticking. I finally gave up and started to wait for Something Big to happen. NW_R's posting re the body mount pts got me under the truck again but my body nuts were tight(odd how this was not reassuring and somewhat disappointing). Out of frustration I started grabbing things and Really shaking them. My rear torsion bar moved. Went to the front and the Front torsion bar really moved. Maybe 1/8". I fixed them with shims I made from a plastic oil container and drove around- thunk Gone!

ACE it seems, has a different program below 25 mph than above.

Bake

 

Sway bar links and bushings all look good without any play in them. Possible this is internal issue with ACE actuators on the sway bars?

 

My thunk returned as well. I am thinking long arm bushings or actuator or maybe air in hydraulics.?

 

I've got the same THUNK when braking from higher speeds, 45mph or so. It's starting to happen a big more frequently now though, and at lower speeds. Had some work done at a shop recently and they didnt' drive it enough to repeat the sound.

They did however check all the body mounts and motor mounts. They weren't loose.

99 DII 102k miles, drive shaft rebuilt.

 

My lattest find:
I shook the truck the other day in the garage by grabbing the brush-gaurd and pushing fore and aft. That is when I noticed the brush gaurd was loose and the entire bumper moved in sequence. Found this disturbing to say the least.

I discovered the main frame rails (left and right) have a major crossmember on the front of the truck (where the bumper attaches.) The four bolts attaching the bumper/member to the frame were loose.

After tightening these, I have noticed the thump is much lighter but I noitice the lighter thump happens more often. Possibly the ACE system is engaging and causing the frame rails to twist and clunk in a loose crossmember? Not sure yet. I will be sliding under the truck and looking for more loose brackets, crossmembers, equipment hopefully this eve.

 

Ever notice a LR with the brush guard that is leaning forward and not sitting upside like it is supposed too? The mounting bolts come loose all the time.
Just check them once or twice a year, re-tighten if needed.
I used lock washers when I intalled mine.