Sounds like someone swinging a sledge

JL Rockies · **Posted:** Sat Dec 20, 2008 3:28 pm

Since a have a long trip coming up, it makes sense that everything is starting to break (I even have the red circle of death on my 360).

I first noticed it right after I got my new front diff installed a few months ago. It only happened once at first so I let it go but now it's getting more common.

Days after I had my new front diff w/ DTT and 4.10 gears installed I wanted to feel what the new gears can do on acceleration. From a stoplight I mashed the accelerator and launched the Jeep. There was a big bang as I look off I thought maybe I hit debris because I actually felt it on the floor it didn't happen again and my Jeep moved fine down the road.

It never happened again for a while until I would go off road. When we tear down dirt roads and I hit a bump, I hear and feel that bang again (it's very loud). On my way home minutes before typing this, I was making a right from a stop and "bang" again.

Is sounds and feels like there is someone under the floor hitting it with a hammer. It's never done this before I have this stuff installed, it feels like its coming from right under my feet.

In an unrelated incident, I have the carpet and padding pulled out so I hear more stuff now. What I hear now is as I drive down the road and sounds like bolts vibrating around in a coffee can; again it sounds like it's right under my feet. This noise could be new or it could be a noise I never heard with a padding and carpet down.

It's probably has something to do with the work I had done since there is a bit of a talent vacuum here in FL. What do you think?

If it is installer error, what could they have done?

tommudd · **Posted:** Sat Dec 20, 2008 3:39 pm

Since they had to pull the front diif clear out I would first check all the mounts make sure they got them tight. Also check the front driveshaft to make sure its OK and tight. Since you have the carpet and padding out and with no frame etc you are going to hear the whole body flexing, moving more which the carpet has covered some of that sound. Now IF you only hear it when say you nail it, it could be just the DTT locking up, but should not be a hammer hitting the floorboards

I would start with the bolts that hold the front diff in and go from there

JL Rockies · **Posted:** Sat Dec 20, 2008 3:42 pm

I am going to drop the engine skid and poke around and see what there is to see.

InCommando · **Posted:** Sat Dec 20, 2008 6:55 pm

Sounds like the drivetrain is rotating to much. Check the motor mounts, too. The DTT makes no noise like a locker or a drop-in, IIRC.

Fulltimer · **Posted:** Sat Dec 20, 2008 8:13 pm

I think the KJ is just telling you to hurry up and hit the mountains! :lol:

Terry

KJ04 · **Posted:** Sun Dec 21, 2008 8:12 am

Is this bang noise happening when you jump on it 2 wd., 4 wd. or both?

dieselenthusiast · **Posted:** Sun Dec 21, 2008 10:54 am

InCommando wrote:

Sounds like the drivetrain is rotating to much. Check the motor mounts, too. The DTT makes no noise like a locker or a drop-in, IIRC.

Yes, check the motor mounts. I'm pretty sure my '93 GMC did something pretty similar to yours when driving through a bumpy field. Every time I hit a rough spot, I would hear a loud banging sound. I couldn't see anything from down below, so I opened the hood and noticed my engine was vibrating more than usual in the engine compartment. Sure enough, the drivers-side engine mount was destroyed.

JL Rockies · **Posted:** Sun Dec 21, 2008 12:28 pm

KJ04 wrote:

Is this bang noise happening when you jump on it 2 wd., 4 wd. or both?

The banging happens in 2WD on the road. Off road it's happened when I hit big bumps. At first I thought that the rock rail came loose.

Are the motor mounts involved in front diff swap?

tommudd · **Posted:** Sun Dec 21, 2008 12:46 pm

JL Rockies wrote:

KJ04 wrote:

Is this bang noise happening when you jump on it 2 wd., 4 wd. or both?

The banging happens in 2WD on the road. Off road it's happened when I hit big bumps. At first I thought that the rock rail came loose.

Are the motor mounts involved in front diff swap?

no motor mounts are not invovled when you remove the front diff, but I would still check them and also everything they removed, even a bolt that seems tight will move some if it is not torqued to spec when under load

dieselenthusiast · **Posted:** Sun Dec 21, 2008 12:48 pm

JL Rockies wrote:

Are the motor mounts involved in front diff swap?

No, there shouldn’t be any reason to lift the engine to do a front diff swap. A bad motor mount is usually due to lots of wear to the point of weakness, then it finally breaks. I’m not sure how many motor mounts the CRD has. Actually, I know very little about the KJ suspension, so I’m not a good one to make a guess. Sounds like there is something in the suspension that is broke or loose. I also had a torsion bar that broke on my Tahoe and it sounded like a hammer was beating on the underside of my driver side, plus I could feel it. :shock:

But again, we are talking about two completely different vehicles. You may want to take it to a dealer and let them look over everything before you make the trip out West.

USAFCOP · **Posted:** Sun Dec 21, 2008 2:51 pm

Joseph, first look for worn suspension bushings, and your diff mount bushings. Mine knocks pretty hard on bumps, and my sway bar link bushings are pushed out so the link will hit the lower arm metal to metal.
next, maybe first since you feel it under you, check tightness of the 8mm bolts around the front prop shaft, mine had one bolt that had come loose, and made all kinds of racket, not really a thunk, maybe prop shaft cv is bad (I do not know how to tell, but I have a good one for sale we could put in when you get up here :wink:

)
Like others said, I would verify torque of all suspension and front diff mount bolts. Including struts and clevis bolts. also look at your cv shafts at the diff, if you see fluid, the shop who installed the diff may have screwed up yout axle seals by putting the shafts in at an angle (a shop did that to mine after fixing my ARB because they did not remove the strut/clevis assembly before removing and reinstalling the driverside shaft. That clunked, but it wasn't hard, just noisy.

SO you got a lot to look at, better to do it in FL, as it is real cold up here...

tjkj2002 · **Posted:** Sun Dec 21, 2008 9:04 pm

There has been issues before with loose motor mounts in CRD's,seen many threads about it in the CRD section.

JL Rockies · **Posted:** Fri Dec 26, 2008 11:28 pm

I finally got off my butt and took down the engine skid to find out what might be loose. I checked the sway bar bolts first and all seemed tight.
It didn't take long to find a VERY loose bolt which seems to be associated with the front diff. Here is the pic I took:

It seems to be a bracket that holds up the front diff. There is a single bolt shown in the picture up front and a few others that bolt to the diff on the opposite side. I tightened it as much as I could but I only had 1 19mm and an adjustable (I bought another tonight).
I took it for a test drive and the loose bolts in a coffee can sound is much reduced but not completely gone. Now that I have two good wrenches, I will torque them down better tomorrow. I was not able the get the banging noise, but that does not happen all the time anyway.

My questions now are:

Does this bracket need to come down to install the front diff?
Does this bracket require any adjustment when changing the diff fluid?
I had 1 shop do each and I was curious which one was at fault.
Has anyone had this bolt losen all by itself?
If this bolt was super-loose, do you think it could be the source of the banging?

When I pound on this bracket with my hand I still get that rattling sound but I am reserving judgment until tomorrow.

Thank you.

tjkj2002 · **Posted:** Fri Dec 26, 2008 11:46 pm

Yes to if those bolts are lose it will cause a banging sound.There is 3 brackets that hold the front diff in,make sure to check all 3 and all the bolts.The pic above is the front bracket and has 2 more bolts that hold the bracket to the diff itself.No need to remove any brackets to change the front diff oil,the front diff has a drain plug on the bottom and the fill plug is on the diff cover.

JL Rockies · **Posted:** Fri Dec 26, 2008 11:51 pm

So it's more likely that it's the fault of the guys who installed the diff in the first place then. I assume that if these were torqued properly, they should not be loose.

I am going to be very happy if all the noises go away.

tjkj2002 · **Posted:** Fri Dec 26, 2008 11:55 pm

JL Rockies wrote:

So it's more likely that it's the fault of the guys who installed the diff in the first place then. I assume that if these were torqued properly, they should not be loose.

I am going to be very happy if all the noises go away.

Probably,between the 3 brackets there is 11-12 bolts.

JL Rockies · **Posted:** Sat Dec 27, 2008 8:30 am

Chalk up another one for the talent vacuum around these parts.

JL Rockies · **Posted:** Sat Dec 27, 2008 10:31 am

Got a good wrench on it today and took it for a drive; no more noises! As for it running hot on the highway, thats another story.

JL Rockies · **Posted:** Sun Dec 28, 2008 12:28 pm

I confirmed that this was the source of the banging. After looking at the inside of the engine skid, I could see where the diff cut through the plastic and dented the metal.

Sounds like someone swinging a sledge

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