Help with thumping sound in 4WD

[TC70C10]

Trying to determine if my NP 205 is ready for rework. In 4wd under any kind of load I get a thumping sound. If I leave the hubs locked and go 2 high, No noise. Front drive shaft has all new u-joints. I put a 4 inch lift on a couple years ago and I can't remember if it made the noise before or not. Running 33 inch tires

Any advice would be appreciated.

Thanks,
Tim

[Zoomad75]

You checked the u-joints, but what about the CV portion of the front shaft? The ball/socket was shot in mine and even though the u-joints were ok, you couldn't drive the truck over 10mph in 4hi without it shaking your fillings out. The clunk/rattle was unmistakeable on mine. When I shifted into 2hi even with the hubs locked and the vibration vanished.

Check the CV!

[TC70C10]

Huntsville Driveshaft reworked the front shaft after hunting season last year, replaced spline in slip joint, new spicer ujoints. CV was given a passing grade.

Initially after the lift, I think the CV was hitting the crossmember. I had it lowered an inch with the spacers.

Two weeks ago I dropped it and hit it with the grinder to make addtional clearance and still had a thumping. This past weekend I removed the spacers and went back to the stock location. Thought it would reduce the inclination angle and maybe the noise. First hill on the way up to the cabin it still thumps but it looks like I have plenty of clearance. No noticeable vibration just the thump.

[Zoomad75]

How consistant is the thump? As far as the shaft actually touching the cross-member and making the noise, it should leave a mark. On both the shaft and the cross-member. The witness mark should be smooth/shiney if it's really fresh or it could have some flash rust on it depending on how humid it is. In any event, if they were touching, it should have left a mark. Look for it. Yet another option to rule out the shaft or the front output of the t/case would be to remove the front shaft again and run it in 4hi. If the thump persists, you might have a problem with the front output of the 205. If the noise is gone I would say the t/case is ok and you still have a shaft issue.

I know you got the cv checked recently, but it still could have worn since then. I wiped mine out in a couple of months with all the snow driving I was doing after the blizzard in Denver back in 06. Seems to me that cv's don't like power put through them at highway speeds for any length of time.

[TC70C10]

The thumping is like a heartbeat, thump, no thump, thump, no thump. It increases with mph/rpm and load up/down hills.

I need the get the truck up on jack stands or a lift. It's so hard to track down a noise when you're sitting in the cab.

Here's what I think I'll do to try to narrow it down
1). Front and rear end up on jack stands. Lock hubs and engage 4wd high and spin tires by hand to see if I here the sound. I almost think a dyno would help because I could put some type of load on the front end.
2). Check CV clearance with transmission crossmember
3). I was wondering if I would do any damage if I removed the front drive shaft and try it in 4 high.

I've heard these 205's are virtually indestructable.

We only have one 4x4 shop here and they love Jeeps and dog everybody else.

I only want to go there as a last resort.

Thanks for you thoughts,

Tim

[TC70C10]

Removed front driveshaft and in just might be in the CV. No thumping in 4wd without the front d.s.

I'm going to carry the ds up to Huntsville Driveshaft tomorrow to have him inspect.

[Zoomad75]

My money is still on the cv. Let us know what they find out.

[TC70C10]

Put the driveshaft back on the truck late last night. When I looked at the transfer case id tag I was surprised to see I had a NP 208C. I'll get the truck out of my garage on Saturday for a test drive in 4wd. I got the rear sliders windows out and it's going to rain for a couple days. I've had leaks around the two rear sliding windows and I'm trying to get it fixed. This will be my third set of rubbers from LMC. This time I ordered a different part number. Also waiting to see if my glass guy can get me new replacement windows.

[CG]

Anyone in the neighborhood missing a cat?

[TonyJohnson]

Originally Posted by CG

Anyone in the neighborhood missing a cat?