TNT Belly Pan + Stock Height = Vibes

Hoping for some help. 2000 Sport, AW4, 231, Stock

I installed the TNT Belly Pan on my Jeep about 6 months ago. Since then, I get vibs at 23 - 2400 RPM's. By all accounts, it appears to be RPM specific. Vibes are worse if I gun it, somewhat unnoticeable if I REALLY take it easy. Regardless, vibes appear at that RPM.

This is what I have done in order to pinpoint this.

Pulled Rear Driveshaft - vibs still there. While I was at it, replaced U-Joints.
Pulled Front Driveshaft - vibs still there.
Put Stock Xmember back on both shafts installed - vibe free.

We measured the rear driveshaft angle from the t-case side and it measured down at 5 degrees for both the Belly Pan and stock Xmember. I have read where this Belly Pan can push the tranny up a tad (I am still using the Tranny stock mount) though it appears that if it does, it has to be a VERY small amount. Small even for these vibe prone 2000's. I have contacted TNT and I was told that if I kept the stock mount, there shouldn't be any issues.

Anyway, I am pretty committed to keeping this Belly Pan as I think it is a bad ass piece of equipment.

Anybody have thoughts? No stupid questions. Let it fly. I am just learnin'. I would appreciate any input.

Cheers.

Is everything torqued down to spec? The only thing (other than that) that I could think of is the LPD30 on the 2000s, but you said you've already adressed that so... I dunno. Check to see that everything is tight and that your mount aren't worn out.

yup, torqued to spec and from what I can tell, the mount looked fine. thanks for the reply.

I thought that the TnT belly pan had a x-fer case drop built into it. If it does put a spacer between the skid and mount.

same thing happened to me when i switched my tranny crossmemeber, you definately disturbed something, my guess is to drop the t case a bit to see if thats what the problem is. I just went to a sye becasue i was sick of it.

opracer315 said:

I thought that the TnT belly pan had a x-fer case drop built into it. If it does put a spacer between the skid and mount.

Click to expand...

I don't think his does though. We measured the TC output with the stock cross member installed and the TNT installed. Neither changed the height of the TC. My latest theory on this one is that it involves something with the front DS and its operating angle. We did not measure the angles up front. Starscream my have it...could be that the LP D30 is just not havin' it. I suppose if that's the case then the best fix would adjustable LCA's? Certainly a PITA to have to go that route on a stock XJ.

-river

riverfever said:

the best fix would adjustable LCA's? Certainly a PITA to have to go that route on a stock XJ.

-river

Click to expand...

1000$ lock outs ! :laugh:

Maybe you have a bent output shaft? Driveshaft balancing. Tranny mount, motor mounts... etc.

I agree, this is a nice piece of kit.

I have 4" lift and SYE with Wood's driveshaft, so not exactly apples to apples. I've done the drop thing, bad idea. Mine was having some clearance and banging issues after install. Turns out the tranny rubber block was old and worn. A new mount fixed the problem. Unfortunately it is stock since I was unable to locate a poly type replacement. I expect the failure to happen sooner next time due to reduce clearance/tolerance.

Get a SYE asap, it really makes a difference, I suspect even with stock height. Best bucks I've spent.

xjj33p3r said:

Maybe you have a bent output shaft? Driveshaft balancing. Tranny mount, motor mounts... etc.

Click to expand...

I checked tranny, motor mounts, harmonic balancer. I would suspect if the DS were out of balance it would be the same result regardless if the belly pan was on or not. Same with output shaft.

To answer some of the questions, earlier versions of the TNT Belly Pan did incorporate a t-case drop. Mine doesn't.

At one point I certainly thought about the SYE however if that was it I figured I would be vibe free when I pulled the rear and drove around with the front only. Same thing with the thought of the front driveshaft angles. If that was it, wouldn't they have gone away once I pulled the front?

If I did incorporate a t-case drop, the only problem there was the upper 2 holes that are drilled up on the frame rail. Those would no longer be of use. I am not sure if there is room to drill 2 more once I drop it an inch or so. Of course I don't have to use those holes I suppose, but I have to figure they are there for a reason, to firm things up.

I really do appreciate the responses. Though obviously I have been living with it for the past 6 months, I can't say I don't think about this issue daily.