Learn from my mistake: clunking diagnosis

[Joe_Black]

Since the mounting boss on the tranny is aluminum you could re-tap, say 12x1.25mm, without having to hog out much material. Just take it slow and use cutting oil, then you'd have a solid OEM-look repair. Otherwise go with 10mm grade-8 or grade-10 hardware from your local fastener supply to properly through-bolt. Then you should be covered for shear.

[Ldub]

Since the mounting boss on the tranny is aluminum you could re-tap, say 12x1.25mm, without having to hog out much material. Just take it slow and use cutting oil, then you'd have a solid OEM-look repair. Otherwise go with 10mm grade-8 or grade-10 hardware from your local fastener supply to properly through-bolt. Then you should be covered for shear.

I think we're on different pages of the same book Joe, I was talking about through bolting the mount itself, to make it solid (and to keep from $pending money on a new one)...
Here is what I meant...

[Joe_Black]

Oh, gotcha. Roger roger!

[TOKKA]

I think we're on different pages of the same book Joe, I was talking about through bolting the mount itself, to make it solid (and to keep from $pending money on a new one)...
Here is what I meant...

Great Pics, great point, and great info from all, but I don't really see what's wrong with the XMSN mount pictured. I see the bolt through it... BTW turned out that my left side bolt was in fact loose, however the "clunk/tap" did not go away. In fact, I can reproduce it with the drivetrain in Hi or Lo, forward or reverse, as long as I'm increasing acceleration between 25-50 mph. I'm very afraid to drive far! I have never had a jet, helicopter, or weapon system stump me for so long.

[tom4bren]

TOKKA

25-50 mph in reverse ... that's some hard core wheelin bud.

IMHO, keep the diagnosis simple and work towards the harder stuff. Check CV boots for tears. Check bushings for cracks. Grease anything with a Zerk. Check that all bolts are tight. Check heat shields around exhaust. If you have skid plates, make sure they clear all exhaust and suspension components. Check tire balance. Check brakes for any trapped stones.

Service Tranny. Replace fluids in both pumpkins & TX case.

Even if it's none of those things: 1. should do it every few years anyway & 2. you may locate the real problem at the same time.

[TOKKA]

tom4bren,

In reverse, the acceleration required to reproduce the "clunk/tap" was significally lower, lol, but I try to be hard.

Thanks for your suggestions, all were previously checked and serviced to no avail. On helicopters we had to balance the driveshafts that link the XMSN to tailrotor, or there would be a dynamic vibration produced throughout the aircraft. I'm wondering if something similar could be happening here... pinions, universal linkage, ??? It actually feels like the tapping produce from a Cobra (helicopter) vibration supression system VSS used to counter vibrations.

Anyhow, I'm still looking. %-(

[tom4bren]

JK about 50 mph in reverse. I've only done that once and that was in a rental (definitely not the VX).

There actually are similarities between rotary wing aircraft and autos. While the RPM and load are much less on the VX (thus not needing VSS), things can get out of whack. If you're lifted, you may have added an out of phase angle to the drive shaft U-Joint. That can cause some odd clunks & vibrations.

CVs typically only let you know of their ailments during de-celeration so I kinda ruled that one out.

I assume that the tranny is still shifting smooth since you didn't mention it so I kinda ruled out the shift sensor.

Can you have your tire balance checked (also make sure they are all wearing evenly and have the same pressure) so we can rule that one out?

[FlyingV77]

i get all kinds of clinks knocks and rattles... i thought she was just being nice and have ing a convestaion during our drives.

[TOKKA]

FlyingV77,

Unfortunately I'm getting more of a knock on the door, urr floor, instead of the usual conversation.

tome4bren,

No lift, smooth xmsn, tires rotated and balanced last month, and now I'm beggining to hope it's a different manifestation of a bad CV axle so I can just get past this issue. I've tapped and shook everything on the undercarriage so I'm thinking it has to be internal to some component... The feed back from the "clunk/tap" is enough to periodically register a light or two on the TOD indicator. I tried some hard wheeling in hopes of forcing a "break" that would reveal itself, but all I got was the knocking on the floor. The search continues.

[JAMAS]

Perhaps the transmission bolt was tight, but the connection between the top mount part and the lower mount part has come loose. That is the problem that ldub had which was fixed by running those bolts through the middle.

I had the clunk every time I turned. The issue seem to be a missing bolt. I replaced both my transmission mount, as well as all of the bolts(with loctite). No more turn-floor-clunking.