Learn from my mistake: clunking diagnosis

[Joe_Black]

For some time the IronMan had been making some "clunking" noises not of the normal Isuzu driveline flavor. At first I suspect maybe the CV joints were failing and after inspecting found them just fine. Visually inspecting the chassis and driveling above and below revealed nothing obvious, so I continued to drive and listen. The noise began to worsen and I noticed the shift levers moving significantly during accelerating gear-shifts. This is typically a sign of failed or failing engine mounts. I also noticed the noise, and even felt it to some degree, during turns with lateral acceleration which further strengthened the engine mount diagnosis. So, confident I had determined the problem an order was place to Autozone.com for a pair of new engine mounts.

This past weekend I set aside some time to exchange the IronMan's engine mounts. While preparing for the swap I was getting a closer visual inspection of the mounts from below and noticed they looked fine. Perplexed, I began going down the driveline with more scrutiny. As I grabbed the transfer case to pull myself toward the rear it shifted. Taking a closer look at the transmission mount, the 3rd member of the drivetrain mounting trio, I dicovered the left-side bolt and heatshield missing along with the right-side bolt. So I dropped the skidplate to find the left-side bolt and heatshield laying on the top of the plate. Somehow it managed to rest there after it's fall! Inspection of the bolt revealed thread damage near the bolt head lessening toward the end, showing how it supported the torsional load from the tranny until finally dropping out. There was no sign at all of the right-side bolt.

A quick trip to the local Grainger secured two replacement bolts which were installed and torqued to spec. Problem solved! Thankfully I can return the unused engine mounts to Autozone, so total out-of-pocket for this repair was less than $5. So when you hear some clunking going on, just slide under the side and give the transfer case a good pull and shove. If it moves, then you've got an issue with the transmission mount (AKA rear engine, or motor, mount).

Here are a few pics taken during the repair where you can see the deflection of the transmission relative to the mount on the crossmember:

[biju]

good info. I've never really poked around the underside too much, but this is inspiring. I'll take a peek this weekend just for the fun of it...

-biju.

[carlymac]

Thanks Joe,
I'm gonna go yank on that thingy near my cross member right now...lol

[johnnyapollo]

I'm fond of yanking my cross member as well...

-- John

[thedutchguy]

I also had a "clunk"when backing up.
It turned out to be 2 loose bolts of the upper suspension on the right hand side.These are the bolts that also permit to place shims for camber adjustment.
Has anybody else encountered this problem?

[Joe_Black]

I'm fond of yanking my cross member as well...
Under the VX? Have the neighbors complained? :p

[-x-]

Im unfortuanetely in the smae boat, probly further up creek though. Not only are my bolts missing but the holes do not line up (tranny is forward of hole). This i admit i am certain is due to a accident i experienced some time ago =' ( you guys think i should get under there with a pry bar? ...x

[Joe_Black]

Im unfortuanetely in the smae boat, probly further up creek though. Not only are my bolts missing but the holes do not line up (tranny is forward of hole). This i admit i am certain is due to a accident i experienced some time ago =' ( you guys think i should get under there with a pry bar? ...x
Loosen the two 17mm nuts that secure the transmission mount to the crossmember, then try to line up with the transmission. (You'll have to remove the skid plate first, two 14mm bolts) There is some adjustment there, so you should be able to get it in line. If you need a hand let me know and I'll head up your way on an upcoming weekend. ;)

[Jonnie]

So, what size are the missing bolts? :eek::rolleyes:

[don moore]

I'm fond of yanking my cross member as well...

-- John


lol ..your a bad boy.....:rolleyes:

[Ldub]

So, what size are the missing bolts? :eek::rolleyes:

I'm having this same issue...I'll get back to you after this weekend with the diameter & pitch of the bolts in question. My bolts are still there, it's the mount that's toast...:sighwgray
Gonna try to "fix" the old mount, possibly by through bolting it, as I don't have the $80+ to buy a new one right now.

[Thmstec]

Umm, this is making me a little concerned. When I shift into D from P or N there is an audible mechanical sounding "clunk." It has done it since I first bought it, so i just assumed this was normal. Is it? :confused:

[Jonnie]

I think that is normal.

What happened to me is I broke the passenger side cat pipe at the flange behind the manifold.

While driving I was hearing a knock.

Jonnie

[Joe_Black]

Just discovered this on another VX and remembered to post the bolt size: 10x1.25mm, length not less than 35mm or more than 40mm. Preferably a shoulder bolt with lock washer. If you've lost your heat shield (left side) do replace as it protects the rubber in the tranny mount from heat degradation due to proximity of left catalytic converter.

[Ldub]

I'm having this same issue...I'll get back to you after this weekend with the diameter & pitch of the bolts in question. My bolts are still there, it's the mount that's toast...:sighwgray
Gonna try to "fix" the old mount, possibly by through bolting it, as I don't have the $80+ to buy a new one right now.

Man, I dropped the ball on that one...:sighwgray
I will say, that through bolting the mount didn't work well at all. The torque laod from the massive Isuzu 3.5L was more than 1/4" grade 8's could handle...both sheared off...:_crying:

Gonna upgrade to 3/8 or 1/2" & give it another try, but suspect that there is a new tranny mount in my future.:rolleyesg


Just discovered this on another VX and remembered to post the bolt size: 10x1.25mm, length not less than 35mm or more than 40mm. Preferably a shoulder bolt with lock washer. If you've lost your heat shield (left side) do replace as it protects the rubber in the tranny mount from heat degradation due to proximity of left catalytic converter.

Thanks for remembering Joe, I didn't put my heat shield back on, but will, since I still have it.

[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. :bgwo:

[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. :bgwo:

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)...:_wrench:
Here is what I meant...

http://www.vehicross.info/gallery/data/500/DSC02863.JPG

http://www.vehicross.info/gallery/data/500/DSC02862.JPG

http://www.vehicross.info/gallery/data/500/DSC02877.JPG

[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.