Drive train clanks when clutch engaged

[StephenA]

Anybody familiar with this?:
When shifting, and only after engaging the clutch abruptly, the drive train clanks once almost like a motor or transmission mount has come loose (I had them inspected, and the mounts were all sound). The noise comes from the area of the transfer case or dual mass fly wheel, but sounds like some bolts are loose between the tranny & engine or what have you. The U Joints are also sound. When I engage the clutch smoothly, there is no clanging, but when I use the cruise control, and the clank intensifies when it cuts in, even if I haven't changed gears. Ideas?

[damork]

StephenA,
I'm having what appears to be something similar on my truck, but I have an automatic.

When pulling away from a stop under light throttle, I get a clank which I originally blamed to a transmission shifting delay.

I talked to tranny shops and they said it was not transmission related but either the transfer case or the diff.

Apparently a snap ring in the output shaft of the transfer case has been known to break, snap or come off and can lead to symptoms like this. I bought the snap ring and it only requires pulling the output snout from the transfer case to get at it. Pull the drive shaft first, then 4 bolts hold the snout on the case. A new seal is probably in order. I have yet to do it but plan to soon. The ujoints are not loose and I can't find much play in the diff either, but will pull that cover and have a look there too.

Good luck.

[BuffaloGuy]

Got the same problem. I have always attributed it to the wonderful spring assemblies on either the dual mass flywheel or on the clutch in the single mass flywheel option.

I don't know why they have to add all these springs but they are a weak link in the drive train. I just shift very careful, especially with a big load.
Ken

[Turbo Al]

Carefully check the transmission mount BASE, it took me quite a while to fine this, the steel base that it was attached to was 3/4 of the way (lenghtwise) cracked, it is almost impossible to see just by looking at it -- I had someone let out the clutch (partway & slowly with E-brake on) while I was under the truck -- don't do that at home. This is about a $20 item from GM and worth changing out on spec.
Also check that you torsion bars are not touching the trans cross member -- you will see a mark on the torsion bar and a worn groove on the cross member.

[Chad Mac]

I had a similar problem recently but maybe more severe than yours. Mine sounded like a shaking a can of rocks. In addition, I had a vibration at higher speeds (60-70 mph). My mechanic pulled the gear case and found that the dual mass flywheel was coming apart. The springs in the flywheel were broken and flying around in the bell housing. A new flywheel, clutch and slave cylinder . . . and $1300 later and I'm back running just as smooth as ever. I can barely hear the engine now. Good luck!

Chad Mac

[StephenA]

You guys are the berries! I love this doggone site!!
Damork- I'll check the snap ring you mentioned- you'll probably get to yours first, so please, keep me posted when you do..
Buffalo guy- I shift careful too...although maybe it's not the dual mass springs? Love your truck mods!
Turbo Al- I hope the $20 base is my fix too- :) I'll check the bars...
Chad Mac- ouch! I hope it's not my fly wheel! That's a lot of $$$ -We'll see.

Thanks guys!
Stephen

[catmandoo]

mine developed a clank which i thought was u-joints and they were nice and loose no binding. and after checking everything under the sun and truck and got thinkin it was awhile since i greased it.so i greased it and no more clank i think the front joint took the most,then the slip joint behind the hanger bearing. might be worth trying grease for the heck of it.

[StephenA]

Grease- now that's real easy fix. Haven't had a chance to look at it yet...