Lots of vibration >40 mph

[Howru]

My car vibrates when accelerating past 40 mph or so, with a clunk every upshift. It still vibrates when coasting around in neutral then stops after a while. It's odd that it just started a few weeks ago.

I'm going to toss it up on jackstands on Monday and see if the diff mount is acting up. Any other recommendations on what to look out for? Mod list is in my sig.

[Whizbang]

check the u joints as well

[Max777]

does it increase only with speed or with RPM? I had a bad trans mount that added to my vibration issues if I revved the car high while parked, or went above a certain speed on the freeway.

Does your vibration go away in any gears?

[Howru]

Anything in particular when checking the driveshaft on/off car?

Doesn't vibrate when revving while stationary in a parking lot in neutral.
Loud clunk when starting from a stop and on occasional upshifts.
Vibrations start ~30-40mph. I've noticed they start around the same speed, regardless of gear.
On the highway in 5th (65-70mph, 3k RPM), it vibrates under light throttle, and drops in intensity as soon as I let go of the gas.
If I shift into neutral and coast along the highway, it'll vibrate then decrease.

[Max777]

so it's not rpm specific, but it IS speed specific? Ok, that helps a little.

Have you put the car up on jacks or a lift and inspected the underside for any obvious damage?

The driveshaft has stick on weights, if one of those came off, it would come out of balance, or if it got dented.

The loud clunk makes me think that a diff mount might be a problem here, however dont rely on this alone, as there might be another problem. You could try to do the pinion snubber mod, and see if that helps at all. It does wonders for wheel hop issues.

[Whizbang]

a bad u joint will clunk as well

[Howru]

Going on stands tomorrow. I got a spare driveshaft from an old parts car (from the "pile of useless stuff I'm never going to use" ) that I'll likely swap in.

Kinda odd if it was the diff mount. It's a comp. mount I installed right before Sevenstock, but if it did blow I'm installing a snubber.

[Howru]

Yep, it was the driveshaft. Rears were OK, but the front was shot to hell -- there was so much play that the yoke ears made contact with the center section's.

Swapped in the spare and going to see if I can rebuild my busted one. No more vibration or clunking now. Thanks for the replies!

[Howru]

Problem is back. I've got another to swap in...I lucked out and it looks like it was rebuilt at one point -- it's not as beefy as a TII, but definitely larger than my original one.

I've got an RB Al flywheel w/ a 6 puck sprung clutch, comp mounts all over. Anyone else with this setup blowing up driveshafts as often as I am?

[Max777]

Wait, are you sure it is the driveshaft again and not something else this time? Are the u joints worn again?

[Howru]

Throwing up on stands again tomorrow, but going through all the same symptoms again. On the plus side, the little pedometer/step counter I've got counted ~5000 steps on my 20 minute commute to work.

I put in a spare I saved from a parts car w/ ~150k. See the pic below of the old, broken u-joint that caused the problem in the first post.

[Howru]

Finished swapping in the newer shaft. Broken in pretty much the same spot. As it stands now, my 15k tune-ups will include a driveshaft swap.

I've got one last spare in storage. I've got some Rockford Driveline u-joints ready to swap in if it fails again.