Drivetrain Vibration

[Dr_Snooz]

The Suburban has a new drivetrain vibration that started a few days ago. It feels like it's coming from the trans tunnel. It starts at 60 MPH and remains as speed increases. It doesn't happen if I rev the engine in Neutral. It does happen at 60 in both 2nd and 3rd gears, as well as 4Hi. Didn't happen in 4Lo, but I didn't run it to 60, of course. The driveline, u-joints, mounts and such are all tight. Nor did I find evidence of a lost balance weight on the driveline.

The last time this happened, I fixed it with a new transfer case chain. I seem to recall a thread around here somewhere saying that someone fixed a similar vibration with a new trans. Both my TH400 and transfer case are super old and sad. I did a hillbilly rebuild of the transfer case, on a table, outside, in the dirt, maybe 2 years ago.

Any suggestions?

[berserk]

I would first figure out if it is speed related or rpm related. My truck currently vibrates at 60mph, after several trips testing different conditions I decided to put the th350 in 2nd and slowly build rpm. At around 2800-3000 rpm the vibration started. This was in 2nd gear though so we'll below the 60mph mark. I then tried it in 1st, 2nd and then 3rd again and found that my vibration was rpm based and not speed based. This eliminated a tire/wheel vibration etc. and told me it was definitely in the Engine/Trans/Tcase/Drive line/Axle.

Second thing to consider is have you made ANY mods/repairs to the truck that may have had an adverse affect on the drive line balance etc? I have done a TON of mods and upgrades, one being a small lift which changed my driveline angle which I suspect is the issue. Especially after having already checked my driveline and having it rebalanced, u joints changed etc. the only thing left is to shim my axle.

As far as the Trans/T case being your culprit I have no idea. Personally I would want to eliminate the easy stuff first.


Look up "Tom Woods diagnosing drive shaft vibration" on YouTube. It will give you a real good understanding and starting point.

[Dr_Snooz]

From the testing I've done, I feel like the issue is behind the torque converter and before the front driveshaft u-joint. Both the TH400 and 241 transfer case are old and tired. If money were no object, I'd already have called Monster and replaced them both. Since money is an object, I'm leaning toward the trans. I don't really know TH400s very well, though, so just wondering if anyone else has ever cured a vibration with a new trans.

[zieg85]

From the testing I've done, I feel like the issue is behind the torque converter and before the front driveshaft u-joint. Both the TH400 and 241 transfer case are old and tired. If money were no object, I'd already have called Monster and replaced them both. Since money is an object, I'm leaning toward the trans. I don't really know TH400s very well, though, so just wondering if anyone else has ever cured a vibration with a new trans.

I can tell you from experience the TH400 in my 85 had a bad vibration it turned out.  It vibrated in park, almost like the engine was out of balance when I rev'd it up.  Changed out the trans and all those issues went away.  Other than the trans vibration, everything else seemed fine, shifted through all the gears fine driving, fluid looked and smelled fine.  It did make a whirling noise if I was in reverse and put in park.

[JohnnyPopper]

When were the trans and xfer case serviced last? Have you checked fluid levels in each?

[Dr_Snooz]

When were the trans and xfer case serviced last? Have you checked fluid levels in each?

It hasn't been long. Both fluid levels are good. The ATF is 2 months old and just under 1,000 miles on it. Of The transfer case fluid is at 2 years. Not sure the mileage because my odo was broken back then. It's not more than 10k miles I'd guess.

[Dr_Snooz]

I called Monster for prices and info. I described my issue and their vote was for the transfer case. They said they've never had a TH400 cause a vibration. My vibration does feel exactly like the bad transfer case chain felt. Like I said, I think both the trans and TC need to be replaced so I won't be too sad either way.

I need to get spline counts and measure output shaft lengths so I can get accurate quotes now.

[VileZambonie]

Monster? Don't be taking advice or buying Monster anything. Double check those u-joints.  Reclock the driveshaft 180 and see what happens.

[Dr_Snooz]

Monster? Don't be taking advice or buying Monster anything. Double check those u-joints.  Reclock the driveshaft 180 and see what happens.

I'm finally getting back to this now. Thanks for your patience. The rear u-joint is a new Spicer piece. It worked better than the crummy Chinese knockoff that I got first, but I can't say I really like it. It seems to be too tall in one direction, not allowing the retaining clips in the driveline to seat fully. In the other direction it is too short, leaving a tiny bit of room between the caps and the retaining tangs in the diff yoke. I could have sworn it was also too tall when I installed it, but either I'm misremembering, or it has shrunk somehow. The joint has a zerk fitting. Dana warned me with bold text to fill the joint completely with grease after installation. Then they put the zerk where I can't get my grease gun on it, or any other grease gun that I know of. Nuts to them.

Anyway, I re-clocked the u-joint in the yoke and the vibration is much better, but still there. Are we leaning toward the u-joint then? If so, feel free to recommend a brand that doesn't suck. When I check these joints, am I just grabbing and shaking, or do I need to use a crowbar?

Also, if you feel like elaborating on your opinion of Monster, and more importantly, who you think is a better supplier, I'm open. I think it's pretty obvious that I'm not the expert on this stuff.

[Shifty]

If the u-joint is correct, it shouldn't be too tall....Either you received the incorrect joint, or you have a needle bearing laying down in the cap.

[bd]

If the u-joint is correct, it shouldn't be too tall....Either you received the incorrect joint, or you have a needle bearing laying down in the cap.

This ^^^^^.

[JohnnyPopper]

I'll bet the vibration goes away when it's fitted correctly

[Dr_Snooz]

Thanks guys. I have new u-joints arriving today. I'll report back when the job is done.

[Dr_Snooz]

Crap.

[Dr_Snooz]

The driveline is in again...



... And the vibration is gone!

Thank you, gentlemen!