My vibration

[gwcrim]

Now that Philoe phinally got his vibration gone I'd like to diagnose mine.  Here are the facts:

If I recall, it originally surfaced after I had a heavy truck mechanic install a 3.55, a posi, and new U joints in my factory 12 bolt.  It is most evident from 72-77 MPH but I think it is there faintly at half that speed.

Since that time I have replaced the wheels, tires, engine, transmission, and driveshaft (used the same U joints).  Driveshaft was built brand new and U joints installed by them.  Had they been bad, I hope they would have caught it. 

If I drive down the road and get it to vibrate, I can put it in neutral and the vibration remains.  Definitely not an engine vibration.  Definitely feels like its coming from the back of the truck.  It's a VERY noticeable vibration and above 77 MPH it goes away. 

If it is the rear end, what would the most likely culprit be?  Pinion?  How could I check it? 

I'm certainly open to suggestions.

[Stewart G Griffin]

Who, where, what, when, built the driveshaft?    Which leads to the question, was it balanced?


2) Are you sure your tires are round?   i know it's a pain, but if you could jack up the rear end and have someone put it in gear while they are in the driver's seat and you watch the tires to see if they are in fact round.  OR put the rear tires on the front and spin them by hand.

i've bought  a few out of round tires unfortunately.

[gwcrim]

The vibration started right after I had the gears installed.  I've changed everything but the rear end in the meantime and the vibration remains.

In this weather, it's going to be hard to diagnose.  Maybe I ought to wait until spring and concentrate on lowering it now.

[SkinnyG]

Sometimes over-tightened u-joint cups will cause a vibration.

The speed at which my truck's vibration occurred dropped when I went from 3.07:1 to 3.73:1 gears.

I had a slight reduction in vibration going from my summers (BFG T/A's) to my winters, and again when I swapped out a tight "Precision" u-joint for a "Spicer" u-joint.  Still there though.

[82silverado]

Check the driveshaft play where it comes out of the transmission and see if it moves up and down. Could be the bushing in the tail shaft of the transmission. Do you have a one piece drive shaft or a carrier bearing set up?

[Captain Swampy]

Would you take some pictures of the drive line so we can see the angles of the u-joints. Have you taken the drive shaft off and turned the pinion by hand?  Does it have the correct oil for your posi? I'd take the rear cover and the drive shaft off to see how things look and feel. I'm surprised they put used u-joints in a new drive shaft. Also measure to see if the axle is installed straight in the vehicle.

[egleaves]

I read Philo’s thread and I’m keeping a close eye on this one.  I, too, have a mystery resonance that doesn’t seem to be consistent with anything.

My observations so far:
1.   The vibration comes on at no certain speed and at no certain RPM
2.   It is a rhythmic resonating sound like…….broooooom……broooooom…..brooooom…..brooooom
3.   I feel it in the whole truck.  Seat. Steering wheel. Floor.  All of it.
4.   It occurs almost exclusively under a “no load” condition.  Accelerating hard or downshifting makes it go away.

About ten months ago I had a vibration that would shake the windows (and my nerves) and it was very pronounced at high speeds.  Turns out the ujoints on the driveshaft were had been going bad for a couple of weeks and by the time I got the truck to a shop they were completely shot.  I don’t know if I am experiencing the slow return of whatever shredded my ujoints before…..or if this is completely unrelated.

Also wondering if this is related somehow to my fan clutch separating from its mounting flange.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=33885.msg288262#msg288262

[gwcrim]

Cap't Swampy, you seek good info.

-Have you taken the drive shaft off and turned the pinion by hand? 

Not yet, but that's first on my list.

-Does it have the correct oil for your posi?

Not at first, but that was corrected.  And still it vibrates.


-I'd take the rear cover and the drive shaft off to see how things look and feel. I'm surprised they put used u-joints in a new drive shaft.

I'm going to dive under as soon as I get a creeper.  I'm tired of cold concrete floors.  The U joints that were on the old shaft still had the new car smell on them.  But they are probably the easiest and cheapest place to start if nothing else looks or feels out of whack.

-Also measure to see if the axle is installed straight in the vehicle.

What points of reference would I use?

[gwcrim]

I put 'er up on jack stands tonight.  The pinion has no side to side play.  It spins when I rotate the yoke.  It's a little snug, but it does spin with one hand.  This photo shows the lash.

[Captain Swampy]

I would try to measure from the center of the front spring bolt to the axle tube. Any place you can get duplicate measurements on both sides.

Since it seemed to start after the gear change, I would drain the axle and pull the  axle shafts. Inspect the brake drums, wheel bearings, and straightness of the axle shafts. See if there is a wear pattern on the gears or use a paste so you can see the pattern.  A quick web search will give you patterns to match against to see if it looks set up correctly. You won't really be able to see the bearings unless you pull the carrier and pinion. If you do, make sure not to mix the shims from side to side. I have no idea how much experience you have. You need to decide if you can do this or not. It's really hard to pay someone for exploratory reasons.

I assume you read Philo's thread. Check your engine and trans mounts, exhaust, loose bolts, etc. Skim back through and check every thing. Maybe make a check list and keep notes as you go though the process. Also, how do you feel the vibration? Your butt on the seat, feet on the floor, arm on the door, hands on the wheel?

[Captain Swampy]

I read Philo’s thread and I’m keeping a close eye on this one.  I, too, have a mystery resonance that doesn’t seem to be consistent with anything.

My observations so far:
1.   The vibration comes on at no certain speed and at no certain RPM
2.   It is a rhythmic resonating sound like…….broooooom……broooooom…..brooooom…..brooooom
3.   I feel it in the whole truck.  Seat. Steering wheel. Floor.  All of it.
4.   It occurs almost exclusively under a “no load” condition.  Accelerating hard or downshifting makes it go away.

About ten months ago I had a vibration that would shake the windows (and my nerves) and it was very pronounced at high speeds.  Turns out the ujoints on the driveshaft were had been going bad for a couple of weeks and by the time I got the truck to a shop they were completely shot.  I don’t know if I am experiencing the slow return of whatever shredded my ujoints before…..or if this is completely unrelated.

Also wondering if this is related somehow to my fan clutch separating from its mounting flange.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=33885.msg288262#msg288262

Being that it is felt in the steering wheel I would start with the front suspension and steering. Probably a good idea to start your own thread to avoid confusion.

[philo_beddoe]

gwcrim and egleaves, you need to seek the VileZambonie, he sits atop the high peaks in Tibet, you'll find him in a small hut drinking a large DD iced coffee watching Star Wars. He can provide your options, choose wisely.

Ok, egleaves, your vibe is VERY similar to what i had. Sounds like its in the driveline. Remove dshaft and rev engine in park and neutral and see if you feel anything.

gwcrim, you stated the vibe started right after you had the gears installed.  I guess change out the gears or new rear end assy.

Although i have mega vibration experience, my advice is not professional.  Please keep us posted.