Vibration at Speed

[bilbo]

I have a vibration/drone noise around 35-45 mph and 65-75 mph. I can’t figure out if it’s engine or driveline but I’m leaning towards engine. Here is what I’ve done so far:

Luk SMF clutch kit
Rearmost u-joint (cup fell off and I lost the needles when doing the clutch)
Rearmost u-joint again (thought I had a bad one, it seemed really stiff)
Center support bearing
Clocked front u-joint off 180 degrees
Clocked rear u-joint off 180 degrees.

The noise is worst when accelerating or holding speed. It drops away quickly when coasting. Overshooting those speed ranges and coasting back down doesn’t seem to create much noise. I don’t remember this happening before the new clutch but I didn’t drive it a ton. One thing I’ve noticed is a faint tapping sound as the clutch engages. The best thing I can compare it to is if you’ve ever rode on a train with a flat spot on a wheel, but much more faint. Varies with RPM.

Wheel bearings feel tight and the steering feels tight too, but I would think those wouldn’t be as rpm/torque dependent as this is. What’s next to check?

 

[frankenwrench]

Is your truck a 6.9? 7.3 idi? 7.3 idit? I made a 350 dollar goof getting a idit flywheel for my 7.3 idi and had similar issues as the idi and idit are balanced differently. Not saying that this is your issue, but I have made this mistake myself.

 

[bilbo]

Mine is a 7.3 idi, na. I used kit 07225 from Luk. I’ll have to dig a little deeper but I thought it had said it was for non-turbo.

 

[frankenwrench]

Then disregard my suggestion. That is the correct kit I corrected my problem with. Someone will surely chime in with more suggestions

 

[bilbo]

Good deal, thanks. I couldn't find anything that made it specific either way so your confirmation is appreciated. I'll admit my heart sunk when I read your first post. But even if that were the issue and I had to spend some more coin, at least it would be solved. I found a vibration chart somewhere that mentioned Axle Noise as a possible cause. I will maybe have to dig a little into that one. Maybe a bad bearing or clearance on the pinion there?

 

[laserjock]

Any lift or anything? Changes to driveline angle?

I’ve had a couple different things happen to me over the years. Two on my current truck and one on a different truck. All related to axle wrap/pinion angle changing under load messing with the driveline.

When you accelerate or put weight in the bed, the pinion angle changes. It raises up. That does a couple things. It changes the pinion angle and it shoves the drive shaft forward. On my current truck, I would be just fine empty but putting a load on it and accelerating caused a vibration. I corrected it by going back to standard flat blocks over the angles blocks I had bought. The other thing that happened was that my slip joint in the middle was ***** due to an incompetent driveline shop and wouldn’t slip. So as it was forced together by driving with a load, unloaded it wasn’t slipping back and it was trying to rip the carrier bearing out of the rubber mount. That caused a binding and a vibration. Pulled the slip joint out of the tcase too far too. The other issue I had years ago was a little different. That truck would be smooth as silk accelerating. Take your foot off the gas to coast and it vibrated like crazy. Drive shaft was too short so when the pinion relaxed it was pulling the slip joint out too far causing it to vibrate.

So in short, make sure your slip joints slip. I had to beat mine apart under tension. It was the stupidest thing I’d ever seen. Make sure the carrier bearing is centered in the housing front to rear (that was my clue on the slip joint). If you haven’t changed anything else, you may have put it together clocked wrong and it may just be worth the money to go have it balanced. Pay the stupid tax for not marking it and move on with your life.

We’ve all done it.

 

[frankenwrench]

Pay the stupid tax for not marking it and move on with your life.

We’ve all done it.

Il second this as well

 

[catbird7]

Weird as this may sound, check the bolts connecting bell housing to engine. If they're loose it can make some odd noises. Another thing, verify trans and motor mounts aren't broken. Last, make certain neither shifter is touching the body. Another that comes to mind, check fluid level in transfer case. Did you change the pilot bushing in the end of the crank?

 

[bilbo]

Any lift or anything? Changes to driveline angle?

I’ve had a couple different things happen to me over the years. Two on my current truck and one on a different truck. All related to axle wrap/pinion angle changing under load messing with the driveline.

When you accelerate or put weight in the bed, the pinion angle changes. It raises up. That does a couple things. It changes the pinion angle and it shoves the drive shaft forward. On my current truck, I would be just fine empty but putting a load on it and accelerating caused a vibration. I corrected it by going back to standard flat blocks over the angles blocks I had bought. The other thing that happened was that my slip joint in the middle was ***** due to an incompetent driveline shop and wouldn’t slip. So as it was forced together by driving with a load, unloaded it wasn’t slipping back and it was trying to rip the carrier bearing out of the rubber mount. That caused a binding and a vibration. Pulled the slip joint out of the tcase too far too. The other issue I had years ago was a little different. That truck would be smooth as silk accelerating. Take your foot off the gas to coast and it vibrated like crazy. Drive shaft was too short so when the pinion relaxed it was pulling the slip joint out too far causing it to vibrate.

So in short, make sure your slip joints slip. I had to beat mine apart under tension. It was the stupidest thing I’d ever seen. Make sure the carrier bearing is centered in the housing front to rear (that was my clue on the slip joint). If you haven’t changed anything else, you may have put it together clocked wrong and it may just be worth the money to go have it balanced. Pay the stupid tax for not marking it and move on with your life.

We’ve all done it.

I don’t believe it’s lifted. Given its previous life as a tow mule for a trade show trailer I doubt it.

it might come to that. When I removed the driveshaft the first time I marked it, but when I had these vibes I second guessed myself. I tried all the other clocking combos and it didn’t change anything. The slip joint does slip, it easily compressed when removing the shaft every time and didn’t bind when I took it all apart for the center bearing. I didn’t see any signs of it, but maybe I knocked a weight off at some point.

I double checked the wheel bearings again and tightened the drivers side about a flat. It had a very small amount of play, difficult to detect. On my other trucks I’ve had I wouldn’t have bothered it, but maybe this one is sensitive?

 

[bilbo]

Weird as this may sound, check the bolts connecting bell housing to engine. If they're loose it can make some odd noises. Another thing, verify trans and motor mounts aren't broken. Last, make certain neither shifter is touching the body. Another that comes to mind, check fluid level in transfer case. Did you change the pilot bushing in the end of the crank?

I will check on the bell housing bolts. Probably this weekend some time before I get a chance to do that but I will check. I also need to check the mounts. Haven’t done that yet.

The shifter isn’t touching, 2wd so no xfer case. Would tranny fluid matter? It’s overfilled by a half quart to try to lessen the noise at low rpm. The only pilot bearing I saw was in the flywheel. I used the one that came with the clutch kit.

 

[IDIBRONCO]

The only pilot bearing I saw was in the flywheel. I used the one that came with the clutch kit.

That's all there is with our trucks.
If you can't find any loose bolts or anything broken, it's back to the question/diagnose routine. You said that it varies with RPM, but you also listed two sped ranges where it happens. If it's RPM related, I think that it should happen in all gears, or at least the upper three. If it's speed related, then the engine RPM shouldn't make any difference. The difference between the two is that RPMs mean engine related such as balance, exhaust hitting something, etc. Speed related usually has something to do with the u-joints, wheel bearings, or something else along those lines. I had a bad u-joint cause a vibration at highway speeds. After a while the speed where it vibrated was lower than before and I could drive faster and it would smooth out again. On the same truck, I put a 302 in it and must have put a 351W flexplate on the engine (one is interanlly balanced, one is externally balanced). It would vibrate at (I'm guessing) around 1200 RPM or so. Not at an idle, not at a very much higher RPM. It was annoying since it would vibrate at the exact RPM that I would use while driving through a parking lot. Other than that, I just lived with it. One morning, on the way to work, I tried to pull away from a stop sign and the truck wouldn't move. It also started making a horrible grinding noise. I called a friend to come tow my truck to his house 1 1/2 miles outside of town. I borrowed his truck to get to work and brought some tools home with me. I was trying to locate the noise underneath when I noticed that the transmission was broken behind the bellhousing almost all the way around. I got another, used transmission to put in my truck and got started. After I got the bad transmission dropped out from under the truck, I saw that the flexplate was also broken. The center that bolted to the crank had completely broken loose from the outer part that had the torque convertor studs sticking through. There was the source of the noise and also the reason that the truck wouldn't move. We determined that I had the wrong flexplate on there. I replaced it and the transmission and got to drive the truck again. I'm not trying to scare you with this story. I'm only trying to point out the difference between a speed vibration versus a RPM related one and show the issues that can come from ignoring either one.

 

[bilbo]

Yikes that sounds horrible. I’m not going to ignore it. I think I understand what you’re saying. I wonder, if I try a run up in fourth, if I will find the vibes in the same places. If not, then it must be engine rpm. If so, it must be more driveline/road speed.

 

[IDIBRONCO]

That's the best way to check that I can think of. Sometimes, if it's an engine related vibration, there's not enough load on the engine to make it rub if you try revving the engine in neutral. This could be because a worn motor mount will let the engine rock a little to the side when it's under a load from driving. It wouldn't hurt to try in neutral, but it's not a guarantee to work.

 

[bilbo]

This morning I was able to mess around a bit. There seems to be two distinct noises going on. There's a pulsing drone type note that I think is all engine. I can make it do it from 2k-2.5k+ sitting still in neutral. There's also something going on driveline related, as I could hear/feel it at 40mph. It's there driving, coasting through clutch engaged, and coasting clutch disengaged, so it's got to be driveline. My theory at this point is that they resonate together, in normal shifting, at the speeds above.

The engine noise doesn't create a vibration I can feel anywhere, more just a loud drone. The driveline vibe also creates a drone but I swear I can kind of feel it in the cab, seat, etc. too.

The motor/trans mounts are probably all original, 25yrs and 280k miles old. When I get the next chance I'll see how much the engine rocks when revving it from idle, unless there's a better way to check them. How big of a PITA is it to replace the motor mounts?

 

[laserjock]

Motor mount could be letting something touch the cab when the drive train is loaded. That may be one issue.

Check your pinion nut and make sure you don’t have any thing coming loose. If this is new since your last service, it has to be related to whatever you did (stating the obvious). If it’s more of a hum or drone that’s something probably turning faster than tire speed. So from the pinion forward. It could be a bearing roar I suppose but I don’t think that would go away???

Driveline vibrations suck. I wish you luck. Took me forever to find a bad wheel bearing on my half ton. I swore the front diff was hosed. I could feel it in the floor. It was traveling up the front driveshaft. Finally found it by disconnecting one driveline piece at a time and drifting the truck down the hill on my street looking for changes.