High rpm rythmic vibration, mid rpm hum.

[kraut83]

So I did some searching and so far have not found anything that sounds quite like what I'm experiencing.

What I'm hearing and feeling are 2 different vibrations that happen at high rpm in drive or neutral. The first happens right around 40-45 mph (sorry no tach) then the other starts from 50-55mph. The 40-45 is more of a rhythmic humming and it just recently started. The other is a rhythmic vibration I can hear and feel and it's only barely visible in the rear view mirror.

The only thing I've done since the newest hum started is put in new injectors. I replaced the IP a few months ago and wanted to finish off the fuel system. On the 3rd drive to work (35miles) with in the first five miles, on slowing for a curve I heard a loud clacking for about 10sec and it went away, has not returned. The hum was there before and after.

At 35k miles it got a new motor because of a broken crank. The new motor has a fluidamper. I checked the torque on it recently and it's still tight. I assume the slight rhythmic vibration at 55 is what the damper is dampening. Its the same thing I felt/heard before braking a crank but on orders of magnitude more than now. I have not checked the flywheel bolts, I'm pretty meticulous with torque specs and double checked them when the motor went in. Pretty sure it's not the flywheel because I had to pull the one that came on the new motor and put the one from the old motor back on because it caused a nasty vibration on the first test drive.

The hum does not show up as much under hard acceleration. And the rhythmic vibration is definitely less under load with 2 round bales of hay in back, nearly imperceptible.

I have noticed that the power steering pulley doesn't look perfect when it spins but I have a hard time believing it's the culprit.

I can't think of anything that I haven't had my hands on and replaced already that could be causing either vibration. Both alternators are new(well rebuilt anyway), psp is new, water pump only has 10k miles on it, fan clutch spins freely and was new when installed, IP/injectors/lift pump and lines all new. All the fluids are with in range, TC aswell. Belts are new. All the support brackets for accessory drives are tight and in place. The closest I've ever been to the inside of the motor is resealing the valve covers to stop some oil seepage.

I can be over observant at times. My lady didn't notice either until I pointed them out. I try to keep telling myself the truck is almost as old as me and back then things just shook more and where louder. Hell I remember the ancient tractors I rode as a kid would rattle my teeth. Am I over thinking this or is there something I'm missing? Any thoughts or advice would be welcome.

I'm thinking of recording it on the drive into work tonight. Maybe it will come through.

Thanks for reading.

 

[ezgn]

So I did some searching and so far have not found anything that sounds quite like what I'm experiencing.

What I'm hearing and feeling are 2 different vibrations that happen at high rpm in drive or neutral. The first happens right around 40-45 mph (sorry no tach) then the other starts from 50-55mph. The 40-45 is more of a rhythmic humming and it just recently started. The other is a rhythmic vibration I can hear and feel and it's only barely visible in the rear view mirror.

The only thing I've done since the newest hum started is put in new injectors. I replaced the IP a few months ago and wanted to finish off the fuel system. On the 3rd drive to work (35miles) with in the first five miles, on slowing for a curve I heard a loud clacking for about 10sec and it went away, has not returned. The hum was there before and after.

At 35k miles it got a new motor because of a broken crank. The new motor has a fluidamper. I checked the torque on it recently and it's still tight. I assume the slight rhythmic vibration at 55 is what the damper is dampening. Its the same thing I felt/heard before braking a crank but on orders of magnitude more than now. I have not checked the flywheel bolts, I'm pretty meticulous with torque specs and double checked them when the motor went in. Pretty sure it's not the flywheel because I had to pull the one that came on the new motor and put the one from the old motor back on because it caused a nasty vibration on the first test drive.

The hum does not show up as much under hard acceleration. And the rhythmic vibration is definitely less under load with 2 round bales of hay in back, nearly imperceptible.

I have noticed that the power steering pulley doesn't look perfect when it spins but I have a hard time believing it's the culprit.

I can't think of anything that I haven't had my hands on and replaced already that could be causing either vibration. Both alternators are new(well rebuilt anyway), psp is new, water pump only has 10k miles on it, fan clutch spins freely and was new when installed, IP/injectors/lift pump and lines all new. All the fluids are with in range, TC aswell. Belts are new. All the support brackets for accessory drives are tight and in place. The closest I've ever been to the inside of the motor is resealing the valve covers to stop some oil seepage.

I can be over observant at times. My lady didn't notice either until I pointed them out. I try to keep telling myself the truck is almost as old as me and back then things just shook more and where louder. Hell I remember the ancient tractors I rode as a kid would rattle my teeth. Am I over thinking this or is there something I'm missing? Any thoughts or advice would be welcome.

I'm thinking of recording it on the drive into work tonight. Maybe it will come through.

Thanks for reading.

What year is your engine. Maybe a rocker arm keeper button. Might be worth a look under the valve covers to inspect your rocker arms.https://www.gmpartsgiant.com/parts/...1986&submodel=&extra1=&extra2=&filter=(e=LL4)

 

[Barrman]

You only mention speeds and engine as the cause.

How is your transmission mount? I had a loose one in a truck that caused a bad harmonic at 50-60 mph.

Are the front hubs un locked and have you verified they are unlocked by turning the front drive shaft and watching both axle shafts spin?

How about your rear drive shaft u-joints?

Has your rear axle shifted or rotated somewhat to change the pinion angle?

 

[nyoffroad]

Barrman beat me to it, check the rear U-joints. Also check BOTH hubs are in the free position, just because the left one is doesn't meant e right is too. I've never had a lock out hub 'freeze' up but wouldn't hurt spinning that front drive shaft like he said. Take a look at your tires too, could have a shifted belt. The side walls should be smooth all around , look for dents or dipps in the sidewalls.

 

[kraut83]

Tires look good. Front axles spin freely. Took the front down to the king pins a couple of weeks ago and regreased everything and replaced the cones that sit on the king pins.

The trans mount was replaced along with motor mounts with the new motor instal. Ill check for looseness this week along with the ujoints in the rear. I'm pretty sure the rear hasn't shifted. How would I check to be sure?

I mention engine speeds because I put it in neutral and reved the engine and it still made the hum and had the vibration at high rpm.

 

[Barrman]

OK, I didn’t catch that in your first post.

With a cold engine, try pulling all 3 belts off. Start it up and see if the humming and harmonic are still there. You can run and rev the engine for about 3-5 minutes without the water pump doing its thing.

The stock air filter also makes an annoying hum if it even a hair loose. Check those wing nuts and crank down on them.

 

[kraut83]

Never occurred to me I could start it with out the belts I'll definitely give that a try. I did put the wing nuts on a little less tight than normal last time so I'll tighten them up too and see what happens.

Also just now realized I missed the reply about the rocker arm keeper button. I'll also give that a look. My days off are filling up fast, and I thought I had run out of things to do haha.

 

[kraut83]

I tried to record the noises while driving to work. I can hear them on the file I have bit haven't verified if it translated to YouTube yet.

 

[kraut83]

What year is your engine. Maybe a rocker arm keeper button. Might be worth a look under the valve covers to inspect your rocker arms.https://www.gmpartsgiant.com/parts/...1986&submodel=&extra1=&extra2=&filter=(e=LL4)

No lie, I might be a bit angry if this little plastic part is causing that vibration. I guess even in the 80s they took shortcuts and used cheap parts. My lady had a Buick a few years back and had a coolant leak because of a plastic elbow, the aluminum one was only 2 bucks more ffs...

 

[ezgn]

No lie, I might be a bit angry if this little plastic part is causing that vibration. I guess even in the 80s they took shortcuts and used cheap parts. My lady had a Buick a few years back and had a coolant leak because of a plastic elbow, the aluminum one was only 2 bucks more ffs...

They are actually good quality parts. 38 years and counting is a good part. Under three bucks apiece and a little time and effort and they will last another half of a life time.

 

[kraut83]

They are actually good quality parts. 38 years and counting is a good part. Under three bucks apiece and a little time and effort and they will last another half of a life time.

Fair enough. Not the perspective I was giving it. The motor I believe was 85 btw.

 

[ssdvc]

I'm no expert, but your truck sounds pretty strong to me. I couldn't make out any really strange noises or vibrations. With zero insulation, our vehicles are prone to see (and make heard) every single, little noise and vibration that you never hear in most other vehicles. It a rattle can and we love'em !

 

[kraut83]

Hell yea! Thanks! I have a tendency to listen and try to catch anything a vehicle is telling me about. I dont want to be stranded if I can help it. This one has a lot to say, that's for sure haha.

 

[ezgn]

So I did some searching and so far have not found anything that sounds quite like what I'm experiencing.

What I'm hearing and feeling are 2 different vibrations that happen at high rpm in drive or neutral. The first happens right around 40-45 mph (sorry no tach) then the other starts from 50-55mph. The 40-45 is more of a rhythmic humming and it just recently started. The other is a rhythmic vibration I can hear and feel and it's only barely visible in the rear view mirror.

The only thing I've done since the newest hum started is put in new injectors. I replaced the IP a few months ago and wanted to finish off the fuel system. On the 3rd drive to work (35miles) with in the first five miles, on slowing for a curve I heard a loud clacking for about 10sec and it went away, has not returned. The hum was there before and after.

At 35k miles it got a new motor because of a broken crank. The new motor has a fluidamper. I checked the torque on it recently and it's still tight. I assume the slight rhythmic vibration at 55 is what the damper is dampening. Its the same thing I felt/heard before braking a crank but on orders of magnitude more than now. I have not checked the flywheel bolts, I'm pretty meticulous with torque specs and double checked them when the motor went in. Pretty sure it's not the flywheel because I had to pull the one that came on the new motor and put the one from the old motor back on because it caused a nasty vibration on the first test drive.

The hum does not show up as much under hard acceleration. And the rhythmic vibration is definitely less under load with 2 round bales of hay in back, nearly imperceptible.

I have noticed that the power steering pulley doesn't look perfect when it spins but I have a hard time believing it's the culprit.

I can't think of anything that I haven't had my hands on and replaced already that could be causing either vibration. Both alternators are new(well rebuilt anyway), psp is new, water pump only has 10k miles on it, fan clutch spins freely and was new when installed, IP/injectors/lift pump and lines all new. All the fluids are with in range, TC aswell. Belts are new. All the support brackets for accessory drives are tight and in place. The closest I've ever been to the inside of the motor is resealing the valve covers to stop some oil seepage.

I can be over observant at times. My lady didn't notice either until I pointed them out. I try to keep telling myself the truck is almost as old as me and back then things just shook more and where louder. Hell I remember the ancient tractors I rode as a kid would rattle my teeth. Am I over thinking this or is there something I'm missing? Any thoughts or advice would be welcome.

I'm thinking of recording it on the drive into work tonight. Maybe it will come through.

Thanks for reading.

You said you heard a loud clacking the same noise you heard when you're old motor let go. If you do decide to open up you're valve covers, I would run the motor without the covers on to make sure everything is working properly. You could also remove you're push rods and roll them over a piece of glass to make sure they are not bent, and if you have the plastic buttons make sure you don't have any broken or cracked ones ready to break. You might have a sticky or bad lifter. A compression test might help diagnose a bad or leaking intake or exhaust valve problem. You can also do a leak down test to determine any leaking valves.

 

[kraut83]

You said you heard a loud clacking the same noise you heard when you're old motor let go. If you do decide to open up you're valve covers, I would run the motor without the covers on to make sure everything is working properly. You could also remove you're push rods and roll them over a piece of glass to make sure they are not bent, and if you have the plastic buttons make sure you don't have any broken or cracked ones ready to break. You might have a sticky or bad lifter. A compression test might help diagnose a bad or leaking intake or exhaust valve problem. You can also do a leak down test to determine any leaking valves.

The clacking was actually new. I've never heard that before. It only lasted about 10 sec and it hasn't come back or changed how the truck behaves. The rhythmic vibration is what I've felt before. I can definitely do the compression test. Never done a leak down before, I'd have to do some reading.

So far drive shaft u joints are fine. And the air plenum is on tight and hasn't changed.

 

[ezgn]

The clacking was actually new. I've never heard that before. It only lasted about 10 sec and it hasn't come back or changed how the truck behaves. The rhythmic vibration is what I've felt before. I can definitely do the compression test. Never done a leak down before, I'd have to do some reading.

So far drive shaft u joints are fine. And the air plenum is on tight and hasn't changed.

If you have the ability to do a compression test that would tell you a lot about the internals of the engine. If you have good compression on all the cylinders a leak down test would not be indicated. If your compression is not what it should be then a leak down test would tell you where your losing compression.

 

[ezgn]

The clacking was actually new. I've never heard that before. It only lasted about 10 sec and it hasn't come back or changed how the truck behaves. The rhythmic vibration is what I've felt before. I can definitely do the compression test. Never done a leak down before, I'd have to do some reading.

So far drive shaft u joints are fine. And the air plenum is on tight and hasn't changed.

If your drive shaft has been removed it has to go back on in phase or else you could get a wobble. Have you checked your drive shaft? http://www.pirate4x4.com/tech/billavista/PR-shaft/phase.jpg Green is correct.

 

[kraut83]

If your drive shaft has been removed it has to go back on in phase or else you could get a wobble. Have you checked your drive shaft? http://www.pirate4x4.com/tech/billavista/PR-shaft/phase.jpg Green is correct.

I have. I removed it once to check the u joints a year or so back found out the hard way it only goes on one way.

 

[dougco1]

I tried to record the noises while driving to work. I can hear them on the file I have bit haven't verified if it translated to YouTube yet.

Check your air cleaner wing nuts for tightness. I had odd/loud/irritating noise that I ultimately traced to a loose air cleaner cover.
Also, it sounds like your cold advance switch may not be working and is stuck on. I can hear some hammering on the cylinders as your driving it. Does your truck go into high idle when first starting it then back down after it warms up? If not your cold advance could be your issue.

 

[kraut83]

So turns out the psi Guage I have is for lower compressions. The book I have on the 6.2 said I could do a power balance test. All the cylinders warmed up do drop the engine idle down the same amount. I did notice my alternator belt is slapping the coolant hose guard.

Regarding the cold start advance solenoid, and start ups it actually seems more like it does the opposite. It usually starts off low and rough then after a a few minutes the idle speeds up just a hair and evens itself out.

Took the belts off and revved it up for about 30 seconds. No more rhythmic vibrations. I found the pivot bolt for the PSP was missing. Guess I didn't tighten it enough and it vibrated off. The other 3 mounting points where tight though.

Going to put the belts back on and see what it does. Instructions say 1/4-1/2 in deflection.