Harmonic Vibration

[gotyourgoat]

Goddamn, think I've lost track of all the fixes that didn't stop the issue. Can we get a revised list of things done so far?

 

[Frankenchevy]

This is just unbelievable...

you're telling me.

I had a high mileage engine with excessive crankshaft end play causing a vibe once.

New L31-r from Chevrolet. honestly, it's crossed my mind, but everyone I ask says it would be nearly impossible to have a bad one straight from chevy.

Just wondering, how much have you really looked at the front driveline? Perhaps the t-case isn't disengaging the front output, or maybe a locking hub is stuck engaged?

I'll try that. I rebuilt the front hubs. the spindles looked perfect, put new bearings in, did the specific torque sequence on the two spindle nuts(I think 50lbs, back them off, 35lbs back them off, snug them up plus a bit, then tabbed washer and outer nut). I swear I can hear them click when I put it in reverse after disengaging the hub locks. I'll try disconnecting the front driveshaft and if that doesn't do it, maybe go through the front hubs again.

quick question on wheel bearings: I'll check them after a 40+ mile drive and everything feels great temperature-wise...barely discernibly warm to the touch. is that a good sign or meaningless? I know at least it means they aren't too tight or dry, right? probably less indicative on the rears since they're open bath in the diff fluid and that amount of lube volume won't build heat easily... also the diff feels barely warm after the same distance. not sure if that means anything either.

Goddamn, think I've lost track of all the fixes that didn't stop the issue. Can we get a revised list of things done so far?

at this point everything has been replaced on the truck except: 14ff rear differential and associated bearings, rear wheel bearings, np208 transfer case(with the exception of the rear yoke seal, yoke bushing and rear output shaft bearing--which I just did those three this past week) and TH400.

TH400 is my last suspect as it shifts flawlessly, and the oil was mint when I was rebuilding the truck. not even slightly dark, still bright red and new. the filter also looked good. similarly, the transfer case and rear end's fluids looked perfect when I drained them for the first time. The PO did swap the 4.56s and Detroit out for 3.73s and a G80. I replaced the pinion seal, but punched witness marks into the pinion stud, nut and yoke/counted threads before removal for the seal replacement; then reinstalled and lined everything back up. IIRC it had this harmonic starting before I did the seal.

It is possible that when the PO had the rear end stuff done that everything wasn't set up properly. I've owned the truck for 7ish years but only put about 4-5k miles on it tops in the first 5 years. the last time I drove it before tearing it down was an attempt to pull out a stuck concrete truck (unsuccessfully) on my property. I was spinning all tires in the gravel going nowhere and I know G80s don't love that. However, it didn't come apart and as I mentioned earlier; when I removed the diff cover to put new oil in, the oil looked clean. Since it's been back together I've put less than 2k on it.

Remove front shaft. Get your spare tire balanced and make sure it's true. Swap it one position at at time.

I was going to get a spare about a month ago, but American racing stopped making the 8 lugs that I have in 16x8. I guess I can do one of my steelies that I use for a spare now with a new tire. the tires on the steelies I have(one of which I use for a spare) are 4 10+ year old Yokohama geolanders or whatever are on the three that @Craig 85 gave me. between the 7 I'd be lucky to find one that isn't too clapped out to give me more vibration issues, lol.

I should get a steelie with a fresh tire, though. the yokos still look good all things considered.

 

[SquareRoot]

Pinched nerve in the ass? Just throwing it out there.

 

[Frankenchevy]

Pinched nerve in the ass? Just throwing it out there.

I'd think that'd cause the same feeling in all my vehicles.

 

[shiftpro]

Maybe paint the truck a different color?

 

[Frankenchevy]

Maybe paint the truck a different color?

satin army green is planned for later this year.

 

[shiftpro]

I know it's scary but you need to get it up on a lift and run 'er up to 60mph or whatever the best speed is to get it twerking.
With the right lift and technique it's not dangerous.
You need a 4 post lift with the big ramps/platforms, one on each side. The good ones have these slide-on-rails air lifts underneath. Get the truck up to a comfortable working height overhead. Then the secondary air ram lifts go under the axles and pick the truck up so the tires are free to roll.
The axle can be chain and boomered to the secondary lifts... or a bad ass ratchet strap. The truck will not go anywhere like this. Get someone
you trust to run it up to speed and hold it there while you poke around underneath. Be VERY careful you don't bump into the spinning tires.

 

[shiftpro]

You can do it Jer I believe in YOU!

 

[idahovette]

WASH it ..... just kidding. I can't believe all the things you've done and still have this problem. It's kinda mind boggling, but we all have faith in you!!!

 

[shiftpro]

WASH it ..... just kidding. I can't believe all the things you've done and still have this problem. It's kinda mind boggling, but we all have faith in you!!!

He made the whole story up looking for attention...

 

[idahovette]

He made the whole story up looking for attention...

I think he got it!!

 

[SquareRoot]

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Subscribed. Popcorn please.

 

[bucket]

You know, I tend to ignore a lot of the things my clapped-out junk does. My '78 has had various vibes that I've never really cared about, but today as I got on the interstate and hit about 75 mph, I realized my truck has the exact same symptoms as your truck. That on/off/on buzzy vibration. But it has a 40+ year old engine and trans, old u-joints, old carrier bearing, stock axle, old shocks and ****** old tires from '06 that are dry rotted.

I think I'm just going to leave it all alone and save a bunch of money

 

[Frankenchevy]

You know, I tend to ignore a lot of the things my clapped-out junk does. My '78 has had various vibes that I've never really cared about, but today as I got on the interstate and hit about 75 mph, I realized my truck has the exact same symptoms as your truck. That on/off/on buzzy vibration. But it has a 40+ year old engine and trans, old u-joints, old carrier bearing, stock axle, old shocks and ****** old tires from '06 that are dry rotted.

I think I'm just going to leave it all alone and save a bunch of money

OCD is the bane of my existence

 

[Poppy 87]

you're telling me.


New L31-r from Chevrolet. honestly, it's crossed my mind, but everyone I ask says it would be nearly impossible to have a bad one straight from chevy.


I'll try that. I rebuilt the front hubs. the spindles looked perfect, put new bearings in, did the specific torque sequence on the two spindle nuts(I think 50lbs, back them off, 35lbs back them off, snug them up plus a bit, then tabbed washer and outer nut). I swear I can hear them click when I put it in reverse after disengaging the hub locks. I'll try disconnecting the front driveshaft and if that doesn't do it, maybe go through the front hubs again.

quick question on wheel bearings: I'll check them after a 40+ mile drive and everything feels great temperature-wise...barely discernibly warm to the touch. is that a good sign or meaningless? I know at least it means they aren't too tight or dry, right? probably less indicative on the rears since they're open bath in the diff fluid and that amount of lube volume won't build heat easily... also the diff feels barely warm after the same distance. not sure if that means anything either.


at this point everything has been replaced on the truck except: 14ff rear differential and associated bearings, rear wheel bearings, np208 transfer case(with the exception of the rear yoke seal, yoke bushing and rear output shaft bearing--which I just did those three this past week) and TH400.

TH400 is my last suspect as it shifts flawlessly, and the oil was mint when I was rebuilding the truck. not even slightly dark, still bright red and new. the filter also looked good. similarly, the transfer case and rear end's fluids looked perfect when I drained them for the first time. The PO did swap the 4.56s and Detroit out for 3.73s and a G80. I replaced the pinion seal, but punched witness marks into the pinion stud, nut and yoke/counted threads before removal for the seal replacement; then reinstalled and lined everything back up. IIRC it had this harmonic starting before I did the seal.

It is possible that when the PO had the rear end stuff done that everything wasn't set up properly. I've owned the truck for 7ish years but only put about 4-5k miles on it tops in the first 5 years. the last time I drove it before tearing it down was an attempt to pull out a stuck concrete truck (unsuccessfully) on my property. I was spinning all tires in the gravel going nowhere and I know G80s don't love that. However, it didn't come apart and as I mentioned earlier; when I removed the diff cover to put new oil in, the oil looked clean. Since it's been back together I've put less than 2k on it.



I was going to get a spare about a month ago, but American racing stopped making the 8 lugs that I have in 16x8. I guess I can do one of my steelies that I use for a spare now with a new tire. the tires on the steelies I have(one of which I use for a spare) are 4 10+ year old Yokohama geolanders or whatever are on the three that @Craig 85 gave me. between the 7 I'd be lucky to find one that isn't too clapped out to give me more vibration issues, lol.

I should get a steelie with a fresh tire, though. the yokos still look good all things considered.

Just got thru reading your post. Isn't the L31 a small block? The photo in post #69 shows a flex plate with a huge weight as seen on external balance 400 or 454 engines. Just a thought

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