Vibration at 2500 RPM (1 Viewer)

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Jan 21, 2022
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Albany, Oregon
Okay Brain-Trust, I have noticed a fairly pronounced vibration at 2500 RPM's which is worse the faster I am going. The vibration is only present when the engine is under power with a load on it (in gear). I thought it was the rear differential as the pinion flange had play in it. Had my local shop rebuild the rear diff with a Cruiser Outfitter rebuild kit. Vibration persists after the repair. The engine generally runs fairly smooth, but there are some hesitations in accelerations at certain points which I was chocking up to vacuum leaks, bad fuel flow, carb issues, or other areas which may need attention at some point. Stock 2F w/ Smog - 4 Spd - 31" Tires on 2" OME Lift

Thoughts on what this vibration could be:

1. Engine Mounts - Cracked or maybe damaged? When I hit a certain harmonic the engine is vibrating in the mounts?
2. Bad Cylinder - Getting a misfire or have a dead sparkplug in one of the cylinders maybe?
3. Weird Harmonics - Something where the right engine RPM creates a harmonic I will never be able to track or fix?
4. Something in the Knuckles - I redid the knuckles myself with Cruiser Outfitter kits and some very detailed YouTube videos. Torqued to spec and checked pre-load. Not sure what if anything could have gone wrong to cause this issue. This just the first major project (other than the lift) I tackled myself.
5. YOUR GUESS GOES HERE....
 
drive shaft or old tires?
 
drive shaft or old tires?
Tires are good, and I checked the driveshaft and u joints for movement when I first noticed it. That was how I located the play in the pinion flange. I am guessing if they were going out I would notice some slop in the u joints when I put pressure on them other than rotational?
 
Was the truck recently lifted?

I had my rear DS die almost instantly after lifting the truck from a busted up stock suspension to an OME Heavy. Once the pinion angle changed it started vibrating as the "home" position of the U-joints changed.

New u-joints and a dynamic balance fixed it. It also happens to the first easiest thing to check, with tires being a close second.
 
Was the truck recently lifted?

I had my rear DS die almost instantly after lifting the truck from a busted up stock suspension to an OME Heavy. Once the pinion angle changed it started vibrating as the "home" position of the U-joints changed.

New u-joints and a dynamic balance fixed it. It also happens to the first easiest thing to check, with tires being a close second.
So I started noticing this after I did the OME lift as well. Would it just be easier to buy a new shaft and u joints or have the old one rebalanced?
 
I'd remove the rear shaft and drive around on the front shaft to see if the vibration is still there - this will give some insight.
 
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So I started noticing this after I did the OME lift as well. Would it just be easier to buy a new shaft and u joints or have the old one rebalanced?
You can find a place to do it locally or you can buy a new one from Tom Woods.

I paid about $175 for new u joints and a dynamic balance locally.

Tom woods is good stuff but about $500 ish
 

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