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Ideas on vibration sources

dyeager535

dyeager535

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This isn't a pointless post, but it's not likely to have a resolution for months. I'll have a little hands-on time to spend on the truck to hunt this down before I have to use it. I'd really rather not find the cause due to failure while I'm in the woods.

There is a vibration that is felt (and heard) through the whole truck at most vehicle speeds, but pronounced the faster the rig is moving. Only notice it on deceleration. Any amount of throttle seems to "stop" it. It's a very rapid vibration. Happens in or out of gear, but appears to be more pronounced when in gear. Its a bit of a growling sound I'd say. Trans and engine mounts are both new, and both poly. Vibration started well after their replacement.

New (sub-10k miles) L31 crate long block, runs good. Exhaust is fine. Manual trans, new clutch with engine. NP241 with SYE. Rear shaft is in good condition, front is as well. Both regularly greased. 10 bolt front, 14SF rear. Stock 15" wheels, 33" BFG AT KO2's. Don't feel any weird slop in the rear driveline/pinion/CV. Can't recall any impacts or events that could have bent a wheel, damaged an axleshaft, etc.

I'm thinking that best idea is to put it up on jackstands and statically check all four wheels for axle/axleshaft issues. Next, start it and let it run in gear to see if I can replicate the issue on the stands.

I wonder if the front axleshaft u-joints aren't a potential cause. Would that even be noticeable in 2WD with the hubs turned out? The joints are factory original, but last I checked still looked ok externally. Hadn't started to walk out the caps or anything obvious like that. They've got to be bone dry lol. Would an issue with those likely be more easily felt or heard on the jackstands with the wheels turned either direction, wheel spun by hand? (vs. being straight where the joints aren't really doing any work)

14SF is also suspect I suppose, it was fairly abused when I got it, but when I put it in there were no obvious bearing issues.

I did smoke the front wheel bearing grease a number of years back, but replaced the spindle (had gotten hot at some point, but that seems very common from people misadjusting wheel bearings, no idea what the cause was on this one) and re-greased both sides. But the repair and re-grease was a number of years ago, and I've checked the wheel bearings through the wheel push/pull method a few times since then. This vibration definitely did not arise immediately after that "repair".

Any other ideas? Thoughts/better ideas on my process to try and ID the noise?
 
Checking a drive shaft by trying to move it will not show stiff joint bearings. You have to pull the drive shaft to check the u-joints by hand.
 
If it WAS the front axleshaft joints, under power vs. decelerating (in 2WD of course) shouldn't make a difference, right?

I know everything will turn from the parasitic drag if the vehicle is moving, but without the front axle being driven, perhaps that's not a place to look?
 
Definitely chock the wheels and pull the rear shaft. Not only can you feel the state of the u-joints, you can give a fair inspection of the pinion/nut.

The axleshaft u-joints really don't care if you're on coast or light accel. If anything up front is changing with load, the T-case is staying engaged. A stuck hub usually spins the other axle backwards as much as turning the driveshaft, but it doesn't care what your throttle is at.
 
If the noise is most noticeable on deceleration I’d really look at the driveshaft angles. The fact that the noise/rumble goes away when you tip back into the throttle is the thing that tips me off.

The pinion gear “climbs” the ring gear under acceleration. On deceleration it drops. Your u-joint angles may be close enough that it’s ok under load as they are canceling each other out. But it may not be enough that it’s out of line on the decel.

I’d check the angles with the truck on flat ground. Ideally you want the angles to be within 2 degrees of each other to properly cancel out.
 
ZooMad75 said:
I’d check the angles with the truck on flat ground. Ideally you want the angles to be within 2 degrees of each other to properly cancel out.
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Sounds like he has a CV out back?

I've heard bad U-joints grumble on accel, but have also experienced it from a pinion nut backing off, which is why I suggested checking that nut. If he has 0 degrees in the rear U-joint and dry bearings, it will be quiet until it gets some angle in it - because at 0 it's not turning.
 
Blue85 said:
Sounds like he has a CV out back?

I've heard bad U-joints grumble on accel, but have also experienced it from a pinion nut backing off, which is why I suggested checking that nut. If he has 0 degrees in the rear U-joint and dry bearings, it will be quiet until it gets some angle in it - because at 0 it's not turning.
Click to expand...
Good points for sure.

With a cv the shaft angle and pinion angle should match. If the pinion isn’t high enough it may come into an acceptable position under load but drops when off throttle.

The fact that the vibration comes and goes depending on acceleration/deceleration points directly to the driveline. Double check the angles before taking the shaft out to check the condition of the u-joints.
 
Yep, CV in the back. It's an ORD shaft I've had for a long time now, but when I did the CV a couple years back, I checked and greased the U-joint of course. Doesn't mean it couldn't randomly die I suppose. I want to say I checked the pinion nut as well, but it won't hurt to check. Not like it's tough to remove the shaft.

The angle hasn't changed since the vibration began. Of course if something is going horribly wrong like loose U-bolts or a broken leaf spring pin then I could see angle change being an issue, but I'd think that would be something felt as well, such as very squirrely handling...?

I did do a cursory roadside inspection of the leaf spring axle pads/axle tubes, didn't see any signs that anything was loose/moving around.
 
Got the thing up off the ground, pulled the driveshaft, checked everything I could while up in the air.

Pretty sure I found the source. The SYE yoke nut was loose. Tightened it down, and did not have the vibration anymore.

The JB Conversions SYE output thread is 7/8-20 if anyone else ever needs it. As the provided nut is quite small, and deformed to try to hold it in place, it's one time use. I'm going to figure out a replacement that is more likely to stay put. Loc-tite is a bit tough to use here, as silicone is needed to seal the shaft to yoke and it's near impossible to do that without contaminating the threads.
 
I think you can use Dana spicer 44189 yoke nut. It’s a flanged stover nut that is 7/8-20.
 
obijuank5 said:
I think you can use Dana spicer 44189 yoke nut. It’s a flanged stover nut that is 7/8-20.
Click to expand...

Thanks for that info. I started to Google 7/8-20, seems pretty common among trucks.

I think this is probably the same piece, or similar enough to work? https://www.fordpartsgiant.com/parts/ford-nut-7-8-20-hex-lock_-390313-s100.html

Edit: ended up using https://www.northerndrivetrain.com with shipping, cheapest I could find it. $17 for two, to my door. 44189 is one of the part numbers you can search for to find these nuts on the web.
 
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That’s a sterling pinion nut and should be a perfect fit. I’d just make sure you have 7/8 or better thread stick out with your yoke. I have a feeling this is a shallower nut than the spicer but only by 1/8 probably.
The 205 idler shaft nut is real shallow if you got one of those handy.
 
Good point. I'll have to tear it down to see how much thread I've got available, but I think there is plenty. Appreciate the insight!
 
About 10-11 years ago, I saw an iPhone app for diagnosing vibration sources in automobiles. You could set your phone on the dash as you drove and it would provide a location for the vibration source, I watched Youtubers that used the app with success.
 
Recently I have started using liquid Teflon to seal splined yokes. It works. You should be able to use Teflon and lock tight.
When I switched from a yoke to a small pilot flange I had to get a smaller od nut to fit with a socket
 
ccj8008 said:
About 10-11 years ago, I saw an iPhone app for diagnosing vibration sources in automobiles. You could set your phone on the dash as you drove and it would provide a location for the vibration source, I watched Youtubers that used the app with success.
Click to expand...
Was it this perchance? https://apps.apple.com/us/app/nvh/id1026086455

Never even considered that as an option.
 
Wes Harden said:
Recently I have started using liquid Teflon to seal splined yokes. It works. You should be able to use Teflon and lock tight.
When I switched from a yoke to a small pilot flange I had to get a smaller od nut to fit with a socket
Click to expand...
I think I've got some liquid Teflon, suppose I could try it when I replace the nut. Pretty sure there is plenty of thread there, I'd almost prefer using a jam nut to a "locking" nut.

I can't recall exactly the reason for the difficulty I was having (probably due to the very deep seating surface in the yoke), but I remember cleaning up the threads, but having a very difficult time from keeping the silicone from contaminating them as I put it together, which I felt would interfere with the loctite.
 
Nvh is pretty cool I didn't know they made an app. I have had my eye out for a used reed tach for along time. Briggs and Stratton made tool that used a wire and dial, needs two people one to drive and one to work the tool.
Only got to use a real Reed tach in training. Made finding the vibration easy
 
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