Help me identify a vibration

[crazy4offroad]

The "vroom-vroom" vibration is typically always driveline, be it u-joints, pinion bearing, dent in the driveshaft, driveshaft weight fell off, trans output bearings, worn splines, worn slip yoke, etc. Next time you take a long-ish drive, say 20 miles or so, feel the diff cover and see if it's warmer than normal. If so, carefully check the snout that houses the pinion bearing. It may be very hot if the bearing is too tight. Bearings can flat-spot but as long as they're getting oil they wont make a sound for a long time. The "45mph only" vibration is typically always tire/wheel related if you feel it in the seat only then it's out back. Front of course could be steering components as well as tires/wheels. If it were me I would try doing a good burnout and see if it gets worse/better/same or different speed. My cousins pulled a prank on my uncle by putting 2 flaps of duct tape on his truck's driveshaft, with 2 opposing flaps about an inch long. It vibrated so bad at 15 mph on their street their dad had to crawl under it and see wtf was going on lol. So at 70mph the imperfection can be so minuscule you may not see it at all.

 

[da_raabi]

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Geez, I read the whole thread...annnnd after all that I should have said the same thing I thought after reading the original post!
BUT! I figured it was necessary because I didn't want to look like a ********* and repeat something that's already been said. Yet somehow, I still ended up looking like a doucebag, lol.

Anyways!

My first thought was "lemme guess? 45 m.p.h.?
"and only 45 m.p.h"
Ah hah!
Maybe my first hunch is/was correct?
Omg. It's a 1986?!

Okay. This is worth examination.
Wait!
You rebuilt if yourself? I think this may the right tree.
AND 70?
Hmmmmmm....

Okay dude...my FIRST thought was T.C.C.
T.c.c. solenoid?
Yeah....probably...at least maybe? Be sure to check that plug & wiring too!

Transmission fluid level-WHEN hot!

This is a one-ton with a TH400. There's no TCC. Only one wire goes into the trans, and its for the pedal-switch kickdown wire.

So I'm thinking that's probably not it lol.

 

[da_raabi]

The "vroom-vroom" vibration is typically always driveline, be it u-joints, pinion bearing, dent in the driveshaft, driveshaft weight fell off, trans output bearings, worn splines, worn slip yoke, etc. Next time you take a long-ish drive, say 20 miles or so, feel the diff cover and see if it's warmer than normal. If so, carefully check the snout that houses the pinion bearing. It may be very hot if the bearing is too tight. Bearings can flat-spot but as long as they're getting oil they wont make a sound for a long time. The "45mph only" vibration is typically always tire/wheel related if you feel it in the seat only then it's out back. Front of course could be steering components as well as tires/wheels. If it were me I would try doing a good burnout and see if it gets worse/better/same or different speed. My cousins pulled a prank on my uncle by putting 2 flaps of duct tape on his truck's driveshaft, with 2 opposing flaps about an inch long. It vibrated so bad at 15 mph on their street their dad had to crawl under it and see wtf was going on lol. So at 70mph the imperfection can be so minuscule you may not see it at all.

Ok, this sounds promising. Let me provide some details:

1. Driveshaft was rebalanced (in front of me) with new u-joints and center bearing. That's probably not the issue.
2. I did not replace bearings when I did the trans rebuild. They all looked good. Output bearing could be the culprit.
3. Trans center splines (where the 2 pieces come together) were kinda boogered up. PO had apparently tried to pound them together the wrong way (its a keyed spline). But the balancer guy cleaned them up and they seemed ok.
4. I'll check the diff temp when I get home from work. Thats about a 20 minute highway drive.
5. I'm thinking about pulling the outer rear wheels and running on just the inners to see if the vibration goes away, then vice versa with just the outers. The vibration is most definitely "seat of the pants" only. Nothing in the steering wheel or anywhere else. I did feel the wheels/drums/hubs for heat in case it was a stuck drum or a bad wheel bearing but they were barely warm.

Thanks for the ideas everyone!

 

[Rusty Nail]

This was my second thought...

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[da_raabi]

Ok, so today I bumped it up to 70 for the whole trip to work. Lots and lots of vroom vrooming. It's not a long commute (20 mins total). When I got here I stuck my hand down through the hole in the bed (PO cut a GIANT hole for a 5th wheel) and proceeded to burn the crap out of my hand on the exhaust pipes... SO after a bit of cussing, I found that I could place my hand on the case of the diff, but barely. It was definitely hot. Not scorching, but hot enough to notice. The pinion snout was cooler, as was the cover. The heat was definitely centered on the middle of the diff.

Is this kind of heat normal for a diff, or do they usually run pretty cool? I have no idea.

 

[crazy4offroad]

They get warm to the touch, sounds normal.

 

[Snoots]

I don't know. You should be able to rest your hand on it.
It seems to be a rear axle bearing to me tho. Carrier perhaps and not pinion. But if you go in there, replace all three, with seals.

 

[crazy4offroad]

I think you have PTSD from grabbing that hot exhaust pipe. I'm not saying that can't be it, but I would do them last, it's not an easy chore. Have you tried taking loose the driveshaft from the pinion and check the pinion for any looseness?

 

[da_raabi]

I thought I would come back and update this thread. I still have the vibration, but I've got some new info.

1. I've got a couple bent dooley rims. Of course its the "pretty" ones.

2. I lowered my air pressures with no change (was 60psi, now its 40psi)

3. I noticed when I had the wheels off to check the pressures that the driver's inner wheel was not wanting to seat fully on the hub/drum. It was like there was something preventing it from seating flat, making the wheel wobble on the lugs. I never noticed this before. The pass side sides nice and flat, you can feel it "clunk" when you put the wheel on. I'm going to pull it back apart and see whats up...

 

[theblindchicken]

I thought I would come back and update this thread. I still have the vibration, but I've got some new info.

1. I've got a couple bent dooley rims. Of course its the "pretty" ones.

2. I lowered my air pressures with no change (was 60psi, now its 40psi)

3. I noticed when I had the wheels off to check the pressures that the driver's inner wheel was not wanting to seat fully on the hub/drum. It was like there was something preventing it from seating flat, making the wheel wobble on the lugs. I never noticed this before. The pass side sides nice and flat, you can feel it "clunk" when you put the wheel on. I'm going to pull it back apart and see whats up...

Thanks for the update! Sorry to see you've still got the issue, but getting closer to have it 100% narrowed down.

 

[73c20jim]

I've had tire vibration issues with a nail in the tire with no leakage. And rocks stuck in tread causing thumping.

 

[da_raabi]

Took the wheels off again yesterday (man does my back hurt...) and now I've got a question.

On a dually, are both wheels meant to be hub-centric? Are they both meant to ride on the 1/2" (roughly) machined ridge on the hub?

I ask because I noticed that while the OEM inner wheels fit over the inner hub "ridge" and sit against the flat hub bolting surface, the aftermarket wheels (that have been on the truck since before I got it years ago) have smaller hub holes and will NOT fit over the "ridge". I could never swap the wheels inner-to-outer for this reason. I noticed that the ridge appears to protrude beyond the inner wheel when it is installed, which makes me wonder what it is doing to the outer wheel when I torque it down.

Thoughts on this?

 

[da_raabi]

Finally figured it out!

At loooooong last!!!!

I drove to work today in silence! NO VIBRATION!!!!

It wasn't the wheels.

It wasn't the tires.

Even the driveshaft was found faultless.

The engine was fine.

The transmission is happy.

After all that, it was the torque converter.

And even then, there was nothing wrong with it. It simply needed to be clocked differently on the flexplate!

On a whim my Dad recommended that I rotate the converter one bolt on the flexplate. So I did, and just like that, no more vibration!

CRAZY.

Thanks to all of you who have helped me fight my way through this. Best part is, in the end the fix was 100% free!

So anybody ever dealing with something like this, think about converter clocking. Apparently it is a thing!!!

 

[rpcraft]

You might want to take a close look at your flex plate and see if any weights fell off or if there is a crack in it. Normally they are balanced so as to not vibrate, as are the torque convertors.

 

[Snoots]

Glad you found the bug and shared your solution!

Kudos to you and a beer for your Dad!

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