Strange vibration at 60 MPH and above.

[The Swed]

Some facts, my truck has a rebuilt 350 and rebuilt TH350, rims are straight and balanced both brake drums in front are new/replaced. The vibration starts at 60 MPH and the tac reads 3000 RPM and 3500 at 70 MPH. I have disengaged the transmission at 70 and the vibration is still there I also put the transmission in 1st and ran it all the way to 4000 RPM with no vibration so I believe it’s mostly likely the drive train? So U joints, drive shafts, or that axle bearing? What are your thoughts? Thanks in advance for your inputs!

[MARKDTN]

Sounds like driveshaft.

[Stocker]

Put it on a lift -- have someone in the driver's seat start it, put it in gear, and gradually increase speed while you eyeball the ujoints & bearing.

[yuccales]

Don't forget to check all four of your tires. I had a shake up front, turned out to be a big bulge on the inside of a front tire.

[weq92f]

My guesses in order:

Carrier bearing
U-joints
shaft balance

-klb

[demian5]

Do you feel it in the steering wheel/feet or the seat?

Steering Wheel/feet = Front end.

Seat = Anything rearward of the front end.

I tested it just like you. I aligned mine and it made a huge difference. I do have a bad upper ball joint I need to replace that i imagine makes it a little floppy still. But the alignment and front wheel balance and its a new truck.

[Orange67]

Hey man, got your pm. I will text you later, been out of work sick.

I would start by grabbing the driveshaft (either side of the carrier bearing) and push it side to side, or up and down. You should have VERY little movement if any at all. I would watch the bearing closely, if it is worn out, you will see it.

[davepl]

In these trucks the carrier bearing is a normal wear and service item and needs to be replaced. How often I don't know, but if you haven't done it on that truck, odds are that's the culprit.

After that the normal suspects of driveshaft, u-joints, wheels, etc...

[The Swed]

Do you feel it in the steering wheel/feet or the seat?

In the seat!

BTW that bearing may have a 136,000+ miles on it

[brad_man_72]

I have never seen a carrier bearing cause a vibration until its coming apart. The rubber that holds the bearing is relativly soft and allows some movement of the shaft and dampens driveline vibrations, ifthe rubber is loose that would be a sign of a vibration. Check for lateral play in te slip and stub, check for play in the ujoints, make sure the shaft is in phase the way it was balanced, make sure the trans yoke has just a little lateral play.
If the front shaft is out of balance it can cause an uneven wear pattern around the tranny yoke.

[The Swed]

Well it's not the carrier bearing... took it to the shop that rebuilt the engine and they can't figure it out. I can' t effort to just throw money at it until it's fixed so it's going into to the garage to be stored. Thanks for all the input.

[brad_man_72]

I doubt the shop that built the engine knows anything about driveshafts much less has a $60k driveshaft balancer. You wouldn't believe the wrecks that professional mechanics bring me to fix.
I've seen shops that couldn't diagnose an out of round tire. Hell its hard to find a mechanic these days in a world full of parts swappers and hammer pilots.

[The Swed]

Well the local six state driveline mechanic in Ogden, Utah is now working for the place that rebuilt my motor which restores vehicles from the ground up and everything in between so in my mind that gave them more credibility in the driveline area. They did find that the drive shaft was clocked wrong and fixed it but the vibration still remains. BTW the vibration feels more like a hopping up and down and I've never felt that in vehicle before accept at the drive in movies. I must admit I had to rework work performed on my newer vehicles that I paid top dollar for at a dealership that was so screwed up so I hear you brad_man_72. I refuse to replace parts hoping I luck out and get it right. There has to be a way to isolate the problem.

[The Swed]

Update,

I'm driving the truck daily putting 70 miles a day in and 95% of the time the truck doesn't have an issue. Does anyone have any other ideas what this may be? The fact that it comes and goes should be a clue and point to something.

Thanks

[demian5]

Originally Posted by The Swed

Update

I'm driving the daily putting 70 miles a day in and 95% of the time the truck doesn't have an issue... and more idea what this may be?

Thanks

Old truck?

[davepl]

I had a REALLY strange one (bad shudder under light accel from a stop). After trying just about everything and giving up, I took the driveshafts to a local specialty shop. They found wear in the splined section.

I couldn't feel it, and honestly thought I was being scammed, but I was desperate and so I relented and let them replace the whole splined section. They did that and it solved the problem.

Lesson learned: there's a lot about driveshafts that I don't know, and I was surprised at the weird problems they can solve/cause.

If you have a friend or some other access to a 2-piece driveshaft, it'd be a cheap test if you could swap to see if the problem transfers over or goes away.

[DBK81]

It's 100% in your driveshaft area, but the million dollar question is where? What if anything did you do to your drive line just before these issues appeared? Might help diagnose the cause.

[demian5]

Originally Posted by DBK81

It's 100% in your driveshaft area, but the million dollar question is where? What if anything did you do to your drive line just before these issues appeared? Might help diagnose the cause.

Or if the engine rebuild has something to do with it like the wrong flex plate or balancer for the engine.

[Metaldoc]

I had a bent axle in an older car that did that. May have have been a pot hole or curb that bent it, but only out a bit.

[The Swed]

It started vibrating again so I took it up to 85 mph and the tach was over 4ooo rpm and it smoothed out. Im trying to break it now so know what to fix. I may end up a stain on the wall but at my age I just don't care.

[Grumpy old man]

From the looks of the picture you posted of the drive shaft it hasn't seen any grease in years . Rebuild your drive shaft and check the spline play while it's apart . These old trucks require regular servicing and that includes a liberal amount of grease . Running it up to 85 to see what lets go may just be a really bad idea ? It's almost 50 years old show it some love ...

[weq92f]

Originally Posted by The Swed

It started vibrating again so I took it up to 85 mph and the tach was over 4ooo rpm and it smoothed out. Im trying to break it now...

Good luck. These old trucks are tough.

Can't tell you how much time I've spend at ~4000 RPM going down the highway as fast as it would go ( 68 short step 350/350 3.73 ). I broke mine once following a semi trailer real close to try to save gas. The tranny got too hot and ate itself.

-klb

[Shinysideup]

Re-balance the tires. Its classic symtom of that. Smooth to 65ish,shakes like heck at 70ish, then smooths back out at 80. Hmmm.

[WorkinLonghorn]

Originally Posted by Shinysideup

Re-balance the tires. Its classic symtom of that. Smooth to 65ish,shakes like heck at 70ish, then smooths back out at 80. Hmmm.

Yeah, and find a place that can do it while on the vehicle. There's a device with an electric motor and a small rubber wheel that contacts the tire and spins it up.

Are your wheel bearings in good shape and adjusted to spec?

[cleszkie]

I had belts in my tires creep one time. The tires would balance out just fine, but were basically out of round. Caused a vibration around 70 mph and no other time. Took me a long time to figure it out. Belt creep caused by rotating tires to opposite side of truck and reversing the rolling direction. They were an old set of BFG KO A/Ts. Replaced the tires - smooth as glass now. Now I rotate front to back to keep rolling direction the same. Just something to consider.