So heres the story behind this:
I had very bad vibrations while braking, so i replaced my rotors and turned the drums and adjusted the back brakes. Well while it was in the shop, I told my mechanic to check everything for me to make sure everything was a go. Well he check everything found that two u joints (front and rear) and replaced them for me. Well after I returned to get my truck I drove it and it did ok, but about a day later I began to have bad vibrations starting about 38mph and lasting till about 48mph. This is a vibration I have never felt before, not like the basic out of balance tire scenario, but it is a very rapid vibration with a slight hum to it. My mechanic is stumped about the situation and quite honestly I am getting tired of being shaken to death, this has gone on for well over a month now. I need some help, if neone has had this sort of problem or if anyone thinks they may have an idea what it could be, please share!

 

wow.. where to start.. now is this vibration felt most in the steering wheel, at your feet, or under your butt or from behind you?? or is it the whole truck.. was it doing this before you replaced the u joints?? are your tires rounding off on the edges?? few things i can think of from past problems with my rigs..
could be the two virtical mounts for your front diff.. those are known for going bad.. and when the trucks on a lift its hard to tell cuz everything is hanging and the gap in the bushing is on the top insted of bottom when its on the ground..
bad control arm busings.. something like a 1/8th of an ich in the bushing equals an inch at the wheel.. your toe wont hold.. rounds off the edges of your front tires... also humms..
any of your steering linkage will cause the same affect.. bad tierod ends wont hold toe..
if your really stumped... drop your rear drive shaft.. take it for a ride.. then drop your front drive shaft and unlock your hubs.. take the locking plate off if you dont have manuals.. if both of those wont make it go away.. then you know its not those shafts.. or your CV's then its probly in your steering or rear axel.. weelbearings maybe.. sorry its long.. but its a good starting point..

 

Check the u-joint phasing:
- http://www.4crawler.com/4x4/CheapTri....shtml#Phasing

Could be the shaft was separated when the u-joints were changed.

 

IRT jtlinna3vze,

Well the vibrations are felt mainly in the seat and from behind. The tires are wearing good, just had it lined up about 3000 miles ago. It wasn't doing this before my mechanic replaced the rear U joints. It's honestly hard to explain, but it is a rapid vibration with a hum that exists within speeds of 38-48 while accelerating. I replaced my driver side rear wheel bearing when i first got the truck in June of 2007, but it was done at a shop that found out i really shouldnt trust. I have also gone through 3 front seals on the rear diff in the last few months. My new mechanic replaced a sleeve, not sure what type but he said it should cure my seal breaking issue. I just got it back today and it seems like the vibrations have gotten worse to me.

 

Check the phasing on the driveshaft. This above statement is indicative of a problem with that. Read the page I posted above for how to check, but in short you want the u-joints lined up end-end:



And if that is OK, pull the shaft and try spinning one end 180 degrees and reinstall it. Sometimes you get better balance that way. And if that does not fix it, pull the shaft and have a driveline shop check it for balance. Might be the u-joints were not installed perfectly centered and that is the problem. Or perhaps a balancing weight was knocked off when the u-joints were replaced.

 

Thanks 4crawler, thats some good info. I am just curious is to why its only doing it at 38-48 mph. And another question is that will it hurt my vehicle if I take out the rear drive shafts and lock my hubs and accelerate to 40mph or more(where the vibrations occur). Kind of a newb question but I have a tendnecy to mess stuff up, lol.

 

It's called resonance. The driveshaft (or whatever is vibrating) has a resonant frequency.


No harm at all assuming the front end is in good condition. I've driven 100s of miles in FWD on my '85, at highway speeds even. Actually drives nice like that.

 

Well my mechanic talked to a guy from toyota and he said its probably in the carrier bearing(i think is the name) but he also told him to take the rear shaft out and drive it with the hubs locked. So my mechanic did so, and it vibrated worse my mechanic said. Does anyone have any clue what this could be? If its coming from the front why do i feel in the seat? Any help is greatly appreciated!

 

I would suggest a second opinion on this before you go and sink a bunch of dough in it.

I'm a mechanic and I think it is not very likely that there isn't something wrong with the u-joint installation. the vibration you are describing sounds like a drive shaft issue.

 

Hey 4Crawler,

Nice call on the resonance.

Hey Target,

I agree.

Thanks Kiwi

 

So a second opinion would be best? What could have gone wrong with the u joints?

 

They could have been installed not perfectly centered, or perhaps with a damaged
bearing or who knows what. Or more likely, the phasing is off (and easy to check):
http://www.4crawler.com/4x4/CheapTri....shtml#Phasing

You want to be sure the u-joint caps are aligned end to end.

 

Just because someone does something for a living doesn't make em good at. U-joints can be a pain to install. If one of the needles fell out or got crushed crooked in the cap, it could throw it out of wack. Have you check your engine and tranny mounts (esp tranny)? I know that's probably not it, but it could cause some of it.

 

Ok I checked the phasing, it appears to be off just slightly off. The front u joint is directly up and the rear u joint is facing the side, bout an inch from being straight up. Can this slight misalignment cause vibrations? How can I solve this problem myself?

 

Yes, see the page I posted a link to earlier for why.

Fix? Unbolt the shaft at one end, pull the slip yoke apart and slide it back together in proper alignment. And there may be two ways that it aligns, one way might work better than the other.

 

Yes just like in the phasing diagram you posted...the front u joint is exactly like the diagram but the rear u joint is just slight off. So if i unbolt the rear of the drive shaft, all i need to do it pull it out and realign it. Sorry for all the questions kind of a newb.

 

anyone?

 

YES! Just like I posted above:

"Fix? Unbolt the shaft at one end, pull the slip yoke apart and slide it back together in proper alignment. And there may be two ways that it aligns, one way might work better than the other."

The slip yoke is splined. Pull the splines apart, rotate one end to align the u-joints and re-engage the splines. Good time to brush some grease on the splines while they are apart.

 

just go out and unbolt the shaft. it's only four bolts, sort of hard to mess it up. you'll be able to see how it works once you're under there.

and hey, if it vibrates worse when you get it back together, you'll still have to take it to a shop, but you've got very little to lose

 

sorry to hijack, but i kind of have that noise, but its at idle... sometimes ill hear a harmonic resonance thats REALLY annoying... my mechanic cant hear it, but then again he cant hear high pitched noises due to shooting bigass guns without ear protection for 45 years(his words). is it something i should look into, or is it 'normal' ? i doubt its the latter....