Funky vibration

[MoGas]

93 FZJ80, 195K mi, 285/75/16 BFG AT/KO (11K on tires), no lockers, no lift or other drivetrain mods.

I have an odd vibration that I had been attributing to my front drive shaft as it is out of phase. (The PO replaced the front ujoint without removing the whole shaft)

The vibration is a high frequency vibration that appears at ~40 mph and increases with vehicle speed. It is similar to mud tire vibration in frequency, but not as loud. It also seems to move. When I say move I mean: sometimes it occours as the vehicle is travelling straight but goes away as I turn right or left, sometimes it occours only as I turn right (highway driving or on/offramp type turn) sometimes it only occours as I turn left (highway driving or on/offramp type turn) Sometimes it is completely non existant (or maybe I don't realize it is there). It sounds as if it is coming from the front.

I removed the front shaft to take to my local drive shaft guy so he can put it back in phase and balance it. I figured I had it dicked but just to be sure I went for a spin (CDL engaged without the front shaft installed) and the vibration was still there.


I have also had the tires completely rebalanced 2X each at seprate facilities, I tried a set of street tires off of my neighbor's 96 so I have ruled out tires and wheels. I have also repacked the front wheel bearings. Greasing the shafts and joints makes no difference.

I have a few ideas to try to isolate the vibe and I wanted to bounce them off of you guys.

1, Remove drive flanges (front drive shaft out) and go for a spin to see if it is indeed a front drive train problem.

2, Remove the rear shaft and with the CDL engaged and no shafts installed, "drive" the truck to <40 mph and see if it still vibrates.

3, Drive on the front shaft only to see if it goes away (might as well have the rear shaft balanced too)

4, Front shaft in, rear shaft out, remove drive flanges, "drive" to <40mph.


Any help or other ideas would be appreciated.

Thanks,
Dave

 

[MTNRAT]

Check front wheel bearings for play?

 

[MoGas]

I repacked them and tourqued them using a pull tester.

 

[MoGas]

I also tried coasting downhill on the highway in neuteral to rule out the engine. vibe was stil there.

 

[alain173]

This might be way off. But I had similar vibes that eventually were confirmed coming from the parking brake not fully releasing.

 

[Grench]

When was the last time you balanced your tires and checked the alignment?

Sometimes you can get vibrations at speed when some of the steering components are a bit worn or loose too. This could explain the link between speed & steering.

 

[MoGas]

I had the tires done a couple weeks ago.

the vibration is more of a 50hz type

 

[IBCRUSN]

Start with #3 - Put the front DS back in, remove the rear and try again. While the rear is out replace the ujoints and balance like you mentioned.

What if any service has been performed on the rear axle? You may have a bearing going TU.

 

[-Spike-]

Sounds like you have a handle on how to diagnose it. I personally think your option #4- spinning up the front drivetrain sans drive flanges if I understand you correctly- is a questionable practice. The birfields were never meant to run without the support of the drive flanges centering them. That sounds like a recipe for disaster. I like #3 a lot, and replacing the u-joints as well (unless you've done them recently)- call it PM if you like.

Give me more history- is this a recent development? Recent purchase? Been doing it for years? If it's a recent development on a truck you previously had no problems with (as I suspect) has anything changed? If not, I would definitely look for a wear item. When you get the re-balanced (with new u-joints I hope) front shaft back, install it and test-drive before removing the rear shaft.

It's not mentioned much, but worn shocks- including the steering stabilizer- can show strange symptoms. Doesn't sound likely in your case, but you can add them to your list of stuff to look into.

EDIT: IBCRUSN's got a point on wheel bearings as well- another wear item to check out.

-Spike

 

[MoGas]

It has done this since I bought it in December, probably 6k miles. I always just assumed it was the drive shaft since it was put together wrong, and when I finally got around to fix it I noticed that ithe vibe was still there.

I'd more like to try driving it without the drive flanges or front shaft installed to eliminate the front drive train from the equation. I can get to 40 mph within a half mile from my house to see if it went away.

Thanks,
Dave

 

[-Spike-]

I'd more like to try driving it without the drive flanges or front shaft installed to eliminate the front drive train from the equation. Thanks,

Dave

That method has had limited success in the past. It's technically sound, but in reality it has limitations. Some vibrations can go away or be introduced simply because the drive force geometry changes. It's a good method to try, just don't get discouraged if it doesn't pinpoint the problem.

What axle maintenance has the rig had? Wheel bearings are a possibility, as well as a pinion bearing (BTDT on a 40, couldn't diagnose it 'till it blew up- in my defense I was a lot younger )

Might be time to tear into both axles if they haven't been done.

-Spike

 

[landtank]

Is this a trick question? That drive shaft in the pic is assembled wrong!

 

[-Spike-]

Is this a trick question? That drive shaft in the pic is assembled wrong!

That's funny; I was about to accuse you of not reading the text, but in reality it was me that didn't look at the pics. Yeah, that DS ain't right, no matter who you talk to.

MoGas, your problem should be fixed when that thing comes back from the driveshaft guy. Except that he'll probably put it together in-phase (or out- I never can keep that straight). The joints on the middle shaft should be 90 degrees off from each other. You might want to mention that to the DS guy before he balances it.

Edited to correct my stupidity.

-Spike

 

[MoGas]

Yep, I gave him the picture from the FSM.

Just to clarify, I thought it was a no brainer on the vibration,(shaft phasing) but, it is still there without the shaft in place.

 

[landtank]

I thought it was a no brainer on the vibration,(shaft phasing)

Just to be clear.....there's more going on there than just phasing.

 

[MoGas]

Yes. The pictures are of the shaft after I removed it.

 

[IBCRUSN]

I figured I had it dicked but just to be sure I went for a spin (CDL engaged without the front shaft installed) and the vibration was still there.

Correct, there are still issues. If the front DS balanced well install it and remove the rear DS and try it. If you still have the vibration start looking in the axles.

Have you drained and filled the tcase, and axles? If you haven't, start there as a bearing going bad will make metal. The bearings in either end can cause vibes if they are going bad. You have the potential for the wheel bearings, pinion or carrier bearings. Checking wheel bearings is pretty easy on the front and not bad on the rear once you get the axles out. At 195K I would be willing to bet that both axles haven't had a good service history. If you get into this far you might as well perform a full frontendectomy and rear axle service just to be 100% certain they are not the issue. If that doesn't fix it we'll ahve to dive a little deeper.

 

[MoGas]

I have a reciept for the Toyota Dealer doing a Birf job when they replaced the USDS knuckle housing and wheel because a caliper bolt backed out <5k mi after a different Toyota dealer did a brake job. All this was <30k ago. I have also done the brakes and repacked the front wheel bearings. the vibration was there before and after I did the front bearings. I drained and refilled all fluids shortly after I bought the truck. None looked neglected. the U joint was a field repair so I can forgive the poor maintenance on that part. Everything else the PO had ever had done was at the dealer.

Dave

 

[-Spike-]

Put the repaired driveshaft on when you get it back, and test drive it. If the problem hasn't changed, look at the rear shaft and axle. The key to diagnosis by elimination is to only change one thing at a time.

-Spike