Twisted/Bent driveshaft...see video

[pmoore4321]

I noticed a vibration at 75mph+ after putting the street tires back on for Power Tour.

Best viewed in 1080p

Would a twisted/bent driveshaft also cause this?:

 

[Chuck Leeper]

Only change is the tires?? How about them getting a re-balance and try again?
As for that d/s: That thing looks like it has terminal rust....if that's what I think it is, I'd be looking to retire it to mail box post duty....

 

[TurboDave]

That is some serious lateral tire wobble!!
I'm betting bent wheels or axles. The last one is the most obvious!

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[getdowngranny]

What kind of axles are you running? Looks like warped or bent axles to me.

 

[pmoore4321]

It's just the stock axles. I turned the shaft 180 degrees at the pinion yoke and it cut the vibration down. I also put a dial on the driveshaft and it looked like at least .045" runout, maybe more, about 4" from the rear. It's hard to tell because of the rust pits interfering with the tip of the gauge.

Looking at the video it looks like .45" runout...

I really want to upgrade to a 3.5" shaft with 1350s, but it would not make it here in time for PT if I order one.

 

[KEVINS]

I think you have two different issues. Stock DS's are typically like that from what I have seen in the past and have never been an issue of vibration BUT with that said I would try a different one that is straighter. It won't cause the tires to do that, look at a bent rim first then take the tires to a tire shop and have them spin the tires 180* on the rims to see if that helps, I doubt it's a bent axle at this point.

ks

 

[pmoore4321]

That's a good idea about rotating the tires. I'll do that Tuesday. I did not notice this problem with the 255 drag radials. I thought maybe running the low pressure in the DRs masked the vibration. The tires are BFG Radial T/A with about 15 miles on them. I'm going to give the car a good run down the freeway and shift gears to see if the vibration is in the driveline or tires.

 

[pmoore4321]

What about the drums causing the run out? They are O'Really China specials.

 

[chopped39]

Pull the rear wheels and brake drum and get that dial indicator on the axle shafts flanges and see what runout you get . keep pressure on center of axle flange while turning the axle. Do not have car running when doing this. Matter of fact pull the driveshaft out so its is easy to turn. When the shaft it out check for up and down movement on the pinion shaft. bad pinion bearing will cause some weird stuff . It wont cause the tire to do what they are doing. Take the tires to have them balanced and bring the dial indicator with you and check them on the machine.Doing it on the car is a pain because of the c-clip's. Thats why I said to keep pressure on the axle when checking the axle flange.

 

[pmoore4321]

That's sounds like a good idea. I did try to move the pinion yoke when the shaft was connected looking for any play and it was extremely tight. It barely moved at all.
I don't have any extra wheels/tires so I'm going to put the front set on the rear and see if the runout condition still exists.

I'll put the dial on the axle tomorrow and see what I come up with.

 

[chopped39]

That's sounds like a good idea. I did try to move the pinion yoke when the shaft was connected looking for any play and it was extremely tight. It barely moved at all.
I don't have any extra wheels/tires so I'm going to put the front set on the rear and see if the runout condition still exists.

I'll put the dial on the axle tomorrow and see what I come up with.

When you had the drive shaft out how did the u-joint feel? Was it real tight one way or the other. Pull the shaft out and check both joints. They should move freely in both directions.If either are binding at all replace them .

 

[Chuck Leeper]

The torsional load on the d/s will be concentrated at the middle. Try the indicator there.
While U R under there, check the ft trans hsg bushing...
As I mentioned B4, that d/s needs to be done away with. [B4 you find it sticking thru the floor.]

 

[olddog]

it is NOT uncommon to have tire wiggle/ movement like that,
when I spin most new tires up on the balancer, almost all have some movement.
I'd recheck the balance, and drive them and look at them AFTER you have driven them,
they may just have taken a set for sitting.

 

[pmoore4321]

it is NOT uncommon to have tire wiggle/ movement like that,
when I spin most new tires up on the balancer, almost all have some movement.
I'd recheck the balance, and drive them and look at them AFTER you have driven them,
they may just have taken a set for sitting.

OK....you think they just need to be broken in? I'm sure the tires had been sitting. Not much demand these days.

 

[Pronto]

Don't forget, the axles do have a little movement in and out too so the C clip is able to be removed. The best to check the driveshaft is to take to a driveshaft shop and have is spun. The yokes on my stock driveshaft were not welded on square. They had to reweld them and balance.

 

[pmoore4321]

Problem sovled. I had Houston Drive Shaft Service build me a 3.5" unit. I dropped it off at 11 a.m. and it was ready at 4 p.m. MUCH more substantial piece! The best $250 I've spent on this money pit in a long time. Rides like a Cadillac now. I'll bet money that out of balance driveshafts have taken out a lot of engines and blame was placed elsewhere.

I won't own another GN with a stock drive shaft. If your running the stock DS and it has runout like in that first video, it's tweaked.

 

[Pronto]

That's quite a difference. Money well spent there.

 

[stickybones]

Even if the ride is now smooth with new new drive shaft, do your wheels still wobble? I would think they would as I can't make the connection between wheel wobble and a tweaked drive shaft. It would be interesting to know that the wobbling wheels aren't causing the vibration you were experiencing. I'm experiencing something similar and I haven't gotten to the bottom of it yet. I'd hate to spend the money on a new drive shaft only to find out that it wasn't the problem.

 

[pmoore4321]

The torsional load on the d/s will be concentrated at the middle. Try the indicator there.
While U R under there, check the ft trans hsg bushing...
As I mentioned B4, that d/s needs to be done away with. [B4 you find it sticking thru the floor.]

You are right, the runout was definitely worse in the middle of the driveshaft. I didn't video the middle of the shaft, but there was a litte more variance in the middle.

Also, when you go to get your driveshaft balanced at a "driveshaft shop", make sure they actually have a balancer?... You would be surprised how many don't even have a balancer.

 

[pmoore4321]

Even if the ride is now smooth with new new drive shaft, do your wheels still wobble? I would think they would as I can't make the connection between wheel wobble and a tweaked drive shaft. It would be interesting to know that the wobbling wheels aren't causing the vibration you were experiencing. I'm experiencing something similar and I haven't gotten to the bottom of it yet. I'd hate to spend the money on a new drive shaft only to find out that it wasn't the problem.

Yes, the tires still wobble. I don't think the wobble is in the wheels, just the tires. Like "olddog" said, I don't think it's uncommon for them to have the runout like mine do.

Amazing how much road noise the new shaft made disappear. I think the driveshaft is an overlooked upgrade.