Bad vibration???

My 1970 Skylark is a 455 and a 2.93 posi rear. Its had a bad vibration at 65 and up ever since I bought it. Finally the pinion gear gave out--presumably from driveshaft vibration shaking the rear and the entire car. We now have retubed the driveshaft and balanced it and the vibration is better but still very bothersome. Before the driveshaft work, I caught a nail and replaced both rear tires --the vibration stayed through the tire swap. My shop measured the pinion angle and found it was plus 1deg at rest and adding 3-4deg making a plus 4-5deg at run. We tried to take up some of the problem by raising the transmission mount about a 1/4 inch. By estimation this raised the rear of the drive shaft by 2inches and took some of the angle out of the driveshaft/pinion hookup. It still has a lot of vibration.

It seemed the raise in transmission mount helped by running it in place at the shop with the rear wheels up but this is a no load situation and therefore the rear isn't torqued to the plus 5deg or more.

Is there any thing inherently bad running at a plus 5deg pinion angle? It seems like the raise in the transmission should have really helped? Also bigger tires than stock 245s so more rolling resistance so the pinion angle at run might be more than 5deg. Also maybe some wear in suspension bushings that is allowing more than 5deg?

The stock upper control arms are actually too long counting bushing movement. The bushings are visually good but something is allowing the plus 1deg at rest so maybe the bushings have given way inside and are allowing more than plus 5deg at run.

I ordered adjustable upper control arms today. Any other thoughts on my vibration will be appreciated. Thanks

 

Let me ask, is this a vibration or a rumble/washboard feeling?

 

Could be as simple as a bent axle hub from hittig a curb. But you shouldn't throw parts at it, you will just waste your money and get aggravated. Take it to a good shop and they should be able to figure it out without all the guessing.

 

I don't understand. The pinion gear gave out, and you retubed the driveshaft? But was the rear end rebuilt, as well?

 

In order to the above questions?

No washboard drumming or roar. With old tires, Vibration at 65-70 enough to knock the CD player out of track.

Will consider the -2deg thanks Larry

The driveshaft was deemed most likely culprit seen running in place with no load. Very amaturish cut job. Couldn't tell about balance.

The rear was rebushed for "crunching" --metal to metal but the upper control arms wern't done. The rear was rebuilt last year and posi added. Pinion bearing was fine then. New axels were added then, it twisted one of the stock axels. (the spline was actually turned) Wheels were spinning true with the run in place.

The shop is good--they love muscle and repair and build rods. Build even high end 100k and up rods. Lots of years of experience.

Any one hear of the upper control bushings collapsing from the torque of the 455? The torque is certainly going to raise the pinion and thats confirmed with the +1 pinion angle at rest also the pinion bearing went bad in just a couple of thousand miles as the result of the shake. That's about the last possibility? Hopefully the rear is tilting over to +6 or so under load and thats whats causing the shake. The raising of the tailshaft was done with the driveshaft and both together improved the vibration. The rearview still "jitterbugs" enough that you can't see through it at 70. I'm out of possibilities after the upper control arms??

It will be a couple of weeks to get it in and get the arms. I'll report back then. Thanks

 

OK, the reason I ask about washboarding, is because if the vibration is similar to that, you would look at driveshaft/pinion. This would be considered a high frequency vibration. Remember that the driveshaft turns 3-4 times for every one tire revolution, so a problem with it will not feel like a tire vibration, it will be more of a rumble/roughness. Jack up the car and spin the tires while looking at them for a hop or shift. Your initial description sounds more like a tire/rim/axle flange issue. If you have a local competent shop that can do on the car balancing, I would take it to them, they should be able to find it pretty quick.

 

My vote goes to the driveshaft because I have fought that same battle. Try this, it won't cost anything but a few minutes of your time. Unbolt the shaft from the rear yoke and rotate it 180 degrees and bolt it back up. Take note when you do this to check to make sure the u-joint is tightly seated in the yoke. Now take it for a drive and see if the speed at which it starts to vibrate changes. In my case it changed from 55mph to 85mph. If it does, get a good driveshaft built for the car by someone who can do it right and can do a high speed balance on it. As for the pinion bearings going out, I think a more likely culprit was improper preload on the bearings. Too loose is obvious, but bearings, like everything else, expand when hot so too tight will cause them to bind and run very hot, eventually destroying themselves.

 

Vibrations suck!

Well i can tell you there are Soooo many things that can cause vibrations.... VERY tough call even for the most experiences repair shops.

You can have tail shaft from trans bushing a problem. Slip yoke can be too loose on the output shaft
bad u-joints
drive line angles, bushings on the rear end, trans mounts mushy,
engine mounts, rims bent, axle end play, run out, bearings in the rear diff - pinion & carrier, drive shaft balance, yoke balanced...and on and on.....


Yes there are some you can just rule out...BUT even when you by NEW parts that does not necessarily rule out that part these days...

Jim
J D

 

It's not common but I have personally seen it twice in my life. Check the brake drums to see if they may have thrown a balance weight.

 

Yep, Some people do not even realize the drums are balanced ... JIm

 

I had major vibrations when I got my car. bad enough at 55 mph that everything on the dash would vibrate, and the glove box would make this high pitched rattle/ squeak
The car needed tires to fit my taste, I wanted 15" wheels so that was first, hoping that the old tires were the problem... nope....no change.
Based on recommendation from another Buick friend, a drive shaft balance for $40 was the next cheapest thing.
Removed the shaft and dropped it off at the shop.

One universal was slightly bad and the tube had a dent. They said they'd replace the joint and do a high speed balance. If it balanced out, then good, but if not, a new tube was needed.
I told them to put 2 new joints in since they're cheap.
Well it did not balance with the dent, so they cut a new tube.
When I got it back I was very impressed, the welds were very nice, and they had blasted and painted the whole thing in a nice satin black. A nice piece. Total cost was $197

I put the shaft back in, and didnt have a whole lot of time so I just went around the block.
I thought it only vibrated at speed, but in the quick trip around my street I noticed a difference. Much smoother.

And now on the highway, at 55 mph +, vibrations are GONE. Best money Ive spent on the car.

 

I think I have most of the above covered--will be putting the adjustable upper control arms in next week and bring the pinion angle back from +1deg to negative -2deg. Yes the vibration is at 2600 and gets worse as you move up from there. Also its torque sensitive, meaning less vibration without drive load. Will try the balance on the drums as the last resort.


I think the vibration has gotten worse over the two years that I have had the car. This is just seat of the pants feel. I'm thinking the torque of a lot of stoplight dashes has collapsed the upper control arm bushings and this accounts for the pinion being tilted up. The car has 120k on it.


I'll report back after the arms are in.

 

Trans tailshaft bushing could be bad.

Pinion bearing is another culprit.

Bent axle

Step by step process of elimination.

 

New arms and its still there. Arms adjusted then car moved onto "run in place rack" Pinion adjusted and double checked by 2nd mechanic--its between 2 and 3 deg neg. Ran it in place vibration still there. Removed both tires and bolted down the drums --ran in place and still had the vibration. They ran out of time--short handed and a shop injury. The run in place is without load. They drove it and still shakes, I haven't run it myself yet so I can't say if its better or worse.

Will try the 180 turn of the driveshaft shaft and run without drums next. Owner of the shop back next week. Will also ask chances of the retube and balance of the shaft being off. It was done by a driveshaft specialist shop--retube and new ujoints. They have a automatic welder that cuts the bead also balance machine.

Summary new tires, and since it shakes with tires off running in place they are not the problem. Axles are new from Moser-- car had vibration with old axles--Drums, rear trans bearing? Fustrated!!


Thanks for all the thoughts and advice.

 

Check the yolk on he diff. If the driveshaft is not centered in the yolk, it will shake. Put a dial indicator on the housing and check the runout on the driveshaft as it spins in place. My driveshaft guy gets them within .005". If there is runout, flip it 180 degrees and recheck, if it is not the same, the yolk is not centering it correctly.

Here is a quick test too. Clamp a wheel weight on the driveshaft with a screw-clamp type hose clamp. A regular one will work too, I suppose. Jack it up and put it on jack stands at ride height. Then, reve her up in gear and see of you can move the weight around to cancel out the vibes.

I have done this with different size weights on the different torque converter mounting bolts to verify a imbalanced converter. I actually got it pretty close, but did actually balance the converter on the machine after the fact.

 

An easy test to isolate vibrations to particular area/system..

Note RPM of vibration, in high gear.

Attempt to replicate vibration by driving vehicle in a lower gear, but at the same rpm.

If the vibration remains at the previously noted rpm, but at a different road speed, then vibrations is forward of the driveshaft. Engine/transmission and related systems, even the cooling fan can vibrate.

If the vibration is high pitched, and at a particular road speed or range of road speeds, then behind the trans.

Worst one I ever had to fix, and it was a vibration like your describing, the aftermarket Yoke on a 12 bolt we had in a 70 GS was not centered. With the car on jack stands under the axle, you could just start it up, put it in gear, and watch the shaft jump up and down as it spun in an elliptical orbit.

Your note that it seems to be "torque sensitive" could indicate you have a vibration induced by components rubbing the body.. look at engine/trans mounting, and the exhaust system. When torque is applied via the throttle, in forward gear, the driver side of the engine picks up, and may worsen the contact.

JW

 

Finally Found It!!!

Sorry for the delay, vacations and lots of rain here in S Fla have prevented any work til now.

It was the drums. Ran it in place without the drums and all was fine. The drums were cast iron for the inside liner and aluminum shells. The cast iron was intact and true and therefore there was no pulsing in the petal. The aluminum shells and fined cooling system had collapsed in places and was warped from age and heat and changed the balance dramtically. New drums and presto. Thanks for all the good advice.

The mechanic took it to the interstate and said he ran 90 with no shake. I will check it on the way home from tomorrow's car show.


The car is ready to travel ---I'm registering her for Daytona's Turkey Run tonight. WA HOO!!!

 

When I turned a wrench for a living I had a Chevy truck in my bay for something. While I had the wheels off I noticed that one of the brake drums. Had a solid 180degrees of weights on it. With the drum off you could see how porous the cast iron was on that side of the drum. In fact you could see light through it in one place!