speedtigger

iTrader: (16)

Ever since I built my car I have had a driveshaft vibration problem. Right around 58 MPH, my car would start to vibrate. Lightly at 58 MPH then progressively worse above that speed. By 70 MPH, it was unbearable.

Since it was a brand new driveshaft from a popular reputable shop, I initially assumed the problem was in my driveline angles. I tried all kinds of different pinion angles, engine/trans angles and combinations. Nothing worked. I even pulled the driveshaft out and took it back to the driveshaft shop to check the balance. They re-balanced the shaft and installed new U-Joiunts. It was slightly better, but still bad. In addition, I started reading about other GM A-Bodies that had similar problems. I almost had myself convinced this was something unique to 64-67 A-Bodies.

I was supposed to go to the dragstrip today, but the thought of another 150 mile round trip limited to 58 MPH just pissed me off. So, I put the car on jack stands and started zip tying washers to the drive shaft at different clock positions on the differential end and viola! I reduced the vibration significantly. I ended up adding 18 grams to the rear of the drive shaft and 3 grams to the front. The vibration is 90+% eliminated. You can feel it a bit over 80 MPH, but below that it is barely detectable. After I got the right weights and positions, I welded the washers in place. It was a time consuming process balancing it this way, but it was very much worth the effort. The car is soooooo much more enjoyable to drive now.

loweredd

iTrader: (2)

I wonder what made such a difference once it was installed? Is the pinion yoke goofed up that bad?

speedtigger

iTrader: (16)

That possibility crossed my mind. I should have measured the runout while it was up, but it did not occur to me at the time.

1989GTA

Interesting. Thanks for posting the results.

bczee

iTrader: (12)

Seems to me, something else is out of balance and that all you did was conrect it with balancing using the drive shaft. Wonder what would you find if you took the drive shaft back to the shop and have them check it.? I assume you cheched everything.. wheels/tires, brake rotors, etc.. sometime cheap rotor will cause virbrations.

also, sometime I don't have a lot of faith in some shops in the way they balance . I have had shaft that where balanced by two different shop to have the virbration fixed. Since I don't know how they do it.. I am not going to comment on what or how they do it or not do it the correct way.

speedtigger

iTrader: (16)

There was no mistaking that this was something that spins at drive-shaft speed. The frequency was much too high to be anything at the wheels. And, since it is directly proportionate to vehicle speed, that narrows it down to the driveshaft, rear end input shaft or the transmission output shaft. Since it took the majority of added weight at the rear of the driveshaft to fix it, that means we are either talking about the driveshaft or the rear end pinion, or yoke. If I would have thought of it, I would have measured the runout on the rear end pinion yoke and the drive shaft. That could have provided more insight.

As for the driveshaft, it came from PST. They have a pretty good reputation. I even took it back to them for re-balance. However, they did confide in me that their "high speed balance" is less than 3000 RPM. And, 3000 drive-shaft RPM is about where the vibration became noticeable.

At this point, I can't be sure whether it is the drive-shaft or the differential yoke. Next time I am under their for maintenance, maybe I will measure runout. Right now I am just enjoying vibration free cruising and I am looking forward to my next 150 mile round-trip to the dragstrip. I can crank it up to 75 MPH, lock up the converter and enjoy the benefits of my overdrive transmission.

Pop N Wood

iTrader: (1)

Interesting.

Found a pretty good reference when I googled check driveshaft runout. The book looks worth buying.

http://books.google.com/books?id=K0K...runout&f=false

Old Geezer

iTrader: (3)

So, to find out if the shaft was really the issue, have PST recheck the balance w/ the wts you added, still on it. If it's out, the poster that suggested it was a correction of another problem, is likely right....Look elsewhere.

In the "FWIW" dept: I've used several of PST's driveshafts... NEVER an issue.

59belair

turn the driveshaft 180* in the pinion yoke. if the driveshaft was the problem, it will still run smooth. if it doesn't…. you'll know that pretty quickly also.

.02

speedtigger

iTrader: (16)

I am certainly not ruling out the possibility that it could be a bent or out of spec pinion yoke, but I can't agree with your logic on this one. You are suggesting that the best test for determining if the problem is the driveshaft balance is to take the rebalanced drive shaft that is not vibrating back to the shop who supplied the driveshaft that was vibrating for them to determine if it is properly balanced?

In pondering your suggestion, I came up with a fool proof test that will determine without question which is the culprit. Since I added weight to one side of the driveshaft, if the drive shaft was not the problem and that added weight was actually compensating for a bad pinion yoke, I must merely unbolt the driveshaft, rotate it 180 degrees and bolt it back up and then test it. If it is the pinion yoke that is out of spec, the vibration should be twice as bad as it was before I balanced it. Fool proof.

speedtigger

iTrader: (16)

HA! treed.

Project GatTagO

iTrader: (7)

I suspect that you have a bad pinion yoke. Does the rear u-joint fit firmly between the tabs in the yoke?

Andrew

speedtigger

iTrader: (16)

It does. From all appearances it looks and fits normal. Bit, it is a 40+ year old used part. So, who knows what it has endured in it's life.

kwhizz

Ask Andrew how he know about that problem.......LOL

toxic99

Some of those brutal 10 second launches for one lol. My vote is yoke as well. Gl

Project GatTagO

iTrader: (7)

It can also be the pinion shaft itself. It doesn't take much for a part to be out of round to cause vibrations. Remember, we are dealing with drivetrain parts that were never designed to spin very fast. Old cars didn't have overdrive transmissions, so the RPM of the driveline was limited to the RPM of the engine. If the car was set up with a 3.73 gear, 26" tires, and a Muncie, the engine and the driveshaft were spinning at 3600rpm in 4th gear (1:1) at 75mph. That's buzzing right along. With that kind of engine speed, the last thing you notice is driveline vibration! LOL

Now take a more modern setup, let's say using a T56. Guys like to run more gear because of the .50 6th gear, but that plays havoc with the speed of the driveshaft. Lets take the same scenario as above.

75 mph
26" tire
4.10 gears
t56

In 6th gear the engine is only turning just under 2000 rpm, but the driveshaft is now spinning at almost 4000 RPM! This is why even on new cars, like a new GTO, the factory never really runs a short rear gear. The new GTO came with 3.42 gears, I suspect mostly to keep the speed of the driveshaft down.

For this reason I really like the new 6L80/90 transmissions. They have a deep first gear, so you can run a tall rear gear, which keeps the driveshaft speed down at higher speeds, but also gives plenty of gear multiplication to get the car moving.

The new C7 Corvette has the new TR6070 7 speed trans and it now has three overdrive gears! With the transaxle set-up it is not an issue, because there is no driveshaft to be overdriven, but that would be a terrible combination for older cars that have a really long driveshaft, especially the 64-67 a-bodies that have a relatively long wheelbase.

OK…I'm done babbling on…

In short, you should check the pinion yoke and pinion gear for runout! LOL

Andrew

speedtigger

iTrader: (16)

That is really it with old cars. The rear in my car had a 2.73 gear in it when I got it, so the driveshaft speed would never exceed 3000 RPM in normal driving where the problem occurs.

I do not suspect the pinion gear at all. It was new Motive Gear and the process by which pinion gears are manufactured would not allow for that kind of runout. There would be much bigger problems at the contact point with the ring gear if it had that kind of runout on the pinion gear.

1989GTA

Regarding the 180 degree thing. I have seen that many times including my Trans Am. We mark it and make sure it goes back in the same way. I have seen just rotating the driveshaft 180 degrees and bolting it back up cure a lot of drive shaft problems. Not saying that is your problem.

speedtigger

iTrader: (16)

As far as I am concerned, my problem is solved.

jlcustomz

If you don't have an original shaft, what difference would 180ing the shaft make? Just wondering.