[Flyin TA]

I have a pretty good vibration about 70mph and up.

I have a TKO 3550 with the kit supplied drive shaft 1350 u joints, dowelled McCleod twin disk clutch, a rebuilt 10 bolt with all new bearings true trac 3.73 and caltracs. Vibration was prensent before the rebuild just at a higher speed.

I assume switching from 3.42 to 3.73 and 28" to 26" tires is the reason for the vibration coming on at a lower speed.

Trans angle is 3 degrees down and the rear is 4 degrees down. I ordered 5 degrees of shims to get the pinion angle to 1 degree.

Is 2 negative angles totaling 7 degrees enough to make a high speed vibration? If the vib is still present after setting pinion angle is it worth rebalancing the drive shft or just get a new Mark Williams?

Thanks for your inputs.

[Keith Seymore]

Originally Posted by Flyin TA

I assume switching from 3.42 to 3.73 and 28" to 26" tires is the reason for the vibration coming on at a lower speed.

Yes.

Originally Posted by Flyin TA

Is 2 negative angles totaling 7 degrees enough to make a high speed vibration?

Yes.

Originally Posted by Flyin TA

If the vib is still present after setting pinion angle is it worth rebalancing the drive shft or just get a new Mark Williams?

Yes

But - keep in mind - a U joint disturbance is a second order issue (ie, two "kicks" per rev of the shaft) and an imbalance is a first order disturbance (one "kick" per rev).

So they are two different (unrelated) root causes (and solutions) even though they are both related to driveline.

K

[68gtoMN]

Ok, after Keith's response, I have nothing...

[Doug]

Without getting too far out in the weeds on this topic, isn't the "angularity" of the driveshaft relative to the driveshaft yoke and to the pinion yoke what needs to be "adjusted" by shimming? (to get the U-joints in phase)

It seems that the proposed shimming is based on a "static" measurement.

I'll admit I haven't thought this through much today, it just didn't seem right to me.

You might want to think this through some more before you get into it.

Good luck!

[Keith Seymore]

The U joint "working angle" is the difference between the pinion nose and the shaft (or the drive shaft and the trans yoke).

So it's not the static dimension of one or the other; it is the subtracted value between the two.

K

[Keith Seymore]

Flyin TA - just had a thought, a couple minutes ago -

If you are feelin' lucky - just take the driveshaft out of the rear axle, rotate it 180* and put it back together.

If it IS an imbalance sometimes that's enough to take care of it.

It's cheap and it's easy and it can't hurt anything.

K

[Flyin TA]

Originally Posted by Keith Seymore

Flyin TA - just had a thought, a couple minutes ago -

If you are feelin' lucky - just take the driveshaft out of the rear axle, rotate it 180* and put it back together.

If it IS an imbalance sometimes that's enough to take care of it.

It's cheap and it's easy and it can't hurt anything.

K

Thx for all one these. I ordered some shims. Hopefully pinion angle is it but I am not always that lucky. One step at a time. Crazy how long it takes to get all the bugs out of a car when you get it all back together.

[Flyin TA]

Well

Got the pinion angle fixed and still has a vibration. Ran it on the jack stand with out the drive shaft and no vibration.

The rear end has been gone through so I ordered a chromoly drive shaft from Mark William
Should get it next week. Hopefully it will work.

[FrankieT/A]

Does your 10 bolt have a 1350 yoke? Or are you using a conversion joint?

[Flyin TA]

1350 yoke.

[andrewb70]

If your vibration is related to high u-joint operating angles, a new driveshaft won't do anything to fix it. If you look on the Mark Williams website, there is a tech bulletin related to driveshaft critical speed. In that PDF, there is a chart that shows a curve of maximum operating angles in relation to driveshaft speed.

http://www.markwilliams.com/servicebull/sb0049.pdf

With the 3.73 gear and the 26" tall tire, your driveshaft speed about 3350 RPM. If you refer to that chart, you will see that your operating angles should be less than 3 degrees, and preferably less.

I would measure carefully and see what your operating angles are now.

Andrew

[Flyin TA]

Originally Posted by andrewb70

If your vibration is related to high u-joint operating angles, a new driveshaft won't do anything to fix it. If you look on the Mark Williams website, there is a tech bulletin related to driveshaft critical speed. In that PDF, there is a chart that shows a curve of maximum operating angles in relation to driveshaft speed.

http://www.markwilliams.com/servicebull/sb0049.pdf

With the 3.73 gear and the 26" tall tire, your driveshaft speed about 3350 RPM. If you refer to that chart, you will see that your operating angles should be less than 3 degrees, and preferably less.

I would measure carefully and see what your operating angles are now.

Andrew

I am right at 2. My drive shaft was delivered yesterday. I have my fingers crossed that when I get home and it will be better

[andrewb70]

Originally Posted by Flyin TA

I am right at 2. My drive shaft was delivered yesterday. I have my fingers crossed that when I get home and it will be better

I'll keep my fingers crossed for you as well. Please let us know how it turns out.

Andrew

[Flyin TA]

Well installed my new MW driveshaft today. All the low speed vibrations are gone. I notice how smooth it was right out of the drive way. But I still have the high speed humming that comes on right at 75-80 mph.

[andrewb70]

Originally Posted by Flyin TA

Well installed my new MW driveshaft today. All the low speed vibrations are gone. I notice how smooth it was right out of the drive way. But I still have the high speed humming that comes on right at 75-80 mph.

Yup....my symptoms exactly...

Andrew

[Flyin TA]

Originally Posted by andrewb70

Yup....my symptoms exactly...

Andrew

What trans do you have?

I guess it has be in my rear end or trans. I am going to try running it on the stands without the wheels and brake rotors and see if that changes anything.

[Flyin TA]

Originally Posted by andrewb70

Yup....my symptoms exactly...

Andrew

What trans do you have? I am going to try running the car on stands without wheels and brakes and see what if I can narrow it to the rear end.

[andrewb70]

Originally Posted by Flyin TA

What trans do you have? I am going to try running the car on stands without wheels and brakes and see what if I can narrow it to the rear end.

I am running a Richmond 6 speed. If the vibration is a more like a "buzz" it's not the tires. The tires spin at (engine RPM in direct drive / rear gear ratio), which in your case is less than 1000 RPM. At 1000 RPM tire speed, it isn't really a "buzz" as more of a "wobble," in other words, its a lower frequency vibration.

Double checking the tire balance is never a bad idea, but I would also start looking at the pinion yoke. I would check the runout at the rear of the driveshaft, then flip the u-joint 180 degrees, and see if it gets better or worse. Circle track racers use a pinion yoke checking tool that can be purchased from G-Force transmission, but it is only available for a 1350 yoke and it is rather expensive.

Andrew