[crustysarge]

I have been chasing a high speed vibration problem on my 77 TA and am pretty depressed on the progress. Car is a factory 4 speed that I converted to TKO 600 and 3.5 aluminum driveshaft. Rear end is a 10 bolt 3.73 with Eaton posi and Moser axles with disc brakes adapted from a LS1 98 TA.

Vibration comes on around 85-90 mph and you feel in the shifter and seat of the pants. Bad. Stays until speed drops down to less than 70 and stays on decel or clutch in/out, makes no difference, once it starts the only way to stop it is to slow down. Car had this with original trans and D/S also but I rarely got to those speeds with the 3.73 gears.

I have a pit so I set car at ride height with rear end supported at ride height with tires off, rotors off and it vibrates the same while running up to speed. Today I measured drive line angles have trans pointing down 2.8 degrees, D/S pointing down .10 degrees and the pinion is pointing down 1.7 degrees.

I have also found the shaft is actually hitting the pinion yoke and u-joint strap bolts, see pix. Not good. How in the hell has the shaft moved that much? Especially into the yoke like that? I filed it down some but it was gouged on both sides.

[steve25]

Any joints, especially the rear joint needs to be centered in the yoke to the tune of less then .010"

Sometimes joint caps are pressed on far enough to get the joint in the yoke yet not have it being close to centered!
You'll need a magnetic dial gauge to check this.

[73LeMans]

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

Keith Seymore is a member here. He wrote a lot of GM articles for GM truck service manuals. The info he posted in that link, and other info on this site, is excellent for setting up drivelines properly. Working ujoint angles, front and back, need to be less than 4 degrees, and both angles ought to be within 1/2 degree of each other.

[Scarebird]

I was having a lot of the same issues.

How much room do you have for the trans to go up? Shimming the trans mount may be a start here, perhaps shimming the rear up too.

[flat-bill]

I thought that if the engine centerline was down in the rear then the pinion should be UP in the front at an angle equal to the angle of the engine. The center lines of the crank and the pinion shaft should be parallel. If I'm reading your info you have the pinion front down. I don't think that's right. Billk

[73LeMans]

Originally Posted by flat-bill

I thought that if the engine centerline was down in the rear then the pinion should be UP in the front at an angle equal to the angle of the engine. The center lines of the crank and the pinion shaft should be parallel. If I'm reading your info you have the pinion front down. I don't think that's right. Billk

In most cases, this is true, but it doesnt take the length of the driveshaft into account.

Think of it this way, you could have the engine and rear end perfectly opposite and parallel to each other, but if they are, for example, only 12 inches from one another, the ujoints are going to see some serious angles to make it work.

[flat-bill]

I see your point but the OP 77TA probably doesn't have a 12 inch driveshaft. You still can't ignore the commonly called for max 3 degree ujoint angle. The parallel shafts tends to cancel out the speed up- slow down action happening in the U joints in the angle. Billk

[NeighborsComplaint]

Drive shaft is twisted and/or yokes are out of phase.

[Scarebird]

Originally Posted by flat-bill

I see your point but the OP 77TA probably doesn't have a 12 inch driveshaft. You still can't ignore the commonly called for max 3 degree ujoint angle. The parallel shafts tends to cancel out the speed up- slow down action happening in the U joints in the angle. Billk

Exactly. I had to raise the trans up almost an inch to get that portion of the vibration to go away. You may be able to shim up the trans a bit and/or use wedges on the diff.

[crustysarge]

Gonna see how much angle I can raise tranny tomorrow.

Neighbor's complaint might be on to something as well but the old Super-T10 and metal D/S had same issues.

Problem over here in Italy is shops can only balance shafts to a couple thousand RPMS, like truck stuff. Hard to get it checked accurately.

[67ramair4]

Loctite on bolts, if not need lockwashers!

[73LeMans]

Originally Posted by flat-bill

I see your point but the OP 77TA probably doesn't have a 12 inch driveshaft.

That's why I said "for example". The length was exaggerated to illustrate the point that you can have proper angles at the trans and rear end, and still have vibration/driveline issues.

[Scott Thelander]

picture 3 has my attention...

cap on u joint looks too small for the yoke just barely isee a shadow coming up the edge ,,that increases in width
and
the straps dont fit flat against the yoke,,, no lock washers
there is several different curves of straps for different u joints and differntial yoke applications

[steve25]

Get a few big screw type hose clamps to put on the drive shaft and tweak the balance yourself by the seat of your pants if need be !

It's highly unscientific, but it works every time once you figure out which end needs it!

Hopefully you can say chow to the vibration issue in short order.

[johnta1]

I have a pit so I set car at ride height with rear end supported at ride height with tires off, rotors off and it vibrates the same while running up to speed. Today I measured drive line angles have trans pointing down 2.8 degrees, D/S pointing down .10 degrees and the pinion is pointing down 1.7 degrees.

Driveshaft angle down only .10º?

I'd say you need to point the rear end up about 1º?
(or possibly lower the rear of tranny, more down angle)

[coonhunter70]

The straps look suspect to me.

[crustysarge]

Take a look: Could be the problem. Have to wait until I get new straps from the States.

[70gtojosh]

The gap between the cap and U joint may cause a vibration but I don't think that explains the driveshaft hitting the bolt heads. Have you considered or inspected for a extreme/bad axle wrap up condition? There is a lot of movement coming from somewhere.

[steve25]

From that photo it looks like they are only resting on the joint straps at the formed shoulder of the bolt flats!
Those look like there made for bigger OD joint caps than your running!

I guess you could try shimming that 180 section on each strap to close up that gap just as a experiment .

Those straps are too long also as they should not hang off the yoke as much as they do.

[73 TRANSAM]

I agree on the last photo that it has the wrong strap . I hate to say this but you may need to look closer to make sure you did not damage the pinion yoke on where the ujoint sits into. It does not like a loose fitting Ujoint in the groove and elongate the housing. Good luck.