'65 mustang 50mph harmonic vibration

[BK911]

Slung a rear u-joint cap around 70mph heading to work a couple weeks ago.
Bought and installed a new driveshaft which came with u-joints.
Also installed a new slip yoke.
Now there is an annoying vibration that starts at 50mph and gets a bit worse up through 70mph.
Noticeable difference when on/off throttle.
Rotated the drive shaft 180^ and no change.
Took the assembly to a driveshaft balancer and they said it was perfect to 2500 rpm.
Reinstalled with no change.
Now thinking to replace the u-joints with a better quality than came with the shaft.
Also thinking maybe the pinion yoke got slightly bent?
Any chance the transmission was damaged?
Any other ideas?

TIA!!!

[masraum]

Super cool and a little jealous that you drive a '65 mustang to work.
But I have no advice on the vibration, other than balance, bent, play in u-joints which you've already thought of. Transmission mount issue?

pics of the car?

[nota]

alinement and or play in the rear mounts
maybe knocked a bit on the part failure or replacements ?
motor or trans mounts old weak shrunk ?

[908/930]

Put a dial indicator on the driveshaft near the diff. Any chance the new driveshaft is too long and is pushing the slip yoke in to bottom?

Have a friend who had a driveshaft vibration problem with his 69 427 Chevelle years ago, he put it to the pin on the highway north of Toronto, driveshaft broke at about 120mph, was better with the new drive shaft, but the cars floor took a beating.

[LWJ]

You just lost the cap?

No damage from that.

The new parts aren't balanced somehow.

I had a 65MGB with the shaft out 180 degrees. Could have killed me. Also had a 73 Blazer with a nasty vibration in the drive train. I wasn't smart enough back then to find & fix it.

I have also owned and driven a 65 Mustang. There should not be a vibration. I think the new yoke / is out of round? I like the dial indicator idea. This isn't rocket science. It's a Stang!

[pwd72s]

check the pinion angle? Might need some pro help on this one.

https://www.speedwaymotors.com/the-toolbox/setting-proper-driveshaft-angles/28855#:~:text=To%20find%20the%20working%20angles%2 0follow%20these%20steps%3A,and%20this%20will%20be% 20that%20u-joint%E2%80%99s%20working%20angle.

[asphaltgambler]

Anything else change when this happened?

[john70t]

Originally Posted by BK911

Slung a rear u-joint cap around 70mph heading to work a couple weeks ago.

Also thinking maybe the pinion yoke got slightly bent?
Any chance the transmission was damaged?

I would guess both sides might be suspect to damage if the driveshaft has been flailing around on the ground.

Is there any movement when the ends are pushed up/down or left/right?
(use a dial gauge with memory)
It may be minuscule but the problem will present at higher rpms.

Any deflection or extreme movement when the brakes are set with the trans put in 1st or Reverse gear?
Springs and bushings can flex to alter driveshaft alignment, both on the front and rear.

[gordner]

How loose were the old u joints? It is possible you always had a vibration that was hidden by slop in the driveshaft, and now is not.

[Danimal16]

Have you checked the drive train mounts. My 65 from back in the day had a very similar problem.

[Nostril Cheese]

Originally Posted by Danimal16

Have you checked the drive train mounts. My 65 from back in the day had a very similar problem.

This...

[BK911]

Spent a little time in the garage last night and checked the runout near the pinion yoke.
0.015".
Google-fu says this is probably a bit excessive.
Since balance shop said they checked runout and it was fine, I am guessing pinion yoke slightly bent.

Most other parts are new:
New engine
New engine and tranny mounts
New u-joints (before and after incident)
New drive shaft
New slip yoke

And there was no vibration before the incident occurred.

Going to check the pinion angle once I understand the procedure a little better.
Hopefully tonight.

Thanks for all the suggestions.

[pwd72s]

Thanks for keeping us posted.

[908/930]

There is also a chance you bent the pinion shaft, does it have a centre drill hole that you can get a dial indicator into? On that new driveshaft is their a counter weight welded to it?

Mark the high spot on the shaft and then rotate it 180deg in the yoke, jut to make sure it is not the way the driveshaft was manufactured.

[911boost]

Nice looking car! Same color as my '66, Rangoon Red?

[masraum]

Originally Posted by BK911

Spent a little time in the garage last night and checked the runout near the pinion yoke.
0.015".
Google-fu says this is probably a bit excessive.
Since balance shop said they checked runout and it was fine, I am guessing pinion yoke slightly bent.

Most other parts are new:
New engine
New engine and tranny mounts
New u-joints (before and after incident)
New drive shaft
New slip yoke

And there was no vibration before the incident occurred.

Going to check the pinion angle once I understand the procedure a little better.
Hopefully tonight.

Thanks for all the suggestions.

Beautiful car. Eager to hear that you've got the problem fixed!

[gsxrken]

I’d suspect the yoke at this point too. That’s too much runout.
Make sure your research how to properly measure your baseline pinion bearing preload so you can reinstall the new yoke to match.

[Danimal16]

If I recall, the harmonic dampener on the 289 and 302 is a two piece. Check to see that the rubber is not disturbed between the inner and outer parts of the balancer. In my case the balancer was not properly balanced and we needed to replace it.

[BK911]

Some progress.
Installed the new pinion yoke and noticed the pinion bearings were clunky.
Replacing the pinion bearings was almost like replacing the 911 front wheel bearings!!
So waiting on a box from summit with new crush sleeve, pinion seal and o ring.
Should have gotten the whole kit with new gear and track loc!!

[BK911]

Also noticed some damage to bearing carrier.
Almost looks like water damage, and it is on the inner bearing at bottom.