Hey Driveline Experts! I need your help

[65notch]

ive got this vibration and i think i need a new driveshaft but i want opinions. here how the story goes: to start. this all is in a 65 coupe 289 C4 8" dropout...
i changed my gears from 2.78 to 3.55 and ever since then ive had a nasty vibration probably around 45-55 mph(speedo says 60-70) its there while accelerating to that mph but not very noticable unless looking for it. then once i hit that mph its nasty for the 10mph range. once i get above it, the vibration is still there but not as quite as bad. the gears have the correct pattern, yoke was marked and installed in correct position. u joints were replaced, wheels balanced. when tranny is in neutral, the vibration is still there so its not in the engine or tranny.
from what i can remember, my car never really liked to go over 80mph. it got pretty nerve racking. i cant remember if it was a vibrations like i have now or what but im thinking it was.
what i can come up with is that the drivehshaft is and always has been out of balance and i never noticed it before because it never spun as fast as it does now because of the gear ratio change.

 

[jikelly]

I'll bet that it is your drive shaft. Hopefully you have a shop in town that can balance it for you.

 

[bnickel]

i had the same problem with mine, but i hasd to have a new driveshaft built because the original shaft was one of the rubber dampened tube within a tube shafts which are not really able to be balanced because they have a tendancy to slip throwing the front and rear yokes out of phase. from the sound of it that is what has likely happened to yours as well.

 

[mustangprodude]

My old 64.5 had the same problem. Come to find out that my driveshaft wasn't centered properly in the yoke. Thankfully it was an ez fix. Had my wife hold my driveshaft (ha ha) while I centered it and tightened the u-bolts to spec.

 

[65notch]

ive checked the placement of the ujoints. and they are centered properly. i had planned on getting a new driveshaft, not even messing with this one because its so old. thanks for the input guys

 

[1966conv]

First of all; it may be your drive shaft or not.

I have 3 66's all with vibrations within a 10 mph range but different on each car. On one car it was the brake drums, one car I can't find the vibration and the other was the tires. I had all 3 drive shafts checked for balance and all were good.

Check the easy things first before throwing money away on something it "Might" not be. Have your wheel balance checked, u-joints, brakes, etc.

Even check the driveshaft balance, they can weld in a new tube and rebalance for about $100, rather than get new.

 

[jb1dsl]

I had a new aluminum built for 150 dollars, if possible I would go that route

 

[65notch]

First of all; it may be your drive shaft or not.

I have 3 66's all with vibrations within a 10 mph range but different on each car. On one car it was the brake drums, one car I can't find the vibration and the other was the tires. I had all 3 drive shafts checked for balance and all were good.

Check the easy things first before throwing money away on something it "Might" not be. Have your wheel balance checked, u-joints, brakes, etc.

Even check the driveshaft balance, they can weld in a new tube and rebalance for about $100, rather than get new.

what were your brake drums doing that caused vibration?

 

[Hissing Cobra]

This could also be a bent driveshaft. I had that problem on my old Ford Ranger. How it got bent is beyond me but after replacing the u-joints yearly and finally breaking the tailshaft off of the transmission, I decided to have a pro look at it. He went to balance the shaft and right away he could tell it was bent. He cut the yokes off each end of the tube, welded in a new tube and balanced the new one. From then on it was mint and vibration free. Just something else to check for.