Drive Shaft Issue?

[Joel Talka]

Hello Again from Florida!

Another issue with my 66 Coronet 440 which I think is driveshaft related...vibration... This car has undergone some major rework, was originally a 6 cylinder automatic car and is now a 408 worked small block mated to a 4 speed. I've spent a couple years on it; installed the 408, rebuilt the 4 speed, etc.. During this time, I swapped the 8 3/4" rear center from the original 2.92 ratio to a 3.73 posi unit along with new axles with green brearings.

The drive shaft that is in there is the one which came with the car when I bought it about 3 years ago. At that time, it had a 318 with the 4 speed. Where the drive shaft came from I have no idea. I do know there are two sizes of universal joints used on them; large and small. This driveshaft had the smaller size, perhaps from the original 6 cylinder(?). Anyway, when I put the car back together I used the original drive shaft, replaced the front universal with a small sized one but installed a "combination" universal in the rear as the new rear required the larger size. I will also say that when the driveshaft is installed the front yoke appears to be more exposed than it should be; I did not measure it but my gut says it is too short...

Problem now is vibration. I had it out on July 4th for about 30 miles. Runs fine a lower speed but when I get on it a bit, say above 60, I get a strong vibration which goes away when I drop down below that speed. I get the vibration while accelerating and even coasting in neutral going down a hill.

Again, I am thinking driveshaft but certainly appreciate any and all input!!

Thanks,

Joel

 

[Mopar Hunter]

I swapped the 8 3/4" rear center from the original 2.92 ratio to a 3.73 Sure Grip unit

I had to fix it for you Joel. Mopar calls it a Sure Grip, GM calls it a POSI.

Have you checked your universal joints for movement?

 

[twecomm]

Check your U joints.. Last fall had strange noises develop from under my 66 Charger at various speeds. Immediately suspected U joints, as far as I knew, they were original to the car. As time passed, noise got worse and finally ended up with significant vibration. Not set up to do the fix myself, took to a trusted mechanic friend. Not only was the forward U joint shot but it also damaged one leg of the tranny yoke which also had to be replaced. Replaced with Moog lube type U joints.

 

[Loulang]

What about tire balance?

 

[Fran Blacker]

Note I have a short dust seal, the trans output shaft comes out of the trans. It's at 1" on tape measure. Picture is with weigh on rear wheels. If you have more showing try moving yoke up and down,if you have more than 4 or 5 thousands might be Vibe.

 

[Joel Talka]

Check your U joints.. Last fall had strange noises develop from under my 66 Charger at various speeds. Immediately suspected U joints, as far as I knew, they were original to the car. As time passed, noise got worse and finally ended up with significant vibration. Not set up to do the fix myself, took to a trusted mechanic friend. Not only was the forward U joint shot but it also damaged one leg of the tranny yoke which also had to be replaced. Replaced with Moog lube type U joints.

Thanks for the idea but the U joints (both) are new. I installed them before I put the driveshaft back up....

 

[Joel Talka]

I had to fix it for you Joel. Mopar calls it a Sure Grip, GM calls it a POSI.

Have you checked your universal joints for movement?

Thanks, I know it is sure grip... I guess old habits die hard!

 

[Joel Talka]

What about tire balance?

Could be, thinking it could also be "flat spots" from sitting... It really doesn't feel like tire balance honestly..gets too violent.

 

[Joel Talka]

Note I have a short dust seal, the trans output shaft comes out of the trans. It's at 1" on tape measure. Picture is with weigh on rear wheels. If you have more showing try moving yoke up and down,if you have more than 4 or 5 thousands might be Vibe.View attachment 1691283

Thanks for this. I saw your picture when I was poking around for this earlier this morning. You basically have less than 2" from the seal to the collar on the yoke. I'll check again and try to get a picture with the car on the ground, but my recollection is that my yoke is much more extended... I'm thinking that I may have the drive shaft from the original 904 when the car was an automatic (??)..and I'm guessing it might be shorter than a correct 833 driveshaft. The tranny is correct for a '66 B body including the tail housing and I rebuilt it prior to putting it back up... Lemme check...

 

[Joel Talka]

Hello Again from Florida!

Another issue with my 66 Coronet 440 which I think is driveshaft related...vibration... This car has undergone some major rework, was originally a 6 cylinder automatic car and is now a 408 worked small block mated to a 4 speed. I've spent a couple years on it; installed the 408, rebuilt the 4 speed, etc.. During this time, I swapped the 8 3/4" rear center from the original 2.92 ratio to a 3.73 posi unit along with new axles with green brearings.

The drive shaft that is in there is the one which came with the car when I bought it about 3 years ago. At that time, it had a 318 with the 4 speed. Where the drive shaft came from I have no idea. I do know there are two sizes of universal joints used on them; large and small. This driveshaft had the smaller size, perhaps from the original 6 cylinder(?). Anyway, when I put the car back together I used the original drive shaft, replaced the front universal with a small sized one but installed a "combination" universal in the rear as the new rear required the larger size. I will also say that when the driveshaft is installed the front yoke appears to be more exposed than it should be; I did not measure it but my gut says it is too short...

Problem now is vibration. I had it out on July 4th for about 30 miles. Runs fine a lower speed but when I get on it a bit, say above 60, I get a strong vibration which goes away when I drop down below that speed. I get the vibration while accelerating and even coasting in neutral going down a hill.

Again, I am thinking driveshaft but certainly appreciate any and all input!!

Thanks,

Joel

Think I found it... See the pix. The car is on the ground and 2 1/2"+ of yoke is exposed. Also, see the front universal looks like it is separating..one side is further out than the other. That will really mess things up...??

 

[Fran Blacker]

The tool to change rear bushing for a 727 trans is probably $100. Sounds like you have a 904 don't think yoke is the same diameter. Picture of tool for 727, on the right removal tool left driver to install. you need to note position of oil hole when you remove bushing. This may not be your problem.