Hey guys and gals... Have a couple things going on i need help with...hopefully...
69 Cutlass with a fresh rebuilt 455 with a muncie 4 speed. I converted from auto to manual during the build. Car also has a rebuilt 10 bolt chevelle rear end. Problem im currently having is when i go faster than 45 mph the car has a nasty vibration/shaking feeling coming from what feels like everywhere but more noticely under my feet and steering wheel...Now i just had it aligned, rebalanced the wheels. New tires new rims, suspension etc. Could it be the drive shaft considering its from an auto not manual?? I did replace the u-joints. Its driving me fricking nutts! Yes i did have my crank drilled and balanced with harmonic balancer and flywheel.. Sorry if i sound irritated but this car has been fighting tooth and nail during the 5 year resto....This is all thats left...grrrr... any help is greatly appreciated!!!!

 

What kind of wheels and tires are on there? Did the balance require a lot of weights? Have you checked the run out on the wheels to make sure they are true? Tire belt separation could be a cause also.


I won't rule out a drive shaft issue, but it doesn't usually show up in the steering wheel.

 

I had a '71 Pontiac Ventura that developed a bad shake/vibration seemingly overnight.
The only thing we did prior to the shake developing was new drum brake shoes on all four corners and tie rod ends.
We changed ball joints, bushings, u-joints, you name it, thinking any of those were the cause.
But nothing fixed it.
In the end, we found we over adjusted the rear brakes when we replaced the shoes. They were binding and causing the problem. The car wasn't down on power at all, so we never thought to look at the brakes as binding in the beginning.

I see you replaced the rear end, maybe give the brakes a once over.

 

I had this happen once but at higher speeds.
Turned out to be the driveshaft.
Put the rear on stands, put it in gear, you will
be able to see it if it is. Don't forget to brake
and stop the wheels before putting it back in park.
Good luck.

 

That was my next thought, was checking the rear brakes. .I have year ones 17 inch rally wheels with bfg gforce kdw tires all brand new. .. the vibration feels more prominent under my feet than anything. .could isolating the tranny cross member help?

 

I've got a 10 bolt chevelle rear in mine too. With stock trailing arms, the diff was at 0 degrees. Not sure what the Olds rear sat at. I needed adjustable upper control arms to get the geometry correct. Pretty easy to check. Make sure you do the angle measurements on all 4 wheels.
Also, depending on what diff was in there before, the driveshaft may be too short with the chevelle rear. Is the yoke engaging the Muncie tail bushing fully?

 

Ok, I definitely know it's not the brakes. . The Chevy rear end seems to have a smaller yoke on it versus the olds unit. . This is what I get for installing rear end and drive shaft on the floor. . Seems that my u joint on my original olds drive shaft is to big for the Chevy rear end. . Will the olds yoke off my old rear end bolt up splined correctly to the Chevy? Don't know if this is causing my issue but the bearing caps aren't seating correctly in the Chevy yoke...

 

Have the driveshaft balanced. My bet is that's it. It's a cheap fix too. i had to have mine balanced after receiving it from my trans maker. It was cut to order and balanced then shipped to me. A looong time to wait. Then the car vibrates. I think it couldn't be the driveshaft. They just built and balanced it. It was the driveshaft. If your rear view mirror creates a circling blur at night. It's the driveshaft.

 

I have another drive shaft to swap in that is the solid one piece unit, but it also has larger u joints than my chevy 10 bolt rear...Do they make an offset u joint to compensate for this? I just unbolted the yoke off my 12 bolt olds and im going to see if it will mount up to the Chevy rear, but my guts tell me it wont... So basically i have two 12 bolt olds rear ends, and one built to the hills chevy 10 bolt... Any help greatly appreciated... I havent ruled out balancing the drive shaft but just trying to rule out the obvious...

 

 

What drive shaft did you use? The stock olds or a Chevy? My olds seems like the correct length but the u joints are too big. .

 

Most vibrations are tire/wheel problems.

 

I'm telling you, if the lights in your rear view mirror are making a vibrating swirl, it's the DS. I've had 3 cars do this to me over the last 35 years.

 

 

I know it could possibly be the drive shaft needing a balance. . But right now I'm just trying to find a conversion u joint to work with my current drive shaft and rear end combo. The olds u joint is to big and won't seat all the way on the Chevy yoke so I'm looking to see if anyone has a part number or at least could tell me where they bought the conversion u joint from. .. Thanks

 

I went through the same thing about 25 tears ago. 69 cutlass , th400 , chebby 12 bolt. I did buy an offset u-joint from a local parts store.( Witch is no longer )Just took the drive shaft with me told them it needed to mate to a chebby 12 bolt . I had it that afternoon and had it pressed in the drive shaft. I don't remember the part no. But I would think NAPA would be a good place to start.
Hope that helps
Chris

 

I ordered a custom driveshaft from these guys:
http://southwestspeed.com/
You need to know what kind of U joint you have on the driveshaft and diff. See this link:
http://www.driveshaftspecialist.com/...D%20Guide.html
U joints are available to adapt one style to another.
You also need to know if the length is correct and the trans yoke is adequately engaged.
Also check your engine and differential angles.

 

Well after re balancing all four wheels and correcting my u joint Problems I have 90% less vibration. . The rest is probably in the drive shaft or the fact my cross member isn't isolated. . Solid mounted. . Now will balance drive shaft and correct cross member. . Car is awesome and goes like a raped ape!! Thanks for all of your help! Olds 4 ever!

 

I believe the cross member is supposed to mount solid to the frame, the only isolation should be the trans mount.