locating drivetrain vibration.

[Racer57]

70 Cuda 383cu Tremec 5 speed TKX

I've had a vibration for several years. Prior to the new TKX which replaced an late 80s Tremec. It starts around 60mph and increases with speed. It doesn't make any difference when I push in the clutch. Tires have been replaced and weights on wheels are minimal. Have had 2 different shops check tires/wheels with no difference between them. Shocks are Bilstein and new 4,000 miles ago. Gromments on torsion bars are 3,000 miles old. Front end alignment checks out with no apparent slop. 

How do I determine whether the issue is with the front, back or somewhere else ?

[Deezel]

Have you checked your driveshaft and u-joints?

I had a truck quite a few years back that had a similar vibration that started at 50mph that I could not find what was causing it. The vibration seemed to be worse if I was going down a hill and let off on the gas. My father-in-law suggested I try changing the u-joints. I took his advice, changed them and just like that, vibration was gone.
I could not visually see anything wrong with the u-joints that would make you think they were bad. 

[blown motor]

Have you checked your driveshaft and u-joints?

I had a truck quite a few years back that had a similar vibration that started at 50mph that I could not find what was causing it. The vibration seemed to be worse if I was going down a hill and let off on the gas. My father-in-law suggested I try changing the u-joints. I took his advice, changed them and just like that, vibration was gone.
I could not visually see anything wrong with the u-joints that would make you think they were bad. 

Interesting. My PW started vibrating some lately. It just doesn't feel as smooth as it did. Maybe new joints are in my future.

[Brads70]

Tricky one I had years ago was a weight on a drum brake came off. How I found it was put the rear end up on axle stands removed rims/tires then started it and brought it up to speed, has both doors open and the the doors would bounce from vibration at speed. , removed drum one at a time till vibration stopped. Just do NOT touch the brakes , just shut the engine off and let it stop rotating on it's own.

[pschlosser]

Have you checked your driveshaft and u-joints?

I had a truck quite a few years back that had a similar vibration that started at 50mph that I could not find what was causing it. The vibration seemed to be worse if I was going down a hill and let off on the gas. My father-in-law suggested I try changing the u-joints. I took his advice, changed them and just like that, vibration was gone.
I could not visually see anything wrong with the u-joints that would make you think they were bad. 

In my experience, U-joints wearing and soon to be failing is the most common cause for unexplained vibrations and noise.

Wearing U-joints takes a sharp eye to spot. 

One method to test:

* lift the rear-end enough to see the drive-shaft movement.
* lock the rear wheels with the parking brake. press hard on the pedal. lock them good.
* start the engine and run at idle.
* with the engine running, have a helper put the transmission in drive, then park, then drive, then park, then drive, then park.  Pausing 2-3 seconds (to allow the transmission to fully engage) between each shift.

When U-joints are solid, the drive shaft DOESN'T MOVE one bit.  Maybe an 1/8 of an inch (or less) in rotation.  But back and forth between D and P, if the drive shaft is moving, you may have one or more worn U-joints.

[Racer57]

In my experience, U-joints wearing and soon to be failing is the most common cause for unexplained vibrations and noise.

Wearing U-joints takes a sharp eye to spot. 

One method to test:

* lift the rear-end enough to see the drive-shaft movement.
* lock the rear wheels with the parking brake. press hard on the pedal. lock them good.
* start the engine and run at idle.
* with the engine running, have a helper put the transmission in drive, then park, then drive, then park, then drive, then park.  Pausing 2-3 seconds (to allow the transmission to fully engage) between each shift.

When U-joints are solid, the drive shaft DOESN'T MOVE one bit.  Maybe an 1/8 of an inch (or less) in rotation.  But back and forth between D and P, if the drive shaft is moving, you may have one or more worn U-joints.

Thanks for the advice, but I have a manual. 

[Gross Polluter]

   I had a bad vibration mid-speeds and turned out to be the crankshaft pulley.  It was a pulley for 3 belts (maybe AC?) whereas I had 2 belts.

[dodj]

  I had a bad vibration mid-speeds and turned out to be the crankshaft pulley.  It was a pulley for 3 belts (maybe AC?) whereas I had 2 belts.

I haven't been able to get high speed vibe out of my car for a while either. Like above 65. Maybe it's my pulleys.Seems more in the front than the back.

[dodj]

How I found it was put the rear end up on axle stands removed rims/tires then started it and brought it up to speed,

I don't think I have the stones to do that....idle or just off idle..ok...at speed? 

[Bullitt-]

 Saw this video about similar issue diagnosed using an electronic device.
    Turned out to be a driveshaft issue....
https://youtu.be/vcMHJOG_MHg?si=_jHFrNn_nuIPEMzf&t=365

[Brads70]

How I found it was put the rear end up on axle stands removed rims/tires then started it and brought it up to speed,

I don't think I have the stones to do that....idle or just off idle..ok...at speed? 

Rear end was up on axle stands, where would it go....

[dodj]

How I found it was put the rear end up on axle stands removed rims/tires then started it and brought it up to speed,

I don't think I have the stones to do that....idle or just off idle..ok...at speed? 

I'm just thinking about what would happen if the shaking of the car made it....come off the jack stands.....

Rear end was up on axle stands, where would it go....

[Brads70]

How I found it was put the rear end up on axle stands removed rims/tires then started it and brought it up to speed,

I don't think I have the stones to do that....idle or just off idle..ok...at speed? 

I'm just thinking about what would happen if the shaking of the car made it....come off the jack stands.....

Rear end was up on axle stands, where would it go....

The vibration wasn't  that bad, thats why I left the doors open as it sort of amplified or showed it better.

[Chryco Psycho]

Check the driveline angle , some of th Tremec installs created nasty driveline angles

[Racer57]

Check the driveline angle , some of th Tremec installs created nasty driveline angles

How many degrees do you recommend and what do you compare it too ?  Also, something thats always confused me. Back in the day when we used air shocks, why didn't that create vibration due to angle changing ?