Repeating rotational sound from rear

[Jack P.]

Hi,
As I was " nearing " the end of my restoration of a 66 L79 Roadster, owner for the last 40 years, This year, Engine rebuilt, tranny , all the usual stuff and with new trailing arm assemblies , brakes, lines , suspension, 5,0000 miles ago,

3.70 posi rear and M-20

I have been putting the car through a good mechanical shake down of 1,500 plus miles , prior to paint.

Vibrating sound and feel from rear. Not influenced by braking. When coasting with engine off and in neutral , to identify sound,

it sounds every wheel rotation, sound with slow speed , vibration with speed and power.

Jacked one rear wheel up and spun tire, I was able to move it back and forth about 1" or more. Is that normal ? , when spinning wheel back and forth, sounds like a clunk and end of movement. U joints appear normal.

Opinions or more questions please

Jack

[Edward J.]

Re: Repeating rotational sound from rear

Jack ,The sound your talking about almost sounds like a u-joint problem, maybe the drive shaft, look for signs of a rusty powder substance on the u-joint caps ,this indicates that a joint is gone. it will also cause a driveline vibration .don't rule out the half shafts also.

[Jeff W.]

Re: Repeating rotational sound from rear

Jack, I also had a ujoint problem doing similar things that was brand new. After pulling my hair out, cause it couldn't be the ujoint it was new, I changed it out and bingo problem solved.

[Ray G.]

Re: Repeating rotational sound from rear

Hi,

Jacked one rear wheel up and spun tire, I was able to move it back and forth about 1" or more. Is that normal ? , when spinning wheel back and forth, sounds like a clunk and end of movement. U joints appear normal.

Opinions or more questions please

Jack

Hello Jack;
Are you writing " 1" of movement" at the top and bottom laterally ?
If so, not good.

Ray

[Joe C.]

Re: Repeating rotational sound from rear

Hi,
As I was " nearing " the end of my restoration of a 66 L79 Roadster, owner for the last 40 years, This year, Engine rebuilt, tranny , all the usual stuff and with new trailing arm assemblies , brakes, lines , suspension, 5,0000 miles ago,

3.70 posi rear and M-20

I have been putting the car through a good mechanical shake down of 1,500 plus miles , prior to paint.

Vibrating sound and feel from rear. Not influenced by braking. When coasting with engine off and in neutral , to identify sound,

it sounds every wheel rotation, sound with slow speed , vibration with speed and power.

Jacked one rear wheel up and spun tire, I was able to move it back and forth about 1" or more. Is that normal ? , when spinning wheel back and forth, sounds like a clunk and end of movement. U joints appear normal.

Opinions or more questions please

Jack

Limited slip rear with one wheel jacked should have zero angular rotation. I assume that you mean you can rotate the tire in an arc of about 1". The torque required to "break loose" a healthy set of posi clutches is (IIRC) about 60-80 ft-lbs applied at the centerline of the axle shaft.

Support the rear of the car on jack stands while restraining one wheel from turning. Have an assistant rotate the other wheel while you go underneath with a drop light. Check for slop in the half shaft u-joints. Observe the stub axles at the differential case. If the stub axles are rotating, then you have clutch problems, which is due to one or a combination of: worn/broken springs, worn stub axle ends, worn clutch pak, or worn spider gear shaft.

Joe

[Jack P.]

Re: Repeating rotational sound from rear

Hi, I did have a friend rotate tire while I held other tire firm. The wheel was able to rotate about 1 to 1/2 " of arc forward and back. Was in hurry at time. I will do again and check areas that you mentioned.

Jack