margr4v3z

Hello I have a vibration at only from 30-35MPH and before and after that it is none existent. I removed the rear driveshaft and it seemed to be gone. Both U-joints are new and the weight is still on the driveshaft. No physical damage appears to the shaft either. Would could be the issue?

1976Mustang

Are your rear tires cupping or anything? Could be that, and removing the drive to them just lessened the problem. I'd start there, check the tired and wouldn't hurt to get them rebalanced.

margr4v3z

I dont think the tires are the issue. When I am pressing the gas between 30-35 it will vibrate and if I let off it stops immediately. So that kind of tells me its not the tires. Any other thoughts?

1976Mustang

Trust me, there isn't must that can go wrong in the rear end to cause that. Physics and torque can do crazy things, and an impropperly balanced tire can cause all kinds of issues. The only other simple option really is your shaft threw a weight you didn't notice or your pinion is loose. Keep it stupid simple for now.

Firestorm500

Did you mark the drive shaft when it was in its original position before removing it to replace the U-joints?

Fred/N0AZZ

That may very well be the problem.

margr4v3z

The previous owner replaced them but when I took it off I put it back on the same way. I thought the shaft could only go on the yoke one way? Is this correct? Should I remove it and try another way?

margr4v3z

I took a picture of the pinion because it seems to be at an angle when it could be close to parallel right? Why would it be on such an angle?

Tony_SS

Sounds like axle wrap.. you want the pinion angle -1-3 to account for any wrap. Yours looks like it might be at 0?

margr4v3z

Okay so what does that mean and is it fixable?

SteveMongr

For the stock driveshaft, the pinion/driveshaft angle should be the same as the transfer case/driveshaft angle. Not pointing at the transfer case.

Looks like the pinion angle is set up for a SYE (slip yoke eliminator) and double-cardan driveshaft.

The angle of pinion is adjusted with wedges that get sandwiched between the leaf springs and perch on axle. Also, longer shackles can affect the angle.

margr4v3z

Yeah I thought it looked like it was at the angle for a double cardan shaft. It does not have wedges under the leaf springs but it does have 2" shackles I believe. Here is a pic of it. Other than the shackles I believe everything else is stock. So what can I do to get the pinion angle back to how it should be?

SteveMongr

I'm at a loss. Did this vibration start after the shackles were installed?

Anyone else have any input here?
Anyone installed shims backwards to lower pinion angle?

margr4v3z

The shackles were already installed when I bought it. So it has always had the vibration but this has to be the issue cause of the pinion angle but I don't know how to solve it.

jdwilliams

"I removed the rear driveshaft and it seemed to be gone."

Ummm...because the vehicle was no longer drivable?

The drivel around here is getting thick.