Shudder in 3rd - 3 speed top-loader

[sargentrs]

A matched set is not necessary.

The factory did not balance them as a set. Think about it. You could buy either shaft separately as a replacement part.

As long as they are balance correctly independently, the only thing you need to be sure of is that they are in phase.

Valid point. I didn't think about it that way but you're right. I stand corrected.

[sargentrs]

The forward section of our trucks has a joint nearest the transmission, the other end is fixed in the center support....

That brings up another consideration. Is your center bearing in good condition? Reminded me of something I encountered awhile back. My truck had been driving fine when, on the way home from work one day, I started feeling this vibration that got rapidly worse the slower I went. I pulled over at a local hardware store thinking it was a flat or a U joint. When I crawled under her I saw that one of 4 bolts holding the center bearing was missing and the one next to it had the nut backed almost all the way off allowing the center bearing to **** downwards. Walked in the hardware store, bought some bolts and lock nuts, put her back together and she drove fine. Just a thought.

[BobbyFord]

A matched set is not necessary.

The factory did not balance them as a set. Think about it. You could buy either shaft separately as a replacement part.

As long as they are balance correctly independently, the only thing you need to be sure of is that they are in phase.

Valid point. I didn't think about it that way but you're right. I stand corrected.

Me too, now that I think about it...