Well fellas the only different thing is the TRANS, so I'm thinking the tail shaft bushing or the bearing. I can't remember if the 904 and four speed use the same length shaft.
Mostly true. Used 3.21 gears for first few months with the A833 (which was not rebuilt) and didn't feel anything between 65-70 mph now, but maybe that has some to do with the driveshaft now spinning at a higher rate of speed that with the 3.21s.
Almost immediately after I left the diff shop for the gear change, I felt the resonance on the highway above 60mph. Two days later, the driveshaft was balanced and new Spicer u-joints were put on the front and rear since they were shot. That re-balance and new joints helped immensely, but as said, still not completely gone.
I should mention that this is the same driveshaft that I shortened to use behind the previous 904 when I swapped in the 8.25 rear. That was the first time the driveshaft was balanced and new joints were installed. The very same driveshaft was used when swapped over to the A833 trans, with ZERO modifications to the driveshaft done.
I will see if I can take some pictures of the driveshaft if I get home the office early enough tonight.
