I'm getting a "controlled" vibration from what seems to be the rear end. by controlled I mean at roughly 2200 rpm in third gear or 2200 in 4th (auto) I get a vibration that comes then goes then comes then goes and so on, not an all out vibration. and by comes and goes I mean 1 second on 1-2 seconds off. I have brand new tranny, balanced drive shaft/ujoints and new moser 12 bolt with true trac posi. seems it's my rearend for some reason? I also get a whine from my rearend at freeway speeds with light or no throttle, do I need to shim it?

 

double check the backlash on those gears for the whine, check the balance on your tires for the vibration.(make sure there is no water inside the tire)

 

I did notice the backlash when I installed the rearend, when I move the drive shaft back and fourth I have 3/8-1/2 inch of backlash, is this too much? I called moser and they said that some backlash was normal.
I thought about the tires needing rebalancing, but with the old drivetrain (last time I drove it with it was late june) I didn't have that issue so that's why it seems odd they would need it now. what do you mean "check for water in the tire"? thanks duck

 

water is very sneaky if your tires have sat still for over a month during the rainy season water can seep into the tire around the bead and valvestem. (have had this happen to mine) you say you have 3/8-1/2 " of lash are you talking about the pattern size or how much you can turn your driveshaft before it engages?

 

yeah 3/8-1/2 inch when moving the drive shaft. I called moser today and they said that's normal and the "whine" I hear at 60+mph with little throttle or coasting is normal and amplified due to the nature of the car having a torque arm (travels the sound) but I double checked transmission mounts, rearend bolts, everything and it still vibrates like a son of a gun over 65 MPH. I"m going to have my tires rebalanced this week just to eliminate that possibility. my driveshaft was new and balanced, is it possible it was balanced incorrectly? it's just so frustrating.

 

apparently you recieved some bad service from mosier. 3/8 - 1/2 " at the driveshaft is way to much. call them back and get them to give you the real specs that axle should be set at. my pickup has about a 1/4 " of play and it needs to be rebuilt( bad crush collar) you should only have around a couple of thousandths of lash maximum.