Alrite the first thing is really stupid... what size is the stock GM 10 bolt? 8.875 or 8.5?
Now the problem... after my rearend rebuild (upgraded to 4.10's) i started having a vibration that started at certain speeds and got worse as the speed increased. The first thing i checked was the driveshaft to see if it wasnt balanced. I was informed that the driveshaft was bent. I replaced with an Inland Empire aluminum DS. This lessened the vibration and got about 10 more mph out of it before the vibration started again. I asked the mechanic who rebuilt the rearend what else he could be and he said to look into replacing the yoke off the differential because that was still the stock piece. Anyone have any other suggestions as to what could be causing my vibration? Any ideas will help thanks in advance

 

are your bearings good? bad bearings will cause vibrations...

you have axle, pinion and carrier bearings....

 

The stock diff is only a 7-5/8" ring gear. That's why they're so famous for breaking (way too small for the power of a small block Chevy ). The same diff used to be just a 7.5", but they made it "slightly" bigger over the years (unless I got that backwards?!?! ).

...anyway, in regards to the vibration, if you KNOW that your driveshaft is good, how about your tranny mount? Is it stock? A polyurethane?? If it's a poly one, that'll explain excessive vibrations. If it's stock, maybe you should upgrade to the LS1 mount?

OTHERWISE, I have 4.10's in my car as well, and I can tell you for a fact that it's just the "nature of the beast" to suffer slightly more driveline noise & vibrations when you start dropping to low gear ratios like 3.73 / 4.10 / 4.56 / etc. Just think of how fast the driveshaft is spinning now compared to when you had 3.42's. If you do the math, it's about ~20% faster. I know my car has a small amount of gear whine (although not nearly as bad as the 3.73's I had 3 years ago) and at certain "critical speeds", there are vibrations that never used to be there.

If you have a pinion/carrier bearing going bad, you should hear it.

 

I forgot to mention I put a brand new rebuilt tranny in... the tranny came with a tranny mount so I assumed it was new. a friend of mine went through a bunch of tranny mounts but the vibration doesnt feel the same as the one he had... this feels more like from the rearend. Anyways i know that the lower gears are more prone to vibrations and noise but this is anything from ordinary... the vibration is WAY to severe to be the gears whining...
as far as the bearings go how do i check to see if they are bad and where are they located?

 

The vibration has only started since changing the rear gears, right? What about the tranny ... when did that get changed? No problems after the tranny install? I was also wondering if it's not a wheel/tire issue, but I'm sure you'd know the difference between a driveline vibration and a wheel/tire vibration. We've actually got the same problem going on right now with my Dad's '73, but we just haven't taken the time to track down the problem just yet. One of our suspicions is possibly a bent axle, but I don't know how you can accurately check an axle?? Or I wonder if a pinion could be bent?? Again, I don't know how you'd check that though. Just more thoughts/possibilities!

 

I had the rearend rebuilt with the 4.10's and i was driving on a busted tranny(missing 3rd). I had the vibration then... then i changed out the tranny... stll had the vibration... the next thing i changed was the driveshaft... still have the vibration.... basically everything from the engine back is new and its driving me nuts cuz right now i cant got over abnout 45 mph without the vibration