Reply With QuoteThis sounds too familiar. let me share my experience here. my vibration started right after i had 3.73's installed. it vibrated around 80mph. I thought it was a problem with the gears. I ignored it and ended up throwing my ds going down the road just like you. i got a new one made at a local shop using thicker walled tubing and upgraded to 1350 u-joints. put it in and it vibrated at ~60mph. i inspected the ds and found it to be too short. had the shop re-tube the shaft a little longer. put it in and it vibrated ~70mph. i was pissed. so i drove 2 hours to jacksonville to get it professionally balance because the local shop didnt have the equipment to do it. on the drive back still vibrated. now i was really pissed. at this point i thought maybe it is the gears after all, so i ordered some new gears (4.10's) and had them installed. vibration still there. so i thought maybe my axels are bent. so i had the whole rearend rebuilt with new parts (axels, bearings, seals,). got the truck back and still have the mf'ing vibration. I continued to drive it at loss as to the cause until the vibration wore out the tranny output shaft bushing and started leaking tranny fluid. took it to a tranny shop and had them replace the bushing. when they did that they told me my ds was too short and that was why my bushing wore out. so i had another ds made a little longer. put the new shaft in and had the vibration still. went back to jacksonville to get the thing balanced again to no avail. at this point i pretty much eliminated all possibilities except for the tranny. so i went to a shop that speciallizes in t56's and they found my output shaft to be bent, which i found happend when i threw my ds going down the road. so i had the shop replace the output shaft in the tranny thinking this was the problem. put the tranny back in and guess what, yep, i still had the vibration ~ 70mph. the people at the tranny shop told me the bent output shaft would cause the ds to warp, so i went back to jacksonville again to have the shaft balanced yet another time. and of course the shaft still vibrates. only on this last visit to the ds balancing shop, one of the techs there told me that ds was borderlining being too long for the diameter/gauge of tubing used and really should be of stronger gauge and diameter. so after all this, i STILL have a vibration at 70mph. ive done some major thought over the past months and have come to the conclusion that the cause of my vibration is still the driveshaft. my reason is this: my ds is steel; my original axel gear ration was 2.73. this combination didnt cause the ds to spin too fast going highway speeds. my new combination of 4.10s and steel driveshaft causes the driveshaft to spin very fast at highway speeds. here is where the problem lies IMO...at high rpms, the steel shaft will warp or become imbalanced causing vibration. solution: aluminum baby! aluminum is less rotational mass therefore allowing higher rpms without distorting. and think about it--gm uses this same principle with its f-bodies. f-bodies that come equiped with 2.73's from the factory come with steel ds's. f-bodies that come equiped with 3.23's and 3.42's come with aluminum ds's. so, one of these days, when i can come up with a spare ~ $325 im going to get an aluminum ds from someone like http://www.iedls.com/
so--alan im not saying for sure that this is your problem, but it is a huge possibility. also, did you check your tranny output shaft? just unbolt your driveshaft and crank up the engine and put the tranny in drive and have a look at the output shaft to see if it is going around in a wobbly motion. what is your gear ratio?
