I swapped my open differential for a true trac posi with 373 gears.... At about 85 mph and above I feel like a vibration at the rear like on and off on and off constantly.... I have a 4/6 drop on 20''s and the gears were used.... Any ideas what can it be? Thanks....

 

Check your pinion angle should be around -2° I think

 

Thanks apex.... I'm new to this... How do I check that out or where should I take it too?

 

What gears ratio did you take out?
Did the vibration appear after the 4/6 drop or after the gears. If you had no vibration after the drop, but the vibration appeared after the gears, it could be that you are now spinning the driveshaft faster and it may need balancing. I'm assuming you lowered the gear ratio. A good drive shaft shop should be able to measure your angles and spin your shaft on a balancer to narrow your problem down.

 

It originally had the 3.42 with the stock one legger differential and I swap it all with a trutrac and used 3.73s.. The vibration appeared after the gear and posi installation.... Thanks Scott