most people ive seen on here used shackles.I want to do a t-bar crank and lift the back, i was curious 2 what the diference between using the shackles or just getting lift blocks? can it be done? whats preferred?

any help is appreciated. thanks.

 

First off which vehicle are you driving?

Shackles are used on S-series trucks because the axle is mounted OVER the rear leaf springs. Putting a block between the axle and rear leaf will actually serve to lower the truck. Hence why everyone uses shackles to lift their vehicles.

K5 fullsize Blazers however have the leaf springs over the axle, so a block can be used instead of a shackle, but IMO shackles in this application would be optimal as well.
Looking at it from a "physics" point of view, putting a block between the axle and spring, actually serves to put more stress on the spring from forward and backward directional forces. It's like putting a lever between the axle and spring, and that lever will apply bending forces to the leafs. This could be dangerous in some on-road situations, like panic stops, the wheels could actually HOP because it'll now be easier for the leaf springs to "load up" and then spring back into normal position when the built up forces get high enough, causing the tires to hop and lose traction. Make sense? It's the same reason people put traction bars on drag cars with a solid rear axle and leafs, to stop that spring from loading up and causing a loss of traction.

Hope that answers your question.

 

/\ Great knowledge there!

Same with lifted trucks with tires 35" and up. With no weight in the bed, sometimes traction bars will help with wheel hop and things of that nature. Both have thier expenses like bushings if you tear up the old ones with the shackles and new U-bolts for the blocks can be expensive.

But if your leaf springs are under the axle, shackles are about the only way to go. You can also do Add a leafs, but you won't get as much height and they will give a slightly firmer ride. Where as the shackles won't affect the ride.