Can someone explain axle shims?

Decided when I do my leaf spring replacement I'm getting either wheelers 5 or 8 pack. Truck currently has stock leafs sitting on top of 3" blocks. I want to eliminate the blocks.

Assuming those blocks gave the rear a 3" lift, will I need axle shims for the new leafs to function properly?

Currently the carrier bearing doesn't have a spacer and the vsb (?) valve on my rear axle is in it's stock location. Are these mods not needed when lifting the rear 3"? I'm only assuming the rear was lifted 3" due to the blocks currently in place. Am I way off here?

 

The general rule I've heard is 1 degree for each inch of lift. I added about 3" of lift, a 3 degree shim, and no vibration at all.

 

Thank you. These shims can't be too expensive, right?

 

$17 for a set is what I paid. I got some 2.5" wide ones (width of the leaf) that were for an older chevy truck, but they worked fine.

 

Not bad at all! So my next question is, if I don't have shims in there now, why am I getting no vibration issues?

 

Probably because those block twist like hell when you drive and create a 3 degree shim by themselves. Blocks are sketchy.

 

Ahhhhh, that makes total sense. I can't wait to see how it rides with new leafs. I know when I drove the truck awhile back when it was newer, the rear was STIFF. It's softened up though

 

So I'm guessing I won't know if I need them until after I get the lift leafs in? I've finally decided on dakars with an aal. Would it be best to get a couple different size shims to see which works best? Is feeling for vibration the way to determine if shims are needed?

 

It would be a pain in the ass to test shims. They go in with the leaf pack before you put on the u bolts and all that. Just get 2 or 3 degree and you won't be sorry later.

 

Ok I'll do that. Just curious, will the worst part of not having shims be vibrations or can drivetrain damage occur?

 

Vibrations. Before axle shims I had vibrations between 25-30. I don't know if anyone has seen premature failure of parts due to these vibes.

 

Hmmm I have 3" blocks under saggy stock leafs and I get a noticeable vibration around 35mph. There's no shims in place either. It's a vibration with a 1-2 second smooth patch.

 

i think thats what my vibration felt like before i got my shims.. can't remember for sure though. for some reason i remember it being around 20 - 30mph.. I think the vibrations can cause faster wear on the u-joints. not sure if I've ever seen someone have a u-joint fail because of the vibrations though.

 

Hmm.. I'm looking into all this info too because I bought mine with spacers and blocks. Redoing everything properly whenever I save up. But for the rear I think I've got 2.5 maybe 3" blocks, haven't checked em, but I've got a bad wobble, like really bad at about 65. Being a newb and not researching I thought it was the carrier bearing. It did need replaced anyways but after I pit it in there's been no change. And the wobble doesn't happen 100% of the time. Some times it's barely noticeable, others it's horrible. Like it comes and goes. But rarely is it not there. I'm trying to figure out what this is if it's axle shims or some other problem. Cuz I'm really getting sick of it. And it's not the tires I've had them balanced and rebalanced multiple times.