I just recently installed some new 5" blocks that are tapered in the rear end of my truck. I replaced the old 4 3/4" blocks. My truck has a weird bouncing motion in the rear end now when you first start moving from a stop or when you move slow & have the brakes applied....It only does it when you first start moving under 5mph....Doesn't do anything odd at all when you going down the road normal speed....What would cause the rear end of the truck to do that after installing tapered lift blocks? does it change the angle of the leaf springs on the axle? I thought that the tapered blocks were supposed to help ride smoother....

 

Did they change the angle that the axle sits at? Perhaps you have too much angle at the universal joint.

 

Where did you get the blocks from? Did they change the pinion angle any from the other blocks? Did you do ANYTHING else besides replace the blocks and then the bounce started?

 

Possibly calipers sticking?
I noticed that my rear end seems to bounce a bit too when unloaded. Trucks suspension is all stock so I guess it's normal.
One of my calipers is sticking so today I lubed sliding pins, hopefully that fixes it

 

I got these blocks from Top Gun Customz:

http://www.topguncustomz.com/Store/p...php?S_ID=18897

I guess the pinion angle has changed slightly since the blocks are tapered...I noticed that the axle sits differently than it used too...Could be what's causing the bouncing at low speed....

 

You might try lowering the center carrier bearing by shimming it down some. I would start with a 1/2 inch and then go from there.

 

Proper u-joint angle would be when the transmission u-joint angle is equal to the pinion u-joint angle. That way the degree of movement of the u-joints angle will be canceled out by the other u-joint. The only way to get around this and are allowed to have 0* at the pinion is if the other u-joint is a double cardan joint because a double cardan already has two u-joints which cancel each other out. Saying that, if your pinion angle only changed a little then I cant imagine it causing anything you're going through, and if it was then you would be experiencing a u-joint vibration at road speed as well. Maybe there's a difference in the blocks which you're unaware of that could potentially be causing the axle to wrap more or that your shocks are now setting in a position that allows more axle movement. Either one would definitely cause something you'd feel while taking off from a stop. You might want to also make sure that the tailshaft bushing isn't sloppy which would allow the driveshaft to wobble during high load situations, like taking off from a stop.

 

Look at the pinion and driveshaft from the side. You want the pinion to be a slight bit below due to the torque of the axle twisting upward when you start moving from a dead stop.

 

If the pinion angle were off wouldn't it cause some vibration at higher speeds? The truck drives really smooth at highway speeds....

 

Read my previous post again..... And as I also asked in the post before that, did you do ANYTHING other than simply replace the blocks?

 

the only thing different about this truck is it has some Deaver mini leaf packs installed under the main leafs....i think that this has something to do with the movement I can feel after installing the tapered lift blocks....i think these leaf packs were designed to be used with the original non-tapered blocks....

i definitely don't think it's axle wrap cause you don't even have to get on the gas & you can just let it start coasting from a stop & it just seems like you can feel any little movement in the rear end of the truck.....i'm going to go back to some non-tapered blocks & see if it fixes it....thanks for the help.

 

Sounds like those other leafs are causing improper u-joint angles.