Aftermarket rear lift blocks - factory shims in place or not?

[lapoolboy]

The factory shim had the pinion angled down slightly when stock.  After putting the tapered ReadyLift blocks in, the pinion was brought up since I am now essentially running a flat block.

 

And yes, blocks are oriented the way instructions state - shorter end toward the front of truck.

Edited December 28, 2019 by lapoolboy

[Flatblack83]

2 minutes ago, lapoolboy said:

The factory shim had the pinion angled down slightly when stock.  After putting the tapered ReadyLift blocks in, the pinion was brought up since I am now essentially running a flat block.

And the pinion doesn't need to be up, needs to be down hense my last post. I would fix that so the pinion isn't up causing the vibes..

[lapoolboy]

Yep.  I just need to find some flat 3" blocks.

[Flatblack83]

Companies like pmf suspension for an example have blocks the ubolts slide thru. Making it more solid and they cannot move.

[lapoolboy]

Well, I took the 2.5 degree factory shims out today and the vibration/resonance is still there at around 60mph!  . It's more of a "helicopter-like" chopping sound.  It starts at 55mph and becomes unnoticeable at 65mph.

 

What the hell am I missing here?  I thought for sure that would solve the problem.

Edited January 2, 2020 by lapoolboy

[19silverrado]

[19silverrado]

Our lifts are different height but still both rear block setups. I took the wedges out of my pack and ran the blocks as suggested and have no issue. Does the vibration go away if you let out of the gas? If you’re still at the speed when the vibration starts can you make it come and go by adding throttle not necessarily vehicle speed? If it’s not emphasized by accelerating then it really shouldn’t be in the drivetrain 

[lapoolboy]

Thanks.  Your blocks are non-tapered and it doesn't look like you have factory shims either.  Does your rear diff have a "nose-down" orientation?  Mine is nose-up right now and the angle with the driveshaft is very close to zero.

[lapoolboy]

I can accelerate smoothly on a good, flat road and I can start to detect it around 55mph.  It is worst right around 60mph and becomes undetectable at around 65mph.  I can let off the gas and coast down back through that range and it is still there.

[lapoolboy]

This is very slight.  My wife hasn't even noticed it.  I think more guys with the 3.5-4" lifts probably have the same thing but doesn't notice because of more aggressive tires.  I'm on the stock Bridgestones so any little noise or vibration is noticeable.

[19silverrado]

My blocks are tapered and like I said I pulled the spring pack apart to pull the factory shim. My pinion is nose down like the pic shows. Did you by chance remove the driveshaft from the pinion flange when you did the lift? If so maybe ClockIt 180° the other way and see if you just changed the factory balance by moving the mounting position. Other than that another simple thing to do is just rotate your tires and see if the vibration changes from your butt in the seat to the steering wheel to rule out a tire balance issue

[lapoolboy]

My blocks are tapered too but they cause the diff to point nose up, especially now that I've taken out the factory 2.5 degree shims.

 

I did not unbolt the driveshaft from the flange.  I will try rotating tires now.

[lapoolboy]

Well, I don't have a Pro-Comp lift, but these snippets from their instructions are telling.

 

These trucks apparently come stock with driveline vibrations (I couldn't detect any pre-lift) and they say DO NOT remove or alter the factory-installed shims.  

 

I guess I'll put the shims back in and just call it a day and live with the shuddering at 60mph.

[lapoolboy]

My blocks are 3" on one end and 2-3/4" on the other end.  No idea how to calculate the taper of them in degrees but I assume they are roughly 2-3 degrees.  The factory shims are 1/4" on thick end and they are stamped 2.5 degrees so I'm assuming the lift blocks are also 2.5 degrees since they have 1/4" of difference in them too.

 

I feel like GM had 2.5 degree shims in my truck for a reason - they wanted the nose of the diff pinion down by 2.5 degrees.  I added tapered blocks that effectively negated the GM factory shims and removed that 2.5 degrees of down angle they wanted.  Basically, like running a flat block at this point.

 

I removed the factory shims as an experiment and ran just the tapered blocks.  They brought the pinion up past horizontal.  The resonance got worse.

 

I now think I need to find some flat 3" blocks and put the factory shims back in.  That will give me the 3" of lift but maintain the 2.5 degree down angle GM had from the factory.

 

Am I thinking logically here?

[lapoolboy]

Now they are telling me to keep the factory 2.5 degree wedges out and spin the tapered blocks around backwards on purpose (big end toward the front).  They think this will maintain the 2.5 degree down angle GM had on the pinion from the factory and solve my issue.