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

lapoolboy

By lapoolboy
in Modifications, Wheels & Tires

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lapoolboy Senior Enthusiast

lapoolboy

Posted
Posted (edited)

I want to get to the bottom of this once-and-for-all.  Those of you who have aftermarket lifts installed (with rear blocks), please indicate if you or your installer left the factory shims in place between the spring perch and leaf spring (the shims will now be on TOP of the aftermarket lift block - see pic).  My truck has less than 3000 miles on it and the ride was smooth as silk prior to installing the lift.  There is now a very slight rumbling/vibrating at 55-65mph.  ReadyLift says to remove the factory shim even though their instructions mention nothing of it and their own pictures in the instructions even show the shims left in place.  I've looked at other manufacturer's instructions - SuperLift says to remove the shims.  BDS, ProComp, etc. all specifically state to be sure NOT to remove the factory shims.  No rhyme or reason - some use tapered blocks, some use flat blocks.  My ReadyLift uses tapered blocks.

 

Now to complicate things further, a member here posted a pic of his 2020 and there are no factory shims installed on his truck.

 

I am not against removing the shims - I guess I just want confirmation that is the problem.  You have to clamp the leafs together and remove the center pin bolt while holding it from spinning with ViseGrips.  Never done it, but doesn't sound terrible.  The angle of the driveshaft at the rear of the transmission is noticably "downward".  The angle of the driveshaft at the rear differential appears to be pretty much in line with the pinion.

 

 

 

 

IMG_20191208_143625~4.jpg

Edited by lapoolboy
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Dunn
Dunn

It's not like its longer axle on same truck (2018)..maybe becuz truck is wider or since diff is narrower like you say it needs longer axle, idk..."point a to point b" ...they put new CV axles in GM fa

Flatblack83
Flatblack83

Long post, trying to help...I only said to remove the blocks to be 100% sure that's your problem. I understand it would be higher upfront. I didnt say leave it like that...a little cali lean..lol

Flatblack83
Flatblack83

Think about that way the diff moves when you step on the gas, you want the pinion to be 1-2 degrees lower so that when u step on the gas the pinion goes up. So that's how it should be close to that. T

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Dunn Senior Enthusiast

Dunn

Posted
Posted (edited)

maybe a diff drop?..think most quality 4in lifts use em...

 

does seem weird to have tapered block and than use a shim to take "taper" out don't you think?....could have just made block flat in first place....no need to put an extra piece in there....just using common sense but idk 

 

may be trial and error....shim is easy to remove it seems

Edited by Dunn
lapoolboy Senior Enthusiast

lapoolboy

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11 minutes ago, Dunn said:

maybe a diff drop?..think most quality 4in lifts use em...

 

does seem weird to have tapered block and than use a shim to take "taper" out don't you think?....could have just made block flat in first place....no need to put an extra piece in there....just using common sense but idk 

 

may be trial and error....shim is easy to remove it seems

"Diff drop" typically refers to the front diff.  

Flatblack83 Enthusiast

Flatblack83

Posted
Posted (edited)

Usually all tapered lift blocks when used the shims come out or it will be extra steep. The rule of thumb years ago was the pinion 2 degree off so when u step on the gas the driveline is right.  If the blocks tapered I'd take em out. I put a 1.5 flat block in mine and its good...  no vibes.

 

 

Think the rumbling might be the front end being too high with cvs too steep..?? With these trucks to be looks like 3 inches is it for the cv angles. I think even 3.5 is too much.  The diff drop you really can't do, I'm pretty sure the member gets chopped like the 1st rough country 3 inch.

Edited by Flatblack83
lapoolboy Senior Enthusiast

lapoolboy

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48 minutes ago, Flatblack83 said:

Usually all tapered lift blocks when used the shims come out or it will be extra steep. The rule of thumb years ago was the pinion 2 degree off so when u step on the gas the driveline is right.  If the blocks tapered I'd take em out. I put a 1.5 flat block in mine and its good...  no vibes.

 

 

Think the rumbling might be the front end being too high with cvs too steep..?? With these trucks to be looks like 3 inches is it for the cv angles. I think even 3.5 is too much.  The diff drop you really can't do, I'm pretty sure the member gets chopped like the 1st rough country 3 inch.

The factory shims are installed with big end towards the front....so they are essentially cancelling out the taper of the blocks.  

 

The vibration is definitely coming from the rear end.  I can almost hear it.  The front-end is smooth as silk....the steering wheel is nice and smooth too with no vibration.  The cv's are longer on the T1's than on the K2's and the front diff is narrower, allowing more lift capability.   There are several other members out there who have the 4" like me and report that their trucks are smooth so I don't know what's different about mine.  All of them have the factory shims still installed too.

Snowcamo Senior Enthusiast

Snowcamo

Posted
Posted

All you need to do is get the pinion angle right. I would not continue to drive it like that. If it takes you removing the Shims so be it.

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Dunn Senior Enthusiast

Dunn

Posted
Posted (edited)

It's not like its longer axle on same truck (2018)..maybe becuz truck is wider or since diff is narrower like you say it needs longer axle, idk..."point a to point b" ...they put new CV axles in GM factory lift and it's only 2 in....I just hear peeps with vibration issues relate it to this alot....

 

If it were my truck I would take out wedges....makes no sense to have taper block and use wedge to take taper out and it's another piece that has "joint" so to speak

 

Mechanics are funny thing, everything effects everything it seems, leaving alot to "scratch their head wondering"

 

Start with easiest and work your way from there

 

Good luck hope it works out

Edited by Dunn
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lapoolboy Senior Enthusiast

lapoolboy

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5 minutes ago, Flatblack83 said:

Take the blocks out, put it to stock and see what happens. 

Then the ass-end would be 3" lower than the front.  I guess it "could" rule out the blocks, but the mis-match in height front-to-rear could induce other vibes.  The shims are attached to the spring pack via the centering pin so I have to disassemble that to get the shims out.  

Flatblack83 Enthusiast

Flatblack83

Posted
Posted (edited)

Long post, trying to help...I only said to remove the blocks to be 100% sure that's your problem. I understand it would be higher upfront. I didnt say leave it like that...a little cali lean..lol

Is the driveline high or low when u look at it..?  Measure the taper on the block, measure the taper on the shim.  U either have too much angle or not enough...so..

 

If the taper is more on the block than the shim I would pull the shims out and put the tapered blocks in. If not I would get a flat set of blocks and try those with the stock shim.  Or order a set of blocks from a company that said to remove em, or vise versa.

 

When you call these companies 8 out of 10 times they have no idea and just answer you with a guess so u go away.  For instance I called icon to see what the coilovers were set at, she said 1 inch over stock. Few hours later I called and a guy answered,  he put me on hold and came back with set at 3 inches over stock with a silverado lt.  So...lol.  he was 100% right when I installed them.

Edited by Flatblack83
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lapoolboy Senior Enthusiast

lapoolboy

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Posted (edited)

Ok, I just crawled under and measured.  The ReadyLift blocks are 3" tall at the back and 2-3/4" tall at the front.  The factory shim is 5/16" So, it is confirmed the angle in the ReadyLift block is cancelled by the thickness of the shim.  (Even makes the block TALLER in the front by 1/16" with it in there!).  The rear diff has an upward tilt and the angle with the driveshaft appears to be very close to 0 degrees.  Removing the shims will give the diff even more upward tilt.  

IMG_20191227_181357~2.jpg

IMG_20191227_181520~3.jpg

IMG_20191227_181218~2.jpg

 

00100lrPORTRAIT_00100_BURST20191227181055160_COVER~3.jpg

Edited by lapoolboy
lapoolboy Senior Enthusiast

lapoolboy

Posted
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Posted (edited)
1 hour ago, Flatblack83 said:

If the taper is more on the block than the shim I would pull the shims out and put the tapered blocks in. If not I would get a flat set of blocks and try those with the stock shim.  Or order a set of blocks from a company that said to remove em, or vise versa.

Thanks.  After getting under there and measuring, this makes sense.  If I leave the ReadyLift tapered blocks and remove the shims, the diff pinion will be angled upward.  This definitely won't be "equal and opposite" the angle at transmission.  I'm thinking I need to leave the shims and just put in some flat blocks.  This will push the front of the diff down.

IMG_20191227_185659.jpg

Edited by lapoolboy
lapoolboy Senior Enthusiast

lapoolboy

Posted
  • Author
Posted

Removing the shims and leaving tapered blocks will shift front of diff upwards and create funky angle that would be opposite direction of last one I show in proposed setup.

IMG_20191227_185913.jpg

Flatblack83 Enthusiast

Flatblack83

Posted
Posted (edited)

Think about that way the diff moves when you step on the gas, you want the pinion to be 1-2 degrees lower so that when u step on the gas the pinion goes up. So that's how it should be close to that. They make lots of shims to fix this problem.  Or are the blocks in the right direction..?? If it's too high now bring it down...

Edited by Flatblack83
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