Normal for lift blocks to be angled?

Hey Everyone,

I just bought a set of 2 inch lift blocks for my tacoma. I was just curious if it is normal for them to be slightly angled/pitched at the top of the block? (both are like that, so I am assuming it is normal....or.....I need to send them back asap.

Thanks for your time and help as always (the response times and help on here are the quickest of any forum).

Stay safe and take care.

-Tom


P.S.

Thank you for the help with picking the right suspension/lift options (she goes into the shop on Wednesday).

 

Lift blocks are often angled to help maintain drive line geometry by changing the pinion angle.

 

If you read about 2 degree, 3 degree shims, you’ll understand why there might be a slight angle on your blocks. When you lift your rear end without changing the orientation of the rear diff, it puts pressure on your driveline and can cause vibration. The angle reorients the geometry so the diff and driveline are at the correct angle.​

 

Thank you Windsor and Hook78. I appreciate your quick help and input (looks like I do not need to lose sleep over it).

Just for curiousity-sake, should it be angled downward toward the front of the vehicle, or should they be angled upward toward the front of the vehicle? And is there a reason for that? (Not necessary that I get that info; this stuff is just cool to know).

Thanks again guys. Much appreciated.

 

I'm curious what kind of analysis these companies are doing to justify angled shims. I've read that you want the front and rear u-joints at equal/complementary angles so that they are both at the same relative angle with the driveshaft (or the rear part of the driveshaft for our trucks). The reasoning is that because u-joints are not constant velocity joints, when a u-joint is rotating through an angle, the output speed of that u-joint is variable if the input speed is constant--it necessarily "wobbles" as the u-joint rotates.

The thought is that with a correctly phased second u-joint at a complementary angle to the first, the axis rotation at the output of that second u-joint is again aligned with the initial input angle (i.e., ideally at the same angle as the output shaft of the transmission/xfer case), thus helping cancel out the "wobbling".

That being said, if the lift is too big, the angle of the u-joints can be too extreme for them to even function properly, so that may be a potential impetus for going with angled agims + a drive shaft carrier spacer to reduce the angles at each u-joint. But to me that seems like just asking for more vibration.

I haven't done this analysis myself, so I'm not sure of the exact dynamics here, but would be interesting to look into.

 

Shorter side faces forward. Rotates the back of the rear diff down and therefore the front up where the driveshaft enters, correcting the geometry.

 

Small end to the front.

 

For shits and giggles, I modeled and simulated this interaction because I was curious. You can do these calculations analytically as well, but I chose to do the kinematic analysis numerically (via simulation software) because it's nice to visually see the motion along with the output data.

The results are: You're best off with a shim that perfectly alights the input rotation with the output rotation with the u-joints in phase (i.e., 0 degrees between the axis of the input compared to the axis of the output) IF your angles aren't so extreme that they cause u-joint binding. Save for that extreme case, any added inclination only appears to reduce the "canceling" effect of the two u-joint system. With all that being said, we have 3 u-joints on our stock drive shafts, so while the same concept applies, that likely has a non-negligible effect on the system as a whole—I did the simulation for 2 u-joints (so this would apply for those of us with a one-piece drive shaft), I might have to try 3 u-joints next.

Regardless, here are the outputs of a two u-joint system, at a relatively extreme driveshaft angle (30 degrees) with an input speed of 20 RPM, simulated with a 0, 1, 2, and 3-degree shim angle. The effect is still there for all non-zero driveshaft angles, just with less magnitude.

We can see that at 0 degrees (equal angles) the output speed matches the input speed (set at a constant 20 RPM for this simulation), but at angles other than 0 degrees we have that "wobbling" effect where the output speed (which directly translates to speed at the wheels) changes through the rotation.

In the end, to answer your question, it is NORMAL for many shims to be angled, but I'm not too sure they really did any engineering/analysis to justify it. It was probably a case of "hey the truck is higher, let's slap an angle on here so the rear diff points up", despite it not making much sense mechanically.