Correct Axle shim direction

Hey all,

I need to install 2.5* shims under my leaf springs to hopefully alleviate driveline vibes after a 2” lift and based on my measurements I need the pinion shaft / bearing to go upwards.

With this being said which direction does the shim need to go in order to lift the pinion up? skinny / blade side to the front and the bigger side to the back?

I’m getting mixed responses on this, seems like such a simple thing that has been made complicated somehow.

 

Skinny/blade side to the front

 

Did you do the carrier bearing drop kit?

 

Yes I tried the OME drop kit it didn’t make a difference, hopefully the shims will do the trick, maybe combined with a carrier bearing drop if needed

 

Thank you! That’s what I was thinking, had someone tell me earlier it was the other way around which didn’t make sense to me

 

Yep, leaf springs are above the axle

 

To angle pinion up the thin part has to be to front picture two flat surfaces to angle the bottom up it have to have the front with less spacer than rear

 

Yep, my bad. I was thinking of a truck with the axle above the leaf springs. I just changed my post but you’re too quick. Lol

 

Welp I attempted to install the axle shims today and they’re slight too wide (thousandths of an inch) for the u-bolts to mount back through the lower axle mount for the leaf spring.

Thinking they will have to be slightly grinded down on both sides in order to fit now, have any of you run into this issue?

They are too wide in width not length.

 

Very common issue. Don't sweat it. Just grind them down as needed.

 

If they're aluminum, a file can do the trick. Does it have the slot to slide them in to engage the locating dowel? The ones I installed were tight, but were easily persuaded into place with some light taps from a dead blow hammer.

 

No these are the solid steel design with a hole through the middle for the locating dowel, got em on now though, just a tiny bit of grinding did the trick

 

Nice job. Did it fix it? I'd highly recommend the slotted shims, at least while you're trying to dial in the pinion angle. They are far easier to install and remove.

 

Could you send me a link for some? The vibrations are gone when decelerating to a stop but still there at freeway speeds 45-65+ Unfortunately, even after taking measurements I still got it wrong, very frustrating.

 

How did you take the measurements? Have seen a few of these posts. Surprised there isn’t a sticky how-to yet.

 

Sure. Here you go:

https://www.headstrongoffroad.com/store/p120/Axle_Shim_KIT.html

You can also find them on Summit Racing. I believe the brand is SPC. They offer more variety.

 

You obviously don’t understand driveline angles and are trying to have someone give you all the answers instead of sitting down and learning what is actually going on.

The axle moves (wraps) when you accelerate and decelerate. This changes the driveline angles which when not matched can cause oscillations because the opposing oscillations from the other joints aren’t matched and cancelling each other out. You should always try and set your pinion angles for best performance at your normal travelling speeds. In your case you have a good angle when decelerating which is pulling your pinion downwards yet when accelerating your pinion rises giving you oscillations which says to me you have too much rise. My answer would be less shim (upward) on the pinion which may behave worse on deceleration.

This is based on internet mechanics which sorry to say is only good for so much. Our trucks are SOA (spring over axle) which makes axle wrap more of an issue and is harder to sort for all situations. I am a big fan of single driveshaft double cardan shafts over the twin driveshaft w/ carrier bearing setups we have.

Anyone who has driveshaft vibes need to do some serious reading. If you don’t fully understand what is going on you will never know how to properly solve the issue or understand why the problem has come back again in some circumstances. The other problem in sorting driveline vibes on the internet is your solution is only as good as your source. On this forum as well as others I have encountered many who don’t have a clue yet are considered “guru’s” and give out 100% inaccurate information. There was an article years back by Jim Allen in J-rations magazine (I think it was written in conjunction with Tom Woods). I believe the article was titled Driveline deliverance. Great article.

Basically you need to learn what is going on with your driveline in order to identify where the oscillations are coming from and WHY. You need to measure the effective angles at rest and know what happens under acceleration and deceleration so you can compare to your numbers you already measured. To someone experienced it is pretty simple stuff as long as there are no other factors (broken mounts, loose bolts) confusing the situation. This is where people screw up. They measure once and then make a conclusion and never go back to verify their conclusions or re-verify the measurements.

If you don’t understand the mechanics of driveline vibrations throwing parts at the problem is like gambling when you don’t understand the card game you are playing. You might win or might lose but won’t know why.

 

Would using an extra leaf spring for a suspension lift instead of a block help with reducing axle wrap? I’m thinking the axle would roll less due to the stiffer springs and the reduced distance between the lowest spring and top of the axle?

 

Yes.

 

Yes. Think back to grade school when they are teaching simple machines. The simple lever is what a block effectively is. Think about how it is mounted and how the driveline forces change once they go through the ring and pinion. The axle shaft is turning one direction so the axle housing turns (or tries to) turn the opposite direction. The leaf springs try and hold the axle housing from rotating (in addition to allowing up and down suspension movement). Once you add a block your leverage changes and you now have a larger lever trying to turn the axle housing. That means the housing needs a stronger force to resist the rotation which means heavier springs or all sorts of contraptions like ladder bars, traction bars etc. Blocks while cheap and easy introduce all sorts of issues that need more expensive solutions to fix the issues they create. Why add a block and then leaf springs to combat axle wrap if the goal was to save money by doing the block and not springs on the first place?