Yet Another Knuckle Rebuild Question

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May 16, 2005
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So I'm mentally preparing myself for a 30 spline Longfiled install and figure I would rebuild my knuckles at the same time. I've read tons of articles between here and PBB so I think I am comfortable with most of the process. I am still a little unclear regarding setting up the trunion/knuckle bearings though. Some articles say you need the SST and others say you can just set the preload with the knuckle. I understand that the SST will allow you to set the preload by "measuring" the shim stack, and it seems like using the knuckle method (no SST) you just add/delete shims until you get the correct preload (right?).

My question, is the SST only used to determine preload or does it also align the trunion bearings (vertically)? Without ever getting into a knuckle it seems that the trunion bearings only go in one way and can't really be "misaligned" right?

If I don't have an SST can I just pop the bearings in and set the preload with a scale adding/removing shims as needed? Like here

Pre-load and allignment comes into play if you are changing the knuckles and/or steering arms. If all are being reused, just reinstall the shims exactly as they are.

I'm pretty sure, the SST tool aligns the knuckle assembly w/the axle tube. A fish wt. scale checks the preload of the trunion bearings
I assume you are referencing the knuckle centering SST. If the knuckles are properly aligned now, ie its not leaking fluid from the transfer case, you wont need the SST. The SST has nothing to do with aligning the trunion bearings, just makes sure the inner and outer axles are aligned. Just keep track of how the existing shims are organized, top and bottom, and add or remove shims from the top to adjust preload.

If the axle halves are misaligned, you will need the SST to recenter the knuckle.

There is another SST that installs the bearing race. Forget it. Clean out seat and tap it down GENTLY. You will hear it when it seats properly.

Good luck.
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I just used the SST on my knuckles last weekend. In my case I was installing mini knuckles for a front disc brake conversion. So I needed to center up the knuckles (so the axle shaft is right in the center of the seals) as well as set the preload. If you are not changing the knuckles like I did then maybe you can get away without using it.
Keep the trunion bearing caps and their shims together in the same order they were in before you took the axle apart. For example, keep the driver's top and it's shims together, bottom and it's shims together, etc. Don't swap them side to side either (passenger to driver, or vice versa). You can install new shims of the same thickness as the old shims if your old ones are chewed (most are marked with their thickness), but other than that, it's a straight R&R procedure. As noted above, the only time you need the SST (or an aftermarket equivalent, which is available) is if you swap the knuckles. The SST centers the knuckle on the axle housing, and will allow you to calculate the shim thickness necessary to obtain proper preload on the bearings. You use the fish scale to confirm preload. You can get the scale from Marlin for about $10 IIRC. I couldn't find one locally to save my life so ... HTH.

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