Knuckle Preload Questions. (1 Viewer)

[INCINR8]

I have searched for days and have come up with lots of info and lots of conflicting info. Bear with me please.

Ive read many times " The top is for preload and the bottom for adjusting the center of the knuckle". After looking at my parts, reading all kinds of threads, I cannot wrap my head around how this is the case.

Question 1. Is it not a fact that preload is a result of the combination of the shims on top and bottom?

Question 2. Wouldn't removing/adding a shim at the bottom to "Adjust center" effect your preload?

Thanks in advance.

 

[atazman]

Not an expert, and I probably have read the same information you have on this subject. Here's my take.....

I believe the answer is "Yes" to both of your questions. But the key is in setting the center position first. Once that is set, you use the upper shims to set preload. Sure, if you go back and change lower shims you will affect both the centering and the preload.

 

[micruz60]

Clear as mud, eh... Yes.
I guess if one keeps getting birfield soup, then one is doing it wrong.... I've always replaced the shims as they came out, and checked for twelve # resistance on the fish scale when pulling on the steer arm or knuckle. Lo tech has worked it the past.
Wasn't a Mud member trying to duplicate the SST for benefit to all?

 

[INCINR8]

Atazman, If I center it first, In theory, why couldn't I use the bottom shims to adj the preload. would it matter what side you use to adj preload as long as its just one side?

 

[atazman]

OK.... talking "theory" first. I suppose if you centered with shims on the upper bearing, you could adjust preload with shims on the lower bearing. I have never used the centering tool so I don't know if the tool would work doing it this way.

Now what is the "practical" approach? From what I read, the normal setup procedure is to center with the lower shim and then adjust preload with the upper shim. This seems to be the generally accepted way of doing the job. If everyone sets it up this way, the next person who works on the rig has a better chance of keeping everything centered, while adjusting the preload for his personal situation. Many people increase preload when they go to bigger tires.

 

[INCINR8]

The 3 ways I have read to center the knuckle.

1, Add or remove shims on the bottom only after preload is set.

2, Add shims to the "tight" side of the axle once the spindle is on.

3, Shift shims from bottom to top or viceversa after the preload is set never adding or removing a shim from the total.

#3 Seems to me to be the most logical . Im in no way saying the others wont work, or haven't worked. Im just looking for a starting point to start reassembling my axle. Thanks for the replies. If any others has advice I would love to hear it. Once again, I appreciate your reply.

 

[shawnfj40]

Your preload is going to be determined by shim total thickness. So I have been pretty lucky with keeping to that. If you need to add .001 to the bottom then subtracting that from the top has gotten me really close to ballpark. That's not to say that it is a rule. It has just worked out that way so far. If you get an odd set of bearings and races that could go completely sideways. I always start out with what I had to begin with. Check the center and preload and go from there. I am pretty that using the bottom for centering is so that gravity is working for you instead of against you.