wheel bearings

[Ken in Oklahoma]

. . . Basically before the axle nut is torqued up, you should be able to feel some wobble in the wheel.
To take this to the extreme, when the axle nut is way loose, there should be a fair bit of wobble. . .

I noted with a lot of interest ME 109's "preload" approach which results in a slight bearing clearance. That's because my practice has been to call the preload good when there was a slight preload as the axle nut is tightened.

For years, on automobiles, my approach was to apply enough torque on the castellated nut to ensure that all the "slack" had been taken out of the bearings. Then I would back off the nut to the first chance to run the cotter pin through a hole. In other words I adjusted the bearings with a little clearance. But on an airhead I had developed the notion that a slight preload was optimum. So where did that come from?

I think it came from my interpretation of Duane's writings about all the massive bearing preloads he has encountered and how remarkably well the bearings have survived; with failures usually attributed to things like contaminants getting into the bearings as opposed to excessive preload. So (I must have intuitively concluded) a slight preload is good.

So, upon reading ME 109's approach I did what most of us probably do and went to the internet. There I never did find anything I could get my teeth into. What I was looking for was a general discussion about preload of tapered roller bearings from somebody who sounded like they knew what they were talking about. I found a lot of formulas, but not the discussion I was looking for. I think the reason that I didn't stumble upon a general statement is because there are so many ifs ands and buts regarding the applications and operating environments.

The chart in this link was about the best thing I found in my search:

http://cpannut.com/newFacts.html

One of my thought questions was what happens to the preload, whatever it is, as the bearings come up to operating temperature? We know that the final drives can get pretty warm from gear friction. The front wheels get plenty of cooling air on the other hand. The question is, does the preload increase or decrease at operating temperature? Since the bearings and surrounding components are mostly steel I'm guessing that the preload doesn't change significantly at operating temperatures? And when the surrounding aluminum would come into play, its greater thermal expansion coefficient would serve to move the bearings apart and increase the clearance.

Ken

[Deleted User 72]

I seem to remember Duane's method having zero lash with about 15-20 ft lbs of torque on the axle nut. If so, then when the axle nut is fully graunched down there certainly should be some preload on the bearings. At the same time, if the lash goes to zero with 15-20 ft lbs of torque the spacers are already serving their function as spacers. I thought I had this down. Now I'm confused again still.

I'll wait for further input before grading ME 109's paper.

[twist]

I finally have the wheel bearings installed right. After assembly, I inserted the axle into the hub and used shims to the threaded side so I could tighten the nut down to about 25-30 ft lbs and checking the preload. So far so good. It all feels right. Had it checked by local guru, he was unavailable to do the work but able to check my assembly and give me the thumbs up! My first wheel bearing job. Now I understand a lot better the concept and procedure. I learned something! Thanks to you all for advice and chuckles.

[ME 109]

I finally have the wheel bearings installed right. After assembly, I inserted the axle into the hub and used shims to the threaded side so I could tighten the nut down to about 25-30 ft lbs and checking the preload. So far so good. It all feels right. Had it checked by local guru, he was unavailable to do the work but able to check my assembly and give me the thumbs up! My first wheel bearing job. Now I understand a lot better the concept and procedure. I learned something! Thanks to you all for advice and chuckles.

Well done twist.
Did your guru loosen your axle nut and checking for wobble as he re-torqued the nut?
Not wanting to sound like a skeptical bastard, but new bearings will feel good even with too short a wedding band.
Until they don't feel good that is.

[twist]

unfortunately, I had greased the bearings quite thoroughly and it made teasing out the exact feel tricky. I plan to install the wheels and run them less than a mile and recheck the preload. I don't know if that will be pointless but seems like a good idea.

[Chuey]

Native/5, yes, you remember correctly. When you reach 25ft/lbs of torque on the axle, the freeplay (wobble) should disappear. That way, the remaining 10ft/lbs of torque will result in a very slight bit of load on the bearings.

I just did a 2,400+ mile trip on my new bearings. Oh, that's right. I had done that same trip on them last year, so it's 5,000+ miles on the bearings with over half of the trip done at hellishly high temperatures; over 100degrees Fahrenheit. My leg burned but my wheel bearings were stellar.

Chuey