Taper roller bearing preload is a huge importance on heavy trucks. I've seen professionals that didn't realize this. With many first time heavy truck owners on the forum I thought I'd throw it out there for discussion.
Dennis....

 

In what sense? Wheel bearings? Transmissions? Drivetrain/gears?

 

Any taper roller bearing preload is crucial

 

yes it is however that doesn't make it rocket science. in a past life as a heavy duty mech i installed many tapered bearing sets. every last 1 of them was installed the same way. as tight as possible, while rotating, then back off til loose, retighten, an back off 1/8 to 1/4. no come backs or failures. the company i wrenched for did heavy off road hauling(oil drilling rigs) so they certainly beat their iron harder than any highway hauler dreams of. the informal company motto was "nothings unbreakable". I did check afterwards to make sure it spun free and wasn't binding

 

This is true.I always used my own method and in ove 40 years in heave equipment and trucks never had a come back

 

I'm just trying to get a rookie think about it. If you ever lauched a drag car, your eye ***** are the weight of golf *****, the diff didn't break, you understand preload.
Dennis.....

 

Interesting thread-

I allways seated the bearings as tight as possible, rotate wheel/assembly several times, back off, and tighten a tad more than hand tight. Again no problems in 25 + yrs.


Was working a chain problem on a bobcat talking with a gentleman that claimed he was retired from Caterpillar-he was convinced tapered roller bearings needed to be tightened up as tight as possible-not sure how many hours that would last....


Brent

 

When you see a pit in a wheel roller it was probably from running loose, pounding the bearing and spindle.
Try this: Everytime you have a wheel off the ground that spins freely, give it a spin before you take it apart. When the wheel is slowing to near the resting point but suddenly reverses rotation. You just found a pitted bearing. No kidding... You'll find a pit in a roller if you look long enough. The pit causes the rollers to bunch up, lock and reverse rotation.

The Cat guy has worked on some very large bearings and assemblies. I'm not going to agree with him 100% but why would he say that? He learned something somewhere?

Drag racing diff was a bad example because your preloading the casting more than the bearing to gain strength.

Got you thinking, Best to you, Dennis....

 

on very large rollers that turn slowly and don't build a lot of heat, your preload will be higher. on most applications though, you set with some free play and as it warms up the freeplay is taken up by thermal expansion

 

Hello,
First sentence I agree.
Second sentence sounds like a good lab experiment for a bearing company. Hmmm..... But I don't agree...
Best, Dennis........

 

It's always seemed to me, that for the most part, if the bearing is lubed with grease, the manual says to back off 1/8-1/4 turn or some other small amount, so there's no preload.

On gear-oil lubed bearings, preload is usually a must, especially with gear sets like rear ends, trannies, etc.

Interesting topic.

I once remember a machinist I know talking about this in terms of front disc-brakes on certain vehicles. The manufacturer had a heck of a time with overheated rotors, and used a "back it off 1/8-1/4 turn" method on the wheel bearing preload.

Turned out that it didn't dissipate enough heat to the axle that way, and the way to solve the situation (at least, temporarily) was to preload the bearing so that the heat from the rotor could dissipate quicker into the axle.

Now as the "thermal expansion" argument, again, in terms of vehicles with brakes, be it rotor or drum, the part that will expand the most is the hub, not the spindle. So if they are loose to begin with, they will only get even looser as the hub heats up and expands. Some preload is good in this case because they will get looser as they heat. Of course, the hub and spindle design dictate how much they expand or contract with heat, but you get the idea.

 

Pitting can be caused by running loose but also from contamination or inadequate lubrication
The rollers can't bunch up unless the separator is broke
If the wheel reverses rotation the bearing is too lose

X2 on that one

Normally when you back the nut off it is from a determined torque which only reduces preload
I have always preloaded oiled or greased bearings the same

I worked with taper bearings for 40 years sizes from 1/2" to 12" shaft sizes

All taper bearings need some preload

 

Double post

 

The seperator wasn't broken but the next time I'll tighten the bearing and try it again. I did not know a loose bearing could reverse the wheel. Makes sense to me.
Thanks, Dennis...

 

I'm kinda glad this post has been resurrected, since it gives me an opportunity to vent a bit. I HATE unitized wheel hubs, but this post explains to a T why they gained popularity. Whether it was from laziness or ignorance, the "art" of setting tapered bearing preload became lost on technicians and the shadetree mechanic in recent years.

Rant mode off...I feel better now
Pat