setting knuckle bearing preload without SST

slickrock · 10-05-09, 02:40 PM

This post is about the shims that are on the top and bottom of the kunckles.

A buddy of mine was helping me tear down an axle and before I knew it, he removed the knuckle bearing preload shims without marking. About all I know is that one pair goes to the left axle and the other pair to the right axle.

I looked at coolerman's faq http://forum.ih8mud.com/40-55-series...tions-faq.html
and he used an SST. Without one, is there a way to tell on the origional shims which one goes where?

IS one usually thincker than another?

ElliottB · 10-05-09, 02:58 PM

From just doing mine, I learned the best way to do it is to place the shims where you *think* they originally went. Then test the bearing preload with a fishscale (should be between 4 and 11 lbs I think... see FSM). If it's not right, add or subtract shims as neccessary.

Are you going to recenter the knuckles while everything is all apart?

wengejor · 10-05-09, 04:14 PM

^^ that's what I did. Along with a marlin crawler seal, you'll be all set.

slickrock · 10-05-09, 07:27 PM

great. thanks for the responses. Should be no problem now.

ntsqd · 10-06-09, 09:17 AM

If you have the correct shims for each side then you very likely have the correct pre-load. The bearings don't vary much at all.

What you don't have is a way to center the knuckles. If they are off then you're hoping that the Marlin Seals are up to the job. Normally seals don't like the shaft to be eccentric in the bore by very much or they leak. I don't know what the range of eccentricity is for the Marlin's, but it is likely to be greater than a normal seal since that is part of what they're designed to deal with. I'm going through centering the knuckles right now. The best that I've gotten is 0.040" off. I don't think that is close enough.

Moby · 10-06-09, 02:05 PM

If you've got the original shims I agree - use those and test with a fish scale. When I got mine apart I was missing shims (no shims at all) and my bearings and races had deep scoring as a result. I end up getting the SSTs so that I could compute what I needed since I had no good baseline.

And get those Marlin seals - even with my top and bottom shims computed as accurately as possible with the SST my first rebuild leaked within a year with stock seals. Rebuilt them again with Marlin seals, no changes to the shims, and they have been leak free for a couple of years.

slickrock · 10-06-09, 05:09 PM

where did you get the SST from?

Moby · 10-06-09, 05:34 PM

SPX/OTC? Something like that. I think it is SPX Toyota | How To Order

Unfortunately I don't have a link handy at work for site that I used, I was looking for it the other day to price the rear wheel bearing puller. Had little luck with a slide hammer until I cut the cage out, removed the rollers and TIG welded a couple of beads around the inside of the shells to get them to contract enough so that the slide hammer could get them out

But I digress...

ntsqd · 10-06-09, 08:08 PM

That looks like the page that I ordered my SST from. Figure ~$113 plus shipping.

Randy88FJ62 · 10-07-09, 09:37 AM

I am in the process of rebuilding my front axle and I don’t understand what the bearing preload is. From what people have told me; if it’s too loose the wheel wobbles and if it’s too tight then it generates heat. I have no idea which bearing we are talking about. I have seen the FSM showing how to test it with a fish scale but I still don’t have a mental picture of how it all comes together inside the knuckle.

From the posts above I am confused even further because I see people talking about the shims on top and bottom of the knuckle. How do different shim thicknesses have anything to do with the bearing preload? I thought the only use for the shims was to center the axle shaft allowing a fine runout that would make sure you don’t ruin the seals?

Any good pictures illustrating which bearing we are talking about and how it relates to the centering of the axle shaft?

I have not downloaded the pages out of the chasis FSM which may solve a lot of these questions. I hate that the FSM I bought does not include all the information for a proper knuckle rebuild.

79fj40 · 10-07-09, 11:32 AM

Randy, I am doing this now on my 40. look in the 40 section in the faq and see centering knuckle tool directions. from what i understand the bottom shims center the axle and the top shims set preload. you are setting the preload on the trunion bearings that fit over the steering arm on the top and bearing cap on the bottom. the thiner the shims get the more the preload will be.

Randy88FJ62 · 10-07-09, 11:47 AM

Quote:

Originally Posted by 79fj40

Randy, I am doing this now on my 40. look in the 40 section in the faq and see centering knuckle tool directions. from what i understand the bottom shims center the axle and the top shims set preload. you are setting the preload on the trunion bearings that fit over the steering arm on the top and bearing cap on the bottom. the thiner the shims get the more the preload will be.

Thank you for connecting the dots for me. That makes sense. Assuming I am using the same shims that were there before I should not ahve to worry about preload. Correct?

Only when redoing the shims with the SST and centering the axle would a new preload need to be checked...right?

ntsqd · 10-07-09, 11:50 AM

If the knuckle or the housing haven't been changed then the existing shim stack should be right on to really, really close. It is only when the shims are missing or were put back wrong or housing or knuckle have been changed that checking the centering should need to be done. The FSM would do it every time the steering bearings were replaced, but be real.

79fj40 · 10-07-09, 12:11 PM

yes in theory as long as you know it has never been worked on. its easy to check preload though and make sure you are within range. a fish scale on the steering arm, pull scale and read how many lbs it took to move it. a scale is cheap insurance imho.

Butt Ugly Chuck · 11-02-09, 06:00 PM

I replaced shims exactly the way they came off and my preload is less than spec. As evidenced by chiseled spindle nuts

, my knuckles were redone at least once long before I took possession of the rig. I can't say I trust that the last mechanic did anything right

.

What say mud? Do I start removing shims to chase the right preload? If I start monkeying with shims, I don't have the SST to check for centering.

Butt

slickrock · 11-03-09, 10:39 AM

It was really easy to do mine with the shims and bearings simply reinstalled in the same place. Checked preload with a fish scale and was good to go. I do need to replace my bearings at some point as they are in just OK shape. But that will be another project in another year.

ntsqd · 11-03-09, 11:15 AM

Do you have a way to measure the shims that you have now?

If you only mess with either the top or the bottom then the current centering (or lack of it) shouldn't be moved much. It is frequently said around here that the bottom sets the centering and the top sets the pre-load. Eh, both do both depending on where you start, but if you only change one side (top or bottom - not both) then mostly what you will change is the pre-load. The centering will change, but only by 1/2 of the total shim thickness change.