Topic: Knuckle Centering Issue

[ntsqd]

When using the SST the instructions have you scribe a line in the body of the tool when in the knuckle and when in the housing. Then you measure the distance between those two scribe lines and subtract 3mm from that distance to get the shim stack thickness for the bottom bearing cap.

What do you do if the scribe line distance is less than 3mm? Can't easily install negative shims. Best that can be done is put it together with no shims at all. This is what I've done, but it results in the axle shaft being low by about .040". Which is enough to cause the inner seal problems. Note that I do have Marlin's seals, but I'm tired of leaking knuckles. I'd like to have it better than this and not have to rely on the seal's misalignment ability.

Any suggestions? Did I miss something?

[79coyotefrg]

if you are using Marlins knuckle rebuild  kit all you need to do is put one thick shim and one thin shim on the bottom and the same on the top, tighten them down and check the resistance with a fish pull scale,   inever actually used the scale but just used my hand and head and got the "feel" for it

[79coyotefrg]

once you get the knuckles lower cap and steering arms tight, if it is too tight you need to add a thin shim,  if its too loose  remove a thin shim


i've never seen the special service tool used or even read how to use it since its really not needed

[ntsqd [OP]]

I should have mentioned that this is a from scratch front axle build, there is no known previous shim configuration. Were I just replacing the steering bearings I wouldn't be bothering with the SST. Since I have no starting place for the shims the SST is a requirement.

[79coyotefrg]

I should have mentioned that this is a from scratch front axle build, there is no known previous shim configuration. Were I just replacing the steering bearings I wouldn't be bothering with the SST. Since I have no starting place for the shims the SST is a requirement.

did you buy a rebuild kit?? new bearings and  all??

[ntsqd [OP]]

Yes, I did. Bearings, shims, swivel ball wipers/seals, etc., but again there is no existing shim arrangement. I have no baseline to work from, which is why the SST. This axle was taken apart several years ago and may or may not still have the original knuckles. Only a couple of the original shims are even still around.

[79coyotefrg]

Yes, I did. Bearings, shims, swivel ball wipers/seals, etc., but again there is no existing shim arrangement. I have no baseline to work from, which is why the SST. This axle was taken apart several years ago and may or may not still have the original knuckles. Only a couple of the original shims are even still around.

why do i feel like i'm talking to a wall

AGAIN, if you are using Marlin's rebuild kit,  assemble the knuckle with 1 thick shim and 1 thin shim (they come in the kit) on the lower cap and then 1 thick shim and 1 thin shim under the steering arm,  then tighten down  ( this is your baseline )THEN you measure the resistance of the knuckle with a fish scale 10-12 pounds of pull is the projected resistance

AGAIN  if your knuckle is looser than 10-12 pounds  then you need to remove a thin shim

HOWEVER  I've done this on several knuckle rebuilds I've done for friends ALL WITH A BOX OF PARTS ,( < no baseline as you say ) and AN EMPTY HOUSING AND THE MARLIN KIT,   and every one I've done has been within spec with 1 thin and 1 thick shim from the kit on top and bottom on new bearings and races

if your not using Marlins kit then that's another story

[ntsqd [OP]]

Your method contradicts the FSM and as far as I can tell (at this point) makes no effort to center the knuckle. I get about 3 years per set of trunnion bearings, and that is about as often as I wish to have to work on the axle.

I have the bearing pre-load set. I know what the total shim stack needs to be to get the correct pre-load on the bearings. That part of the two step process has been done. Next is to center the knuckle so that the inner seal does not wear out prematurely and turn the Birf grease into soup.

The problem is that there is no way to center the knuckle. The best that it can get is 0.040" too low. I was hoping that someone who has done a lot of set-ups using the SST could tell me that either something is really wrong and where to look, or that it is common for them to be that far off and not to worry about it.

[79coyotefrg]

Your method contradicts the FSM and as far as I can tell (at this point) makes no effort to center the knuckle. I get about 3 years per set of trunnion bearings, and that is about as often as I wish to have to work on the axle.

I have the bearing pre-load set. I know what the total shim stack needs to be to get the correct pre-load on the bearings. That part of the two step process has been done. Next is to center the knuckle so that the inner seal does not wear out prematurely and turn the Birf grease into soup.

The problem is that there is no way to center the knuckle. The best that it can get is 0.040" too low. I was hoping that someone who has done a lot of set-ups using the SST could tell me that either something is really wrong and where to look, or that it is common for them to be that far off and not to worry about it.

  unless your housing is bent having the same "1 thick and 1 thin top and bottom" your knuckle will be centered

[diggtbks]

Might be that centering the knuckle is not your problem as far as inner seals wearing prematurely, might be you need to run Marlin's heavy duty inner seals.

[OOPS]

Here is a link to a much simpler tool for centering the knuckle if you have access to a lathe. The factory SST can be a bear to work with.

http://www.pirate4x4.com/forum/showthread.php?t=734345


All of you that say 1 thick 1 thin shims on the bottom is not always true. The bottom shims are how the knuckle is centered but not all knuckles measure the same from flat to flat. I have six different knuckles laying around and not one of them measure the same flat to flat. One of the best things that you can get for the front end is Marlins "Super Seals". They are made so in case your knuckle is not complety centered they will still seal.

why do i feel like i'm talking to a wall

  Not nice!!!!!!!

[ntsqd [OP]]

Prior to buying the SST I built something like that without knowing anything about the POoR thread. It falls short because of the camber that is machined into the OE knuckle castings (no idea about the aftermarket knuckle shown), but it is what I'm using for a relative reference.

I mentioned in my first post that I have Marlin's seals. (They're installed now, my deadline isn't giving me much time to sort things out.) I just don't want to rely on them too much. If the knuckles are centered, or at least fairly close, then the seals have a much less tough job to do and will last longer.

I need to look at it again. I'm saying that it's low and I'm saying that adding shims won't help. That doesn't make sense sitting here at work, but it made sense when I was working on it. Whether my head's on straight or not, the FSM procedure resulted in a negative number in this case, and it makes no mention of that possibility. At 0.04" and assuming that shimming it does work then one thick shim on the bottom should make it all good.

[79coyotefrg]

     ntsqd, I apologize,  what you were trying to do didnt get thru to me and I was, well, in a word, RUDE.   I  must say ive learned 2 things today. 
1. when you're convinced you know the right answer, you never do.

2.  the old saying "you learn something new everyday"   applies here.  Thanks OOPS, that link is very informative.  I was under the impression as long as the shim thickness was the same (or at least close) that the knuckle was centered   

[79coyotefrg]

you said you were going through trunion bearings every three years??  may i ask what size tires your running and where do you wheel??  that seems like alot of trunion bearing rebuilding

[ntsqd [OP]]

No worries!

33-10.50's & I chase desert racers with the truck. It's not all that I do with it, but most of my off road driving is similar to chasing. I know, I really should have an IFS truck for that use, but Patch is what I have, so I chase with a locked up, live axle truck. There have been 2 times that I can recall where what I did to the truck didn't matter - I HAD to get there! Both were rolls and comms were bad enough that we didn't know their condition. That kind of driving is pretty hard things like the trunnion bearings.
Unfortunately no time to look into it further tonight.

[NATER623]

Props for taking the time to to do it right.  I slapped mine together and it leaks bad.  double check that your bearing races are fully seated.  re-measure and make sure youre adding or subtracting shims in the right direction.  If you cant remove any more shims check that trunion cap for wear where the bearing sits, it could be worn from a seized bearing slipping.  measure that cap and compare it to the one from the other side that set up correctly.  If you suspect a bent housing look closely in the skinny area between the ball and the weld at the end of the tube.

[hilux-1983]

Aint that cute,   

[ntsqd [OP]]

I think that I've corrected my rectal-cranial incursion. The SST/FSM's resulting number is how low the knuckle is sitting. NOT the shim thickness required. It is mostly semantics, but it is important to my way of thinking. A negative number means that the knuckle is low. A positive number would be mean that the knuckle was high. With no shims installed it would be really hard to deal with a positive result. A negative result is easily corrected by adding shim(s) (adding a positive to a negative moves it closer to Zero, right?). I've had to modify my own checking tool (POoR link above) to work with the seal installed. I hope to be able to check the DS tonight. If my (new) thinking is correct, one of the thickest shims moved from the top to the bottom should put the knuckle within 0.001"-0.002" of being on center.

[ntsqd [OP]]

I thought that I'd show a picture of the tool that I made prior to learning about the Camber issue. With some thought the tool may still have some uses for checking, but maybe not for setting the centering of the knuckles.



The large OD step on the aluminum piece fits the seal bore tightly. If I were going to make it again I would include a bigger third diameter flange that would sit on the face where the seal's flange stops. The smallest diameter fits into the bore of the seal itself so that checking can happen with the seals installed. I used the same diameter as the seal installation tool that Marlin sells for this feature. The small diameter on the piece of Plexiglas fits into the spindle locating bore on the knuckle. The bolt through the plexi is necessary to keep the thinness of the plexi from allowing it to wobble on the tube.


The small tool on the lower left is for pushing the caps out of the bearings. Sure beats any other method that I've used. It is just a piece of 1/2-13 B7 All-thread inside a piece of bar stock bored to accept it. Had 1/2-20 been laying around I'd have preferred to use that. The SHCS in the slot is threaded into the side of the all-thread and keeps the all-thread from spinning inside of the bar stock. One of my caps was tight enough to need some channel-locks to hold the bar stock and keep it from spinning. I contemplated adding some sort of threaded-on handle, but getting the tool inside of the knuckle can be a bit of a challenge so I decided that channel-locks method was fine.