Knuckle Centering using SST - Shim thickness question (1 Viewer)

[jackbrad]

I went through an exercise like this and actually got negative shim values.. and it was the brass bushings. After replacement I saw expectations inline with ideas and documentation. I've done this 3 times, others have surely done it many more than me but, now I recommend replacing the bushings. It seems wise to replace the brass bushings for no more work and cost and considering they will effect the maintenance down the road.

 

[reddingcruiser]

This is certainly a lively discussion, but I respectfully disagree with the concept of removing shim from the top AND bottom to adjust the preload. Removing shims from the BOTTOM of a correctly 'centered' knuckle effectively raises the centerline of the spindle in relation to the centerline of the axle housing. The bottom bearing is essentially always 'loaded' by the weight of the vehicle and this measurement will remain static, except for the play created by wear and tear on the bearings.

 

[RWBeringer4x4]

I went through an exercise like this and actually got negative shim values.. and it was the brass bushings. After replacement I saw expectations inline with ideas and documentation. I've done this 3 times, others have surely done it many more than me but, now I recommend replacing the bushings. It seems wise to replace the brass bushings for no more work and cost and considering they will effect the maintenance down the road.

I'm not sure how/why this would be that huge an issue. The scriber, installed, had no apparent play. It installed easily (It basically just slid in/out) but the wasn't any apparent "play" in the system once installed. I know we are discussing fractions of millimeters here (which is why I posed the question in the first place) but I'm not sure the brass bushings are the culprit in my case - they are in pretty good shape...

This is certainly a lively discussion, but I respectfully disagree with the concept of removing shim from the top AND bottom to adjust the preload. Removing shims from the BOTTOM of a correctly 'centered' knuckle effectively raises the centerline of the spindle in relation to the centerline of the axle housing. The bottom bearing is essentially always 'loaded' by the weight of the vehicle and this measurement will remain static, except for the play created by wear and tear on the bearings.

@reddingcruiser - as usual, thanks for chiming in! I can kind of see both sides of the argument here. I can see how the bottom bearing would remain loaded, regardless of shimming, but I can also see the logic in removing equal shims from top and bottom to maintain the "centered" nature of the axle. Wouldn't just removing a bottom shim change the centering of the axle? Is this insignificant compared to getting proper preload?

While I have you attention - what do you think of the measurements? In your experience, is having shims stacked this high, top and bottom, unheard of, or par for the course?

 

[watrob]

You must always remove equal amounts of shims from the top & bottom as the axles must be centred in the middle of the spindle at all times, that is what this SST is supposed to do. If the preload is to light remove a thin shim from the top and bottom and re-torque the nuts to spec, re-test preload or if preload is to high add a thin shim to top & bottom. Do not remove or add one shim only!!

Build the axle with shim spec you have now and visually check how the axles sits in the spindle, this will give you a some idea how your shim calculations went.

Its easy to check the play in the brass bushes, you should have checked them when you had the CV in your hand, you could slid the CV into the spindle housing to see if there was any play in the bush, also are you using new or second hand CV's? as there could be wear on the CV if they are a cheap China knockoff?

 

[RWBeringer4x4]

You must always remove equal amounts of shims from the top & bottom as the axles must be centred in the middle of the spindle at all times, that is what this SST is supposed to do. If the preload is to light remove a thin shim from the top and bottom and re-torque the nuts to spec, re-test preload or if preload is to high add a thin shim to top & bottom. Do not remove or add one shim only!!

Sounds like a stand-off! I can definitely see your logic in terms of keeping the knuckle centered...

Its easy to check the play in the brass bushes, you should have checked them when you had the CV in your hand, you could slid the CV into the spindle housing to see if there was any play in the bush, also are you using new or second hand CV's? as there could be wear on the CV if they are a cheap China knockoff?

I'm using stock (second hand) Toyota Birfields. I believe the guy I bought them from said they were out of an 81 FJ40 (so large pattern, fine spline, but with the proper inner axle splines as well. They look to be in solid shape, no visible/abnormal wear.

 

[watrob]

"I'm using stock (second hand) Toyota Birfields. I believe the guy I bought them from said they were out of an 81 FJ40 (so large pattern, fine spline, but with the proper inner axle splines as well. They look to be in solid shape, no visible/abnormal wear."

Ok, you have second hand birfs out of a 81 FJ40, 33 years old, I would buy new CV's there cheap.
So:-
1. The brass bushing are probably just as old. So you will have some wear in the brass bushes.
2. Some wear on shaft of the CV.
3. Some wear in the ball race of the CV.
4. Plus wear in your manual locking hubs as well.

In six months your hubs will probably start leaking and you will kicking yourself for not spending that extra $100. It will not matter how good the calculations are you did with the SST, if those 4 components have wear, remembering they are over 30 years old, there could be 1mm to 2mm of play which will damage that new inner oil seal?

 

[RWBeringer4x4]

Ok, so, as I feared, I have WAY too many shims. Assembled the knuckles today, greased the bearings, the knuckle balls, etc. I torqued the trunnion cap/steering arms to 70ft-lbs of torque: Note - no lock washers/cone washers were used - I don't suspect this would affect preload. On both sides, I'm getting about 1/2lb of preload one the fish scale, when pulling from the steering arm.

At this point - is it safe to assume my shim meauserments (and thereby, knuckle centering measurements) are complete junk? I also (stupidly) installed my Marlin inner axle seals today, so a third attempt with the SST is highly undesirable at this point as it would mean destroying two perfectly good seals.

As such, I really need to readdress this argument between @reddingcruiser and @watrob - Do I exclusively pull shims from the top, per reddingcruiser, or from both sides, per Watrob - I guess I'll dig around and see if there's any further common wisdom here. Any idea how significantly I need to alter the shims to get the preload from about 0.5lb to the factory specification of 4.0-8.0lbs?

@Stumpalama - any experience here?

 

[watrob]

Ok, regardless of whether your shim calculations are correct, how did you axle look protruding thru the spindle? you can check by the gap around the axle shaft to the spindle edge? I know mechanics whom adjust the shims this way, but at least it gives a visual view.

And the FSM states if you remove shims they must be equally removed from top & bottom other wise the axle is not centred in the middle of the spindle, if the visual check gives you an indication the axles is centre then remove an equal shim from the top & bottom and re test your pre-load.

PS. Grease you felts before you put the knuckle together, or the first thing the felts will do will absorb water & become a sponge.

Also can currently tell me what thickness of shims are on the bottom and top?

 

[RWBeringer4x4]

Ok, regardless of whether your shim calculations are correct, how did you axle look protruding thru the spindle? you can check by the gap around the axle shaft to the spindle edge? I know mechanics whom adjust the shims this way, but at least it gives a visual view.

And the FSM states if you remove shims they must be equally removed from top & bottom other wise the axle is not centred in the middle of the spindle, if the visual check gives you an indication the axles is centre then remove an equal shim from the top & bottom and re test your pre-load.

PS. Grease you felts before you put the knuckle together, or the first thing the felts will do will absorb water & become a sponge.

Also can currently tell me what thickness of shims are on the bottom and top?

I haven't installed the axles yet - so the short answer is "I don't know." I will plan on checking that, however. With the differential out of the housing, there's nothing to support the axle, anyway. Once I get the diff dialed back in and installed, the axles/spindles will go on.

I don't see anywhere in the FSM that says to add/remove shims evenly from top and bottom. It also doesn't say to remove shims from only the top. Seems like common wisdom swings both ways on this subject. I'll let the orientation of the axle in the spindle tell me what it needs.

I will definitely grease the felts.

The shim thickness is what I mentioned previously in this post (the second set of measurements). I'll repost them here:

Short Side Measurement Set #2:
A: 167.7mm between flats on knuckle centering tool
B: 165.00mm between flats on knuckle housing
C: 167.7-165 = 2.7mm TOTAL SHIM THICKNESS
D: 4.04mm between score marks on the SST
E: 4.04-3 = 1.04mm BOTTOM SHIM THICKNESS
F: 2.7-1.04 = 1.66mm TOP SHIM THICKNESS

Long Side Measurement Set #2
A: 167.62mm between flats on knuckle centering tool
B: 165.06mm between flats on knuckle housing
C: 167.2-165.06 = 2.56mm TOTAL SHIM THICKNESS
D: 4.17mm between score marks on the SST
E: 4.17-3 = 1.17mm BOTTOM SHIM THICKNESS
F: 2.56-1.17 = 1.39 TOM SHIM THICKNESS

Definitely seemed way too thick at the time, confirmed by the low preload setting.

 

[watrob]

Your bottom shims seem to be your problem in my opinion but you have measured it twice now, so you have trust your own judgement. Put your diff in & axles with birfs, bolt your spindle on with 3 bolts and have a look how the axle sit in the spindle. If it looks centred remove 0.38mm - 0.40mm of shims from the top and bottom of the knuckle and re-test pre-load.

Also don't pack your knuckle with that red BEARING grease, use a Molybdenum disulphide lithium base grease for knuckles and use your red high temperature grease for the bearings.

 

[B y r o n]

Have you tried re-taking the measurements with the SST oriented the same direction in both pieces as watrob pointed out?

 

[RWBeringer4x4]

Your bottom shims seem to be your problem in my opinion but you have measured it twice now, so you have trust your own judgement. Put your diff in & axles with birfs, bolt your spindle on with 3 bolts and have a look how the axle sit in the spindle. If it looks centred remove 0.38mm - 0.40mm of shims from the top and bottom of the knuckle and re-test pre-load.

Also don't pack your knuckle with that red BEARING grease, use a Molybdenum disulphide lithium base grease for knuckles and use your red high temperature grease for the bearings.

Out of curiosity - why do you think it's the bottom shims? I'm not really sure how the measurements could have come out *that* wrong - I followed the FSM to the tee with the SST...Then again, I measured it twice, and got very different numbers each time, so who knows...

I have a whole bunch of tubes of Moly Grease on standby for the knuckles, I did read up on this A LITTLE before I dove in...

 

[RWBeringer4x4]

Have you tried re-taking the measurements with the SST oriented the same direction in both pieces as wartrob pointed out?

Yep - there's 2 sets of measurements back on the first page of this post. The second set I trust more. Everything was torqued to FSM specs (if not a little tighter, per Watrob's recommendations). I made doubly sure the orientation of the tool in both the housing and the knuckle.

 

[watrob]

I have read so many knuckle rebuild threads and the ones I have read have had less shim thickness on the bottom than the top. And I have pulled many knuckles apart where owners have thought that the top and bottom shims should be equal.

My average has been around 0.45mm to 0.65mm bottom and 0.90mm to 0.125mm top, always found re-shimming to tighten pre-load at a service inspection where the knuckle bearings are ok but the knuckle needs a little tightening up, always results in the lower end of my shim thickness I just mentioned. Also I like a heavier preload of 11lbs to 13lbs as I run larger wheels and tyres.

 

[subzali]

I forget all the specific steps when using the SST, but for reference my measurements for shim pack thickness were between 1.02 mm and 1.27 mm for both top and bottom, so your top shim pack thicknesses seem high to me, verified by your preload setting. If it were me I would remove top shims until the preload came into spec.

If you are really going to be concerned about it then I would pull the Marlin seals and keep repeating the measurements until you can get some repeatability, and then you'll know for certain what's going on. Remember though that there are only 0.2mm and 0.5mm shims, so the thickness is an approximation anyway.

 

[RWBeringer4x4]

I forget all the specific steps when using the SST, but for reference my measurements for shim pack thickness were between 1.02 mm and 1.27 mm for both top and bottom, so your top shim pack thicknesses seem high to me, verified by your preload setting. If it were me I would remove top shims until the preload came into spec.

If you are really going to be concerned about it then I would pull the Marlin seals and keep repeating the measurements until you can get some repeatability, and then you'll know for certain what's going on. Remember though that there are only 0.2mm and 0.5mm shims, so the thickness is an approximation anyway.

Well, at least my measurements don't seem that far off by comparison. Although if these things were truly "apples to apples" it probably woundn't be necessary add add shims at all!

It's pouring rain all day today, and I'll be back traveling for another couple days, but hopefully I'll get back to this soon, and mess around with the preload some more.

 

[subzali]

Well, at least my measurements don't seem that far off by comparison. Although if these things were truly "apples to apples" it probably woundn't be necessary add add shims at all!

It's pouring rain all day today, and I'll be back traveling for another couple days, but hopefully I'll get back to this soon, and mess around with the preload some more.

So looking up Ricardo's numbers using FJ60 knuckles on an FJ40 axle he had a swing from 0.47mm to 1.9mm required for his various shim locations, so I guess it can be all over the board:
http://risingsun4x4club.org/forum2/showpost.php?p=79800&postcount=39

 

[Stumpalama]

"I'm using stock (second hand) Toyota Birfields. I believe the guy I bought them from said they were out of an 81 FJ40 (so large pattern, fine spline, but with the proper inner axle splines as well. They look to be in solid shape, no visible/abnormal wear."

Ok, you have second hand birfs out of a 81 FJ40, 33 years old, I would buy new CV's there cheap.
So:-
1. The brass bushing are probably just as old. So you will have some wear in the brass bushes.
2. Some wear on shaft of the CV.
3. Some wear in the ball race of the CV.
4. Plus wear in your manual locking hubs as well.

In six months your hubs will probably start leaking and you will kicking yourself for not spending that extra $100. It will not matter how good the calculations are you did with the SST, if those 4 components have wear, remembering they are over 30 years old, there could be 1mm to 2mm of play which will damage that new inner oil seal?

For clarity, The inner axles and birfs are out of an '81 FJ40 (mine). However, the left birf itself is from an '86 FJ60 since the original broke. I'm curious as to why you recommend new birfs? I would argue that these birfs will out last any new manufacture birfs (non-cryo) even if the are 30+ years old (in actual time). In 4wd driving time they probably have 5 years on them... maybe. Remember, the majority of part time 4wd trucks rarely see 4wd for extended periods. I've owned the truck those came out of since 1997 and I can probably count the days the truck was in 4wd. So, My opinion is don't sweat the birfs (How'd they look when you took 'em apart?)

The knuckles and spindles are from a 1989 FJ62 with 150K-ish miles on it, where I'll bet less than 25K of that was in 4wd. The spindles bushings are probably fine too and I wouldn't sweat them either. I just don't see what you base your 1mm-2mm measurement and 6 month prediction on. I think you over estimate the wear factor of these parts.

 

[RWBeringer4x4]

For clarity, The inner axles and birfs are out of an '81 FJ40 (mine). However, the left birf itself is from an '86 FJ60 since the original broke. I'm curious as to why you recommend new birfs? I would argue that these birfs will out last any new manufacture birfs (non-cryo) even if the are 30+ years old (in actual time). In 4wd driving time they probably have 5 years on them... maybe. Remember, the majority of part time 4wd trucks rarely see 4wd for extended periods. I've owned the truck those came out of since 1997 and I can probably count the days the truck was in 4wd. So, My opinion is don't sweat the birfs (How'd they look when you took 'em apart?)

The knuckles and spindles are from a 1989 FJ62 with 150K-ish miles on it, where I'll bet less than 25K of that was in 4wd. The spindles bushings are probably fine too and I wouldn't sweat them either.

As I'd mentioned previously to Watrob, I detected very little (by that I mean none) "play" in the stylus tool when mounted in the spindle. It wasn't a "tight" fit, but it wasn't a loose fit either...Long story short, I agree with you - I think the spindles and bushings are OK to use as-is.

I haven't looked at the actual JOINT/bearings in the birfs because you already packed them with grease. the axles/bell/splines look 100% ok all around. I was under the impression that, since they'd already been pulled out and re-packed, you'd already inspected them. If not, let me know and I'll go in and take a look.

My guess is that they are fine too. Given how often this truck will be in 4WD in the next couple years while I fix what ails it, I'm not overly worried.

 

[Stumpalama]

I repacked the birds when I last did the knuckles in 2008. The truck has less than 5000 miles on it since that time and less than a few 100 in 4wd. As you could see there was no oil leakage and the grease was in great shape. It is up to you if you wish to repack them, though I thought they were fine.