What's up studs?

Jody Treadway

Jody Treadway

Croc wearing fool
Moderator
Joined
Mar 20, 2005
Location
Hendersonville, NC
Looking for some feedback from some of the more learned, book smart, ahem nerds on here.

Recently performed a pretty major overhaul on @thebrotherinlaw's XJ. Part of the rebuild was correcting the front driveline angle. Previously, the Dana 300 transfer case was clocked flat, which resulted in a super steep front driveline angle. It was clocked flat using a standard 7/8" thick clocking ring.
To get a better angle, I clocked it down quite a bit. In doing so, the holes that gave the best driveline angle was the ones intended to bolt the ring to the case. The threaded holes on either side of the retaining hole made the angles either too high or too low.
So I simply slid the clocking ring over the new longer studs my BIL picked up, bolted it up and rocked out.

This happened 2 wheeling trips later.
studs.jpg


The studs he picked up were not graded appropriately. They weren't even a grade 5. Notice no shoulder and the internal color of the stud looks to me like they aren't intended for use in this application.

So, I picked up some Grade 8 shouldered studs, 3" long (FWIW) replaced the broken ones and all seems to be fine. But I am wanting opinions on WHY the studs broke. Crap studs or because the ring isn't bolted to the case and has created a stress point.

Seeing the studs broken flush with the case makes me wonder if the ring MUST be bolted to the base and then studs untilized to secure it to the transmission. I can't see that being the case. But I'm no expert. When this happened on the trail, extraction was somewhat easy, but had we been on a trail far away from camp, it would be a bad situation.

Cliffs: Were the orginal studs just garbage and I'm overthinking it.
Do I need to pull the case, AGAIN, and machine the hole that the studs slide through for a nut that will secure it to the case and allow the remaining threads to pass through the transmission.

@Fabrik8 @shawn @jeepinmatt @Mac5005 @anyothernerdswhomayknow

EDIT: I will likely install a support ring on the rear output anyway
 
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Got a close-up of the shear plane (broke off spot)?
 
in my unedumacated opinion something wasnt clamped appropriately and applied torsional force.
I cant tell you why hat happened as Im not familiar with the intended installation
 
Probably had something to do with the ring not being bolted to anything. It sorta lets everything work around. Couldn't you just take the clocking ring out if it's not being used?

I've seen similar things happen between uni-mount dual tire setups where they had something between them, worked loose, and exited stage left. I also have studs of an unknown grade holding the 205 to the NV4500 in my K30, no clocking ring or anything between them, but have broken an axle and the rear Detroit locker. The transfer case is still happily nestled in its proper place though. That joker can put out some torque too.
 
Ron said:
in my unedumacated opinion something wasnt clamped appropriately and applied torsional force.
I cant tell you why hat happened as Im not familiar with the intended installation
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This or they were weak studs that could not handle the shear load. Maybe both?
 
I would say without the studs bolted into the clocking ring, you created a longer section of the stud that is under tension, but not engaged with threads, which likely resulted in additional necking of the stud at the point of engagement in the transfer case. A higher grade of stud will reduce necking, but it will not eliminate the stress risers created by the unsupported loading.
 
There is no specific reason that the ring can't just have the studs passed through it, assuming that everything is piloted properly so there is no relative motion (that includes the ID of the ring or whatever onto the transfer case, which it looks like there is). What you have done is no different than adding a thin wheel spacer onto lug studs, so there is no problem as long as you haven't eliminated features that make the wheel hub-centric, etc., and that proper clamp load is maintained. This is obviously not the same as a thick wheel spacer, where you can then run into problems with relative motion.
I don't know the diameter of the ring, but I would imagine that it's large enough that a 7/8 thickness isn't going to be any problem.

It would be good to have studs with a proper grip length (unthreaded length) to pick up that area in the clocking ring. BUT, a quick Google search shows much of the clocking rings on the market use fully threaded studs so this is likely not the issue.

Based on what you said about the stud quality, I would say you yielded the studs, which then lost clamp load and then either failed in fatigue or sheared (a relative motion problem either way). If you used the normal torque value for those studs, that probably killed them right off the bat because the tensile strength was too low for that torque value.

It's possible that the proper studs would work perfectly fine.
 
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I'd bet the studs yielded like @Fabrik8 said and then you lost you clamping load and sheared the studs. If you can't free hand spin a good nut down the remnants of the old studs then they stretched and that was the initial cause of the failure.
 
shawn said:
What @Fabrik8 said.

This sounds familiar. Did you and I talk about it once before?
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We did. As did @jeepinmatt and I. @thebrotherinlaw and I were discussing an upcoming trip and the subject came back up. Figured I would try to get some more "likes" on here with a witty reply to a rhetorical question.
 
I would love to see the failed end of at least one of those studs, that should solve the "shear or fatigue" mystery as the last failure mode. The root cause is most likely the low tensile studs though.
 
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You need Studnuts. Where did that guy go?
 
Exaggerate the thickness of the spacer and think about it more. What if the spacer was 6” or 12” instead of 7/8”. Assuming clamp force is maintained between the two and you used the same spec stud, would your opinion of the spacer and pass thru studs change if the spacer is 6” or 12” instead of 7/8”?

Any time you have a spacer like that in a torque application, it over stresses the studs. Clamp force remains the same but its now divided between two surfaces instead of one like it’s originally designed. The torque is going to cause the transfer case to want to rotate around the input centerline. Any longer stud and spacer is going to exaggerate the shear loads on the studs and you’ll continue to have issues.


I’d find a way to install additional studs. Or, is there a way to key the spacer or add in some pins similar to a bellhousing on an engine?
 
The broken studs are not shiny, so it would not be fatigue loading. My guess is the studs are low quality steel and simply failed from being overloaded. There is a huge range of yield strength within hardware from something like a grade 2 to a grade 8.
 
rockcity said:
Exaggerate the thickness of the spacer and think about it more. What if the spacer was 6” or 12” instead of 7/8”. Assuming clamp force is maintained between the two and you used the same spec stud, would your opinion of the spacer and pass thru studs change if the spacer is 6” or 12” instead of 7/8”?

Any time you have a spacer like that in a torque application, it over stresses the studs. Clamp force remains the same but its now divided between two surfaces instead of one like it’s originally designed. The torque is going to cause the transfer case to want to rotate around the input centerline. Any longer stud and spacer is going to exaggerate the shear loads on the studs and you’ll continue to have issues.
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Not true. You are adding additional force due to moment/bending from the weight, but still relying on clamping force and friction to handle the torsional load (ignoring the torsional deflection within the 7/8" or 12" spacer, which is negligible). The clamp force is the same, and is equal whether it is 1 surface or 100 surfaces. With your 12" spacer example, there would be additional tension on the upper studs to counter the added leverage from the weight it is supporting, which could then result in decreased clamping force, and decreased friction, thereby allowing slippage/shear, but this is unrelated to the number of shear planes or length of stud, and fairly irrelevant in this application because 1 stud is more than enough to support the weight.

Bottom line, don't buy cheap studs, and don't overtorque them.
 
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drkelly said:
The broken studs are not shiny, so it would not be fatigue loading.
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Shiny is not a good indicator of fatigue failure, because it depends on the speed and size of a fatigue area, and also depends on the alloy. In the cases where that may be true, the shinier surface would be at the area of propagation, not the rest of the cross section that failed as a brittle fracture because of it.

That picture is not nearly high-res enough to say if it's fatigue or not, and I certainly wouldn't rule something out based on "shiny".
 
rockcity said:
Clamp force remains the same but its now divided between two surfaces instead of one like it’s originally designed.
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Where did you come up with that theory.....?

One of the fundamental bolted joint equations to calculate shear bolt shear force in a friction connection is basically:
(coeff of friction) X (number of slip planes) X (a constant depending on the hole type) X (axial bolt tension)

Notice that the number of slip planes is a multiplier, not a divisor. You're saying it's a divisor.
 
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Get a room nerds! Oh wait this is the room. Please excuse me!
 
Fabrik8 said:
Where did you come up with that theory.....?
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With one single sets of studs, you have 2 friction surfaces (both sides of the spacer) to overcome with one set of studs. With studs on both sides, each set of studs is responsible for just one surface of the spacer.

Imagine having 6” of spacer made up of a bunch of .010” shims and just one set of long studs. You really think that would be the same? Of course not. The studs would shear off pretty quickly.


Long studs and spacers simply don’t work like the correct studs would. They are just fine for clamping force but poor when they get torque applied to them. You’ll likely continue to have issues.
 
rockcity said:
With one single sets of studs, you have 2 friction surfaces (both sides of the spacer) to overcome with one set of studs. With studs on both sides, each set of studs is responsible for just one surface of the spacer.
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You're trying to argue that a double shear friction joint is a bad way to do things. Think about that for a while.

If your studs are properly tensioned, your joint doesn't slip, and you don't have a relative motion problem either way. It's not really an issue with a spacer that thin. The only reason for studs on both sides with a spacer that thin is to actually perform the adjustable clocking. It's just not necessary otherwise.
With studs on both sides, you're still going to fail the joint if the studs are not adequate strength or are not tensioned properly. If you have too much compliance or relative motion, you're going to have problems no matter what.
 
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Your wheels are single shear studs. What’s the point? Each type works effectively.


Similar idea... driveshaft spacers. If you believe in your theory, you should have a neutral stance on driveshaft spacers since essentially it’s the same with regards to torque (forget about the physical weight the transfer case studs carry).

Personally, I wouldnt run a driveshaft spacer; I’d have a proper driveshaft made. And, I wouldn’t run long studs on that spacer on a D300 either. But, I do shit differently than most, not that either way is right or wrong, just preference.
 
rockcity said:
Similar idea... driveshaft spacers. If you believe in your theory, you should have a neutral stance on driveshaft spacers since essentially it’s the same with regards to torque
Click to expand...

Eccentricity would be my first concern there. Hard to get the whole thing centered.
 
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