Torque value for seating new hub studs? (1 Viewer)

[gummycarbs]

Anyone know the correct torque value to use when installing new hub studs?

The cone washers and nuts are listed as 26 ft-lbs, but what about the studs themselves?

I searched 'mud and turned up a lot of discussion of the nut torque value, and some other big studs (I'm omitting the name so this doesn't turn up in search results), but not for the hub studs themselves.

 

[bajaphile]

Stud torque is a weird thing. You should just get the stud essentially "snug". I've seen values in the 10 ft lbs range. Generally the torque of a bolt is dependent on the shaft diameter, as it puts the bolt in tension for clamping force. The stud on the other hand, when torqued without the nut, is putting those forces directly into the threads. Too much torque when installing the stud will just cause damage to the threads.

Looked through ASME standards as well as talking to several guys at work in the standards department and there really isn't torque values for studs when installing them. The final torque value applied by the installation of the nut is identical to the same diameter bolt in most cases.

 

[Tools R Us]

Snug until firm, done.

 

[LandCruisinMy93]

Never seen torque value for the stud itself on anything @gummycarbs , but if you want a torque value find the torque value for a standard fastener of equivalent grade and install it as if it were a bolt or screw. I don't recall that stud size but believe it to be M8x1.25 which is a 10 lb-ft fastener.

 

[baldilocks]

If it mattered there would be a value specified in the manual.

 

[inkpot]

If you torque them in really tight, and maybe even LockTight them, then you will have lots of entertainment trying to remove them when they are broken/damaged!

 

[gummycarbs]

Okay, thanks everyone. I'm definitely not going to Loctite them, but I thought I saw it mentioned that not torquing the stud itself properly could lead to it backing out or contribute to shearing. I may have misunderstood, though.

 

[baldilocks]

When I did my HG I used ARP studs. They did not bottom out in the block. I called ARP for clarification and as it turns out it matters not if the stud bottoms out. The main concern is having thread engagement of about 1.5xstud dia. Most of the stress and, therefor, clamping force is in the first several threads.

But definitely don’t torque them in. This can “mislocate thread stresses increasing the possibility of failure”.

Stud Installation (Tap-End Studs) - Pile Hammer Equipment

 

[Malleus]

The reason there's no specified torque value is that when you sandwich the drive flange between the hub and nut, you create a clamping force. There is a nut torque, which is what's important. The thread engagement in the hub should be at least 1.5 times the thread diameter, but not more than 2x (more doesn't hurt, it's just unnecessary).

This situation is unusual; you'd usually place the drive flange against the hub and install a hex head screw (which would have the same torque requirement as the nut currently does), which creates the clamping force. The designers were trying to eliminate a couple of extra parts by using studs here. They also, along with the cone washers, serve to center the hub, once everything's tightened down.

 

[tominboise]

Why not replace the stud with a bolt and the cone washers?

 

[Malleus]

Mechanically, there's no reason not to. My personal design experience, in several industries which have extreme service/maintenance requirements (such as ag/ind/railroad) specify that when critical components (such as the drive flange here) are attached, inspection provisions must be made in the design.

If you had a hex head screw, you'd never know if it backed out (or was backing out) during service. Yes, you could mark it, but the mark might come off. The stud/nut combination allows for immediate visual inspection of the thread engagement. For example, railroad policy is that all exposed threaded connections must have at least two full threads exposed when fully engaged (tightened). This allows the inspector to see whether or not a connection is solid (without the need for a torque wrench, which wouldn't work well anyway, due to static/dynamic friction variation).

I'm not saying that this is why Mr. T designed the drive flange connection this way, but it's a standard practice in heavy industry.

 

[Malleus]

A little axle pron to go along with the explanation above,

As you can see, the hub to disc connection uses a hex head screw, but the drive flange to hub connection uses studs, nuts and cone washers. Mechanically, there's no difference between the hub and flange connections, from a risk/failure point of view.

The drive flange supports am internal torque load, from the driveshaft. The hub, through the wheels, supports an external torque load, during braking and on starting forward motion. I'd argue (without providing the mathematical analysis, but purely from inspection), that the wheel load torque is the greater of the two (due to the longer lever).

So, with all that in mind, the hex head screws are doing more than the studs. If you wanted to make the argument that you could replace the studs with screws, that'd be it.

 

[JeepinPete]

Can't agree with this explanation. The main reason being the stud is not rotating during tightening of the fastener system. As the cone washer is compressed into its tapered bore, it will constrict around the stud/bolt. If you are using a bolt, this constriction will increase the torque required to achieve the same stretch in the fastener.

It may be possible to end up with the same result, but the torque spec from Toyota is no longer relevant if you substitute a bolt in place of the stud.

 

[Gabriel 71]

Malleus if a person were to replace the studs in the drive flange with bolts would you still use the cone washers. As I need to replace the dowel pins in my hub now from loose studs. I assume a correct sized shouldered bolt would need to be sourced

 

[BILT4ME]

Mechanically, there's no reason not to. My personal design experience, in several industries which have extreme service/maintenance requirements (such as ag/ind/railroad) specify that when critical components (such as the drive flange here) are attached, inspection provisions must be made in the design.

If you had a hex head screw, you'd never know if it backed out (or was backing out) during service. Yes, you could mark it, but the mark might come off. The stud/nut combination allows for immediate visual inspection of the thread engagement. For example, railroad policy is that all exposed threaded connections must have at least two full threads exposed when fully engaged (tightened). This allows the inspector to see whether or not a connection is solid (without the need for a torque wrench, which wouldn't work well anyway, due to static/dynamic friction variation).

I'm not saying that this is why Mr. T designed the drive flange connection this way, but it's a standard practice in heavy industry.

Now, I'm not an Engineer, I don't play one on TV, and I didn't sleep at a Holiday Inn Express last night.
Using a stud, cone washer, flat washer and nut has MORE parts in it than a Hex head cap screw, cone washer, and flat washer. (4 vs 3)

If the idea is to see if it is backing off by the thread count, what happens if the STUD is backing out of the threaded hole, rather than the NUT backing off the stud? If the stud backs out, then it is no different than a hex head cap screw.

If you have the reason that a stud typically has COARSE threads on the INTERNALLY threaded part and FINE threads on the EXTERIOR part for the nut, I'd really like to know why.

 

[Malleus]

Can't agree with this explanation. The main reason being the stud is not rotating during tightening of the fastener system. As the cone washer is compressed into its tapered bore, it will constrict around the stud/bolt. If you are using a bolt, this constriction will increase the torque required to achieve the same stretch in the fastener.

It may be possible to end up with the same result, but the torque spec from Toyota is no longer relevant if you substitute a bolt in place of the stud.

Sorry, but I disagree. First, your assumption that torque stretches the bolt, in this case, is incorrect. The torque applied in this case isn't sufficient to do that. Maybe deform the threads, but that's what happens anytime you tighten a bolt. Second, if the cone washer clamps the threads, you have a problem. The bore in the cone washer is a clearance fit for the thread diameter. Third, clamping the fastener OD will not result in greater torque, since the cone washer OD is free to turn. If the OD taper was less than 1.5° per side, it would be a locking taper, and then your argument might hold water.

 

[Malleus]

Malleus if a person were to replace the studs in the drive flange with bolts would you still use the cone washers. As I need to replace the dowel pins in my hub now from loose studs. I assume a correct sized shouldered bolt would need to be sourced

Yes, but that's not to say that I'm recommending this. I was simply answering a question about whether or not it was possible.

I'm not sure what you're referring to when you say "shouldered bolts". A shoulder bolt is a special bolt designed to effectively have a dowel pin between its head and thread. The cheapest ones are pushmower axles. Being bolts, they require nuts and usually have hex heads.

A shoulder screw is a form of socket head cap screw, which is typically used in machine construction.

 

[Malleus]

Now, I'm not an Engineer, I don't play one on TV, and I didn't sleep at a Holiday Inn Express last night.
Using a stud, cone washer, flat washer and nut has MORE parts in it than a Hex head cap screw, cone washer, and flat washer. (4 vs 3)

If the idea is to see if it is backing off by the thread count, what happens if the STUD is backing out of the threaded hole, rather than the NUT backing off the stud? If the stud backs out, then it is no different than a hex head cap screw.

If you have the reason that a stud typically has COARSE threads on the INTERNALLY threaded part and FINE threads on the EXTERIOR part for the nut, I'd really like to know why.

Well, I am an engineer, and I have absolutely no idea why Mr. T did what he did. All I meant to do was shed a little light on the subject, using a little informed guessing, based on my experience.

I didn't mean to compare replacing the stud with a hex head screw. I just mentioned both designs in the same post.

Yes, you're absolutely right, if the stud backs out, you'd never know it, until it fell out.

In reference to your stud question, do you have a L/C part in mind, or were you just speaking generally? If it's generally, the answer is that the internal threads are there for use in removing the stud (they're bigger in cross section and can support a greater load). The external threads are, usually, fine because the studs are used to axially locate something, and fine threads allow for a better/easier/more controllable adjustment.

 

[BILT4ME]

Well, I am an engineer, and I have absolutely no idea why Mr. T did what he did. All I meant to do was shed a little light on the subject, using a little informed guessing, based on my experience.

I didn't mean to compare replacing the stud with a hex head screw. I just mentioned both designs in the same post.

Yes, you're absolutely right, if the stud backs out, you'd never know it, until it fell out.

In reference to your stud question, do you have a L/C part in mind, or were you just speaking generally? If it's generally, the answer is that the internal threads are there for use in removing the stud (they're bigger in cross section and can support a greater load). The external threads are, usually, fine because the studs are used to axially locate something, and fine threads allow for a better/easier/more controllable adjustment.

I am speaking generally. I would have thought that the fine threads would hold more load because there is more surface area.
Does it have more to do with the shear of the root of the thread rather than the surface area?

I see a similar application on the LC's with the flanged drive studs as well as the knuckle studs on the bottom steering arm. There are no "torque values" stated anywhere for the studs themselves, yet there are also no "minimum insertion" specifications.
Do you screw in the stud until it stops, or just before it stops, or in until it stops then back it out two turns? I truly want an answer for this, as it has bugged me for years. I cannot seem to locate any reference info in the Machinery's Handbook.

In the application of the knuckle studs, I'm pretty sure that the thickness of the knuckle ball is NOT equal to or greater than 1.5X the diameter of the stud being installed.

I DO get the difference in rotation during tightening that studs with nuts are typically more accurate and less prone to working loose because it is a more linear pull rather than a rotational torque that can be varied based on thread lubrication, interferences, as well as many other factors.

Thanks for your replies.

 

[Malleus]

I am speaking generally. I would have thought that the fine threads would hold more load because there is more surface area.
Does it have more to do with the shear of the root of the thread rather than the surface area?

I see a similar application on the LC's with the flanged drive studs as well as the knuckle studs on the bottom steering arm. There are no "torque values" stated anywhere for the studs themselves, yet there are also no "minimum insertion" specifications.
Do you screw in the stud until it stops, or just before it stops, or in until it stops then back it out two turns? I truly want an answer for this, as it has bugged me for years. I cannot seem to locate any reference info in the Machinery's Handbook.

In the application of the knuckle studs, I'm pretty sure that the thickness of the knuckle ball is NOT equal to or greater than 1.5X the diameter of the stud being installed.

I DO get the difference in rotation during tightening that studs with nuts are typically more accurate and less prone to working loose because it is a more linear pull rather than a rotational torque that can be varied based on thread lubrication, interferences, as well as many other factors.

Thanks for your replies.

OK, just so I don't get lost here:

1. Yes, you're right on target. The crossectional area (the thread root thickness x length) is the determining factor in the strength of the thread. The design rule of thumb is that you cannot expect more than two fully engaged threads, due to tolerance stack up and machining variance. I'm not saying there won't be more, just that engineers are taught not the use more than two in their calculations. This is also why nuts are so thin; you'll never get more than two threads in a nut on a bolt. The general design rule of thumb for threaded hole depth is 1.5x the thread diameter. This is to make sure that there are threads available when the torque reaches the design clamping load equivalent.

The thread engagement is across the face of the thread, which is the other reason that coarse threads are used for clamping designs; there is more surface area there and friction is the glue that makes machine designs work.

2. There isn't any guidance on this, that I've found documented. My assumption is that the first guys to adopt this design, which has been followed by rote for decades, weren't worried about it, so they never made their feelings known. It's possible that they just assumed that if the correct assembly practices were followed, everything would work out right. This was a fairly common design philosophy in automotive manufacture, prior to 1960 or so. Dr. Demmings (the saviour of Japan) is responsible for "correcting" this approach. His philosophy was based on efficiency (low cost) and effectiveness (high quality). To provide some level of surety of the second, he helped mandate that every process step had to be made (designed) to be foolproof. This practice has been slowly creeping into daily life everywhere since then.

For the record, I hate it. As Eric Bana said, pointing at his head, "This is my safety". (great movie; the real story is even better)

3. You lost me there.

4. That (as I understand it) is the reason for the cone washer. You don't generally see these anymore; they've largely been replaced by split (lock) washers or Belleville washers when additional clamping force is necessary. They're not better, they're just cheaper to make.

HTH