swapping out factory bolts for grade 8 so you can torque them more?
03-23-2019, 09:41 PM
#1
swapping out factory bolts for grade 8 so you can torque them more? something i recently thought of, most the suspension bolts vary from 55 to 68 foot pounds i believe, but when midwest chassis sold me all that stuff they gave me grade 8s with more threads per inch vs the metric stockers. when i asked them what to torque them, they recommended 100 pounds.
so that got me thinking, any real benefit in continuing the trend and replacing some on the front end with grade 8's? my current bolts are in very good shape for age......will that extra clamp really do anything?
so that got me thinking, any real benefit in continuing the trend and replacing some on the front end with grade 8's? my current bolts are in very good shape for age......will that extra clamp really do anything?
03-24-2019, 06:32 AM
#3
well i know for a fact no suspension bolts get torqued to over 66 or 68 on our cars. basically anything with a thru bolt and nut is what im talking about, lower control arms in the front is one i can think of off the top of my head, just wondering if anything is realy to be gained by more clamp
03-24-2019, 02:09 PM
#5
I have no idea what you're even trying to say here. 10.9 grade is for METRIC bolts, as opposed to grade 8, which is for SAE. The two grades are nearly equivalent, just like posted previously.
03-24-2019, 02:28 PM
#6
Torque elongates the bolt, stretching it like a wet noodle. As this happens, the threads come into more complete contact and build up a greater friction force. (So the bolt/nut don't come loose.) This stretch can also put some bolts into other desirable mechanical realms, but usually torque is going to be used to make sure bolts/nuts don't come apart.
The torque one needs for any given bolt is different and is a function of the material (ie: grade), the thread pitch, the diameter of the bolt, the surface coating of the threads, and probably a few other factors I'm forgetting... Regardless, an engineer for the product one is installing will get out the slide rule to figure all this out and provide the proper torque spec for each bolt.
If one does not have an engineer on staff to do these calculations or a bolt does not come with recommended torque specs, then it is probably unwise to do bolt-swapping unless it's done with exact/equivalent bolts.
03-24-2019, 02:37 PM
#7
And you would be wrong. The control arm nuts are all listed between 72 and 85 lb-ft in the GM manual.
I have no idea what you're even trying to say here. 10.9 grade is for METRIC bolts, as opposed to grade 8, which is for SAE. The two grades are nearly equivalent, just like posted previously.
I have no idea what you're even trying to say here. 10.9 grade is for METRIC bolts, as opposed to grade 8, which is for SAE. The two grades are nearly equivalent, just like posted previously.
forget about the grade 8 vs 10.9, i simply said grade 8 because those are more accessible in larger sizes than grade 10.9, at least where i shop.
so a bolt with more threads per inch will usually be able to take a higher torque rating vs a bolt with the same grade and less threads per inch, similar to a factory bolt or very specific, like a rear pan hard bar bolt, which i believe is 60 something. assuming you replace that bolt and nut with a bolt the same grade but more threads per inch will allow a higher torque rating. hence the midwest chassis bolts they supplied finer thread, basically same grade and size, just more threads per inch, assuming thats why they recommended 100 foot pounds. now is that gone be "better" than the factory bolts torqued at 60ish in that area? same goes with rear LCAs.
the point im asking is yes the front lower arm bolts are a finer thread with a higher torque, i think they may actually have more girth than anything in the rear as well, and they have a higher torque rating than the rear. but if i was goona replace the front hardware, would it be better to get a finer thread to torque it more or source a new gm? IS THERE A BENEFIT IN HIGHER TORQUE RATINGS? its not as much of a difference in the front since i guess they felt those bolts needed to be tighter than the rears, where its a much larger difference, but if the bolts up front are larger than maybe you could do 110 or 115 ft pounds with a finer thread non gm bolt......a few of those bolts up front are still available from gm ....actually i think its just the vertical ones but the nuts for both sides are available.
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03-24-2019, 02:42 PM
#8
The short answer is there is no benefit.
Torque elongates the bolt, stretching it like a wet noodle. As this happens, the threads come into more complete contact and build up a greater friction force. (So the bolt/nut don't come loose.) This stretch can also put some bolts into other desirable mechanical realms, but usually torque is going to be used to make sure bolts/nuts don't come apart.
The torque one needs for any given bolt is different and is a function of the material (ie: grade), the thread pitch, the diameter of the bolt, the surface coating of the threads, and probably a few other factors I'm forgetting... Regardless, an engineer for the product one is installing will get out the slide rule to figure all this out and provide the proper torque spec for each bolt.
If one does not have an engineer on staff to do these calculations or a bolt does not come with recommended torque specs, then it is probably unwise to do bolt-swapping unless it's done with exact/equivalent bolts.
Torque elongates the bolt, stretching it like a wet noodle. As this happens, the threads come into more complete contact and build up a greater friction force. (So the bolt/nut don't come loose.) This stretch can also put some bolts into other desirable mechanical realms, but usually torque is going to be used to make sure bolts/nuts don't come apart.
The torque one needs for any given bolt is different and is a function of the material (ie: grade), the thread pitch, the diameter of the bolt, the surface coating of the threads, and probably a few other factors I'm forgetting... Regardless, an engineer for the product one is installing will get out the slide rule to figure all this out and provide the proper torque spec for each bolt.
If one does not have an engineer on staff to do these calculations or a bolt does not come with recommended torque specs, then it is probably unwise to do bolt-swapping unless it's done with exact/equivalent bolts.
im not really saying o i need to go tighter, i want to make sure it dont come out, what im more or less asking is if i were to decide to replace the fronts with grade 8 hardware with a finer thread, is there any benefit in going to saay 25 more foot pounds than stock because the bolt will handle it more.....obviously a finer thread than stock will handle more torque so just go ahead and give it a little more?
side note, while you are here, what bolts up front do they loosen for an alignment? i want to know which ones to thread lock and will be a waste if they will just loosen them for an alignment anyway
03-24-2019, 05:47 PM
#9
as a rule of thumb ....a fine thread is stronger than course thread
GM specs the bolts for the application and determines the TQ for it....so I dont think more TQ is necessary in any application ( i am not an engineer , but i did sleep at a hoilday inn express )
now using different bolts such as ARP where they do test and rate their bolts is another animal
you can use a bolt stretch gage.....but what numbers are good or bad in stretching i have no clue
as far as bolt loosening look into nord locks......i use them on my header studs
GM specs the bolts for the application and determines the TQ for it....so I dont think more TQ is necessary in any application ( i am not an engineer , but i did sleep at a hoilday inn express )
now using different bolts such as ARP where they do test and rate their bolts is another animal
you can use a bolt stretch gage.....but what numbers are good or bad in stretching i have no clue
as far as bolt loosening look into nord locks......i use them on my header studs
03-25-2019, 07:18 AM
#10
i saw this after i posted, so what about midwest chassis telling me to do 100 foot pounds on the grade 8s they sent? i understand the bolt stretch part as well but what i dont know is how much more stretch is 60 pounds vs 100 pounds on a given bolt the size of the rear LCA.
In the end, I would not change your other bolts. Unless you are racing the car aggressively, they are going to be just fine. If you replace more of the metric bolts on the car with standards, the next mechanic to work on the car is going to really really curse you bad.
In terms of torque, a fine thread would have more surface area, more friction area, and should require less torque to make a tight bolt. All things equal, the "threads" would be the same, but with more threads to handle force, a fine thread would be less likely to strip out for the same torque/stretch/force.
03-26-2019, 08:40 PM
#11
With a fastener what is most important is the clamp load. The clamp load is what will help resist slippage and loosening. The highest clamp load you can get is when the bolt has been stretched so far it begins to yield. This bolt can only be used once, it is TTY (torque to yield) and permanently deformed. If you overtorque you could yield the bolt which is bad because a re-usable bolt can only be torqued to its elastic limit (it bounces back with no permanent damage). The torque applied isn't necessarily very well associated with this depending on the joint. Here are a couple of examples.
If you lubricate the threads it is easier to turn the nut. You can develop the same bolt stretch and therefore clamp load with a lower torque applied to the nut to due lower friction. Therefore, the coating of the fasteners is important... an oily fastener will not require the same torque as a clean fastener to achieve the same bolt stretch.
Another example. If you have a clevis and the bolt must deform and close the clevis. You will develop the same nut torque, but there could be a significant loss of clamp load because the bolt is being used to close the clevis. In this case it may be helpful to tighten loosen and retighten. This is done at times in the assembly plant for critical joints.
SO, to answer your question. There is likely no benefit to swapping fasteners. The torque they recommended to you is generic for that thread pitch and bolt size, I would not anticipate any significant improvement in clamp load.
If you lubricate the threads it is easier to turn the nut. You can develop the same bolt stretch and therefore clamp load with a lower torque applied to the nut to due lower friction. Therefore, the coating of the fasteners is important... an oily fastener will not require the same torque as a clean fastener to achieve the same bolt stretch.
Another example. If you have a clevis and the bolt must deform and close the clevis. You will develop the same nut torque, but there could be a significant loss of clamp load because the bolt is being used to close the clevis. In this case it may be helpful to tighten loosen and retighten. This is done at times in the assembly plant for critical joints.
SO, to answer your question. There is likely no benefit to swapping fasteners. The torque they recommended to you is generic for that thread pitch and bolt size, I would not anticipate any significant improvement in clamp load.
03-26-2019, 09:48 PM
#12
With a fastener what is most important is the clamp load. The clamp load is what will help resist slippage and loosening. The highest clamp load you can get is when the bolt has been stretched so far it begins to yield. This bolt can only be used once, it is TTY (torque to yield) and permanently deformed. If you overtorque you could yield the bolt which is bad because a re-usable bolt can only be torqued to its elastic limit (it bounces back with no permanent damage). The torque applied isn't necessarily very well associated with this depending on the joint. Here are a couple of examples.
If you lubricate the threads it is easier to turn the nut. You can develop the same bolt stretch and therefore clamp load with a lower torque applied to the nut to due lower friction. Therefore, the coating of the fasteners is important... an oily fastener will not require the same torque as a clean fastener to achieve the same bolt stretch.
Another example. If you have a clevis and the bolt must deform and close the clevis. You will develop the same nut torque, but there could be a significant loss of clamp load because the bolt is being used to close the clevis. In this case it may be helpful to tighten loosen and retighten. This is done at times in the assembly plant for critical joints.
SO, to answer your question. There is likely no benefit to swapping fasteners. The torque they recommended to you is generic for that thread pitch and bolt size, I would not anticipate any significant improvement in clamp load.
If you lubricate the threads it is easier to turn the nut. You can develop the same bolt stretch and therefore clamp load with a lower torque applied to the nut to due lower friction. Therefore, the coating of the fasteners is important... an oily fastener will not require the same torque as a clean fastener to achieve the same bolt stretch.
Another example. If you have a clevis and the bolt must deform and close the clevis. You will develop the same nut torque, but there could be a significant loss of clamp load because the bolt is being used to close the clevis. In this case it may be helpful to tighten loosen and retighten. This is done at times in the assembly plant for critical joints.
SO, to answer your question. There is likely no benefit to swapping fasteners. The torque they recommended to you is generic for that thread pitch and bolt size, I would not anticipate any significant improvement in clamp load.
03-27-2019, 06:58 AM
#13
Sorry I missed in your first post that you were asking about clamp force. Clamp force is not proportional to torque or the stretch of the bolt. (It's a function of the sizing and properties of the bolt, along with the torque, etc.) So, we're still back to the point to stick to the recommended torque for the particular size/type of bolt.
Another thing that can affect all of this is the coating on the bolt. (Black oxide, etc.) When I replace suspension hardware, I usually bite the bullet and just get the hardware from a GM dealer (online or otherwise) so I'm 100% sure of the properties and specs.
The only threads that matter in terms of torque are the ones you can't see. (The ones that engage the threads of the nut.)
Another thing that can affect all of this is the coating on the bolt. (Black oxide, etc.) When I replace suspension hardware, I usually bite the bullet and just get the hardware from a GM dealer (online or otherwise) so I'm 100% sure of the properties and specs.
The only threads that matter in terms of torque are the ones you can't see. (The ones that engage the threads of the nut.)
03-27-2019, 07:23 AM
#14
Stock front LCA bolts will slip at the stock torque rating depending on what the car is being used for. 100 ft-lbs on stock bolts will stop it. The aftermarket UMI bolts I tried to use at some point were functionally way worse than the stockers and slipped more in addition to being a bigger pain in the *** to use.
03-27-2019, 06:29 PM
#15
Sorry I missed in your first post that you were asking about clamp force. Clamp force is not proportional to torque or the stretch of the bolt. (It's a function of the sizing and properties of the bolt, along with the torque, etc.) So, we're still back to the point to stick to the recommended torque for the particular size/type of bolt.
Another thing that can affect all of this is the coating on the bolt. (Black oxide, etc.) When I replace suspension hardware, I usually bite the bullet and just get the hardware from a GM dealer (online or otherwise) so I'm 100% sure of the properties and specs.
The only threads that matter in terms of torque are the ones you can't see. (The ones that engage the threads of the nut.)
Another thing that can affect all of this is the coating on the bolt. (Black oxide, etc.) When I replace suspension hardware, I usually bite the bullet and just get the hardware from a GM dealer (online or otherwise) so I'm 100% sure of the properties and specs.
The only threads that matter in terms of torque are the ones you can't see. (The ones that engage the threads of the nut.)
i understand the basic concepts of bolts, and understand what makes bolt A take a higher torque than bolt B, thats why i was wondering if switching to a finer thread bolt and getting and additional 15-20 lbs of torque on it could have any benefits, but taylor i believe says this is an actual issue
03-27-2019, 07:06 PM
#17
If you want to push the bolts some, you can take a look at what you are doing with these two pages. (These equations ignore some of the considerations needed to look at bolt/nut loosening, but that's not your concern.) As you play with additional torque, you can calculate the axial force on the bolt and how close you are getting to that critical 80% of tensile strength you should be maxing out at. (I imagine that GM designed this car with a much higher margin of safety!)
https://www.engineersedge.com/calcul...orque_calc.htm
https://www.engineersedge.com/torque.htm
03-27-2019, 07:08 PM
#18
Not precisely. Finer threads (in absence of calculations) would give you a greater chance of yielding the bolt before the threads strip and would give you a lesser chance of stripping the threads as you march towards that yield point.
If you want to push the bolts some, you can take a look at what you are doing with these two pages. (These equations ignore some of the considerations needed to look at bolt/nut loosening, but that's not your concern.) As you play with additional torque, you can calculate the axial force on the bolt and how close you are getting to that critical 80% of tensile strength you should be maxing out at. (I imagine that GM designed this car with a much higher margin of safety!)
https://www.engineersedge.com/calcul...orque_calc.htm
https://www.engineersedge.com/torque.htm
If you want to push the bolts some, you can take a look at what you are doing with these two pages. (These equations ignore some of the considerations needed to look at bolt/nut loosening, but that's not your concern.) As you play with additional torque, you can calculate the axial force on the bolt and how close you are getting to that critical 80% of tensile strength you should be maxing out at. (I imagine that GM designed this car with a much higher margin of safety!)
https://www.engineersedge.com/calcul...orque_calc.htm
https://www.engineersedge.com/torque.htm