Choosing Between Bolt Strength Classes 12.9 and 10.9 for Car Suspension Repair

Question

The problem arose because of the suspension repair in the car - when unscrewing, due to corrosion, the bolts securing the wishbones broke off. Therefore, the question arises how to practically approach the class of bolts determining its strength. In general, I read that the higher the bolt...

tadkli9743 · Accepted Answer

Welcome I looked through the Mitsubishi Colt manual, only found the tightening torques of the bolts depending on their class. greetings

tadkli9743 · Accepted Answer

Hello. I found such materials, maybe they will be useful to you. greetings

kkknc · Accepted Answer

You got the knowledge almost in the initial post. And then you keep repeating the questions.

kkknc · Answer

You can break seized screws in every class. In the suspension, 10.9 is most often used. Where not where 12.9.
Yes, it is true that the harder the more brittle. Only the screws are surface hardened. The core is soft. So there is no problem with cracking. On the old ones you have the hardness class stamped on the heads. Harder prices.

pawlik118 · Answer

price does not matter. Unfortunately, the broken bolts do not have any markings. So I wonder how the fragility compares to the endurance defined in the class.

bearq · Answer

In addition, there is also some kind of workmanship, thread type, pitch or diameter. It is impossible to clearly answer the question of what bolts, because what brand or model is something else.

kkknc · Answer

Apply what is meant to be.

pawlik118 · Answer

I am asking about the class of screws and not the quality of their workmanship. Pitch and diameter also have nothing to do with the strength class of the bolt.
The basic questions are:
- is the 12.9 bolt always more durable than 10.9 or maybe less due to its greater "brittleness" (somehow I doubt) ??

kkknc · Answer

She is always tougher.
After all, the first digit is the information about the minimum tensile strength Rm in N / mm2 divided by 100. And the second digit is the ratio of the yield stress Re to the tensile strength Rm divided by 10.

bearq · Answer

Of course, it is related, because even a fine thread will have a lower breaking strength in the case of the same class as the normal screw. You ask too general a question, it is like asking what is better steel or cast iron and one cannot be replaced with another. The use of the appropriate class of bolts is primarily related to the forces acting on them.

kkknc · Answer

Doesn't matter, see what I gave above. The class indicates the strength of the bolt in relation to the cross-section. The shear strength of the thread is another matter. Don't get confused.

Anonymous · Answer

What is the dispute about? After all, the thread remains the same, the material does not change, and the heat treatment of the bolt and its strength do not change.

The 10.9 bolt has a tensile strength limit of 1000MPa and a yield strength of about 900MPa. Instead, you can screw in A4-90 bolts with a tensile strength of 1030-1100MPa, yield strength 900MPa, the bolt can protrude from the nut as much as it wants and will not rust, unscrewing it will never be a problem.

Regarding vibrations, 12.9 is found at the connecting rod feet, main bearing caps, at the flywheel, where vibrations and loads are enormous, and rigid materials. The suspension is full of damping and spring elements, the body itself is springy and absorbs vibrations well.

tata1 · Answer

Also, gentlemen, pay attention to the quality of the screw. For example, the one from Łańcut 8.8 (LF) will withstand more than the unknown brand 10.9.
Coming back to the "car", these bolts supplied with rocker arms and pins "replacements" are a fear to install - they look like indulgence. In such cases, I prefer to mount it on the old, original screws. Often, mounting such a screw is asking for trouble when unscrewing it again. The original will always unscrew.

kkknc · Answer

You buy a good replacement from a well-known company, no problem. And as the cheapest is what you are asking for trouble yourself.
And somehow the use of acid-resistant screws in the suspension does not make sense, but who will forbid the rich.

ociz · Answer

Not necessarily. For example, TRW will have worse screws in the kit than Delphi. Master Sport cheap Chinese food and the screws give a decent ...

Strumien swiadomosci swia · Answer

But you can buy only high-end bolts for clutch, flywheel, suspension at automotive wholesalers.

Besides, for example, I collect bolts from the demolition of cars, I currently have about 60 kg of various bolts and nuts, mainly from English.
They are useful and there are much better niches for thick PLN.

The question of whether 4.2 versus 8.8 or 12.9 is more durable is childish.

przemek25l · Answer

Just let the author of the post not forget about the nuts of the appropriate class because he threads the screws as he releases the thread in the nuts.

Strumien swiadomosci swia · Answer

The greatest loads are on the connecting rods feet, head, shaft, satellite basket, joints, wheel hubs. There you need cosmic bolts and apply exact moments in order not to stretch the limit of elasticity of the bolt.

pawlik118 · Answer

what should be?

Strumien swiadomosci swia · Answer

You know what bolt and where you buy it.

pawlik118 · Answer

Thanks for the two answers in the topic and the other dozen not related to the question. Main question - is the 12.9 bolt always more durable than 10.9 or maybe less due to its greater fragility (somehow I doubt) ??

Strumien swiadomosci swia · Answer

YES.

pawlik118 · Answer

I am also concerned about this brittleness - that is, what happens when the bolt is subjected to stresses greater than its strength class. Is it not the case that a lower class screw will be able to elongate more than a higher class screw that will break faster (because it is less plastic)?

kkknc · Answer

Yes, it will be longer. Although the difference is slight. The only question is what will this knowledge give you and how will you use it? 'Cause you start to go round and round.

ociz · Answer

Often, after the number of the original, you can find substitutes or even the original in stores, and the prices are not discouraging at all, not counting the eccentric ones that adjust the geometry of the suspension, because they are usually expensive.

pawlik118 · Answer

I just want to know what it is like with the class and strength of screws. Knowledge is the main factor that made me start this topic.

pawlik118 · Answer

The whole discussion in my group was about the broken bolt securing the yoke holding the brake pads. The yoke in the Nissan Almer is fixed with an M10x1.5 bolt (that's all I know). The screw is screwed into the yoke by about 7mm - not enough. The yoke is made of cast iron. According to the comparison from col. Tadkli9743, 12.9 is more stiff. Another complication is the influence of variable temperature - will the stiffness of the bolt greater than the assumed stiffness cause faster fatigue degradation of the threads in the yoke. The safest way is to order the bolts through the service. It is not known what class of screws are better at this point in practice.

kkknc · Answer

The yoke screws are practically always 12.9

robokop · Answer

But this bolt only holds the yoke - the shear moment is minimal as there is still friction between the yoke and the knuckle ears. And you do not have to tighten it until all the juice is released, a torque in the range of 60-90Nm (screws 10.9-12.9) is enough to tighten it. In the absence of a torque wrench - a ring spanner, without an extension, plus a thread braking agent - from the Loctite offer or the much cheaper Prolok. Not only will it not unscrew by itself then, but the thread will not stick to rust.

Choosing Between Bolt Strength Classes 12.9 and 10.9 for Car Suspension Repair

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