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I hope to be replacing the shock absorbers on my 2005 Mazda 3 this weekend. I have purchased the shocks themselves (Monroe P/N 5607), as well as new mounts. The only thing left to get is new bolts....

From watching this video, I can tell that it is a 17mm bolt. The question is can I just go out and buy any 17mm bolt that is the same length as the current one, or is there some kind of material requirement?

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Is there a reason you can't reuse the original bolts? This is what is typically done. –  mikes May 30 '13 at 10:34
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@mikes: When I replaced the lower control arms on my vehicle, the bolt attaching one to the shock was completely broken. I suspect it's a good idea to replace these bolts even if they're not broken yet, given the load they're subjected to. –  R.. May 30 '13 at 12:58
    
@mikes, R.. sums up my thoughts on the matter. –  tarheel May 30 '13 at 13:10
    
I've also had bolts break when removing them. Worse, I've broken bolts when putting them back in: mechanics.stackexchange.com/q/3742/57 Sometimes the original piece just isn't available. –  Bob Cross May 30 '13 at 18:55

2 Answers 2

up vote 7 down vote accepted

The question is can I just go out and buy any 17mm bolt that is the same length as the current one,

No.

or is there some kind of material requirement?

Yes.

Think about the jobs that those bolts are doing: they support the steady state mass of the vehicle and the transient spring loads of the transmission. That means that those bolts need to be strong enough to handle steady loads as well as sudden impulses.

You aren't going to be able to just throw any old bolt in that slot and expect it to hold up.

A lot of the bolts under transient loads on the car are grade 8. Check the bolt that you're removing against this handy reference sheet. You want to make sure that any replacement bolt is at least as strong as the one that's coming out.

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I ended up finding out through the shock absorber manufacturer that the bolt had to be an M12 (I was introduced to this measure of strength as well) with 1.25 threading. Problem was the dealer said I had to wait a week to have it shipped, and no hardware store around me carried that. So I had to use the original bolt on the new shocks. Will keep this in mind for next time! –  tarheel Jun 3 '13 at 14:25
    
@tarheel glad to hear that it worked out. –  Bob Cross Jun 3 '13 at 15:51

Not sure why you want to replace the bolts you should be able to reuse the original bolts. If you do decide you want new replacement bolts make sure to get the correct size. Bolt size is determined by the size of the bolt (not the head) and the thread. You will need to get the correct thread pitch, diameter, length, and strength. You could call your local dealer and they may have the bolt or be able to tell you the size if it's a standard bolt.

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+ you need to match the bolts strength. –  Krom Stern May 31 '13 at 10:12
    
@KromStern Very True, my whole bolt bin is grade 8 so I didn't think to mention that :) –  Larry May 31 '13 at 12:35

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