replacing springs help

[hanabie]

i'm using impact wrench to tighten the strut top nut. it says 41 ft lbs. Is it ok to exceed the torque?

the torque wrench could not tighten the strut

thanks

[kodyo]

Ok, here's the deal with bolt torques. They basically set the preload on the bolt, but are extremely dependent on the lubrication (friction factor) used on the bolt. In that respect, they are a generally accepted to be within 25% of actual stated value (ie: torquing to stated value will get you within 25% of desired preload). I would suggest not going much over the recommended value, but going a little over wont make a big difference. The issue with over torquing bolts is that if you over torque them (let's say to near the yield point of the bolt), any extra load on the bolt will cause the bolt to yield. Once that load is relaxed, you will basically lose all preload and have a loose bolt.

I have a lot of experience in bolting applications in oil and gas industry. Check out Machinery's Handbook if you want to see the formulas for bolt torque on a bolt.

[hanabie]

I figured the same way too. I just measured the thread length. Was that ok to do so? My torque wrench would not do anything. It did not give me click sound, but it just could not tight the nut as it seemed to be pushed by the spring. I had to use the impact wrench to go deeper.

[kodyo]

Out of curiosity, what is the size/strength of the bolt? I want to compare the suggest torque to one of the standards we use.

[hanabie]

41 ft lb, hex size was 17mm. thats the bolt on the strut axis.

[pche]

I've done hundreds of struts and I've always used an impact gun. No body I've work with has ever torque that nut to spec. Never had a problem

ETA: I should probably state that I use a 1/2 inch air gun with tons of torque, it doesn't allow the strut to have a chance to spin free. And I don't go crazy with it, just a quick "snug" should be all it takes.

[hanabie]

thanks. now I think Im on the right track. yes, the impact gun prevented the shaft from spinning freely.

[kodyo]

For what it's worth, 41 ft-lbf seems right for that size bolt (assuming its an M10 or M12). Be extremely careful not to go a large amount over that value. I would stay less than 50 ft-lbf if it was my car. Use these values at your own risk. I don't know what lubrication factor is acceptable for these bolts or the coatings that were applied. I didn't run any calculations and don't claim to know the designers intended preload. Strength of bolt also plays a key role in this, and I don't know the strength of the bolts being used.

[frsdiy]

http://www.harborfreight.com/21-piec...set-67974.html

There is no risk of spinning the strut shaft with this tool. This is only around $20 and it includes an extension socket for the rear strut tightening through that tiny hole. I wasted money on an electric impact wrench for 3x the price of this. Of course you will need a metric hex key to hold the shaft in place as well. Just tighten till it feels solid. Main point of the torque spec I think is to prevent over-tightening the nut. This is hard do to with this because the spring will twist before you end up over-tightening. If you dont have harbor tools the tool you want is "go through socket" 17 mm 14 mm