I had the left one drop off with my wife putting her full weight on it and she weighs all of about 110 lbs. When I inspected the bolt it was clear it was cracked most of the way through and the last strand was holding it on. There is a problem with over torquing these bolts. I believe the correct torque is 35 in-lbs. Which most all of us will over tighten these. Mine came that way from the factory, and took two years to give way. Easy solution is new bolts, blue Locktite and the correct torque.

 

there was an old thread here awhile back on one or two years there was reports of the bolts shearing believe it was incorect tourqe from factory think there may even be a service bulletin on this?

 

I agree, the grade 5 will bend with side stress where as the grade 8 will just shear off.

 

Totally false...the grade 8 is stonger in shear, tension, and bending. Assuming the bolts are properly manufactured and in equally good condition, the grade 5 will ALWAYS fail before the same sized grade 8.

Harry

 

I don't see where anyone said that the grade 5 was stronger than the grade 8. The difference is when a grade 5 bolt has to much side load it will bend quite a bit usually before it will break giving you a chance to see you have a problem before it's to late. A grade 8 bolt is much harder which keeps bending to a minimum before breaking, you usually won't know a grade 8 bolt is loaded to much until it breaks. The company I work for changes alot of grade 8 bolts out to grade 5 on machinery where side load or vibration has been causing the grade 8 bolts to break, the maintenance guys can't visually see when the grade 8 bolts are about to break, but with the grade 5 they have been able to spot trouble areas in time to change out a bolt before it breaks and shuts everything down. I learned about the bending of grade 5 bolts in my atv racing years by thinking the grade 8 would would be better in my front suspention components since they were stronger. I found out the hard way that when in the middle of a race and an accident happens that grade 8 will snap with a hard lick just about every time, when a more experienced racer told me to go to grade 5 bolts I thought he was crazy, until I tried it.

 

As always, have enjoyed the lively discussion. That is what it is all about. Here is an interesting article. http://www.rockcrawler.com/techrepor...ners/index.asp
Give it a read and always use the fastener that lets you sleep. Me? If it came with grade 8, then that is what it will get. If it came with a grade 5........

 

the bolt in question is 3/8" grade 8, is that right? Shear and tensile capacities are readily available. However, as a millright/machine repairman I can say that if Momma can bust that puppy, she needs a weightwatchers membership now. I am just guessing but probably a couple thou tensile. Use your shop manual, blue locktite 242 torque to a number between the specs. Remember that the torque used to tighten a bolt (stretch) uses a portion of the tensile strength of said bolt. Thats why we only tighten lift rings to less than 10 ft/lbs.

 

one point on the grade 5 vrs 8 thing. This is a safety point that the engineers at HD must have looked at with hard numbers not seat of the pants engineering like we do on the floor. This is not something I would lose any sleep over.

 

However, as a millright/machine repairman I can say that if Momma can bust that puppy, she needs a weightwatchers membership now.

Gary: you da' man! Just another reason to say no to fat chicks. They will break your bike.

 

30-35ft/lbs (40.7-47.5Nm) which is just snug for a bolt this size