Rear spring hanger bolt ramblings

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The Artist formerly known as Turbo84
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Clinging to my guns and religion in KCMO.
Now that I'm back in the midwest and in the middle of some winter downtime, I'm trying to catch up on a few minor annoyances. One of the items is the rear hanger bolts. Due to the combination of a C3 batwing (and the attending low position of the spring mount) and C4 knuckles (with the high height of the hanger bolt "tab"), I need a damn long set of hanger bolts (12-13 inches, and the current multi-bolt setup I'm using is a bit too busy). The selection of bolts in the local hardware stores is pretty thin for bolts this length. I see McMaster Carr has bolts long enough, but they're all grade eight (which seems overkill), and are a bit expensive. Before I pull the trigger at M-C (along with the postage), I've got a technical question. The hardware store (half inch) bolts are grade two. According to a couple technical sources these bolts should have a tensile strength of 60-74 kPSI. The area of a half inch bolt is .196 square inches. This gives a max load capability of .196 x 60k = 11760 pounds. Cutting this maximum load in half to get far away from any yield issues gives us 5880 pounds. I'm estimating that each rear corner of my car is less than 750 pounds. Assuming I hit a good bump and the suspension bottoms (maximizing the spring compression) I would have an additional two inches of travel at 420# spring rate (adding 840 pounds of force to the bolt), resulting in a peak load of 750 + 840 =1590 pounds on each bolt. 5880/1590 = 3.7 safety factor (or 7.4 if I don't divide the bolt rating by two).
So, I need some help convincing myself that I'm not wasting money if I go for the Grade 8 bolts.
Thanks,
Mike
 
So, I need some help convincing myself that I'm not wasting money if I go for the Grade 8 bolts.
Thanks,
Mike

I'm not going to help you. I've had grade 8 break because they're more brittle. Think about that. Does the spring pull the bolt straight down? Or is there some slight bending going on like on my shortened spring?

When my bolt broke i could hardly tell any difference. Suspension settles on bump stop and you keep on motoring. Definitely not a catastrophic or serious failure at all.
 
have you tried a tractor store? my local John Deere has a fastener catalog I used to find all kinds of stuff in.
 
If i remember right 5/8 diameter will fit. so you could use grade 2 and the difference in strength won't be so great.

1/2 grade 2 shows a proof load of 7800 lbs. The 5/8 shows 12400

1/2 grade 8 has 17050
 
I wouldn't use a "farm" bolt on my bicycle. Why not a grade 5?
 
I have two 5/8 bolts and nuts , bolts are 13" from McMaster... grade 8 .......

these are currently installed but I won't need them anymore once the dual mount spring is installed, how quick do you need the bolts ???
 
I have two 5/8 bolts and nuts , bolts are 13" from McMaster... grade 8 .......

these are currently installed but I won't need them anymore once the dual mount spring is installed, how quick do you need the bolts ???

Fortunately not 'til April or May.

I'll mock up something with some 5/8 bolts for some clearance measurements. My preference for 1/2" bolts is for the slight additional hole clearance due to how much the knuckle moves forward under droop due to the length/geometry of the two trailing links. IIRC, I did some fitting with 5/8 bolts a couple years ago when I first got the suspension installed, and had a couple concerns.

I appreciate the offer. :thumbs: I'll let you know what I find out about the clearance issue or any luck finding a better grade half inch bolt.
 
Dean Caterpillar. Cat's bolts are tougher than Grade 8- not more brittle. I have a pair of 10 or 11" bolts I got for the rear spring on Ol' Red, but didn't need them. Not all that expensive either.

I've used CAT bolts in places that grade 8's and everything else that was tried snapped.
 
Try Feldmans Farm And Home in Liberty. They have a big supply of nuts and bolts.

I stopped at Feldman's today to get some stuff to get my barn wood stove back in operation (after hauling it over from Indiana), and wandered through the bolt section. Found a pair of half inch by 12 inch grade 5 bolts at a decent price so I picked 'em up. Those ought to do the job.

Thanks for all the suggestions, guys. I hadn't thought about a few of those places before, and this gives me a few more future options. :thumbs:
 
Well why you were in Feldmans,you should of stopped by the shop and said HI to me. You probably had no idea that i work there :smash:
 
Well why you were in Feldmans,you should of stopped by the shop and said HI to me. You probably had no idea that i work there :smash:

You're correct. (Crap, now I have to think back to all the stores that I've pissed off people lately to figure out if you were one of them. :eek:h:)

I doubt that i am one of them,i stay in my hole in the back turning wrenches.
 
I've been using grade 8 on mine for years, including many miles on track, and never had a failure. Nice thing about living in a relatively big town is there are several sources for some more odd bits and pieces. I think I bought my lowering springs 6-8 years ago and paid less than $20 for both bolts, jam nuts and nyloc nuts.
 
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