7/16" grade 8 hardware enough for spring brackets?
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Postmaster
Joined: Apr 2003
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From: Virginia Beach
7/16" grade 8 hardware enough for spring brackets?
I have made some progress on my project truck. . . As usual, I have gotten ahead of myself with buying hardware before I asked here first 
On the rear suspension, I had removed the front spring locating brackets and the rear hangers so I could knock and rust from behind them and put a coat of paint down. The brackets have also beem painted. I went ahead and redrilled the holes a little to fit 7/16"-20 grade 8 bolts, washers and nylon locking nuts. I thought about 1/2", but figured it to be overkill for a truck that will haul nothing more than me and a full tank of gas around. . .no X3TRe|^|3 offroading. . .
As with so many other things that I have done, I'll ask now since I'm only half way done
Will the 7/16" bolts hold up?
Also, whats the failure rate per quantity manufactured of something like this? I torqued down the bolts on the truck today (80 ft-lbs) and ended up stripping out 2 of them before I even reached 50 ft-lbs
On the rear suspension, I had removed the front spring locating brackets and the rear hangers so I could knock and rust from behind them and put a coat of paint down. The brackets have also beem painted. I went ahead and redrilled the holes a little to fit 7/16"-20 grade 8 bolts, washers and nylon locking nuts. I thought about 1/2", but figured it to be overkill for a truck that will haul nothing more than me and a full tank of gas around. . .no X3TRe|^|3 offroading. . .As with so many other things that I have done, I'll ask now since I'm only half way done
Will the 7/16" bolts hold up? Also, whats the failure rate per quantity manufactured of something like this? I torqued down the bolts on the truck today (80 ft-lbs) and ended up stripping out 2 of them before I even reached 50 ft-lbs
Post Fiend
Joined: Jul 2003
Posts: 11,945
Likes: 3
From: Spokane, WA
I drilled out all my holes and went to 1/2". I was gonna do 7/16 but figured better safe than sorry. I don't think it's necessary but I like to overbuild things. IMO for the $20 new bolts will cost you I'd go to 1/2". Don't know about the 7/16 bolts but I torqued my 1/2" stuff to 100 pounds. Stripping at 50 doesn't sound right.
Fleet Mechanic
Joined: Nov 2003
Posts: 1,372
Likes: 14
From: West Cornwall, CT
7/16" Grade 8 fasteners should not even begin to strip at 50 ft-lbs of torque. When using the grade 8 stuff, make sure that both the nuts and bolts are high strength stuff. Grade 8 bolts and low grade nuts will cause the problem you describe.
When replaceing rivets with bolts, go up one size higher. Your truck will have a mixture of 3/8 and 7/16 rivets so you would have a mixture of 7/16 and 1/2 bolts when you were finished. Ivan's choice of 1/2 bolts makes lots of sense. Also, those 1/2 grade 8 fasteners are *very* tough - normal folk could not break them.
Lou Braun
When replaceing rivets with bolts, go up one size higher. Your truck will have a mixture of 3/8 and 7/16 rivets so you would have a mixture of 7/16 and 1/2 bolts when you were finished. Ivan's choice of 1/2 bolts makes lots of sense. Also, those 1/2 grade 8 fasteners are *very* tough - normal folk could not break them.
Lou Braun
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Postmaster
Joined: Apr 2003
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From: Virginia Beach
Good points fellas! Not like I wont be able to use the 7/16" stuff for other parts of the truck, of course I won't be able to buy 1/2" stuff till Saturday 
Since I have your attention, any special considerations for washers?
The 2 stripped bolts failed at the threads of the bolt, the nuts are fine. The bolts have 6 tic marks (and this little trianlge between 2 of them ). All hardware is yellow-gold plated. I'll try and get a picture up if you want to see what I'm talking about.
Thanks
Since I have your attention, any special considerations for washers?
The 2 stripped bolts failed at the threads of the bolt, the nuts are fine. The bolts have 6 tic marks (and this little trianlge between 2 of them ). All hardware is yellow-gold plated. I'll try and get a picture up if you want to see what I'm talking about.
Thanks
Freshman User
Joined: Sep 2005
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You shouldn't use nylon lockwashers on suspention. They only have about 1/2-3/4 the holding threads of a standard nut, so its not that surprizing that they stripped the bolt out easily. Ny-locks put all the stress on fewer of the bolt threads. A regular nut and lock washer has a LOT more holding strength. If your going to use a locknut, use a grade-8 1 piece steel locknut. Any industrial supply house or fastener supply house should have them.
Last edited by old_ford_iron; Sep 6, 2005 at 08:15 PM.
"Mifflin Clay"
Joined: Jul 2005
Posts: 3,177
Likes: 4
From: Mifflin, PA
One thing nobody mentioned - be careful when you drill those holes - keep them round, and not oversized. In fact, if possible, drill them slightly undersized. There is a point where the threads will just clear but the bolt body starts to drag. This is the ideal situation, and use the nut to "pull" the bolt shoulder through. You are aiming for "no slop" between the bolt and the frame/bracket. Shear strength is predicated on a tight fit in a radial direction.
I used to have a set of drill bits that were ground down for just this purpose. (Note that the rivets "filled" the frame holes, which is why you have to drive them out)
.
I used to have a set of drill bits that were ground down for just this purpose. (Note that the rivets "filled" the frame holes, which is why you have to drive them out)
.
Post Fiend
Joined: Jul 2003
Posts: 11,945
Likes: 3
From: Spokane, WA
There's some really good info here. I drilled my holes just large enough to get the bolts through, it was a tight fit. Because of this I don't need to use flat washers and never like to myself as they leave more room for movement and problems. As pointed out you should be using a lock washer and regular nut, not a nylon-locknut here for strength.
All this talk makes me want to go upgrade to 5/8". Thanks guys.
All this talk makes me want to go upgrade to 5/8". Thanks guys.
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Butt-Head
Joined: Apr 2004
Posts: 9,437
Likes: 2,925
From: Reed Point, MT
I used 7/16" fasteners on my 95 PSD when I moved the rear hangers on my front springs back 1.5 inches. (I did a shackle reversal and had too long of springs.) I have tons of miles on this setup with 49's. No strength issues to speak of.
Oh, I used the same bolts when I moved my rear spring shackles forward, too.
Cody
Oh, I used the same bolts when I moved my rear spring shackles forward, too.
Cody
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