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Unread 10-23-2013, 09:22 PM   #1
kawegit
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mysterious bolt situation

So I have a buddy who was trying to tighten down the bolts on his differential and each one would tighten to the specified 30ftlbs of torque. However, upon going back over the bolts they would continue to tighten without the torque wrench giving the sign that they were properly torqued. He tried 2 different wrenches and then came and got mine yet the bolts will not stop torquing down. One of the bolts eventually twisted and broke... wtf is going on here?

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Unread 10-23-2013, 10:49 PM   #2
TSEJEEPERS
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stock cover and bolts?
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Unread 10-24-2013, 12:27 AM   #3
ReDinTX
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The bolts are prolly all greasy where the heads contact the cover. Same reason why anti seize for lug nuts and spark plugs should ONLY be in a few threads and NOT on the mating surface of the neck/flange/seat
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Unread 10-24-2013, 07:51 AM   #4
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Quote:
Originally Posted by kawegit View Post
...However, upon going back over the bolts they would continue to tighten...
Stop after the first click?
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Unread 10-24-2013, 08:41 AM   #5
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So they torqued to 30 but he kept cranking on them until they snapped?
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Unread 10-24-2013, 02:59 PM   #6
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He didn't realize they were getting tight? Was he using a 3' torque? Lol
Is his name garren? Got a buddy that works for service dept at a Chevy lot. He does stupid stuff like that too. Like using an impact on brake calipers.
30 lbs is snug.
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Unread 10-24-2013, 04:51 PM   #7
kawegit
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Yeah stock cover and bolts. They went and bought new bolts though after breaking one of the originals. Find out tonight if they got it on there
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Unread 10-24-2013, 05:57 PM   #8
5-90
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Quote:
Originally Posted by kawegit View Post
So I have a buddy who was trying to tighten down the bolts on his differential and each one would tighten to the specified 30ftlbs of torque. However, upon going back over the bolts they would continue to tighten without the torque wrench giving the sign that they were properly torqued. He tried 2 different wrenches and then came and got mine yet the bolts will not stop torquing down. One of the bolts eventually twisted and broke... wtf is going on here?
Nothing mysterious there.

When a screw fails, it's because it was overtightened (for the material.)

Torque specifications are generated according to anticipated loading, load-sharing between fasteners, and the like.

Your differential cover only need 30 lb-ft per screw because it's a low-pressure seal for a viscous fluid, you don't need to clamp it down stupid.

Being that you're using 5/16"-18 screws, you obviously don't need a lot of clamping force (if you did, they'd have used bigger screws. The cylinder head uses 1/2"-13 screws, for instance.)

The fact that there was "some turn left" after reaching specified torque isn't surprising to me. I'd have to look it up, but the maximum recommended torque for a 5/16"-18 screw (SAE5 or SAE8) should be rather higher than 30 lb-ft.

This doesn't mean that you really need to get stupid with torquing the screws - but, the fact that you've fractured an (OEM, I presume?) screw tells me you did. (If you went and bought a replacement, all bets are off! I was replacing an oil pump - 5/16"-18 screws again - and had screws fracture before reaching specified torque! Why? Chinese crap. Running into stuff like that is what makes me such a picky bastid...)

When given a torque spec, you torque to that spec and then stop. There's no reason to "see if you can turn it a bit more" - doing so will invariably stuff something up, and you end up making more work than you need.

Just as you did here.
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Unread 10-25-2013, 01:35 PM   #9
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Yea, what was the deal with that? More turn left? I can get more turn on any spec until the fastener fractures or twists off. When it says 30 pounds, it may just mean 30 pounds.

And, the fact of a torque spec, especially one as low as 30 pounds tells you that they don't need to be tight. I'm thinking my little 3/8 inch wrench is up to 150 pounds.
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Unread 10-25-2013, 05:22 PM   #10
kawegit
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Apparently every time he tried to check the torque, the wrench wasn't giving the noticeable click. I personally always recheck the torque after getting other bolts tightened down. Never had a problem like this. If you simply tighten down the bolts and move on without ever rechecking you may not reach recommended torque specs. Such as reinstalling an oil pan... might want to go over those bolts again...
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Unread 10-25-2013, 08:35 PM   #11
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its a diff cover, why use a torque wrench? 3/8" standard ratchet, tighten till snug and done.

but yes, it is possible to have reset the torque on some fasteners after initial torque is set. however it should never get to where it over torque's them. i use a bar style torque wrench so i don't mistake the click or miss it.
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Unread 10-30-2013, 02:24 AM   #12
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teachable moment. turn until it snaps, then back off 1/2 turn, LOL. Yeah, its a sickening feeling and good luck getting out the broken stud. clean mating surfaces help. also as noted, for a diff cover, just snug down and go. don't over analyze it.
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