Rausche Posted April 10, 2008 Report Share Posted April 10, 2008 Hey guys... got a pretty interesting quandry here: A buddy of mine has a 1970 Chevy K20 with a full floating rear end... A while ago he did a brake job on it, and everything went smooth. He used an impact gun to reattach the axle hub studs... About 100 miles later 3 of the studs had backed out, and the other 5 had sheared off at the mating surface. To try and repair it we went out and got some new studs, read our repair manual (said to go 115 ft/lbs), and double-nutted the studs to get the first half to 115, then we were going to put the tube in and torque the nylocks down to 115 (proper procedure, no?). Well, the stud's threads stripped out... badly. We then decided that it was pointless to have studs in there, so we went with Grade 8 bolts. Put everything together, tightened them down evenly, and went on with the torque wrench. At about 80 ft/lbs (just a guesstimate), the Grade 8 bolt sheared, again right at the mating surface. We are now thoroughly confused... The bolts are not bottoming out, and the threads are all clean, so what's the problem? Can Grade 8 not hold 115 ft/lbs? Nobody around here that we've talked to has even heard of the problem we're having... I searched around online and found nothing that will help us out... Any tradecraft knowledge on here that can help us out? TIA everyone... Quote Link to comment Share on other sites More sharing options...
misterp Posted April 10, 2008 Report Share Posted April 10, 2008 (edited) Well I've never heard of such a thing. What I do know is that if you have a fastener loose on the axle (or, lug nuts) then eventually the bolt/stud will work harden and over a short amount of time crystalize and fail; this is why it is imperative all your axle nuts/bolts and lug nuts be seated & torqued evenly. This may also explain why the threads in the hub are weak, they might now be 'brittle' from work hardening but that's a WAG. I know it sounds like total BS but I have once driven a pickup which was missing a lugnut, and within 2 days of normal commuter driving four of the remaining five had crystalized and snapped off (that was a bad afternoon lol). AFA the shear load on a grade 8 fastner, depends on the size of the bolt; if it's only 3/8" or 7/16" then NO it won't, I would use grade 12. When using studs and nuts the procedure is this - you install the stud very loose, like only 5-10 ft-lbs. Screw the stud in finger tight, then double-nut and cinch it down like 1/8th turn with the wrench and it's good. THEN after assembly you torque the NUT down to required load (115 ft-lbs in this case). The whole purpose of a stud is to move the stress of the fastner away from the part and to the threads of the nut. A person that can help directly would be a good automotive machine shop, they can look at the hub and tell you exactly what the issue is if it's more advanced than what I've shared here. Mr. P. Edited April 10, 2008 by Mr. P. (see edit history) Quote Link to comment Share on other sites More sharing options...
desrtrat Posted April 10, 2008 Report Share Posted April 10, 2008 you have to remember also your dealing with parts that are 38 years old.. my advice would remove all the Axel studs, and spray break cleaner in the stud holes and compressed air to clean them out good. check the threads out REAL good. if need run a tap Thur carefully and and clean again. if any are stripped you can try a helicoil to repair it, or you may need to go to the next larger stud. when you reassemble everything put some loctite on the studs when installing...IMO.. i would NOT use bolts, if bolts would have worked, then they would have used bolts to begin with...also get new grade 8 lock washers and nuts and replace all. sorry i can't be more help.. BTW..when you have it all apart and cleaned, look for stress cracks around your stud holes if there cracking, you may want to think about replacing the rear.. Quote Link to comment Share on other sites More sharing options...
misterp Posted April 10, 2008 Report Share Posted April 10, 2008 I tell you what could be an additional factor, and that is that northeastern road salt CRAP you guys up there have to suffer with. 38 years of that corrosion could be a contributing factor if it was assembled wrong for a long period, I know it sounds bogus but I just saw a Ford 5.0 cast exhaust manifold totally eaten away to the point of cracking and leaking, and it was only 5-6 years old Mr. P. Quote Link to comment Share on other sites More sharing options...
Rausche Posted April 11, 2008 Author Report Share Posted April 11, 2008 Thanks for the advice so far guys! Steve, when new cars come off the trucks at the lot and go for inspection, their exhaust is already rusted. I live between a saltwater bay and the ocean. Don't get me started on corrosion, lol... Just to clarify for you all, this is the axle hub bolts, not the wheel studs. I can get you some pictures if you need a better idea of what I'm talking about. It looks so far like the threads in the hub are just fine... It's the hardware that has been failing. I worded the part about the stud stripping out poorly; It stripped out underneath the double-nut when we were tightening it down... So far the threads in the hub have eaten everything we've given them... Thanks Steve, for the shear load on a grade 8... We're calling around to the local large truck shops to see what their general procedure on larger trucks is, and then we'll be deciding where to go from there... AFA Nuts vs. Studs... His truck has studs, but all the repair manuals and articles online and even other trucks we've seen have bolts... Granted we haven't seen a truck exactly like his (used to be a brush breaker for the fire dept, had a massive water tank on it at one point, so who knows how far off stock it is...). Quote Link to comment Share on other sites More sharing options...
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