Did you notice if the rears have the capacity for M16? Looks like that's what Grimm uses in their replacement kit.
From what I found, a 10.9 bolt should have a min Yield Strength of 940 MPa.
I was actually thinking about mentioning torque to yield the other day, and knowing that couldn't be the case.This bolt torque saga continues to be weird. I used to do this kind of analysis so while I wait for replacement bolts I went to work on the various specs. I won't bore you with the math. It is interesting how Torque + Angle works to minimize the effect of friction on loading the joint. You can read about that in a few places. Also, these aren't (or shouldn't be) torque to yield fasteners. I'll put up the example of the Rear LCA to Axle fastener since that's the one that started failing on me.
The bolt spec is: M14x1.5x104.15 mm, Class 10.9. Mine is roughly 107 mm long right now.
The Torque + Angle spec is 100 Nm (74 ft-lbs) + 50°. I calculated a clamping force of 66.3 kN (~15,000 lbs) and Axial Stress of 593 MPa (~86000 psi). So we're a little above halfway to minimum Yield with that torque spec.
I calculated the (roughly) equivalent torque to the Torque + Angle spec to be 158 Nm (117 ft-lbs) by backing it out from the total clamping force that I came up with.
The AEV and the other Mopar chart agreed that the torque should be 122 Nm (90 ft-lbs) on that bolt. That gives a clamping force of 51.1 kN (~11,500 lbs) and Axial Stress of 457 MPa (~66,300 psi). Substantially lower forces for some reason, but now we're at less than half of Yield.
The WRONG instructions that I have call for a torque of 251 Nm (185 ft-lbs)! That results in a calculated clamping force of 105 kN (~23,600 lbs) and Axial Stress of 941 MPa (~136,500 psi). Hey, that's more than the minimum Yield! Remember where I said it gets weird? I never got that bolt to 185 ft-lbs. My torque wrench reported a max torque of 155 ft-lbs before it kept reporting lower and lower peak torque values as the bolt continued to turn and stretch. At 210 Nm (155 ft-lbs) the clamping force is 88.0 kN (~19,800 lbs) and the Axial Stress is 787 MPa (~114,000 psi). So it's possible that the bolt is faulty!
Before I got to the Rear LCA to Axle bolt I managed to tighten the Rear UCA to Frame bolts to 200 ft-lbs, which actually puts their Axial Stress at 1016 MPa (~147,400 psi). That is just below what I found for a maximum Yield on a 10.9 bolt: 1034 MPa (150,000 psi). So those might be okay. The Rear LCA to Frame and Axle have the same torque spec and the ones that didn't fail might still be within their limit. I'm not going to take the chance though. I haven't torqued the Rear UCA to Axle bolts as that will require some kind of torque adapter. Or maybe I could just guess and keep an eye on it since the torque specs are all over the place!
Wow! Thanks for sharing!I have more interesting findings that I might as well write down in case anyone else goes through this in the future. The torque wrench I’m using is an AC Delco ARM303-4A-340 1/2" Heavy Duty Angle Digital Torque Wrench. It reports the final torque after you reach the required angle in the torque spec, so now I have some real-world numbers for OEM bolts. I still wouldn’t rely on the end numbers that I got to torque up used hardware. Even new, I would prefer the torque + angle spec rather than trying to match these numbers. I think you’ll see why.
The rear lower control arm to axle torque spec in the FSM is 74 ft-lbs + 50° - That translates to about 125 ft-lbs. I say ‘about’ because one side hit 125.4 ft-lbs as the final torque and the other side was 129.3 ft-lbs. I calculated that it would be about 117 ft-lbs so I don’t feel too bad about the calculation. There could be some small error from the friction coefficient that I used or the modulus of elasticity that I used or something else. The Mopar lift instructions suggest 90 ft-lbs for that bolt. That’s quite a bit lower, but it’s probably what you want if you’re reusing the fasteners. Just don’t try to go to 190 ft-lbs like my instruction sheet said. You can see the results of that in the bolt that stretched. You can see the elongation compared to the new replacement and you can see the necking that happened compared to the straight edge of a ruler. The galvanizing was also flaking off of the bolt. I’m glad that bolt didn’t break!
Final angle measurement on the digital torque wrench.
And the final torque after going to 74 ft-lbs + 50°.
These bolts should be the same length. The one on the right was stretched an additional ~3mm while under tension.
Necking deformation of the failing bolt. So glad this didn't break!
The rear lower control arm to frame torque spec is also 74 ft-lbs + 50° - This one gets interesting because one side got to 135.4 ft-lbs and the other got to 133.5 ft-lbs. I’m guessing that the difference has to do with a slightly different grip length between this fastener setup and the one on the axle. The bolts are the same length but something else is different.
The rear upper control arm to frame bolt torque spec is 74 ft-lbs + 80°. That seems like a much higher torque, and it is higher, but not as much as you might think. Again, I think the grip length has something to do with getting a final torque value of about 145 ft-lbs. I caught 145.6 ft-lbs on one side but didn’t catch the final value on the other side.
I have not had a chance to get the alignment checked yet and have only been doing a little bit of local, lower speed driving. Today a message came on the screen saying, “Exhast Filter Nearing Full - Safely Drive at Constant Speed to Clear”. I was on my way to a different vehicle dealer to pick up a different problematic diesel vehicle so I changed plans and did my best to get on the freeway so that I wouldn’t be stuck in stop and go traffic. The message changed to, “Exhast System Regeneration in Process Continue Driving”. So I took a different highway that wouldn’t take me sooo far out of my way. On that highway there was a diagonal road imperfection. When the Jeep came off of that bump it went into full death wobble at 70mph! Maybe it’s time @JeepCares took a look at this thread and my other thread about this problematic diesel Wrangler.
Hello, thank you for tagging us and bringing this to our attention. Please send us a private message with the last eight characters of the VIN and mileage so our team can look into this for you.This lift is the gift that keeps on beating me over the head.
First thing to check is the torque on the track bar bolts.This lift is the gift that keeps on beating me over the head.
