SOS. Need help with lower control arm.

[Sw00per]

If they appear similar to OE, then they are probably UNF 5/8 - 18 which has 18 threads per inch.

The OE bolts have thread pitch of 1.5 mm, so 25.4 / 1.5 = 16.9333..... threads per inch.

There are reasons that I didn't end up in a mechanical engineering / material science career but 65/360 x 1/18 = ~0.010031 inches of additional compression / bolt stretch. Whereas 65/360 x 1/16.933 = ~0.010663 in. (25.4 / 1.5) / 18 = ~0.94074. So ~6% less.

I suspect the actual clamping force delivered to the assembly is a function of the actual material the bolt is made from, as well as the difference(s) between metric class 10.9 and SAE grade 8.

I learned this lesson when I initially went to install the LCA skids on my JTR. The longer aftermarket bolts that came with the skids were coarse thread, and trying to use the +degrees spec resulted in them being drastically overtightened.

What torque did you end up using? Currently I am at 111 and was going to add the degree today.

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[Pliny]

What torque did you end up using? Currently I am at 111 and was going to add the degree today.

I ended up replacing the aftermarket coarse thread bolts because they were rusting with longer gold zinc ones with the same thread pitch as the OE ones, so I torqued them to 185 ft lbs as the instructions said.

Details on the replacement bolts in this thread.

 

[Sw00per]

I ended up replacing the aftermarket coarse thread bolts because they were rusting with longer gold zinc ones with the same thread pitch as the OE ones, so I torqued them to 185 ft lbs as the instructions said.

Details on the replacement bolts in this thread.

Thanks so due to the difference in the bolt determines the torque. So the factory is 111 + 65 degrees did that = the 185? I will have to check with MC but when I last spoke to them I think the said 120 was the torque. Here is the bolt in question not sure if this would help indicate the final torque.

 

[Pliny]

So the factory is 111 + 65 degrees did that = the 185? I will have to check with MC but when I last spoke to them I think the said 120 was the torque.

Sorry, I didn't try to verify that 111 ft lbs + 65 degrees = 185 ft lbs. The instructions for the RH skids said to go to 190 ft lbs for the bolts they supplied (the coarse thread ones) and since the Mopar instructions said 185 ft lbs I just went with that cause it seemed reasonable (I did assume that my aftermarket gold zinc plated ones were similar enough to the OE dull zinc ones). Drove around / wheeled for over a year with RH ones and nothing came loose or fell off.

120 ft lbs seems low to me for this size bolt.

Looking stuff up on line you need to be aware of what finish is on the bolt / nut that they are referring to in their table. For example this one lists two sets of numbers, one for plain (higher) and one for plated (like the zinc plated ones). Whereas this other one just has in the notes grades 2, 5 and 8 are for plated bolts. This Fastenal table gives three different "K" factors, one for lubricated, plated, and then plain and dry. Different torque values are required in each case to end up with the same clamping force applied by the bolt.

I'd suggest confirming with MC before going with 120 ft lbs.

 

[Sw00per]

Ok so I have an update. Spoke to MC, and the torque is 190 ft lbs, which jives with what you posted. On another note, the passenger side bracket was attached with a larger gap, so the LCA skid will not fit or line up correctly. I decided it was better to alter the LCA skid instead of the frame bracket. I will give it another try next weekend. I marked the photos in red to make it easy to see. The adventure continues.

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