Materials nerd stuff

[Digger]

9/16"(14mm) is common for track bar bolts are on vehicles weighing 4000-5500lbs. The new Dodge 1-tons are up to 18mm.

One thing to keep in mind regarding bushings and their bolts, the bolt should not be considered to be stressed in sheer. What keeps in the bushing in place is the friction between the inner metal and the bracket as a result of the compression forces created by the bolt. This is why some bushings are serrated on their ends, so that they mechanically key into the bracket, assisting the friction forces.

I'm replacing heim joints that came with my Bloody Knuckle radius arms with Metal Cloak bushings. The heims came with 1" grade 5 hardware. The Metal Cloak bushings & Ruffstuff link mounts are built to accept 9/16" hardware. I know these are built specifically for Jeep suspensions. Is this adequate for our Broncos? Also would grade 5 or 8 be preferred? Not only for strength but also considering the likely hood of grade 5 to bend vs grade 8 to break.

Would it even be smart to drill out the MC bushing to accept a larger bolt?

9/16" is more than adequate. The whole bend vs break thing is a bit of a misnomer. Grade 5 and 8 have roughly equal seperation of the yield point of the bolt (where it starts to bend) and the ultimate tensile strength (where it breaks) The grade 8 just sits higher on the strength scale. Mosty OE hardware is metric 10.9 which is between grade 5 and 8. Either will work fine without fear of breakage. I use a mix of grade 5, 8 and even 10.9. It has more to do with availability of the sizes I need.

Jeep has been using 14mm (9/16") lower control arm bolts on vehicles as light as the Cherokee all the way up to the JK which starts out at 4500lbs before any mods or cargo. Many weigh up to 5500-6000lbs. Bolt breakage is rarely an issue. 99.99% of the time, other components will fail first. Our Broncos on the other hand weigh much less. Mine with 35's, lockers and a 351W weighed 3700lbs. Fully loaded out with furture mods and four people, it will weigh in at ~4500lbs.

[Gunnibronco]

Thanks for the reassurance. Awesome info. I didn't think a JK would be so much heavier than our old iron.

[Gunnibronco]

I ended up with some 1.75 OD, .25" wall DOM. Would this be adequate for rear four link? Ruffstuff kits come with 2" x .25 wall. I figure the 1.75 is ok, but wanted to make sure.

[Digger]

You'll be fine. My rear link setup is 1.75" x .120".

If I wanted to seriously crunch numbers, I could likely get away with 1.25" x .090" or 1.25" x .083".

The straight-line force along the axis of the tube is not what usually kills it. It would be from taking a rock hit near the middle of the tube. Here is a picture of the stresses in a 1.25" x .070" DOM tube supporting 10,000lbs. As you can see, the maximum stress is less than 38,000 psi and the tube will not yield until about 60,000 psi. (Ignore what the picture says yield is)


I had a tube bumper made from 1.75" x .083". I dropped the truck off a large rock (~2ft) and hit the bumper. It put a dime-sized dent in the tube barely deep enough to notice it, but didn't buckle it. I painted over it and kept going.

[Justin]

x2. The guys who are destroying .25 wall links are running them on buggies and dragging or dropping rigs on them.

[crawlercreations]

I've bent a .25 wall tie rod once. It wasn't a hard bend but it was definitely bowed. That was after about a year and a half of hard wheeling every weekend. Even though I tend to hit the harder trails out there I do not beat on my bronco. Once I saw the bent tie rod I sleeved the new one I built with some .120 wall DOM to make the tie rod .370 wall 1.75od. I went ahead and sleeved my rear lower links while I was at it just for peace of mind. The only issue I have now is I'm worried I moved the weak point to something more difficult to repair on the trail, like a knuckle.

I guess what I'm saying is; for my uses I'll not run anything thinner than .25 wall on anything that will see consistent rocks. For most people thinner wall stuff will work for their uses. But one drop on a rock with the thin wall stuff and it is very likely to bend.

Digger, we need to take a look at my bumpers and see why the .120 wall tubing gets dented so much. Maybe I'm just harder on my bronco than most but my bumpers tend to get dented a lot.

[Gunnibronco]

Thanks guys, I'll stash it and hopefully use it when I link the rear in a couple years.

[Digger]

I've bent a .25 wall tie rod once. It wasn't a hard bend but it was definitely bowed. That was after about a year and a half of hard wheeling every weekend. Even though I tend to hit the harder trails out there I do not beat on my bronco. Once I saw the bent tie rod I sleeved the new one I built with some .120 wall DOM to make the tie rod .370 wall 1.75od. I went ahead and sleeved my rear lower links while I was at it just for peace of mind. The only issue I have now is I'm worried I moved the weak point to something more difficult to repair on the trail, like a knuckle.

I guess what I'm saying is; for my uses I'll not run anything thinner than .25 wall on anything that will see consistent rocks. For most people thinner wall stuff will work for their uses. But one drop on a rock with the thin wall stuff and it is very likely to bend.

Digger, we need to take a look at my bumpers and see why the .120 wall tubing gets dented so much. Maybe I'm just harder on my bronco than most but my bumpers tend to get dented a lot.

You should slow down below 25mph when wheeling.

I did bend a 1.25" x 5/16" wall tie rod after a nasty slip off of a large rock. Slight bend, but was still drivable. The only links I run that are 0.25" wall are the radius arms because they are so long. I have put a pretty good bow in them sitting turtled on a rock, but they snapped back to straight once the weight was removed.

I'll admit I'm not in the upper 5% crowd that needs a Cro-Mo cage and 300M axle shafts. I just don't wheel that hard.