View original topic: Broken adjuster screws
dustymojave Fri Jul 17, 2020 12:27 pm

So I took my next door neighbor out for a ride in my Baja today. I 1st offered that ride nearly 2 years ago and we've been trying to get a chance ever since. I'm retired so I can do such things most any time. He's still got 25 years to go towards that status. They commute to and from LA 5 days a week and his wife keeps him CONSTANTLY WAY busy.

So this week he's on vacation, and the wife is working today after 3 days of vacation. They can’t go places like they normally do, so they’re mostly doing a “staycation”. So after he painted the trim on both ends of his house this morning and needed to let it dry before painting the walls of the house, he said, "OK, we can go now."

We jumped in the Baja and I gave him instructions on how to put on and adjust the 5 point belts. He's never seen any such thing before. Never been in an offroad car before. Never seen a race car other than a couple I’ve had here at the house.

We took off and headed out into the desert. He was having fun and we got about 6 miles east out into the dez when I was going to turn south. Just cruising gently in 2nd gear and... WHAM! The front end slammed down into low rider mode and the car steered slightly left into the bushes, whether I wanted it to or not.

It turns out that the front wheel and tire combo I have on it these days is a little different than the ones I used when I set the car up. I cycled everything quite carefully when I last re-built the car to the form you guys see in my pictures these days. Everything cleared with a minimum of room for my pinky finger between components at full bump and full steering lock. But it turns out that now the tires at full bump rub against the ends of the front bumper and that restricts steering at full bump.

I couldn’t steer more than a few degrees so driving it home wasn’t an option. I had to call a friend to go to my house and get my trailer, then bring it out to fetch us. Only about 6 miles and fortunately, we were close to a graded dirt road, so he was able to get close to us with the trailer without trouble. THANKS MANNY! We were having fun sitting out in the 100°. Good thing we’re intelligent enough to take water and Gatorade with us on the jaunt.

Although I’ve used the car quite hard since that last rebuild, this was the 1st time I’ve actually BOTTOMED the 10-1/4” of front suspension. The rear has always, in spite of the 28 short torsions with stock length trailing arms, occasionally bottomed. I’ve had this wheel and tire setup for several years but this was the 1st time the issue has raised it’s head.

So I'm gonna have to cut the ends off the bumper and repair the adjusters.

So that brings me to the adjusters and why they broke. When I last built this beam, I bought adjusters that were supposed to be Sway-A-Way brand. They probably were not. They have 1/2” coarse threads in the inner blocks. THAT is the problem. The bolts that serve as combo grub screws in the adjusters are in shear. The coarse threads that dig deep into the screw reduce the functional cross section of the screw to less than 3/8”diameter. By comparison, fine threads result in a cross section of about 7/16” diameter. That may not seem like a lot, but it has a substantial effect on shear strength of the screw.

When I worked in Plastics research back some 40-45 years ago, this effect was something we considered in choosing plastic materials and we had tests for it. Such as the Izod-Charpy Tensile Impact Test. In that, you take a piece of flat material such as 1/8” thick, shaped like a dog bone. You test pieces by inserting them in the end of a weighted pendulum and clamp one end to the pendulum. The other end is clamped to another weight that fits in the pendulum. The pendulum alone will swing freely. But there is an anvil at the bottom, and the weight that clamps to the test piece will strike that anvil and not continue beyond. You draw the pendulum back to a latch, then release the latch to drop the pendulum. There is an indicator needle pushed by the arm to show how much force is removed by the impact. If the piece does not break or stretch, then the indicator is at “0”. A free swing with no test piece in the clamps will take the indicator to full travel. So you 1st test pieces that are in the prescribed dog-bone shape of a known cross section at the center. Then you take samples and notch the side in the middle of the dog bone. That notch is very precise width and depth with a precise full radius in the bottom of the notch. Some materials are little affected by the presence of the notch. Some material are dramatically affected. Some materials will lose over 80% of their strength with that notch. 4130 chrome moly steel, while without the notch is more than 2x as strong as 1010 (mild) steel, with the notch, is weaker than 1010 with the notch. One of the reasons I’m not real fond of 4130 for roll cages.

So in the case of the screws in the adjusters. The bigger notch of the coarse thread results in a far weaker screw.

Now I have to get those old adjuster block out of the center of the beam where I welded them in without cutting the beam back apart. Because I don’t want to just put a bandaid on the problem and let it happen again. I want to install bigger stronger screws in the adjusters. The stock grub screws are 14mm fine thread. So their cross section is just a hair under 1/2” or 12-1/2mm. So maybe I will be able to re-tap the inner adjuster blocks to 9/16”-18 and get new set screws and jam nuts to match. Seems to me that is the size they SHOULD HAVE BEEN from the beginning. Especially since the adjuster screws are longer than stock and are under shear loads that the original never are. I would use metric, but in the US, availability of metric hardware is still not equal to the availability of inch sizes.

Getting the inner adjuster blocks out of a beam with the adjusters welded in is usually a problem if the welds have full penetration as they should. Just the other day there was another thread in the Samba about doing just that job. He was lucky and was able to use a pipe to drive them out past the welds. I MIGHT be able to, but might not. I COULD drill and tap the blocks in place. I’ll have to ream the outer blocks to 9/16” as well. I hope they will stand that without having to make new blocks and new adjuster brackets. If I DO have to make all new, then I’ll upgrade the outer adjuster screws to 9/16” as well.

dustymojave Fri Jul 17, 2020 12:30 pm

Images to follow. I started this yesterday evening, then visitors arrived and then dinner, feed the dogs and take them out............So I'm back to it today.

jsturtlebuggy Sat Jul 18, 2020 4:19 pm

Sorry to hear about the breakage. It sucks when that happens. Will the newbie want to ride with you when you get it fixed?
The SwayAway King Kong adjusters use a 5/8" fine thread socket head bolt for one that use as a grub screw and holds the adjuster block. They still use a 1/2" fine thread socket head for the adjuster bolt.
I redid my Meyers Manx Kick Out for more off road use since I sold my orange Subaru Powered Manxter Dual Sport that you saw me in at Big Bear a few years back.
I went with a King Pin style beam and got rid of the Ball joint beam. It is a beam made by the guys that use to be Suspension unlimited. Had to go through a shop to buy it. Had them install the King Kong adjusters in it when they were building it. I still reinforce the brackets more that hold the adjusting screws. This was after seeing how the brackets bending on the Ball joint beam adjusters and they looked the same thin thickness.

dustymojave Sat Jul 18, 2020 7:41 pm

Promised pictures.

Both of the broken pieces wound up down in the bottom of the front skidplate.

66 Shorty Sun Jul 19, 2020 1:14 pm

The adjusters I have on mine are M14 x 1.5. That's roughly a 1/2" minor diameter for the threads... that should be pretty good, I'm hoping...

dustymojave Mon Jul 20, 2020 4:30 pm

I've ordered 9/16 fine thread bolts (can't find set screws in 14mm or 9/16"), jam nuts, and drill and tap.

This evening I plan to start working on drilling out the old broken set screw and bolt.

Bolt because I had broken a set screw many years ago and replaced that set screw with a bolt as I wanted to replace both at the same time, had only one spare screw, couldn't find a set screw at the time, so one got a bolt with the tip re-shaped.

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