What steel needed for STRONG shackle pins?! Broke my OME ones!

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This might not help, but, a long time ago on deuce and a half military trucks, there was a method for greasing pins. I never did it myself, just attended the class, but the method involved parking the truck for high camber on one side, both axles. this allowed you to squeeze grease in on all four (4) wheels, the inside of 2 and the outside of 2. Then park the truck in the opposite direction and do the other sides of each wheel, either inside or outside.

Another thought.. There's some metal heads on 60 and 80 forums here that sound like they really know what's what, maybe they could help with the right choice in alloys.
 
Chester - hmm might work with my old, worn bushings, but with the new ones I don't think that works ;)

Here a pic of the old pin... as said, to me not very well made. On the side where the grease pin is (weakness) they made the diameter 11.6mm, the rest is M14 or 14mm. 11.6mm plus the greasing hole seems to me not very smart. Why would Toyota make a pin of this big diameter to have it at some spot at 11.6mm? That's also the spot where all 3 broke.
I thought to have both sides made the same at 14mm and drill out the thread on the braket where the pin goes in. I thought to torque it with the nut so the pin can't turn.
OME_Pin.webp
 
Toyota didn't make it, Old Man Emu (or a copy of one) did. The factory pins are solid and you DO NOT grease them.
 
i just checked, they made an 4mm greasing hole at this 11.6mm spot, not really smart such a big hole in my opinion!

I was told to use 4140 steel. I can get this in Lima and delivered here to me in Cusco. Not cheap (I have to buy 4meters) but it's 99% sure the real stuff, no chinese crap... what do you guys think? The right steel to go?
 
I'm struggling with the physics of this. Is the shackle limiting the motion of the spring pack? Which spring packs and shackles are you running? (Say "hey" to Sicuani when you pass through for me. Spent some time there 25 years ago)
 
all can move free. using OME heavy springs, means 12 leafs on rear on each side.

ordered now 4meters of 4140 steel in lima for 40 $. found a machine shop that will make the pins for 5 $ each. will make 24 (12 for later use)
the machine shop said he can cut the thread up to the shaft. no reason to cut down to 11.6mm between thread and shaft. so i will have a M14 thread going all the way. greasing hole i will reduce to 2mm. should be much stronger like the original OME design.
 
4140 is high tensile steel, can be nitrided (like case hardening) for wear resistance. it's pretty tough massive gains compared to mild steel. I would still put a grease nipple in them well at least a few of them see how they go. Just ask them to make the hole dia slightly smaller, but really 4mm would probably be ok.. Was the thread undercut on the original so the pin tightened to the shoulder? I would consider copying the original design if so? Possibly just increasing the rads on the undercut ( shear point) would also help! Good luck!
 
Carpet -

Yeah, the thread was undercut A LOT (see picture above!) I see no need for this or am I missing something? There is a radius, but not very big. Look at my propostions below...
I very probably have no possibility to nitride that here in Cusco! MAYBE in Lima, but I am already very lucky to have found good steel here where everything is made of crappy chinese steel. But I always use MOS2 grease, so that should help against wear.


Which design should I make?

On top I drawed where the side brackets are. The right side has a M14 thread where the pin goes in, the left side only a 14mm hole where the shaft sits.

Either I make it with the M14 thread going all the way to the shaft, I can keep the brackets as they are and have no 11.6mm section but the thread goes down to about 12.5mm instead of 14mm like on solution 2.
Solution 2 means I have to drill out the right bracket to 14mm and probably need to install the pin and bracket in a vise and lock it with the nut.
I think this SHOULD work fine for the shackles, but not sure if this is smart to do for the front pins where it goes through the frame and this thick round holder on the outter side of the frame. I would also have to drill this holder out to 14mm.

What do you guys think? Any opinions?

design_type.webp
 
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Blade:

I'm a mechanical engineer with 30 years experience designing machinery. The following are my comments/opinions.

- The undercuts after the threads, are there to facilitate cutting the threads on a lathe.
- The large radius at the 11.6mm section is there to minimize the stress concentrations at that point. A sharp corner would have failed much sooner.
- There is no shoulder on the grease fitting end due to it threading into the shackle. That puts the under-cut in shear, and obviously increases the stress.
- The grease fitting bore doesn't help, but it doesn't hurt as much as one would think.
- 4140 will be about equivalent to Grade 8 bolt strength once the threads are cut as you propose. It can be a real bear to machine, depending on it's state of heat treating, and the machinist will probably have difficulty cutting the threads. And it will need to have an undercut also.
- Your "New 2" is the way to do it if you are fixated on having pins machined. Beware of the sharp corners at transitions in diameter.

Personally, what I would do is get some great honking Gr8 or 12.9 bolts (20mm?), drill out the shackles or make new ones, and bolt the assembly together. Use a castellated nut and cotter pin. Failing that, double nut, or drill the nut and pin it.
Things to watch:
- The shank of the bolt will be undersize relative to it's nominal size - deal with the holes and the threads on the bolt appropriately.
- The length of the bolt needs to be selected so that the shackle does not bear on the threads - some of the bolt threads will likely need to be cut off. Use HARDENED washers to get the stack height correct.
- Don't over tighten!

Alternatively, you could use a 14mm bolt, and machine a sleeve the length of the bearing section of the current pin..

In closing, the existing pins likely failed by taking a hit sideways - like falling into ruts on the road. Thus putting the threaded section into combined bending and shear. Strengthening the weakest component will just move the failure point to the next weakest. Sometimes that is not a good thing.

Hope that helps.
 
Jim_Hbar said:
Strengthening the weakest component will just move the failure point to the next weakest. Sometimes that is not a good thing.

Hope that helps.
Click to expand...

Like putting a 30 amp fuse in a 15 amp circuit because you keep blowing fuses. Next up: an electrical fire.......
 
Jim_Hbar - as much as I learned and also hear often is that bolts no matter what strengh are not built for shear forces and in this application it's a lot about shear forces.
I got now 20mm 10.9 bolts that I let machine down to 18mm but with no greasing hole. Problem here is that ALL bolts are chinese made. Even if they write it's 10.9 or 12.9 it's still probably weak chinese steel that I don't want to trust!
That's why I now ordered 4140 steel from a very big company in Peru that also delivers to mines etc.

The question is if the 4140 steel is the same strength as the original OME or even stronger? Do you think OME uses stronger steel than 4140?

Can I use also lock nuts instead? (nylon etc)

Isn't this crack due to fatigue after 90'000km of forces working on those pins? The surface is very worn down, up to 1mm deep grooves! Is a shackle pin something like a fuse that is SUPPOSED to break when too much force is used? As said, we didn't drive harder than usual in Peru...
 
Pressed into the hanger.
 
I'm a physics hack (on a good day), but is this right? The weight of your truck pushing down on the spring (with or without Peru's crappy roads) forces the leaf pack to flex, which elongates the eye-to-eye distance of the leaf. When this elongation force exceeds the shear force of the pin, pin goes bye-bye? Sounds like a longer shackle that would allow more rotation, and hence more eye-to-eye distance increase, would help. Either that, or you're massively over loaded, and that truck is just coming down, no matter what suspension parts are in it's way. But it's crazy that you don't blow tires or shred PU bushings before shearing the pin... What is that plate thing hanging down from the frame behind the shackle?
 
re_guderian said:
I'm a physics hack (on a good day), but is this right? The weight of your truck pushing down on the spring (with or without Peru's crappy roads) forces the leaf pack to flex, which elongates the eye-to-eye distance of the leaf. When this elongation force exceeds the shear force of the pin, pin goes bye-bye? Sounds like a longer shackle that would allow more rotation, and hence more eye-to-eye distance increase, would help. Either that, or you're massively over loaded, and that truck is just coming down, no matter what suspension parts are in it's way. But it's crazy that you don't blow tires or shred PU bushings before shearing the pin... What is that plate thing hanging down from the frame behind the shackle?
Click to expand...

I'll bet it's all of that, and more. More or less static where the moment is 90 deg, up and down. I think the harder to figure is the torsional distortion where the moment geometry is everything but 90, and all that weight is a multiplier. Tough to imagine a better solution to the issue than more pin, but what gives next, the gusset?
 
Chester said:

I'll bet it's all of that, and more. More or less static where the moment is 90 deg, up and down. I think the harder to figure is the torsional distortion where the moment geometry is everything but 90, and all that weight is a multiplier. Tough to imagine a better solution to the issue than more pin, but what gives next, the gusset?
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How does this not bottom out on a bump stop before the range of motion of the shackle is exceeded? Sounds like OME didn't design the shackle correctly for the length of the spring pack. Either that or the shear strength of the pin is less than the force required to compress a 12 leaf pack all the way to the bump stop? Plus all the torsional forces...
 
re_guderian- I check often on the axle housing to see if the bump stop (you can see it on the picture) touches the axle, means bottoms out. I don't see the print of the bump stop often on the axle, that means, I don't bottom out very often. On the front it happens more often, but the distance from bump stop to axle housing is also less on the front.

I think the shackle lenght (bolt to bolt distance) is the stock length from Toyota. I compared it to my friends HZJ79 and it was the same if I remember correctly.

Never had any issue with tires (BFG Radial TA and now my 2nd set of Toyo MT, both Load Range E) and the stock bushings had around 90'000km when I replaced them. They were all ok, worn (around 22hole instead of 18mm) but nothing cracked.
I had issues with the rims! Broke 2 Mickey Thomson alloy rims (not really made of offroad use) and then Nissan Patrol steel rims. Got in Colombia Made in Japan J8 series OEM rims (almost double as thick as the Nissan Patrol rims) and so far they hold up good!

Overloaded yes... around 300-400kg. Got 3.8-3.9tons, although trying now to go down to 3.7-3.8tons.

Why did Toyota design a 18mm pin, presses it in on their shackles and OME uses 11.6mm? You can have a 30mm pin, if at one spot it's 11.6mm it's like having a 11.6mm pin all the way, right? Still not sure if OME really did design this pins well...
 
Blade said:
...I think the shackle lenght (bolt to bolt distance) is the stock length from Toyota. I compared it to my friends HZJ79 and it was the same if I remember correctly...
Click to expand...
You would think the shackle should be longer. If the lift springs have more arch, then the eye-to-eye distance when compressed would be longer than OEM springs, hence requiring the shackle end to move through a longer arc as it compresses. Otherwise, the pack is going to compress, and the shackle arc will limit it's travel, at which point it can't compress any more, and then put all the stress on the pins, no? Be interesting to compare the arc length of your spring pack v OEM, and the shackle pin to pin v OEM.

anyways, plenty of cool things to see in Cusco while you wait for new pins to be made!
 
Blade: "as much as I learned and also hear often is that bolts no matter what strengh are not built for shear force"
- That is a black and white statement and the real world is gray. Have a look at the bolts used in steel structures.

Problem here is that ALL bolts are chinese made. The issue isn't where they are made, it's whether they were made to the standard and tested. Some Chinese manufacturers will stamp "Made in Germany" on the part if you want. Your call.

From what I can see of the failed pin (where you are holding it in the picture in post #4), it appears to have fatigue crack(s) at the top and bottom. That case is likely due to bending forces on the pin, and is a result of the design with the threaded connection. Then it likely failed in shear from an impact.

18mm dia. = 254 mm^2 x-sectional area
14mm dia. = 154 mm^2 x-sectional area
11.6mm dia = 105 mm^2 x-sectional area and 93mm^2 will the grease hole.:(

On top of that, the stress concentration due to the undercut design is likely almost a factor of 2. (Just a SWAG)
The 18mm bolt will see between 20% and 40% of the shear stress that the 11.6 mm section does/did...
14mm - between 40% and 66% of the shear stress....
 
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