You guys are making a mountain out of a mole hill. If someone doesn't build a car using quarter inch plate, you think it's going to spontaneously fly apart going down the road. Yet, you're more than comfortable to trundle down the interstate at 75 mph with a 40 year old suspension, with serious design flaws, in a 20 gauge tin can. Could the design be more robust? Absolutely. Is it unsafe? No. The rear shackles will flex side to side within their bushings, but no more so on this design than any other. Let's say this car will weigh 3,000 lbs. Let's also assume a 50/50 weight distribution. Both being fairly safe assumptions for load on the spring. There are 4 mounting points for the leaf spring, so 1500/4 = 375 lbs per bolt. Since this bolt is in single shear, you can divide the load by the area of the bolt to find the stress. Let's assume it's a half inch bolt. That's 750 psi shear stress in the bolt. The average shear strength of low carbon allow steel is 36,000 psi. That gives a margin of safety of 47. Even if you assume 10 times the load from a heavy impact, that still gives a MOS of 4.7. This is why I seriously doubt it will fail. However, nothing in life is certain. 47 times as much strength as you need is a good place to start though.
Is it unsafe !!!! For the last 100 years not one american, foreign or even a yugo automobile mounts the rear springs without supporting the other side of the bolt. I would say its not safe despite what your friends say. I can think of one good reason to add support to those bolts "Safety" I can think of only one reason not to add it "ego" Ever heard of leverage? 47 times stronger wont help! the pressure on that bolt 3 inches out will be about 300% greater than any other car.
Because it is still under construction. Look and you see the mount has 4 bolt holes to hold it to the frame. I'm no rocket scientist, just a old country boy from Georgia, but a simple C channel welded to the frame will improve this design. Spring steel gets lively bouncing down the road and this vibration will cause metal fatigue on the bolt. Even a small utility trailer has supported on both sides of the spring.
I showed my work. Let's see the goodman diagrams and shear/bending diagrams from the rest of you engineers.
The concept is very simple here. With two shear point not only distributes the load, but eliminates rotational force on the load point. The shear is not the major issue. Over time the rotational force will cause stress cracks near the load point. As far as proof is concerned, the burden of proof is on you. It's your car and you're going to drive it. People are just giving their opinions. If you don't like what they have to say, you can ignore it. I don't know why people get so bent out of shape over this stuff. There's no reason to get mad about someone telling you you're wrong if you know you're right, is there?
I don't believe your load assumption is correct. Being that the bolt is contained within a bushing, and is also pre-tensioned, modeling it as a cantilevered beam wouldn't make much sense. It should be modeled as a pin in single shear. If it was indeed modeled as a cantilevered beam, then it would fail as soon as he put the wheels on the ground. It's not the right vs. wrong, it's the dissemination of bad science and information. If people think this joint will fail, they should back it up with some calculation, or else they're speculating without any basis to back it up. There's already enough bad info on the internet, IMO. The endurance strength of 1020 hot rolled steel is 18.8 ksi. Even assuming a 10x cyclical shear load, the stress point falls well below the goodman line. Since he's using a grade 8 bolt (assuming) the Endurance strength for thread root is 54.1 ksi, giving even greater margin.
Hmmm....... Point blank that isn't going to fail....... Is it the best design I have seen.......no..... Some of you are not seeing how this really works.... The whole weight of the car is not on one bolt.....lol...... There is leverage involved here but not the kind of forces you are thinking...... The spring is tied to another mounting pointing limiting any leverage that could shear that bolt...... I have seen many fords come in with the rotted out spring mount deal......They are less weak than this set up........
36000 x the area of the bolt .196sq" = 7068 pounds to shear it. 7068/375 = 18. Your math is a bit off; you only have safety x 18 not 47. Shear strength is not in question. Under lateral loads it will suffer from bending moment. Every time you turn a corner the bolts will be stressed with an angular load equal to (using your assuptions) 1/8 the weight of the car times the vertical distance, from the spring mounts to the bolt, in feet. The area of the 1/2" bolt is .196 squre inches. With 375 pounds and a moment arm of 6 inches (two inches below the shackle) that is 188 foot pounds of lateral force on each bolt. Add to that the sheer force on the loaded side and you easily exceed the safe beam strength of your 1/2" bolt when fixed on one side. Remember that the bolt only feels the effect of bending moment from the side that is fixed to the frame and the other side where the spring is acting upon it. All the stress is transferred through the single point from the outside weld to the inboard edge of the shackle mount. The shear and tensile strength of the 1/2" bolt is more than enough to hold the weight - I have no doubt about that. I do disagree with your assertion that you will have purely shear loads. Even when loaded vertically there will be some bending moment involved and there is no question that in cornering the loads are almost entirely trasferred as bending loads. (there are some tension loads but I feel they are too small to be considered as a part of the equation. There is no doubt in my mind that it will work for a time but I would consider it risky at best under real world stresses in a street car and completely unacceptable in any application where high cornering loads are possible. Some science, some opinion, a lot of "over-engineering" experience born from failures in the field. "a temporary fix should last for 5 years - a real repair should never fail."
BTW ever look at a trailer....lol.....the rear of the spring isn't attached on many models.....lol It's called a hook end/flat end... Trailers are not made to handle but point is this....there is not the load some of u guys think there is.....
nope but they may have a Car or a truck sitting on top of it I get it but seriously this guys design is fine and I did forward it to a Ford Engineer I am waiting his reply......but I already know what he is gonna say....I talk to him all the time about this kind of stuff.....Larry Head is his name been at ford for 30 plus years in fact he retired but he is the only person qualified to do what he does(which I cant really say) so they hired him back for some crazy amount of money.......I will let him weigh in.... Just so we are clear you guys can see this not a stud welded to a piece of steel right? It is a bolt properly graded and sized that is inserted through a sleeve.... Also the fact that it has bushings and shackles reduces the stress it receives by absorbing it? that is called flex......It's fine......Now if the front mount was made in a similiar fashion I would say it would fail....It isn't. Since a vehicle is driven forward the axle wrap puts most of the stress on the front bolt .......I have studied suspension to design to the point I can recite this stuff in my sleep...I love it!!!!! OH OH OH!!!! I forgot to add the main reason we have spring shackles on cars is this........Drum roll please..........and Mr. rthomas771 is the winner.... drive train rotation torque stress.....see that is why this guys set up will work......He has the aforementioned Shackle that was designed to combat this specific stress in a suspension system designed for an auto......
I think i figured out how to explain it so some of you cavemen can get it.... Just kidding guys..... That bolt receives x amount of stress but it's only stress is from the shackle itself....now it is linked of course but we are talking about direct leverage. now I want you to take a 6 inch extension and go and try and pry up a sewer lid....... or grab a 6 foot spud bar and try the same......maybe some of you are nodding now......maybe some of you are still in a haze from all the drugs you did in the 60's and that's ok I suppose..... the force was the same in this test(whatever muscle you got) the only change was leverage. The inherit design of a shackle also makes it a pivot which reduce direct leverage
Thank God, engineers have never been wrong otherwise we would have something called "Re-calls". Cant wait to hear his reply
