Front shackle bolt breakage

[LongT]

I just saw a thread on the HAMB (Technical Should I be pissed or is this my fault? - THE H.A.M.B. a guy with a sedan that had the front spring shackle bolt break while driving. The bolt broke where it attached to the batwing not where it goes through the spring. Looked like a fatigue failure to me.

Anyway, since most T's have a similar "suicide front end" I was wondering if many on here have seen similar failures. The front end in question was from Speedway. This is the second of this type of failure I've seen on the HAMB in a year or so.

Bill

 

[Todd]

It could also be that the guy over torqued the thing and stressed it.

 

[LongT]

A small part of me wants to ask the guy for the parts. I used to work in a different lab in this company. It was a metallurgical failure analysis lab. I could probably get my old boss to look at it. He is even a car guy.

Bill

 

[bill4u6]

the first thing i looked for was the shock mounting location guess what there are no shocks on this front end. i am not saying that that the lack of shocks caused this but it sure did not help eather.A rail road track will put a shock on a front end just like a pot hole. there are a lot of other thing that could have gone wrong or were wrong to blame speedway.

 

[GAB]

Seems like it might be a design problem. It looks like the threads come out pretty close to the face of the shackle and they are a stress riser at a very critical point as the primary loading on the part is perpendicular to the axis of the threaded shaft. A solution would be to increase the distance to the threaded portion of the shaft and increase the radius of the fillet between the shaft and the shoulder. While at it, make it a shouldered design and use a sleeve welded to the backside of the plate to increase length of the bearing area on the stud portion on the shackle.

Just an idea.

 

[Youngster]

i agree George. your design is far better. i have to wonder with all the pivots Speedway sells if the application might be at fault.

Ron

 

[LongT]

George, I just knew you would have a quick and well thought out response! Your ideas are always top of the line.

Bill

Seems like it might be a design problem. It looks like the threads come out pretty close to the face of the shackle and they are a stress riser at a very critical point as the primary loading on the part is perpendicular to the axis of the threaded shaft. A solution would be to increase the distance to the threaded portion of the shaft and increase the radius of the fillet between the shaft and the shoulder. While at it, make it a shouldered design and use a sleeve welded to the backside of the plate to increase length of the bearing area on the stud portion on the shackle.

Just an idea.

 

[butch27]

Hey: Can Pope or Young make these? Probably put the other ones out of business. Good job George.

 

[RPM]

I used to make those pivots and sell them. Pretty simple really. 1" tube with an 1/8" wall and a 1/2 bolt weld em together and you are good to go. Then I got to thinkin about what if that bolt breaks? So I quit selling them. I made all the ones on the cars that I have built with no problems. But mechanical stuff breaks, sometimes for no good reason.

 

[Youngster]

george's design is a good onr and makes sence in so many ways. problem is $$$. most people will still order the pivots Speedy sells anyway. and why not. there are a whole lot of them in service with no problems.

Ron

 

[Wild Mango]

I have a Mr Roadster front end on my bucket a' building.
Threaded fasteners will of course fail if they are over torqued (exceeded elastic limit) but they will also fail if they are under torqued or loose, especially in a situation like the shackle bolt because the joint will "work" and "fret". With normal size wrenches it would be hard to over torque a 1/2" bolt, most people tend to under torque
Of course there is always a better way and Georges is how it would be done to get an aircraft "release note".