Jerry Feather

After concluding that the original 928 bumper struts cannot be repaired or restored to their original function, I have figured out how the remains of the failed struts can possibly be converted to function instead with a spring.

I originally thought that I was not too interested in this prospect, but based on what I had learned in the other thread about how they are made, and with a little bit of thought about how to do It, I think I have figured out how to use what is left of any one of these failed struts to make a different kind of strut that is solely based on a spring rather than any kind of complicated hydraulic system.

Stay tuned.

Jerry Feather

My original consternation about this prospect was pretty much based on the complexity of what I have found in these struts. When I had a few moments to think more about it, and even make a sketch or two, I was able to recall that these struts can be completely taken apart with only one cut in the lathe, although that cut has to be through both the outer shell and the inner shell of the struts. After that happens the rest is pretty much cutting and fitting and fabrication to put it all back together. The real trick is going to be to find just the right spring to put it back together with.

Kiwi928S4

Hi Jerry,
Were these hydraulic struts just for the USA cars or ROW also as an optional extra - as I see that you can still get these and the non-hydraulic version?

Cheers

Ken

Jerry Feather

Does it really matter? The question is can the failed struts be put to some useful purpose rather than being trashed?

928Myles

...

Speedtoys

When it releases it, is the important part.

Shawn Stanford

You will be pushed clear of the wreck, at which point you can drive away!

DHS928

Boinnnnnng!

Jerry Feather

Thanks, Myles. That is the kind of thinking I am hoping for in this thread. However, I think you are missing one step and that is that the spring must also absorb energy in order to store it, so I don't see them being opposite. As others have already pointed out (I think) the "boing" is the benefit with a spring because you end up not having to replace the struts as with the originals.

Jerry Feather

I am beginning to think about the spring needed for this project idea. The first criteria is the ID of the inner strut housing. That is 1 3/8 inch. The OD of the original hydraulic cylinder is 1 inch. I find that the upper end of the inner housing that the cylinder fits into is kind of fluted or splined so that the cylinder fits snugly into it for about 2 inches. The openings between the flutes or splines is where the 6 staggered oil release holes must be aligned. Those flutes or splines must be reamed out.

My spring is looking like it needs to be about 1 1/4 inch in OD and about 6 to 7 inches long. It will need to have the compressibility of about 3 inches. That will allow for up to two inches of travel in its intended operation (the original struts have 1 5/8 inch travel) and I will plan to load or compress the spring some in the original fabrication or assembly, maybe a half to one inch. So I am now thinking about a spring that is wound with about a quarter inch spring steel rod and about 12 or so coils. That is all just intuition at this point and very subject to some kind of formal engineering.

Shawn Stanford

Wouldn't a spring also work on the outside of the tube?

Jerry Feather

I don't think so. I think it would not fit in the hole in the frame.

And that is not the only reason. Make a sketch and try to figure out just how the thing would function.

And further, consider that the tube fixed to the car is on the outside. The part that moves back and forth or in and out is on the inside. The spring has to function between them in some way. On the outside the spring would not be between anything.

Wait. I have to take some of that back. On the outside the spring would be between the frame and the strut. So all we really need, if the spring will go into the frame and the strut into the spring, is a spring long enough to reach from the back of the hole and out the front about 2 inches. Then we just slip the failed strut, as failed, into the center of the spring and tape it there with duct tape and then bolt the bumper bar to it. Problem solved and no fabrication required.

Eplebnista

Part of me believes this is a problem crying out for a pyrotechnic solution.

Jerry Feather

As to the spring my thoughts are not focused on any kind of MPH for an impact at the bumper, but rather on the strength of a spring that will keep Hacker and me satisfied about not shifting any force to something else, (like the front of the frame), that will fail before the spring reaches its limits of compression or the end of its permissible travel, but still being right there at the limit. I actually have just about no idea of how to determine that.

Jerry Feather

Do you mean like some kind of explosion? Or maybe something like the air bags in the passenger compartment? Now there is a thought.