I have a set of Ground Control coil overs for my 72 240Z... the question is: Do I have to cut off the old spring perch and weld on the supplied smaller spring perch?

My only reservation with doing so is that, if I at any point want to go back to stock springs, I wont be able to... thanks.

Dave.

Yup, I'm afraid you do have to remove the stock spring perch. There would be no way to put the spring collar on the strut tube if you don't. If you are cutting the strut tube to shorten it would be doubtful you would want to use the bottom stock perch anyway.

I found the easiest way to remove the stock perch was to use a 6 inch grinder and grind off the weld on the bottom just enough to let the perch loose. When you cut out the section just cut it above and below the weld seam where you just removed the stock perch. Saves a lot of grinding that way. You can usually rent a large tubing cutter (for up to 6 inch pipe) that will work great to cut the strut tube. Not only do they cut straight but it will be easier to chamfer the edge of the tube when you go to weld it back together, it will already have a bit of chamfer from the tubing cutter, just add a little more with a file and you are good to go.

Really stupid question I have wondered a lot about: When you cut your struts (take a section out of them for more travel), How do you know what length cartridge to buy? I have never seen a reference chart for cartridges based on size (like radiators). Everywhere I have shopped just want to sell you the one for "your car".

steve77

Well, with the Ground Control set up they will sell you a recommended strut cartridge for your car. Then when you cut the strut housing you will measure the cartridge they supply in the housing with the top mounting nut installed. You will extend the strut cartridge (won't have to worry about it with a gas cartridge since it will be fully extended), install the top mounting nut and drop the cartridge all the way to the bottom of the housing and mark it with a piece of tape on the shaft of the cartridge. Then you raise it all the way to the top until it comes in contact with the mounting nut, then mark it with tape, and measure the distance between them. This is how much you will remove from the housing when you cut it. In effect you are shortening your housing to fit the strut cartridge, so in the future you may run into a problem if you try to change to a different type of cartridge. You will have to make sure it is the same length as the one it is replacing or it won't fit into the housing. Not all strut housing will be cut the same amount from one car to another unless they are all using the same cartridge, although there may not be much difference , it will depend on the brand of cartridge and what type it is.

Hope that answers your question. I thought it odd when they told me they were selling me a set of cartridges for a drag racing application, but they worked OK on my 280 IT car. All depends on the compression/rebound of the cartridge in order to fit it to your application.