Broken 300ZX subframe stud

MarcusMcRae · **Posted:** Mon Aug 20, 2007 5:19 pm

So, I have been helping a friend of mine remove the damaged rear subframe from his son's '90 300Z. I have not been able to stay there to do it all at once and he has been doing some of the little stuff in order to remove the subframe. Loong story long, he decided to remove it without me and broke one of the four studs that hold the subframe on.

Everything we have found says that the stud is welded/built into the frame and has to be cut out and replaced from a donor car. Anyone know someplace that can do this??? I was thinking competition cages.

Wes Eargle · **Joined:** Mon Oct 27, 2003 9:47 am **Posts:** 3683

Any chance that you could get a nut welded to the top of the housing and put a bolt into it from the bottom?

MarcusMcRae · **Posted:** Mon Aug 20, 2007 8:41 pm

Wes Eargle wrote:

Any chance that you could get a nut welded to the top of the housing and put a bolt into it from the bottom?

The top of the stud is totally enclosed in the frame. There is no way to get to it from the top. From what I've read you have to cut the section of the frame around the stud out and replace that section from another car.

Richard Casto · **Posted:** Mon Aug 20, 2007 9:54 pm

Marcus,

I don't know if you can find anyone in the area who does this, but there is a process known as EDM (Electrical Discharge Machining) or "Spark Erosion". Basically an electrode is used to electrically cut a hole into metal. For example if you have something like an expensive engine block or head that has a broken stud and you don't think you can easily weld a nut on, or drill a hole, you can use EDM. They can either cut it so close to the threads that it just falls out, or cut a square hole and then hammer in an easy out and back out the stud.

A quick Google search didn't help me find anyone local. But here is a UK location that will at least give you an idea on how it works...

http://www.foretract.com/marine-stud-removal.php

My guess is that even if you find someone local that is it not going to be cheap. But I have heard of this being used to save Porsche heads and cases that had studs broken off in them.

Good luck and hope you find an easy and cheap solution.

Richard

George Bright · **Posted:** Mon Aug 20, 2007 9:56 pm

Here is a thought. Cut a hole in the frame section opposite the stud so you can insert a nut. Then weld a nut in place after you have driven out what is left of the stud. And finally weld some metal over the hole if it weakens the frame section.

Dustin Fredrickson · **Posted:** Tue Aug 21, 2007 12:56 pm

How about just welding the new subframe on over the broken bolt? Worst case is that the subframe needs to be removed again at some point, and this section has to be replaced anyway. Much less complex and likely stronger than doing all that work just to put a new bolt in. Of course, this assumes there's not bushings or other gorp in the way.

Richard Casto · **Posted:** Tue Aug 21, 2007 1:37 pm

I am looking at George's diagram and I am thinking how he has it drawn is not how I envisioned the problem. But his idea of cutting in from the top gave me an idea.

George shows the stud sticking out below (which I assume is not how it is, otherwise you would just weld the nut on it). I expect there is a nut (or something like that) welded on the inside of that section and the stud is just screwed into that nut.

Maybe you could cut a hole in the top like George suggests, but if the stud goes all the way through the nut on the inside, you may have enough of the stud sticking out on the inside to weld a nut on inside the box. Then remove the stud from the inside (via the cut hole). However that is a lot of "ifs". Especially since you could cut your way in and find that there is no room to weld on the nut.

If non of the above is possible then I guess you may need to cut out that section and replace. Assuming that section is good (just a stuck stud), I would use a thin cut off wheel on an air die grinder so that once removed, you may be able to find a way to get the stud out and then weld the same piece back into place.

George Bright · **Posted:** Tue Aug 21, 2007 4:53 pm

I am not sure how the stud is attached to the subframe to start with. In my old PL510 a couple of the studs in the unibody were put in like a wheel stud. A knurled piece pressed through the box section before it was attached to the floor pan. My suggestion was based on the original 300zx stud being assembled like that. On the old car the studs that held the rear suspension crossmember were threaded into a captive nut in the unibody so they were threaded on both ends. I think I still have a couple of these in my parts pile in Winston Salem. I parted out two PL 510s while I played with them. Boy do I miss that car. :cry:

The problem with welding a piece over the old section is that you will change the spacing which will tweek the suspension geometry.

Dustin Fredrickson · **Posted:** Tue Aug 21, 2007 5:52 pm

George Bright wrote:

The problem with welding a piece over the old section is that you will change the spacing which will tweek the suspension geometry.

Well, my suggestion was not to weld a piece over, but rather grind any offending bolt pieces off and replace the bolt's function altogether with weld. If that's possible given the design, of course.

Richard Casto · **Posted:** Tue Aug 21, 2007 5:55 pm

After re-reading the original post, it sounds like your diagram might be right George. It sounds like the body had a stud sticking out. It still might have been in a captive nut in the unibody. Everything I have been working on (Honda and Porsche) seems to be of the style of a captive nut that is integrated into the body and then you just use a bolt vs. a nut on a stud.

Marcus, any news on this?

MarcusMcRae · **Posted:** Tue Aug 21, 2007 9:09 pm

George Bright wrote:

The problem with welding a piece over the old section is that you will change the spacing which will tweek the suspension geometry.

This would be the simplest solution but the subframe butts right against the frame. Like George said, this would change the geometry.

I am still going to try and heat up the frame and take a pipe wrench to it and see if I can get it to budge. It seems completely idiotic to weld the stud into the frame like that. I just have not had a chance to give it a good whooping.

I had my friend email Chris Schimmel a couple pics of the stud to see what he thought we could do if it does not come out.

Bernie Baake · **Posted:** Tue Aug 21, 2007 10:26 pm

You guys have totally missed Dustin's sugestion. Instead of bolting the subframe to the frame, weld it to the frame. Forget the stud. If you position it properly there will be no suspension geometry problems. You stated that it butts right against the frame make your welds where it butts up to the frame. game over

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Broken 300ZX subframe stud

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