Al Trailing arm "Upgrade" nightmare

[drwhosc]

OK Long story, but looking for some help on this issue. I have a 71e. I got talked into doing the Al trailing arm update, and It was a mistake.

Here is my issue. My driver's side shock bolt is having bad days. It sheared itself off about a year ago. I did replace it, but went with a helicoil solution. I went under the car last night, and the bolt has backed itself out. I took it completely out, and thankfully it was not sheared, but the threads and the helical were rounded off. Still some threads left, but obviously not providing the support needed to handle the stress.

I was able to turn it bak in and get it to seat, but now it will not tighten. the bolt spins and will not torque. So the system failed. and I am looking for advice on a potential solution.

1. I still have my old steel arms, and I am seriously thinking of undoing this upgrade.
2. get a longer bolt. It looks like I can get a longer bolt in there. (used a porsche stock 8,8 bolt)
3. Modify the arm to cut into it to return the geometry as per threads on this forum
4. Epoxy in a steel leave.

Believe it or not, I am thinking about option 4 and trying to source a steel sleeve with a hex head, any ideas ?/

So what do you all think I should do.....

thanks -- rr

[37yrold911]

post a pic - not clear if you need a new bolt or what

you mean at the bottom I assume?

this would have happened anyway when you went to replace the shock

[Jim Breazeale]

I am not a fan of "aluminum trailing upgrades" for 69 thru 71 cars. Installing aluminum arms on a 69 to 71 car throws the rear shock geometry off and causes problems with clearance between the rear shock tube and the shock. Most people wind up removing the dust covers on their rear shock absorbers to "bandaid" the problem. If you insist on doing it, I will be more than happy to sell you some aluminum arms. They will come with a warning, though. That way when people complain, I get to say "I told you so!"

Ciao

Jim
PS: rr, put your original trailing arms back on the car, but replace the rear axle bearings before doing that. You won't have to think about your rear trailing arms ever again.

[72targa]

Worked nice on my '72 (with great negative camber!)...

[Jim Breazeale]

Worked nice on my '72 (with great negative camber!)...

I have no problems with doing it to a 72 or 73

[drwhosc]

I do not want to take it apart for a picture just yet. basically the end of the threads are fine for about 2-3 turns, then rounded for about 10-15 turns then normal again. I looked at the helicons on the inside, and they are flattened at the very end. Unfortunately the oil was too deep for a helical, so it sites in the deepest 2/3rd of the hole. This left a gap, and I think the assembly pistons, and thus I do not think this is a solution to this problem. When my original bolt sheered off last year, I tried like hell to use an extractor, but could not budge the bolt, so I had to drill it out. this messed up my step insert, and I was forced to go to a helical solution. I also read you could not but them back to back so I could not fill the entire gap.

Long term I am going to reinstall my old steel arms. But that will be a winter project. I am having difficulty finding a fine pitch M14 bolt..... BMW has a longer one the is 100mm in length, and the extra bite may allow me to get another year out of this.

Unfortunately I am going to have to resource my hubs as I sold them from my old arms about 8 years ago when I did this. I am not sure if the ones on the al arms will fit the steel ones. and I will have to get new shocks.

Also I am really curious about a Steel sleeve. Does anyone know where to source one of those. that looks like a better solution then the Helicoil,

[John Z Goriup]

Switching to aluminum trailing arms is only a problem involving 1970 and 1971 911s. For some inexpicable reason the top cross-member which contains the upper rear shock-mounts was changed for those two model years, and when aluninum arms ( which appeared on later model cars ) are installed, the angle of the shock changes and can cause problems. I say "can cause problems" because it's not a universal problem everyone encounters who performs this operation - appearantly there was sufficient variance in the parts of the chassis affected by this modification that it's not a guaranteed problem. I have seen conversions where only one side is problematic, I've even seen folks get away with no problems at all, but chances are if you installed alum. arms and made no other changes you will experience interference and problems such as described above. Aluminum arms can be installed so there will be no interference, but it may take some welding and maching to arrive at a satisfactory solution - what I mean by that is that you can do this the shade-tree, hammer mechanic way, or you can modify the arm and the crossmember so it works correctly in all situations under all circumstances and restores unhindered shock function, and you, the owner contemplating this change, will have to decide if it's worth it to you and if it will benefit the way you use your car.

Personally, I find the additional strength of the aluminum trailing arms and their reduced unsprung weight a worthwhile improvement. Another benefit is that you open a lot of options to mount bigger, more effective brake calipers if you find there is a need for that in your cspecific case.

If there is sufficient interest ( what I mean is if there's more than just one owner who seems less than fully committed to carry this modification through ) I'd be happy to post a detailed thread to once and for all put this "mysterious" issue to rest, since it appears there is a great deal of confusion, 'old wives tales' & less than detailed, thorough knowledge of what happens when you try to install alum. trailing arms on these two model year 911s.

JZG

[RSTarga]

The alu arm needs to be modified to accept the different angle of the shock. I have a pdf of an article that came out in Excellence years ago that details the process. Cant post here but I can send it to your email.

[37yrold911]

that is from Sherwood Lee's web site - it's under the name of his company (which I forget)

[Chuck Miller]

that is from Sherwood Lee's web site - it's under the name of his company (which I forget)

Seine Systems...........