rear suspension- update to Al trailing arms

[jpnovak]

Part of my project includes an upgrade to the aluminum trailing arms from my 78 SC donor. I know you are supposed to mill(or otherwise remove) some material from the rear shock mounting point to restore shock geometry and clear the heat exchangers.

While prepping my arms for installation the other night I pulled out the tired steel bananas for comparison. The position of the shock mounting point is exactly the same between the two.

I measured from the hub to the shock mount and the eight of the arm. dimensionally these are the same.

I guess I don't have to mill them afterall.

Any ideas on this?

[Paul Thomas]

Jamie
I have heard the same thing about grinding a little off of the mount. There was even an article on this in European Car Dec. 2000. I have had mine in for a few years and the only rubbing is on a side of the shock that this mod wouldnt fix.

I have always thought that a better fix would be a sherical bearing in place of the rubber bushing. I emailed Elephant Racing one time to see if anyone there had ever considered this. They did not bother to email me back and i didnt try again.

The biggest plus, with the bearing, in my book would be that the bearing might not fight more negative camber like the rubber one would. If you want a few pics of where mine rubs let me know. I have a spare set of rear shocks, i may try to work out the bearing thing from a place in town and see how it works before i try it on the car.

Paul

[Paul Thomas]

Ok, here you go Jamie. I have nothing better to as i am on vacation this week. Obviously the car is on the ground so you can't see the rub, but it barely touches.

Paul

[jpnovak]

Thanks Paul,

So I guess you did the mod and it still rubs a little on the side of the shock. Is this correct?

What rubs? Is it the hats in the shock tower/cross member?

I would love to do spherical bearings but the funds will not allow right now. The rubber ones seems to be in good shape so I will leave them in.

Enjoy that vacation. You should head up to the mountains and run the car a bit.

Jamie

[Paul Thomas]

Actual it only rubs a little at the entrance to the tube? that goes to the top mount. I know there is a word for that thing but it escapes me. I would just do it up and check it later. That grinding is any easy job once the car is together. Heres a pic of the old shocks, you be the judge.

Paul

[jpnovak]

Doesn't look bad enough to worry about. I think I will install and see what happens.

Thanks for the great picts.

Jamie

[Chuck Moreland]

Paul, sorry about the non-reply to your email. In all honesty I never saw that email.

We have had some web hosting issues and it is possible you sent your message while we had a problem.

To answer your question monoballs for the top of the rear shocks aren't in the plan. The rear shock tops don't affect alignment settings the way the fronts do, so no benefit there. As for the rubbing issue, I'm not sure a shock top monoball would buy you much if anything.

[jluetjen]

As far as the rub that you're trying to avoid, it has more to do with the shock rubbing on the heat exchanger and less to do with the shock rubbing against the shock tower. The shock tower rub can happen and seems to be fairly minor. The left heat exchanger is further forward then the right side, and on early cars will interfere with the shock body at at full bump if you don't cut away some metal where the shock mounts to the trailing arm. In my case ('69E) I took off most of an inch and also gently hammered the seam over on the heat exchanger. Rather then grind down an inch of metal, I found it faster to take a cutting wheel and cut straight in at the point where I wanted to stop taking off metal, and made a second cut from the other direction to take off about 90% of the metal. Then I used the grinder to finish the job. What you may not see is that there is hardened steel insert cast into the trailing arm which can be a "female dog" to grind through.

Have you done a search through this BBS on the subject, there have been a number of threads.

[jpnovak]

John,

I did do a search. In fact I wrote a thread a while ago asking how to do this. I am just now cleaning the suspension to make my car a roller again.

My question comes from the measurements of the arm itself. If the stock steel arms clear the HE's, and the Al arms are the same dimension, one could deduct that the Al arm would not need to be modified to fit in the same manner as the steel arm. I was thinking I did not have to modify anything to get it to clear.

[Paul Thomas]

Chuck,
No big deal about the email, i figured i got lost in the shuffle.

Actually i was refering to putting a sherical bearing in the bottom shock to trailing arm mount. If i added any negative camber to the rear of my car, the bolt would be fighting that rubber insert and, i think, trying to push the shock top inwards. With a bearing there and at the trailing arm to body mount, camber adjustments should be smoother.

Paul

[Elombard]

isnt there a sway bar mounting issue also??

[Tspringer]

Can someone post a photo indicating where on the aluminum arm the grinding will need to happen?

I have a set of aluminum arms and was planning on converting in the next month or so on my '69 911S. Ive also heard the 1/2 shafts will need to be changed or modified? Is this true?

What else is involved in this conversion? My car is running SSI's and Koni shocks and is an otherwise stock bodied '69. I will be upgrading to adjustable spring plates and 30mm torsion bars at the same time. I am leaving the stock anti-roll bar in place with the stock rubber bushings.

Thanks!

Terry

[jluetjen]

Ive also heard the 1/2 shafts will need to be changed or modified? Is this true?

That is what I had to do on my '69E. I believe that it depends on the year of the aluminum arms that you are installing. In my case they were '76 aluminum arms. Then when I updated the halfshafts, I had to change the stub-axles to match. I found that I could use 915 stub-axles if I had the OD of the bearing surface turned down by 1 mm.