aluminum trailingms

[Boydskyking]

what year did porsche start instailing aluminum trailing arms and I was told that the rear bearing is 10mm wider on the aluminum ones ,Is that true?
thanks

[75 911s]

I think 74? Lighter stronger, same dimensions in terms of fitment from 69-73.

The bearing is bigger in the aluminum trailing arm. I took the answers from here:

https://forums.pelicanparts.com/porsche-911-technical-forum/953171-911-trailing-arm-wheel-bearing-question.html

[rgofast]

No, the fitment will not be the same for 69-73. In 1972 the arms changed slightly to accommodate the 915 transmission. The 69-71 arms are different from the 72-73 arms. The shock mounting points changed, which changed the shock angle. This becomes a problem with installing aluminum trailing arms in the earlier cars where the tubular area around the shock is very narrow. One has to be creative to get the shock to clear. I had to have special narrow shocks built, with no dust covers. For our 69 chassis.

[Trackrash]

Originally Posted by rgofast

No, the fitment will not be the same for 69-73. In 1972 the arms changed slightly to accommodate the 915 transmission. The 69-71 arms are different from the 72-73 arms. The shock mounting points changed, which changed the shock angle. This becomes a problem with installing aluminum trailing arms in the earlier cars where the tubular area around the shock is very narrow. One has to be creative to get the shock to clear. I had to have special narrow shocks built, with no dust covers. For our 69 chassis.

You nailed it. I will add one thing. The shock is quite a bit longer after '72. Some have modified the lower shock mount on the aluminum arms to help with the shock clearance.

[rgofast]

I had Chuck From Elephant Racing build me some special bilstien triple adjustable shocks with canisters for my setup. They were special length designed for a lower car, to keep the travel correct.

[SWS911]

What about running a 915 in a '69-71 with the stock steel arms?
Is there a clearance issue where the axles "meet" the shocks?

[Trackrash]

Originally Posted by SWS911

What about running a 915 in a '69-71 with the stock steel arms?
Is there a clearance issue where the axles "meet" the shocks?

No. I have a 915 in my '71 and there are no problems with the shocks or axles. You will have to use a BFH to clearance in the rear seat area, since the 915 is a little fatter there. But no trouble with the shocks.

Also be aware, that if you use a '76 to '84 (I think those are the correct years of the 100mm CVs) 915 you will have to deal with the CVs not matching.

[SWS911]

Originally Posted by Trackrash

No. I have a 915 in my '71 and there are no problems with the shocks or axles. You will have to use a BFH to clearance in the rear seat area, since the 915 is a little fatter there. But no trouble with the shocks.

Also be aware, that if you use a '76 to '84 (I think those are the correct years of the 100mm CVs) 915 you will have to deal with the CVs not matching.

I knew about the BFH, but was unsure about other clearance issues.
Thanks for the insight!

[Evans, Marv]

I put '74 swing arms on my '69. The angle of the shocks in the towers won't allow the shocks to be installed without machining off an inch on the bung the shock bolt screws into. Eventually I went to coil overs and had to get shorter springs to get the right ride height. The changeover to aluminum swing arms sounds good on the surface, but unless you have a good reason for doing it, it's not worth it. Originally the reason was to use the larger bearing and reduce weight. The weight reduction is minimal. So unless you have a decent reason for the changeover, the stock ones are plenty good.

[rgofast]

My shocks are not stock and have a thin boss with monoballs, so I didn’t have to mill anything off of the retailing arm boss. Mine look similar to coil over bodies, without the springs and are pretty narrow. If you zoom in, you can see the mount area, and how my shocks with canisters mount. This is also a 69 chassis.

[chapo]

So the weight savings is 4-6 pounds per side depending on who you ask. Worh it? It does allow for bigger calipers

[kent olsen]

I ate up 2-3 wheel bearings on my 72 when I first purchased it. Went along with the idea of the aluminum trailing arm mainly for the size of the wheels bearing but later when I was reducing weight was happy with the pound or two it was worth. That was 20 years ago.

[rgofast]

It was worth it to me. My car is way to light in the front, and I am trying to transfer or remove every pound of weight I can from the rear. Along with the aluminum trailing arms, I have lighter SC axles, Hollow torsion bars, and special alloy vintage rear calipers on the rear. I have the matching aluminum crossmember up front. The rear calipers saved an additional 7 lbs of unsprung weight. It all adds up.