Aluminium trailing arms upgrade ?

[RS-GT]

We often see or read that people upgrade their 69-73 trailing arms with the lighter later one (74-89). Somebody just told me that this will change the angle of the shocks ; is this right ? any long term issues with this upgrade ?

Thanks,
John

[Mr9146]

This is only true on cars with 901 transmissions (69-71).

It's no big deal, really, as all you'll need to do to run the aluminum arms is run the shocks without the dust covers. I did this conversion on my car with absolutely zero hassle, and I just did this conversion to my friend's 1969 912 as well.

Note: make sure that you get all the aluminum trailing arm hardware as they are thicker than their steel counterparts.

[911pcars]

We often see or read that people upgrade their 69-73 trailing arms with the lighter later one (74-89). Somebody just told me that this will change the angle of the shocks ; is this right ? any long term issues with this upgrade ?

Thanks,
John

John,
It depends on the year. As Marco says, the 69-71 chassis has a slightly smaller space for the upper shock and the lower mounting location was moved slightly in 72 and remained unchanged all the way up to '88 or so.

With the change in control arms for 69-71, compatible shock absorbers must also be installed due to a larger lower mounting bolt requirement. Some shocks can be problematic due to the smaller upper mount space on the 69-71 models. For example, the Koni Sport shocks I use are larger in diameter than the ones fitted to steel control arms. The slightly relocated lower mount changes the angle slightly even with some metal machining in an attempt to compensate. The revised shock angle and the larger shock dia. required deleting the outer dust cover. I could rationalize that as additional weight reduction. Both alloy arms save about 11 lbs., some of it important unsprung weight.

While some massaging is needed for the earlier chassis, alloy arms are pretty much a bolt-on for 72-73 MY 911s. There might be some sway bar attachment issues depending on the type of sway bar and the vintage of the alloy arms. Early al. control arms (74-77) use the same ball pivot to attach the drop link. Thereafter, the drop link attaches with a bolt into a threaded hole.



More info here:
http://members.rennlist.org/911pcars...ContrlArms.htm

There may also be CV joint compatibility issues, but there are some links on one of the above pages that address this.

Hope this helps,
Sherwood

[RS-GT]

Thanks guys !
I'm always impressed about how nice people are here and with all the information I can get on this site !!

JD

[joetiii]

In doing more research on this topic I uncovered that the ebrakes are different between years and may not be compatible. Does anyone who has done this upgrade have comments or suggestions?

[911pcars]

Joe,
Not sure about any meaningful differences, but I installed a pair of post MY'77 arms in my '69 (threaded rear sway bar mount). No parking brake issues at all.

FWIW,
Sherwood

[RSTarga]

here is a great article from excellence on the subject. I am redoing all my bushings and decided to stick with the original steel.
David

[Kaefer]

I've got an extra pair of '77 trailing arms with the ball pivot to attach the early sway bars. Please let me know if anyone here is interested in them.

Thanks!