Swap steel trailing arms with alu trailing arms?

[lkadams]

Corrected link for the WEVO E-Z pins:
http://www.wevo.com/Products/Suspens...cts-EZPins.htm

[Scott Clarke]

A couple of additional points: The aluminum arms use different bearings than the steel ones, and hence different hubs. You will want to use your existing drive flanges so that your CVs will fit. The '70-'71 drive flanges will fit in the late hubs. Also, the bolts and eccentrics that secure the trailing arms to the spring plates are different for aluminum arms. Make sure you have the late parts. Finally, the brake hard lines attached to the arms are different.

[s2guy]

Wow, what a great thread.

Is this modification necessary only for the '70 and '71 cars, or for all LWB cars? I've got a '69 S and want to know if this mod applies to my car.

Thanks a lot guys.

Mike

[Neunelfer]

Thanks for the details John,

At the risk of sounding negative and defeated, I think I'll stick to my original post. If you recall:

* Works better with Bilstein’s
* May have to remove the dust cap.

My point is this; I did not notice a difference "at all" in the cars handling and drivability.

In recommending someone who is wondering whether to do it or not... I still feel it's a mod I would question. If you add up all of the goodies needed, the bang for buck is less than negligible "for me". I admittedly don't have a micrometer in the seat of my pants so, again, as stated in my first post YMMV.

I have this mod "working" on my car now (with Koni’s) and I do have a question regarding the machining.

You mention the arm is machined to be "exact dimensions of the steel arms you removed". If I recall correctly, the lower shock mount on the AL arms is quite a bit further back (toward the back of the car) than the steel arms. This is why your dust shields need to be removed now; is this correct? I remember the shock coming down and having the lower bolt holes off by nearly 2-3". If that is the case; is the machining simply to move the lower portion of the shock further out and away from the heat exchangers?

Thanks again for the details, I hope you understand... I'm not trying to denounce your efforts AT ALL. In fact, I applaud them as I may do the machining mod when I switch from the 2.5 to the 3.0 over the winter if it offers a better fit but, I do have the fundamental question; is this mod only to help the HE clearance? The shock angle toward the back of the car is not affected by this mod... yes? No?

Based upon the answer I may even do some metal work to the cross-member/upper shock mount when I swap engines.

[70SATMan]

Based upon the answer I may even do some metal work to the cross-member/upper shock mount when I swap engines.

I've had this mod planned for what seems like forever now.

I've had the same thought about the feasibility of just replacing the earlier shock mount/tubes for the 72-73 version on my 70.

I guess the question in my mind is if the steel trailing arm for the 69-71 is dimensionally different than the 72-73? If not, then all that is gained is a little more clearance for the shock but, still the rear suspension geometry is forced further back with the aluminum arms. If the 72-73 steel arm shock mount matches the aluminum arms then a revised upper shock mount would fit the bill. Then its a cost study between the two as to what is more labor intensive. Not to mention in my case a substantial mod to my original S. If starting with a T with the original intent to hot rod it, then it might make more sense to do this.

I would be constantly worried about the reduction in strength of the lower mount after the mill work.

[Neunelfer]

Michael,

I believe a revised upper shock mount as you mention would answer "any and all" questions I have about this mod. but again;

* New Control Arms
* New Swing Arm Hardware
* New Hubs
* New Shocks
* Fairly Major Metal Work to the Upper Cross-Bar/Shock Mounts (however, this would eliminate the machine work to the arms.)

Benefits: Less weight and a stronger arm. I can't see how this would make the ride quality any better (possibly the shock geometry change helps) and I don't recall the arms being a weak point. If they were, the strengthening kits could remedy all of that for about $50-$100 bucks worth of welding and a trip to the powdercoaters. I would "never" carve up an original S for this mod. Zero - 0 - doubt about that.

I’m anxious to hear what John says about the lower mount because I do have it on my car now and I'll probably stay this way if it can be managed. So far, it looks as though he’s taken it the farthest vs. those who have gone in and changed the cross-bar. My next challenge may be to decide on the cross-bar mod or, as mentioned in the first post, go back to steel and weld in the kits.

I'll add some pictures of the actual 73 RS arms...

[70SATMan]

I have an opinion on the RS arms. Like the difference between a steel frame and an aluminum frame on a road bike, while you get a weight benefit with the aluminum and benefit in power transfer, you pay in terms of increased harshness of the ride due to the stiffness as opposed to the steel which dissipates shock through flex.

I really think that the mods to the RS arms and them still being steel have a lot to do with the "magic" people talk about with the RS suspension. I know the body mods on the RS are bound to play a part. Otherwise what is the difference from the 73S suspension???? Rhetorical.

With the aluminum arms there would be a minute decrease in power loss through the stiffness of the arms and as we know better performance of the suspension but, again...trade off in comfort. Probably to subtle of a change for me to notice but, Hey, I know they will be there which equates to automatic butt dyno increase of at least 10 HP!

[Scott Clarke]

John-
The lower shock bolt is 12mm on '70-'71 cars, and 14mm thereafter. This is why you need new lower shock bushings. Eric and John G- where did you get yours?

Also worth mentioning are sway bar mounts. The early arms had a ball stud just like the steel arms. This changed in '78? Not sure, but SC sway bars mount differently.

I've got a pair of arms sitting on my bench waiting to be installed. Great to see those clear photos of how the machining needs to be done. Thanks for posting those, John G!

[37yrold911]

difference in stiffness of steel vs. aluminum will be nil compared to the compliance of the tires, much less the movement of the arm on its bushings.

[Neunelfer]

Scott,

I just bought later model shocks. Now, where can I get a 2.5 decal? I need one for the plexi window in the GT.

Joel's calipers make it there yet?