Aluminum trailing arm advise?

lateapex911 · 04-10-2005, 11:01 AM

I am re-doing the suspension on my '73 911, with T bars, shocks, poly bronze bushings, Wevo adjustable spring plate/needle bearing set up, rear monoballs, and so on.

While I'm there, I am considering upgrading to alum trailing arms. But the price of used ones is in the $300 range, plus refinishing and other costs.

So..the questions I pose to the experienced voices on the board are: What are the little things I will need, like brake lines, bearings, and so on that will add even more money to the project, and when all is said and done, is it worth it? Why?

Thanks!

Dantilla · 04-10-2005, 01:10 PM

How do you use the car? If you compete on R-compound tires, tha additional stiffness and lighter weight will make it worth it. For a street only car, probably not a big deal.

I had an '87 parts car- Engine, suspension, brakes, yada yada all went into my '73. Having an entire car made it a no-brainer for me.

lateapex911 · 04-10-2005, 01:29 PM

I drive it as a weekend car and track it a few times a year. I have Kuhmo V700s that use for the track, and often on the street

I am concerned with all the bits that might be needed as much as the part itself...if the gains aren't there, is there a point? They sure would look pretty in a powder finished clear coat though!

dd74 · 04-10-2005, 01:35 PM

I think you save about two or three pounds per arm. I think, also, you have to remove the engine for this. I'm not sure, but I'd look into it to see the value. Unless yours is a dedicated race car, I would think over the cost-to-performance ratio. If you do go this route, you might as well install rear monoballs.

lateapex911 · 04-10-2005, 01:44 PM

I *Think* the bolts are facing the correct direction on the inside control arm pick up. I hope so, because monoballs on the arms are on the list!

One advantage to gatting new arms is the assembly cound be completely ready to go, and the process would be more of an R & R. Time savings in the long run.

dd74 · 04-10-2005, 01:53 PM

Well, Jake, like I said, I'm not entirely sure about the modification. My car already had al arms, so it was never on my list. I did consider the rear monoballs once, but my driving style and conditions, plus limited ability to make it to the track - in the grand scheme of things - made it economically unfeasible. They're great pieces, however, yet simply not necessary for me. If the monoballs can be popped onto the al. arms while out, yes, you're ahead of the game time-wise. My only concern would be if you need to drop the motor.

Plavan · Plavan's Garage

Do a search on Aluminum trailing arms... You should get some good info.

RoninLB · 04-10-2005, 03:06 PM

hey Jake.

cramer just posted a thread

Lime Rock Thrash: The Disassembly

lateapex911 · 04-10-2005, 07:40 PM

hey...thanks for the lonk. Looks like Cramer is having a good time! If my weekend were less hectic< i would have loved going out and giving him a hand.

So, it looks like a different brake line (2), and longer bolts are in order. (Assuming the eccentrics)

And bearings and seals are, I assume, one of those no brainers, right?

Shuie · 04-10-2005, 08:30 PM

Ive heard that the weight savings is not a lot, but honestly, Im really surprised at how light my '74 trailing arms feel every time I have to move them around my garage. Maybe its becase they dont have rotors or calipers on them yet, but they cant weigh more than 15lbs each.

RoninLB · 04-10-2005, 08:36 PM

Quote:

Originally posted by lateapex911

And bearings and seals are, I assume, one of those no brainers, right?

you can get wide answers to bearings R&R if their tight.

Grady posted, somewhat, that at 100k mi they have one foot in the grave and the other on a banana peel.

Rufblackbird · 04-11-2005, 12:44 AM

IIRC in '73 they had the dimples on the torsion tube, so your motor and trans does not need to come out. One thing for sure you DO need is the brake lines. I forgot and had to...um..modify mine to fit. As soon as I get a chance I'm gonna have to buy a new line and bend to fit.

304065 · 04-11-2005, 03:51 AM

Jake,

All will be revealed: search under "Lime Rock Thrash."

Having done (half of) it once, it's not that difficult.

I would NOT do it unless you plan on racing or AXing.

Did the WEVO springplates become generally available yet?

arrivederci · 04-11-2005, 04:48 AM

Quote:

Originally posted by Rufblackbird
IIRC in '73 they had the dimples on the torsion tube, so your motor and trans does not need to come out. One thing for sure you DO need is the brake lines. I forgot and had to...um..modify mine to fit. As soon as I get a chance I'm gonna have to buy a new line and bend to fit.

Yep, brake lines are necessary. I bought a new line and bent it to fit. FWIW, the simple brake line benders you can buy at AutoZone, etc, won't bend a tight enough radius. I also bent a wire coat hanger to the shape that I was shooting for. You'll have to -um- improvise. It might've been easier to just buy the factory line (if you're using carrera or SC brakes).

I also went to monoballs at the same time. The trailing arm mounts on the chassis had pinched down over time, so I had to build a press to expand them a little in order to install the trailing arms. On my '72, the engine had to come out as well. Overall, on a scale of 1 to 10, its a 4 difficultly wise, but an 8 PITA wise.

randywebb · 04-11-2005, 12:39 PM

you save 6 lbs. on one hand, that is approx. 1/2 as unsprung wt. otoh, it is only a 3% reduction in the total...

but, they are stiffer too.

lateapex911 · 04-11-2005, 09:08 PM

OK, guys, thanks for the suggestions and good info, along with the educational links. I think I am going to go aluminum for a number of reasons.
1- It's a bolt on part, and a Porsche one at that. No decreased value, not that that is a major concern, but....did anybody see the orange T on E bay that was a no sale at 30K???

2- Aluminum is lighter, and doesn't rust...a more elegant material.
3- Better performance.
4- Exchangability. This is the major reason..I can gather the parts, and preassemble, and when everything is in order, it will be more of a R & R than a long thrash.

So, the final plan is alum arms with the WEVO SPS, the correct brake line as noted above, and Elephant monoballs on the inside. I'll cut the bolts per Dan Jacobs if needed.

Loose ends are: What material do I get them media blasted with, and is clear powder coating a good, or bad idea?

RoninLB · 04-11-2005, 09:33 PM

Quote:

Originally posted by lateapex911

is clear powder coating a good, or bad idea?

anything is gonna chip under there. I used the wrong clear that yellowed 50k mi ago on my trailing arms. I figured to just sand and dab later. Por-15 has a nice clear that's as hard as their other products but doesn't yellow as the rust preventive clear does. Por products are more like a resin than paint. I'll find the name of the nice Por clear if you want? I painted my new carbs with it.

lateapex911 · 04-11-2005, 09:54 PM

YEa! If it doesn't have to go out and have a turn around time associated with it, and it saves money, it's all good!

Did you powder coat your trailing arms? Or use another type of clear?

RoninLB · 04-11-2005, 10:09 PM

Quote:

Originally posted by lateapex911

YEa! If it doesn't have to go out and have a turn around time associated with it, and it saves money, it's all good!

Did you powder coat your trailing arms? Or use another type of clear?

I sand blasted the arms then used the wrong clear. No priming necessary for this type of job. I'm not pulling them for a redo until necessary. And I'm not motivated to sand while it's in there. The best clear I could currently find is Por-15 mfg called "Pelucid". It'll be relatively chip resistant under there. Any future chips require some 400 then a dab like every 25k mi of street use to be neurotically perfect. Otherwise faggetaboutit. A quick wipe and they clean right up. Before they yellowed I was sup-prised about all the nice comments on them.

Rufblackbird · 04-12-2005, 12:51 AM

since they're not in the car yet just polish them