I'm considering (only considering, at this point), designing and fabricating a set of swing arms for my V8 project rather than cluge the stock ones. Primary mission would be to accomodate the later 911 bearing (larger od & length), later 911 hub, Carrera rotor, Wilwood spot parking brake, and possibly a 4x Wilwood caliper (I may just settle for the Carrera calipers since I have them). Initial 3D design concept seems fundamentally good (nothing fancy, just adequate).

Now for the questions: Though not on a surface plate, I measured the angluar difference between the front swing arm shaft and the hub/axle centerline at 12.5 degrees (plan view). Also, it appears that the swing arm shaft and the hub/axle centerline are on the same plane. Can anyone confirm these measurements? Any other dimensions or sources of info would be helpful too.

In the end, this may be more work than I'm willing to throw at it, but we'll see. Materials selection/availability may be the show stopper (don't want to buy a 20ft. bar only to use 12" off of it).

Thanks,
Andy

I think Brad had done some tubular arms, but in light of things, I doubt he's in a position to answer.

Must be some hard core suspension/racing guys out there..........Anyone??

Andy

If you are going to build custom trailing arms go ahead and raise the rear pick up points and move them in towards the driver. This will allow a longer trailing arm. You can make the rear pick up points fixed and located with mono balls. Then make an upright for the end of the trailing arm so that suspension adjustments do not affect roll center location.

You do know the later 911 trailing arms are aluminum correct?
I'd use the 911 parking brake, less hassle and it's already on the 911 rear bearing housing.

If I had some extra money, I'd bid on these Boxster/996 rear hubs as a base to create a new rear trailing arm. They use the 911 or 914 rear wheel bearing if I am thinking correctly...

QUOTE (Brett W @ Mar 15 2005, 08:57 AM)

If you are going to build custom trailing arms go ahead and raise the rear pick up points and move them in towards the driver. This will allow a longer trailing arm. You can make the rear pick up points fixed and located with mono balls. Then make an upright for the end of the trailing arm so that suspension adjustments do not affect roll center location.

Brett,

Read over your response a couple of times, and I am not visualizing what you're saying. When you refer to rear pick up points, is this the swing arm pivot shaft, the mounting ear and outer mount, or the spring/shock mounting? Moving them "in towards the driver" I assume you mean forward? Thanks,

Andy

QUOTE (Mueller @ Mar 15 2005, 10:02 AM)

You do know the later 911 trailing arms are aluminum correct? I'd use the 911 parking brake, less hassle and it's already on the 911 rear bearing housing. If I had some extra money, I'd bid on these Boxster/996 rear hubs as a base to create a new rear trailing arm. They use the 911 or 914 rear wheel bearing if I am thinking correctly...

Mueller,

Yea, I looked at the 911 parking brake; I have the whole trailing arm assembly with brakes. The parking brake cables are entirely in the wrong direction (pointing inward), and likely interfering with the exhaust system. The Wilwood spot caliper only requires a mounting bracket, and can couple up to the existing parking brake cables with only slight modification. Much easier, in my estimation. Yes, the 911 (Carrera) swing arms that I have are aluminum.

Andy

Actually, IMHO, the best thing to do would be use those boxster uprights and fabricate a multi-link setup that pivots off of your transmission.

Ditch the trailing arm design altogether. Those of us racing in production are stuck with it, so we've found out (and disagree about) how to optimize it.

I have to agree with Kevin. Deep six the stock trailing arms and go to a dual A-arm set up. You can machine a housing to use the 911 bearing and hub, maybe get some pin drive center lock wheels. Oh wait you want to keep it reasonable, sorry.

Andy

The pick up points I am referring to are the trailing arm pivot points on the chassis. Set them in the optimum location and use an adjustable up right at the wheels to change camber and toe.

Yeah Kevin and I disagree about the rules but that is what makes this such a great place. Since his car is running and mine is far from it, I guess he wins.

Instead of dual A-arms, I'd go back farther in time and do a 60s style radius rod setup. This works well, and the F1 crowd only stopped using it for aerodynamic reasons. You only need two links (per side) running from an upright to a fabricated center cradle at the diff. You could use those Boxster parts, or many other rear uprights. These give lateral location. Then you have two more links (per side) leading from the firewall back to the uprights, which gives longitudinal location. Putting rod ends everywhere means lots of adjustability. This will be substantially lighter than the stock setup, fully adjustable, and will give a better camber curve. This gives plenty of space around the engine (indeed, reaching the heads will be MUCH easier with the trailing arms removed) and exhaust. You can even have several alternate locations for the links by just using a U-channel with several holes in it, which allows you to change your mind about suspension geometry even after you weld everything up. So, positioning the mounts on the body would be far less critical.

If you want pictures, look at any pre-wing F1 car. The Lotus 49 probably has the quintessential layout. They continued to use the radius rod setup until way into the 1970s, but it gets progressively harder to see behind all of the bodywork.

You'd want to use relatively hefty rod ends and link rods to survive regular use, but I'd think fabricating something like this would be simpler than trying to make up new trailing arms.

Boy, you guys got waaaay off in another direction, but the read was interesting and fun. Thanks loads!

I'm afraid the multi link systems are not for me. This is a street car for which I want to retain a reasonably similar to stock suspension layout (though perhaps not as technically good). Duplicating the existing swing arm with variations to accomodate upgrades to bearings and brakes is where I would like to get to, hence my original questions regarding their geometry.

Thanks again,

Andy