I'm just curious how these will be done, that's all. Will it be a matter of scaling an existing tubular design to fit the FD geometry, or using a fabricator who knows what's good enough by experience? Or a design from scratch?

And FWIW, if someone gives me some loading information (I'm not a vehicle dynamics guy) I'll do a basic 3D FEA of the design. I'm not trying to overengineer this thing, but keep in mind if your front end suspension breaks it's a very bad day. It really is critical.

Dave

 

Really there is NO point in making steel lower control arms without doing some analysis. Mazda did some analysis, they made a forged aluminum control arm. Now we want to bend some tube up and call it good without even checking the stress levels, deflections, etc? The risk of disadvantages of a steel control arm far outweighs the replaceable ball joint advantage. Just fabbing up steel arms are replacing forged aluminum arms is the job of a fabricator, no engineering involved.

There are people on the forum that are capable of doing FEA analysis with expensive software packages like Pro/Mechanica or ANYSIS.

 

Fine, you guys check everything and get back to me.

 

If anyone has a junk or spare Mazda control arms around, I (or any qualified engineer) could model and analyze the OEM design, then analyze the steel design to assure equal/greater strength and stiffness. Without knowing the loads, that may be the only cheap, easy, reliable approach. With the reference parts in hand for measurement, I could probably analyze the new design in a week. It shouldn't be a huge effort. You'll also know precisely what the weight savings are.

Jim, while you do have fantastic custom parts on your own car, making/selling them to the public opens liabilities. I'm not your lawyer, and I'm not trying to run up the price or stop the buy, but at least CYA. A failed bushing or hacked airbox will cause noise or a performance problem. Even a broken engine cradle probably would only result in simple drivertain failure.

On the other hand, a broken or rusted weld in a control arm will cause the car to lose control, most likely in the middle of a high-g maneuver, causing a disastrous wreck. Lawyers fund their Bimmers with this stuff.

Dave

 

Trust me, if I seriously thought that such a part would see the light of day, I'd be more concerned about liability.

Considering that I don't need these parts for my own car, there's very little motivation for me to produce them at what would almost certainly be considerable initial expense, especially since I've made very little profit from the custom parts that I've produced and sold in the past.

 

We both understand this is different from just mass producing a custom part.

I'd be glad to help in any analysis and design efforts. I have access to good analysis tools, and as long as the effort isn't enormous I'll donate my time.

Dave

 

I have an old lower control arm that is basically **** (bad rubber boot and ball joint is dead). I would be happy to send it to you. I don't know if Jim is still planning on making them but it would still be fun to get the analysis anyway.

 

Yeah, it would be fun. I'll PM you my Fedex account number and you can send it on my coin. Just make sure you use ground

Dave

 

this should probably be incorperated into the upper arms. As I beleive one of the reasons a lot of car manufacturers now have people replace the full arm instead of just the ball joint is because the wear and tear of replacing ball joints can wear out the arm, so the arm couldn't hold the ball joint. It was common practice to tack weld the ball joint to arm, with older domestics anyways.

Jim? did you think about just copying the skunk2 design? adjustable and bolt in ball joint?

I wish I knew the taper and size of the rx7 upper ball joint. Then we could see if moog has a joint made that would fit the bill. Does anyone know if there is a replacement part number for the ball joint?

 

http://www.polepositionrp.com/MODIFI...ROL%20ARMS.htm

bottom right 9200RM

http://www.polepositionrp.com/ball_j...e-screw_in.htm

top right 9414

Just need to see if the ball joint would fit the spindle. Or find another import ball joint that fits.

With a price of $139 bucks for the arm and $20 bucks for the ball joint figured those motivated enough might like to know.

rip

 

This is what the ball joint on the upper control arm looks like. Let me know when you find anything even remotely similar.

 

I hope that zip tie is the "race only" version and will hold up to constant abuse.

 

It limits suspension travel on jumps and stuff like that...