its a service part, sometime in 1991 they revised the rear control arms for less camber, instead of -1.3 its -.5. any car made in the last run for 1991 has them, and the service parts were all like that too.

i think they are NLA, and even if they weren't the cost was something like $500 an arm!

 

With everything else you have done for this car would you really be happy using a stock piece knowing you have something better already designed that you could easily make? I think the answer is pretty obvious =p

I'd maybe ask in the road race forum since that's probably where the suspension gurus would be most like to see it and suggest any improvements.

 

I just spend an hour reading through your thread. All i have to say is HOLY MOTHER OF GOD.

 

If you're going to go through the trouble of fabricating new arms, I would say just go live axle. They can handle all the power you want, and you have design freedom with roll center and anti-squat.

I think the biggest downfall to the semi-trailing arms is squat gets really bad when the car is low. Couple this with the fact that the roll couple gets smaller with squat (balance moves towards oversteer) and the crazy camber curve, and you have a suspension that isn't very friendly to high power. Genius for low-mid power cars, not so much when you get serious. I think you'll need very high spring rates all around to keep the back in check, if you have good traction anyway.

Just my 2 cents :-)

 

I was supposed to go out, but I got distracted by this thread and ended up staying home and reading it lol! Awesome work man, I'd LOVE to do something like this one day!

 

such a great thread..

 

John, it really depends on what your goal is for the car. The problem with the stock suspension (on virtually every street car) is that you can't run it really low without problems. So if you plan to lower the car a lot then what you've drawn up may be better.
But after doing a fair amount of analysis of the stock rear suspension geometry, I've really become a fan. What Mazda did is make the camber and roll center adjustable independently. That is really good for guys that are going mostly for handling (like me). I think your design ties them back together. So, like everything else in car design, it's all a matter of trade-offs. Also, in your design, you won't be able to adjust toe without having to go back and correct camber.
Good luck

 

Also, if my model is correct, your design has more toe change and less camber gain than stock.

 

Amazing build. Great work (and this is your first RX? You sure?).

Realistically, being that your car is going to be driven on the street, how low do you plan to go? If you aren't going to be tucking down to the wheel (seeing how you said 40 series or such), why not just do basic mods to the stock rear suspension? If, after a while, it doesn't suit your needs, then let your genius mind nad god-like fab skill make haste on a new set-up. I know you stated you'd like to do it in one go, but even pro-racers take steps in their set-up process. Just a thought...

Keep up the good work and besides the engine, I'm really looking forward to seeing how this FC sits on the wheels (I love those wheels!).

Jose

 

Well when making new trailing arms you can modify the roll center and camber curve. I'm not going to do a live axle, that would require new diff, driveshaft, axles, arms, ect. and I'm not sure if it really would be better on the track, it has it's downsides too.


Mmm yeah you might be right, toe isn't adjustable without messing up camber, but I don't think toe needs to be adjusted a lot. With the quick measuring I did I found that dynamic toe isn't changed a lot, gamber gain is but I did that on purpose.


Yeah this is my first RX7, or any car that I actually do some work on for that matter , You might be right with the suspension thing, the first idea was to go overboard and build a custom double wishbone setup, but when mocking up the diff and exhaust it became clear that it just wasn't going to fit the FC. Then the idea came to go somewhere in between, create dual arms so proper camber gain can be build into it that matches the car and rideheight, but still use a trailing arm. I think the work involved isn't much more than fixing / modifying the current suspension and it sure makes everything simpler and loses a lot of weight. But the FC suspension is proven to work pretty well and there is a lot of experience out there on how to set it up. Decisions decisions... Ah well I guess I'll sleep on it and decide what I'm going to do tomorrow. I just did some work on those wheels by the way, still need to clean them up and get the tires on there but it's getting there

 

Crazy the amoutn of craftsmanship and detail going into this. Great work!

 

such an epic build, seriously can't imagine putting forth that effort or drive...

simply perfect

 

Maybe I missed it, but what did you use to block-off/plug the various holes in your steering rack? Looks like delrin or acrylic....or...? (I've been looking for an alternative to do the same w/mine) -Keep up the good work! LOVE IT.

 

Yeah it's delrin, I machined some plugs, put a dab of tocktide on there and tapped them in. You can also weld the holes shut if you can weld aluminium, or cut the oil fittings off the oillines, weld them shut and screw them in, Doesn't really matter as long as the holes are sealed so dirt can't enter the rack.



Didn't do as much work to the rx7 this week as I wanted, partly because I was too busy doing this with my crappy daily driver bmw





The car is severely underpowered but I still had fun sliding it around the zandvoort track , Really can't wait to take the RX-7 out! So freshly motivated I started work on the rear suspension.
I decided to go with the stock trailing arms, their proven to work well, a lot of people use it and there's a lot of info available on how to set it up. Some improvements are in order though.

This is the mount where the trailing arm is mounted on the subframe. I removed the rubber, machined a thin sleeve, pressed it in there and welded it to the trailing arm. Now I can use a spherical bearing instead of the rubber. Two circlips hold the spherical bearing in place.




Made the lateral links adjustable, this is now used for adjusting toe angle. Those hockeypucks will be transformed into independent camber adjusters soon!




I also removed the rear wheel steering by machining solid bushings for the hubs.

 

whoa, you do amazing work!! how do you like the no power steering on the 7?

 

I wish someone would make toe links like that

 

Ohh but someone does......

https://www.rx7club.com/vendor-class...-links-982800/

Ur welcome.

Nice job John, keep it up.

 

Just sat and read this. What a great build.

 

Did you cut those holes in the control arms to save wight? I dont get what you mean about the bearings how will they will be benificial? Couldnt you just cut out a piece of derlin and drill a hole in it and just make a solid bushing? Im still learning about the rear suspension so it might be a stupid question but still thought id ask cuase of all people you would know...

 

I doubt you've never laid your eyes on the rear suspension, Mazda made those holes
Solid bushings are never a good idea for a proper suspension setup, the suspension needs to be able to move

Keep up the good work john!

 

Yeah I made a few holes, The stock ones already have a few holes, but I added some in the cast iron piece. I saw other people do it and liked the way it made everything look way less bulky. I didn't take it to the extreme like others though, just a few holes here and there. Probably not much of a performance benefit but it was a 10min job. You can't use delrin for the trailing arms, the trailing arms don't just hinge around that mount, it rotates in multiple directions. Delrin mounts only allow rotation in one direction, so when the camber changes (which it does when the rear suspension is compressed) everything binds up and fails. You can use the stock rubber, but when your using individial camber adjusters the rubber starts binding up. Spherical is really the way to go here, cheap too if you can machine the sleeves yourself, the bearings cost me about 8$ each. The same thing goes for the individual camber adjusters too by the way! The stock ones have spherical bearings in there, but the aftermarket ones use bronze bushings that also only allow rotation in one direction , a big nono if you ask me, people have also been breaking them because of this, which is why mine will also have spherical bearings in there aswell.

 

I know About those but I was referring to the use of the stock ends...
those aftermarket ends are high maintenance and noisy..
I will never put anything like those on my car again..
Squeak squeak squeak, the swaybar end links I used like that is all they did, it was obnoxious. The stock ends are awesome.
Keep up the good work John you never seize to amaze me

 

looking forward to seeing your camber links

could you PM the drawings and/or files? I'd love to have my friend with a CNC machine make me up a set.

 

ive propably taken apart more rear suspensions than you have ever seen bud, i just havent set one back up for extensive track use and is why i was asking john theBOSS and not a noob ......

 

thanks john for clearing that up i cant wait to see how it comes out as always im sure it will be BOSS