1st Gen RX7 rear lower links

[roadracer]

Quoted from post number 20 in this thread:

09-12-2007, 08:03 PM
kbailey Offline
Join Date: Nov 2005
Posts: 25



Okay- here is my $.02. What I was told by several people as I was building my car is also what makes sense to me:

The upper and lower links are locating arms, not traction bars.

The popular setup I have seen is:
Add a tri-link to the top of the axle. This is an added traction bar, there is no question it is legal.
Replace the bushings on the stock upper locating arms with soft foam. This effectively renders them non-functional, and it is clearly legal.
Replace the bushings in the lower arms with spherical bearings. I personally think the interpretation of the old GCR wording "any bushing material" meaning spherical bearings was legal was crap. Now the wording has been changed in the GCR and it is officially legal now without argument. The Mazdamotorsports part listing for the bearings is below.

Nowhere do I see allowances to replace ther locating arms or the ends. Just my opinion.......but it seems to be the common interpretation of the folks I race with.

0000-04-7422 C BRG KIT,LOW TRAIL. ARM 1 ALL RX-7 1979-85 $263.40

Kit includes four (4) spherical bearings to replace stock rubber bushings in lower trailing links. Requires pressing rubber bushings out of stock links. Uses stock bolts. Legal for SCCA 'IT' classes. Recommended to use with old, soft, upper bushings to prevent binding. Kit also available via special order that includes modified lower trailing links, fitted with sperical bearings (0000-04-7423).
__________________
Kevin Bailey
ITA/IT7 WDCR

Bringing a thread up from the dead here. I do so with trepidation. However, this thread has no photos and I am seeking a picture showing an example of the suspension described above. Does anyone have one?

Please. Please. I am asking a question here that is specific. For a picture. Not a thousand words.

The topics discussed here in this thread appear like they could be batted back-and-forth and debated forever. And I have read the thousand words already. Probably twice. Maybe three times.

The only reason I didn't post a NEW topic or thread asking my question is so that you would know what thread and topic I referenced in my quote above.

Sorry to sound rude guys, but specific questions on forums most often get watered down and lost among the debates. The thing I'm asking for is a picture. Not an opinion and interpretation. ()

Thanks in advance if you can help!

Don

[dickita15]

Ok, i will give it a shot. hard to get a good picture, hope this helps.

[Tak]

Good conversation, and an example of what is wrong with the SCCA rules process. The conservative interpretation of the GCR tells us that it is legal to take a lower trailing arm/traction bar from a junk yard, remove a rubber bushing, and replace it with some precision machined sleeves and spherical bearings. But it is not legal to buy a readily available piece (circle track radius rod), that does exactly the same funtion as the heavily modified piece, costs less, and is easier to implement.
Doesn't this sound like the ECU rule? Or the Coil over rule?
Instead of focusing on liberal vs conservative interpretation, shouldn't we focus on updating a 30+ year old rule?

Let's go back to the intent of the IT rules. What was the intent of the original traction bar rule? I believe it was to enable solid axle cars to be lowered safely to the limits of the rules (and by safe I mean both reliability and functionally--a car that spits out drive shaft U-joints is not safe; neither is a car that has snap oversteer because of a bind or bottoming issue). Consider the rules allowance for cars of the time with semi-trailing arms (BMW 2002 and Datsun 510)--they are allowed to slot the trailing arm mounting points to correct camber and toe when the car is lowered. This is consistent with safely lowering the car per the definition above. Similarly, most of the solid axle cars of the day had axles located by leaf springs only. A means of lateral location was necessary for functional safety (predictable handling)--hence the panhard rule.

We would serve ourselves much better to develop basic intent of what the rules should be, rather than bickering about the rear suspension links of a now out dated and uncompetitive IT car. The ITAC took the first steps when they rewrote the overall class intent statement a few years ago. We need to help them help us by developing consensus on a reasonable list of high level intent. What is the intent of suspension modifications? What is the intent of chassis stripping? What is the intent of engine modifications? Stuff for a new thread...

Tak
#29 ITA (an Rx-7)
SFR, SCCA
And yes, my car has 5 traction bars locating the rear axle.

[ddewhurst]

***And yes, my car has 5 traction bars locating the rear axle.***

Mine did also. Two traction bars with foam bushings & three traction bars with adjustable rod ends. No one wrote paper, they looked, they smiled & they walked away thinking

[JeffYoung]

I think Kevin nailed it. My car has similar links, and they are more than just traction bars. They are essentially suspension mounting points as the locate the axle, the spring and the shocks.

Dick, to answer your question, a fair number of cars in the SE Div run foam bushings on the top links, sphericals on the bottom and a tri-link. Others just run a panhard in addition to the stock four links.

I'm not aware of anyone replacing links entirely with homebrewed stuff, but I don't look under EVERY RX7 in the SEDiv. Just the ones that beat me......lol....seriously, it may be done, but this is the first I've heard of it and I've talked to a lot of folks here in the SEDiv with 1st Gen RX7s because your rear axle setup is nearly identical to mine.

[JoshS]

Does anyone have any good diagrams or photos of what a stock RX-7 rear suspension looks like?

[JeffYoung]

Hmm..Josh, think of your rear suspension with the lower trailing arms. Then picture a solid rear axle with two additional links running from the body tub, essentially behind each seat, to the top of the pumpkin.

[lateapex911]

Jeffs description was for the TR8. I'll dig around and see if I can find a pic.

RX-7:
Live axle.
Lower links run parallel with centerline of car, (or darn close) are about 18" long, attach to the chassis just inboard of the wheelhousing, and attach to the axle on a bracket on the bottom.

Upper links are essentially the same, BUT. (I think) the are angled inward on the axle a couple degrees, and are shorter, about 12" or so. They mount on the outer ends of the axle as well.

Stock, the car uses a watts link, which has rubber bushings at it's ends.

When you lower the car to race height, the arcs described by the two links are in conflict, and the watts link gets all twisted. It's out of it's designed range of motion.

The solution is to remove the Watts link (or replace the bushings with high misalignment spericals) and change the lengths of the links. But, it's more effective and easier to Keep the lower links stock length, and add a traction bar on the top of the pumpkin, attaching to the chassis in the driveshaft tunnel, and effectively "decommissioning" the upper links by removing the bushings and replacing them with very soft foam bushings.

This allows the axle to remain at an appropriate angle for driveshaft longevity, and the range of motion is restored.

(It's actually quite similar to those old Formula cars where the links could be seen on the outside of the car, usually all chromy, but of course, they had independent hubs)

[ddewhurst]

The "upper & lower links", OEM name are both very similar other than length. A length of tubing with a short cross tube at at each end with molded rubber inside (bushing) with a second steel tube inside the rubber that the mounting bolt goes through. For this discussion please forget the fact that the upper links on the front end mount inward with respect to the mount location of the rear end. That's (binding) part of the reason the Tri-Link was implemented.

The Banjo is positioned in longitude with four links. Two upper links & two lower links. They mount to the Banjo approx 6 inches above & Banjo center line & approx 6 inches below the Banjo centerline.

IMHU of the rule we need to read the words written in the written rule that "ANY traction bar may be ADDED or SUBSTITUTED". The G-Force Tri-Link is ADDED & the DD-Force lower links are SUBSTITUTED.

Now if it's an accecpted practice to foam bush the upper links (accecpted as traction bars) & ADD a new TRACTION BAR which happens to be called a Tri-Link please explain why the OEM lower links do not do the same functions as the OEM upper links.

That ^ is question number one. It needs an answer to coutinue this communication IMHJ.

My answer to this question has all ready been posted in another post. I would like to have others explain their thoughts as to why the upper links are traction bars & why some think that the lower links are not traction bars. Not what Bo Bo thinks. Dam, just wait & see there will be a Bo Bo lurking.

[lateapex911]

David, I know we will agree to disagree on this, but to my eye, the upper AND the power are BOTH suspension members, and ONE of their numerous functions is to resist torque effects.

The bushing change in the uppers is allowed under the free bushing rule for suspensions as is the lower change. The added member is allowed under the rule that allows the addition of a traction bar.

Note that, when the tri link fails, the suspension will still function...not ideally, but it will function.

[joeracerx95]

Hmmmm, trying to decide if I'm sorry I brought this up.

Any way, here's what I'm wondering about.

We all seem to agree that the upper and lower links perform three functions:
1) Fore-aft location of the axle
2) Control of axle rotation
3) Completely screwing up the handling of the rear of the car

We'll ignore #3 for now. :P

So the question is, if a component has multiple functions how does SCCA Tech handle this? For example, if you run a car that has leaf springs in the rear, they are the springs but they also locate the axle fore-aft. (In fact, leaf springs are WHY traction bars exist!) Does that mean I'm not allowed to alter the springs in my Pinto, which the rules allow, just because it could affect their other function? (BTW, if you aren't a SCCA tech official, your opinion doesn't count)

And I'll also observe from a "spirit of the rules" perspective that the end result of using a radius rod and two heim joints will be EXACTLY the same as buying the bearing kit from Mazda and installing them in the stock links. Except that it'll cost about $300 to do it with the Mazda parts vs. $100 with radius rods and heim joints. Would anyone like to contribute to the, "Keep Chuck 100% Legal In Everyone's Opinion" fund?

-chuck-

[Hahn63]

Chuck, follow the set-up on post #20 and you'll have a great handeling race car and you'll be legal for sure. No need to jump through all the hoops and reinvent the wheel, this set-up is fast as anything else, honest!


Roland

[ddewhurst]

***Now if it's an accecpted practice to foam bush the upper links (accecpted as traction bars) & ADD a new TRACTION BAR which happens to be called a Tri-Link please explain why the OEM lower links do not do the same functions as the OEM upper links.

That ^ is question number one. It needs an answer to coutinue this communication IMHJ.***

Have you doubters answered the above ^ question? DO THE LOWER LINKS RESIST TORQUE?????? Lets use the KISS principle. THE ANSWER IS YES or NO.

David YES.........

Roland

Jake

Gerg

Jeff

Josh

joeracerx95

Kevin NO (The upper and lower links are locating arms, not traction bars.) To which I say then get rid of one pair of your locating arms & attach the remaining pair of locating arms to the vertical centerline of the Banjo & let's see how well the suspension functions. It only takes one pair of location arms to locate the Banjo.

Guys, this is not brain surgey. If one of the functions of the OEM named "upper link" is being a traction bar (we agree, YES), then why is it so hard for some of you to admit that one of the functions of the OEM named "lower link" is also a traction bar.

Once you admitt that the lower link is also a traction bar the remainder is simple.

Some of you guys buy into ADDING the third upper link but you just will not open your minds that what I have done for less than $100.00 is SUBSTITUTION of the lower links just as the rule allows. Why don't some of you understand the rule, ANY TRACTION BAR MAY BE ADDED OR SUBSTITUTED.

If some of you don't understand that one of the functions of both the upper & lower links is to resist traction then you need to get to reading in a simple suspension explanation book. I am not attempting to be sarcastic, just trying to be everyday realistic. Come on 1st gen RX-7 owners that are lurking take part in the FUN.

Roland, post # 20 is no different than what I have used for lower links except that I spent less than $100.00 to get the job done based on the written rule..............................

[joeracerx95]

I think we all agree that the lower links are used to limit axle rotation. The disagreement is that you can't substitute them because they also act as a control arm. A traction rod CAN be substituted, a control arm CAN'T. I think we can agreed to that also. Like they do in court, show me a precedent where something similar was argued and decided by SCCA and we'll have an answer. Everything else is just opinion.

Suggesting that this is an prohibited function is not correct. Prohibited function means making a part do something it isn't supposed to do. E.G. True story. A SM guy installed a plate in the right rear of his car to mount one of the bars of his cage to. The problem was, the "plate" was a forty pound block of steel. He was protested and SCCA ruled that the plate was performing an prohibited function; acting as ballast in an area of the car where it isn't legal to mount ballast. He had to remove it. What this driver was trying to do is what the GCR refers to as "strained or tortured interpretation." (GCR 1.2.4) "It's just a mounting plate!" A very tortured interpretation of the word "plate" to justify its use. However, no one is suggesting that the links under discussion do anything they aren't designed and meant to do by Mazda, so there is no "prohibited function" taking place.

What to do, what to do. To save the $200 difference in cost between home grown and a Mazda part I'll take my chances with a protest. Or maybe I'll just leave that part stock. Or not.

-chuck-

[Jim Susko]

As a former member of the Solo Events Board, which is responsible for writing and interpreting the rules for Solo II, I have some insight into how these rules are written and interpreted.
The GCR defines a traction bar as “A link to an axle housing or hub carrier which resists torque reaction from the wheel by acting in compression or tension.”
It defines a trailing arm as “A wheel control linkage locating the wheel in the fore/aft direction, which is attached to the car structure at the forward end of the arm, and the wheel carrier at the rear of the arm.”
It defines a suspension control arm as “A beam or frame intended to limit the normal motion of the affected suspension part to predetermined paths.
Why are there three definitions which overlap in many ways? Because the rules makers want to show that these links are different. When we use these generally accepted terms, we all know what they mean.
When faced with a convoluted reinterpretation of a rule which uses generally accepted terms, rules makers tend to go with the simpler, more straightforward interpretations, based on the intent of the rule. If you take the logic presented by some on this forum, one would wonder why the Comp Board didn’t write the rule to say, “any suspension control arm, trailing arm and traction bar may be added or substituted.” But they didn’t. That’s a big clue.
Why take a chance on a stretched interpretation of the rules which doesn’t make the car go any faster than a more conservative interpretation? As a competitor I would be suspect of any car which had a substituted trailing arm which is adjustable in length. One would wonder how many other illegal parts there were on the car. If the car finished ahead of mine in an important race I would protest the car on principle alone.
Anything can be argued, and this is just my personal opinion.
Jim Susko

[ddewhurst]

***The disagreement is that you can't substitute them because they also act as a control arm. ***

Ahh, this is where some people are NOT understanding (or don't want to admit to being on the wrong side of the fence for Oh so long) the function of the upper links. They serve the EXACT same OEM functions (suspension link/location link/traction bar) as the lower arms. Therefore one may per the rule SUBSTITUTE the lower links.

If I didn't want the Tri-link I could using the rules SUBSTITUTE all four links with home brewed links....... The word ANY traction bar & SUBSTITUTE free things up in a hurry. ( a couple of long standing nerd card holders may need their cards revoked )But first we need to understand the functions up this suspension & the four links.

Anyone try removing removing the lower set of links to see how the car functions. Trust me it would function just like this odd ball :026: , it wouldn't be capable of walking.

If I thought I needed to do a streach to make this SUBSTITUTE of the lower links legal I would say something about the Purpose of the class which has a statement of "to compete in low cost cars". Hey, the DD-Force parts are less than $100.00 & the mazdamotorsports parts are approx $300.00.

Darn, I almost forgot. Did you folks answer the question below woth a YES or NO?

Have you doubters answered the above ^ question? DO THE LOWER LINKS RESIST TORQUE?????? Lets use the KISS principle. THE ANSWER IS YES or NO.

David YES.........

Roland

Jake

Gerg

Jeff

Josh

joeracerx95 YES........

Kevin NO......... (The upper and lower links are locating arms, not traction bars.) To which I say then get rid of one pair of your locating arms & attach the remaining pair of locating arms to the vertical centerline of the Banjo & let's see how well the suspension functions. It only takes one pair of location arms to locate the Banjo.

joeracerx95, the question response trend is positive therefore do the cost effective parts.

[JoshS]

***The disagreement is that you can't substitute them because they also act as a control arm. ***

Ahh, this is where some people are NOT understanding (or don't want to admit to being on the wrong side of the fence for Oh so long) the function of the upper links. They serve the EXACT same OEM functions (suspension link/location link/traction bar) as the lower arms. Therefore one may per the rule SUBSTITUTE the lower links.
[/b]

Here's my take.

In my mind, it's not important whether or not the upper and lower links are the same. One needs to look at any individual part on its own merit, define it, and then decide whether or not the rules allow it to be changed in any way.

Now, keep in mind ... I've never really looked at one of these suspensions, and no one has provided me photos. So the following opinion is based only on the descriptions in this thread. Also understand that I tend to be conservative when it comes to rules interpretation.

Given all of that, in my opinion, I'd probably come to the same conclusion on all four of these links: they are dual-purpose devices. They *are* traction bars, all four of them. But they are also trailing arms, all four of them. The rules say that traction bars may be substituted, but has no allowance for trailing arms. If you replace one of these arms, then it is a defensible position that you have substituted a control arm. If I were hearing the protest, I believe I would find that a driver that had substituted one of these links to be in violation of the rules.

BTW, the function of the arms once you make modifications (such as adding a tri-link on the top that basically replaces the control arm function of some of the bars) is, to me, irrelevant. The definition of a part is based on its function when 100% stock.

[Hahn63]

How do I get sucked into these things!

Ok, here is what I truly believe.

The stock suspension is a 4 link with a watts. The car can be driven with out the watts (been there done that).

The car can not be driven with the lower links gone. (Watts removed) So it has to be stock.

The car can not be driven with the upper links gone. (Watts removed) So it has to be stock.

So both of those need to be in place for the car to move and thus it is its suspension type, a 4 link.

The tri-link is basically turning the car into a different suspension type (a 3 link with a pan hard bar) with the air upper bushings installed. I do not believe this was the intent of the rule but others (of greater power than me) think that it is, so it is legal.

Roland

[tom_sprecher]

Under the subtopic of Suspension Control from the 2007 GCR pg. 300,

"Traction bars used to control axle rotation shall be one piece solid bar or tube. Heim rod ends may be fitted."

The Mazda rear suspension using a 3-link and panhard setup could run effectively w/o the upper links OR the lower links if the 3rd link is properly attached to the top OR bottom of the pumpkin. In either case whichever links you decided to keep must have proper bearings as well, albeit plain or spherical, but not foam. Of course actual removal of any link is prohibited and was suggested only to prove a point.

With this in mind what is the function of any of the links at this point? In the case of the RX-7 are they really all just one in the same? One thing for certain is they all are used to control axle rotation. The only element that truely locates the rear axle and does not control axle rotation is the panhard or watts.

The GCR does not differentiate a traction bar from a location link so why are we trying? The GCR does provide a definition of a trailing arm but it is only referenced in the Formula Section. Are we making up rules based on what each of us feels is right or wrong?

RTFGCR!

On edit: One thing's for sure, when my no longer available, $200 a pair, ISC lower links crap out I'm replacing them with $100 worth of Heims and steel tube available at any of the thousands of circle track speed shops nation wide. I run IT7 in the SEDiv where as gentlemen we tend to look past the BS rules.

[joeracerx95]

"Are we making up rules based on what each of us feels is right or wrong?"

Uhhhh, yeah. And your point was? :P

-chuck-