2014 rules package; the National Director's cut

Questions and answers about CMC and NASA rules

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BADVENM
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Postby BADVENM » Wed Nov 20, 2013 5:07 pm

soundguydave wrote:
suck fumes wrote:I run the 4 link and it works perfect for me. If the 4 link sucked that bad then ford wouldn't have invested a ton of money in development into it and wouldn't have left it on 3 generations of mustangs. It works great if you have the car setup correctly!


Oh, it does work well, if you're out getting groceries or hitting the dragstrip. Throwing it into a corner is another matter. We get grinding noises in left turns (no witness marks mrom tire contact), and short of throwing new arms at it repeatedly, it stll comes down to roll-induced bind. Using bushing torsional deflection is just not the right way to locate an axle laterally.

As for Ford leaving the design alone, yes, they did, but I would bet BIG money that it was a cost-based decision, and not performance-driven. 90% of the people that buy Mustangs don't race them. And 90% of those that do, don't turn in their chosen form of motorsport.



Hmmm, you mentioned grinding noises when turning left. At the beginning of the race season last year I started getting a grinding noise behind my seat somewhere in the middle of the car but slightly back by the axle. I thought my driveshaft was rubbing on the safety loop but no signs of that.

I was getting the grinding noise on hard fairly high-g right turns, not so much on left but I cant completely rule it out. I'm wondering if that noise I'm hearing (last year and this year) is related to the binding issues. I'll need to get under the car and check that out a bit closer.
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soundguydave
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Postby soundguydave » Wed Nov 20, 2013 6:40 pm

Ours sounds like rear tire rub, but with no evidence left behind... I'm putting it down to one or more UCA bushings being shot enough to transmit "normal" NVH vibrations from the axle into the tub. Ours is only on lefts, and only at high load. One ex-Bondurant car in our region does the same thing... The Bondurant folks said "that just lets you know you're pushing hard enough. "
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BADVENM
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Postby BADVENM » Wed Nov 20, 2013 7:21 pm

soundguydave wrote:Ours sounds like rear tire rub, but with no evidence left behind... I'm putting it down to one or more UCA bushings being shot enough to transmit "normal" NVH vibrations from the axle into the tub. Ours is only on lefts, and only at high load. One ex-Bondurant car in our region does the same thing... The Bondurant folks said "that just lets you know you're pushing hard enough. "


Makes sense, last year was the first year I really started getting comfortable in the car and pushing it hard. Pushed it even harder this year and we added max width tires and wheels as well as bigger brakes. We were looking for tire rub too, ours is confined to the fronts.

I have some video in which you can hear it.
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Postby MHISSTC » Wed Nov 20, 2013 8:03 pm

soundguydave wrote:The physics of the stock 4-link just flat suck. It works fine in pure longitudinal axis motion (acccel/brake), but quite literally the instant you put the car in roll, the upper arms are in bind. This puts tearing stresses into the bushing material as well as the mount. Going to a higher-durometer bushing (poly) only exacerbates the problem, and while sphericals would help, the real problem is with the stamped sheetmetal arms themselves, as well as the geometry of the design.


Exactly.

Also, as was explained to me, when the axle rotates about the longitudinal axis during cornering, the geometry involved in the angled upper arms causes one upper arm to go into compression while the other goes into tension (one arm tries to get longer, while the other tries to get shorter) Therefore, spherical bearings are not the ultimate answer in eliminating all of the bind induced from cornering. While some portion of the bind is due to the twisting motion that could be eliminated with spherical bearings, they won't eliminate the tension/compression issue.

The best solution for this that I've seen was from a company that went out of business several years ago. I found an example of it not too long ago, but have been struggling for the past couple hours because I've been unable to find it again. Maybe another fox old-timer remembers it also and can help out.

Anyway, it consisted of two brackets, one that fit between the upper rear control arm mounting ears on the rear axle, and another U-shaped bracket that mounted between the upper rear arm mounting points on the chassis side. These two brackets were connected by a single upper control arm with spherical bearings on either end. This arrangement end up being VERY similar to the current setup on the S197 Mustangs. With a single upper arm located at the center of the axle, the bind from twisting and from compression/tension is totally eliminated. It also eliminated much of the stresses encountered from converting to something like the PM3L. This setup also needs either a watts-link or a panhard bar to locate the axle horizontally. If I was going to completely redo the rear suspension in a fox Mustang, this would be my preferred setup instead of going with a torque arm and coilovers.
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Postby MHISSTC » Wed Nov 20, 2013 8:25 pm

suck fumes wrote:If the 4 link sucked that bad then ford wouldn't have invested a ton of money in development into it and wouldn't have left it on 3 generations of mustangs.


You have to remember this design came about as a result of Ford's efforts to downsize cars to improve fuel mileage and to reduce the number of different chassis they were using at the time in order to save money in the late 79s and early 80s. Ford milked the FOX chassis for all it was worth as it was eventually used on thirteen distinct models, of which the Mustang/Capri was the sportiest and the Mustang was the last one still using it in a modified form 25+ years later. Ford left it along because it worked for what most people wanted from it probably 99+% of the time. And for every model and year they could keep using it, that was one more model and year they didn't have to spend additional R&D money.
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Postby MHISSTC » Wed Nov 20, 2013 8:26 pm

BADVENM wrote:
soundguydave wrote:Ours sounds like rear tire rub, but with no evidence left behind... I'm putting it down to one or more UCA bushings being shot enough to transmit "normal" NVH vibrations from the axle into the tub. Ours is only on lefts, and only at high load. One ex-Bondurant car in our region does the same thing... The Bondurant folks said "that just lets you know you're pushing hard enough. "


Makes sense, last year was the first year I really started getting comfortable in the car and pushing it hard. Pushed it even harder this year and we added max width tires and wheels as well as bigger brakes. We were looking for tire rub too, ours is confined to the fronts.

I have some video in which you can hear it.


To clarify, the only tire rub we can find is in the front. We don't see anywhere the tires are rubbing in the rear, but that's exactly what it sounds like. We had a situation early on when we first built the car where the transmission mount was worn out enough that the tail of the transmission was shifting and the driveshaft balancing weights were hitting on the driveshaft loop bolt heads. It almost sounds like that, but much further back towards the rear axle. However, there is no evidence of contact around the driveshaft. We even had our real mechanic open up and inspect the differential to see if there was anything going on in there. The only thing he could find was that the buttons on the end of the axle shafts where they contact the spider gear shaft had worn down enough that there was a concern there might be too much end play in the axle shafts which might affect the rear brakes, and that the integrity of the area at the end of the axle might be compromised and the c-clips might eventually come loose. We ended up replacing the fox length axle shafts with SN95 length axle shafts as part of our effort to maximize track width.
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Al Fernandez
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Postby Al Fernandez » Wed Nov 20, 2013 9:03 pm

As evidenced by the discussion in the prior couple of pages I think you can see that the jury is still out on the mustang rear upper arms. It sounds reasonable, but certainly more discussion is needed so taking the time and not jumping to a rule change is a good decision. When we reach a more definitive stance then we can change the rule (if thats the direction we choose to go).

As for the wheel weight value...that .0 was on the "to do" list but I overlooked it. It'll be in the first revision.
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Den34
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Postby Den34 » Thu Nov 21, 2013 6:29 am

It would be interesting to see if someone could get video of the upper control arms during race conditions and see exactly what it going on.
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BADVENM
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Postby BADVENM » Thu Nov 21, 2013 7:10 am

Den34 wrote:It would be interesting to see if someone could get video of the upper control arms during race conditions and see exactly what it going on.


Great idea. MHISSTC has some great keyfob cameras, we could put one near each control arm then splice the video together to watch both at the same time and see whats going on.
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Postby ShadowBolt » Thu Nov 21, 2013 7:48 am

MHISSTC wrote:
The best solution for this that I've seen was from a company that went out of business several years ago. I found an example of it not too long ago, but have been struggling for the past couple hours because I've been unable to find it again. Maybe another fox old-timer remembers it also and can help out.

Anyway, it consisted of two brackets, one that fit between the upper rear control arm mounting ears on the rear axle, and another U-shaped bracket that mounted between the upper rear arm mounting points on the chassis side. These two brackets were connected by a single upper control arm with spherical bearings on either end. This arrangement end up being VERY similar to the current setup on the S197 Mustangs. With a single upper arm located at the center of the axle, the bind from twisting and from compression/tension is totally eliminated. It also eliminated much of the stresses encountered from converting to something like the PM3L. This setup also needs either a watts-link or a panhard bar to locate the axle horizontally. If I was going to completely redo the rear suspension in a fox Mustang, this would be my preferred setup instead of going with a torque arm and coilovers.


I saw this set-up once also. The company did go out of business. It would be a great way to go for the Mustang without going to the torque arm. I will try to find it again. I would assume you could still tear out the upper mounts.

I was told the stock upper arms are all gone after MM sells what they have. I don't know when that will be but the price has doubled in the last two years. We will have to address this issue at some point. I (like Aaron) think the four link with the sphericals in the axle side is not bad. For me it is way better than the PM3L was. I had ripped out the upper right mount running the PM3L and welded it all up. I was surprised to tear the left upper out running the stock four link.


JJ

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Postby ShadowBolt » Thu Nov 21, 2013 7:50 am

double post

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Postby SRiner » Thu Nov 21, 2013 9:48 am

MHISSTC wrote:The best solution for this that I've seen was from a company that went out of business several years ago. I found an example of it not too long ago, but have been struggling for the past couple hours because I've been unable to find it again. Maybe another fox old-timer remembers it also and can help out.

Anyway, it consisted of two brackets, one that fit between the upper rear control arm mounting ears on the rear axle, and another U-shaped bracket that mounted between the upper rear arm mounting points on the chassis side. These two brackets were connected by a single upper control arm with spherical bearings on either end. This arrangement end up being VERY similar to the current setup on the S197 Mustangs. With a single upper arm located at the center of the axle, the bind from twisting and from compression/tension is totally eliminated. It also eliminated much of the stresses encountered from converting to something like the PM3L. This setup also needs either a watts-link or a panhard bar to locate the axle horizontally. If I was going to completely redo the rear suspension in a fox Mustang, this would be my preferred setup instead of going with a torque arm and coilovers.


I think the part you are thinking of is Evolution Motorsports (EVM) Tri-link set up. But as previously mentioned, they went out of business. But other people have designed their own three link set-up. But CMC isn't about building your own suspension (thats more of AI or AIX), but improving through aftermarket.

Here is what I don't understand. The wild rides upper and lower S-Box replacement kit is now allowed, good choice, and costs $650 not including installation cost. The MM torque arm for racing costs $450 not including installation cost. Plus no more upper control arm costs. Yes you need subframe connectors and a panhard bar or similar. But those are already allowed modifications.

I understand the reasoning that weight and power might need to be adjusted for the mustangs, since this is a major improvement in handling. But from a cost standpoint I don't see it.

This should be in a different thread, but this is where the discussion is currently at.

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Postby MHISSTC » Thu Nov 21, 2013 11:14 am

SRiner wrote:I think the part you are thinking of is Evolution Motorsports (EVM) Tri-link set up. But as previously mentioned, they went out of business. But other people have designed their own three link set-up. But CMC isn't about building your own suspension (thats more of AI or AIX), but improving through aftermarket.


That may very well be the item and manufacturer I remember, but something seems a little different. It's been a while, so that's probably the right one. Without the manufacturer website being available, I'm having to rely on pictures and forum discussions that have been previously posted and are still available to use as reference.

It seems many folks agree that this setup has great potential for improvements over the stock geometry without making the commitment to go with a full Torque Arm and coilover setup, but a vocal minority seem to have had issues with the parts and the tearing of the floor around the mounting points. Those issues seem to be related mainly to drag racing and high horsepower rather than with road course use.

It seems to me the concept is sound, but that it may require a little better engineering to get it right.


EDIT: The best place I could find anything on this unit was at Corner Carvers. CLICK HERE for the 10 page thread.
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Postby DAlgozine » Fri Nov 22, 2013 7:24 am

Anyone else see the 800lb gorilla in the room :o ?
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Postby MHISSTC » Fri Nov 22, 2013 1:06 pm

DAlgozine wrote:Anyone else see the 800lb gorilla in the room :o ?


Which one are you looking at? :lol:
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