The "Mustang II" IFS Real Info & Debate Thread

Discussion in 'Classic Mustang Specific Tech' started by reenmachine, Sep 17, 2007.

  1. reenmachine

    reenmachine Active Member

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    The last papers I kept from a kit, I think from the red 'vert, say that the rack is from an '84-'93 Mustang.
     
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  2. jp51mustang

    jp51mustang New Member

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    I've got the R&D cross-member in, it's time to buy more stuff... Willie has a bunch of options as far as brake kits. For those of you with experience, which brakes would you recommend? I'd like 2inch drop spindles and something more than a one piston caliper. I don't need top end, just nice/good. Thanks (hopefully this isn't too off topic)
     
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  3. mrmustangman357

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    i met up with a company in new orleans that does alot of eleanor clones and they told me that the MII setup they get from heidts "drives like a brand new car." and the cost isn't too bad either if you know how to fabricate. I would still, however, like to see some rollbar trangulation to the cowl. If one thing statics tells me, a rather large moment of inertia would be placed on the frame rail about the firewall/frame intersection point. Some rollbar extending up to the cowl would give these forces somewhere to go, rather than go into a moment and fatigue the steel. It shouldn't be too hard to use 1 5/8" .120 DOM outside on the fender side in case someone thinks rollcage tubing is too "pro street" for their ride.

    Also, can anyone address suspension travel concerns?
     
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  4. reenmachine

    reenmachine Active Member

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    Correct, and this is pretty much the same whether the shock tower is there or not. That's why the frame rail transitions to a really deep section just before this point.

    This is fairly commonly done. I'm in the middle of doing one right now and I'll post pics when it's complete.

    What are your concerns?
     
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  5. bnickel

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    a stock early mustang has 7 inches of suspension travel a mustang II style system has less but i'm not sure how much less, i think it's around 5 or 6 inches
     
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  6. Gailahan

    Gailahan Member

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    5-6 inches of suspension travel is a huge bump.
     
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  7. bnickel

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    or a really tight corner
     
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  8. rbohm

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    i agree that the mustang uses stamped sheetmetal, but it was designed to transmit the load over a large area compared to the mustang ll design. look at the load paths of the early suspension. part of the load goes through the lower frame rail to the chassis. the upper loads were designed to go through the upper part to the firewall and into the chassis. it is effective, and cheap, but it does require that you minimize the loads and keep the upper control arm bushings properly maintained to maximum life. and yes the mustang, along with the falcon was not designed to last 40+ years, but then no car was back then. this is another reason to run lighter springs than the 620's that seem so popular on the street. it is also the reason that if you spend the time to stiffen up the chassis as much as possible, it pays big dividends in handling, as well as ride quality.
     
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  9. reenmachine

    reenmachine Active Member

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    See, I disagree with this. There is no "upper" and "lower" load. The vast majority of the load is applied at the top of the shock tower via the spring seat. This holds the weight of the car and the dynamic loads introduced by cornering, hitting bumps, etc. The loads introduced by the LCA, UCA, etc. are small in comparison. The top of the shock tower is very rigidly connected to the frame rail by the shock tower itself. That's what the shock tower is for! If the load were taken by the thin sheet metal between the top of the shock tower and the cowl then there would be no need for the shock tower to be such a heavy structure. Sure, the sheet metal in that area stabilizes things to some extent by forming a shell structure, but it's the frame rail that's doing the heavy lifting.
     
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  10. bnickel

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    the loads are carried by the shock tower, the frame rail, the firewall and the cowl not just the frame rail. sure the frame rail is holding everything up, but the full load is not transmitted trough JUST the frame, there is triangulation there and actually quite a lot of it. there is triangulation from the side view from the top of the shock tower to front and rear of the frame rails, from the frame rail to teh top of the tower and back to the cowl/firewall area, from the top of one tower to the cowl and to the top of the other tower and also to the rear of the frame rails in the same direction.


    i think you're just hung up on the fact that the shock tower is sitting on top of the frame rail and can't see it any other way. are there more effective ways to do it? sure but just about every unibody car made, even today, is designed in basically the same way.
     
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  11. car_kent

    car_kent Member

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    R&C MII in 68 Vert

    My 68 convertible has the R&C MII coil over front end with 2 inch drop spindles. It has no extra support beyond the standard convertible torque boxes and global west sub-frame connectors. I've just recently completed the restoration, but with 270 miles on the car, I am very pleased with the ride, handling and stiffness of the chasis (zero cowl shake).

    Kent - a MII fan
     
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  12. reenmachine

    reenmachine Active Member

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    I understand the unibody concept and how each lesser component contributes to the whole. It's just that these early unibodies aren't anywhere as structurally efficient as modern ones, so the effect isn't as pronounced. I probably went a bit far in some of my statements, but it just seems that people think that since it's a unibody that means the load is shared equally by all of the various members. I maintain that a disproportionate amount of the load is carried by the frame rails in this case (stock config) so the effects from changing to MII aren't as great as many think. Don't forget that even though the shock towers are gone the rest of the unibody remains to help out, and the huge crossmember does a lot. Much of that unibody structure is there to try to keep the mounting points of the two sides' suspensions fixed relative to each other, which isn't an issue with the MII due to the crossmember.
     
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  13. mrmustangman357

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    reen, or anyone else, have you tried any testing of sheer stress on these early cars? When we were working on Formula SAE, one of our design aspects was torsional rigidity, expressed in Newtons/angle required for deflection. This is in the elastic plane still, however, so nothing gets hurt. I am curious how a typical MII install would compare with the traditional suspension/monte carlo/export brace setup most everyone has. I'm sure global west, heidts, etc. may have done this intrinsically, but I'm not sure if they ever took an engineering approach to it. Just because the factory setup is the overhead loading way, does not guarantee that this is a superior way of handling load.

    Design-wise, I love the aftermarket MII setup. Its cheap to set up (if you buy a kit), has great adjustability and handling characteristics, and has superior packaging. The only thing holding me up is the loading issue, as I'm sure many others are.

    Reen, I also sent you a PM a couple months ago.
     
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  14. 68GT500KR_Vert

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    My R&C Setup

    OK, tell me how this isn't strong; The stengthen front frame rails extend all the way back to the sub frame connectors; there are torque boxes on the outsides of the frame rails, they connect to the inner and outer rockers and the cowl; the subframes have a cross brace and the convertible plate and lower seat pans. The subframes run back to the rear frame rails which has a heavy duty cross member at the back. Pus we ran supports back from the front of the frame rail back to the firewall and added a additional crossmemeber behind the firewall. The car is solid! I have to update the pictures; I should have them later this week. These are from mock-up.

    [​IMG]

    [​IMG]

    [​IMG]
     
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  15. bnickel

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    ok, so you have additional cross braces and crossmembers, additional bracing from the front of the frame rails back to the firewall plus thicker steel frame rails. what we are talking about is using one of the many M-II kits that just weld into the factory sheetmetal frame rails. that's my whole problem with most of the kits is that they don't do any of the extra stuff bracing and the cars i've ridden in with these kits move around all over the place.

    if you add the extra bracing and heavier frame rails and front framerail to firewall supports then it's fine, that's why i like the Martz kits.

    however, by the time you get done with all the extra bracing and stuff how far really, are you ahead of a bolt in kit, certainly nowhere as far as suspension geometry and handling are concerned but you might gain some ride comfort. now, if you have to pay someone to install the kit you're going to end up paying a lot more money, and then there are all the upgrades to the kits which add even more money.


    personally, i'll stay with the shock towers and work around them, of course i can't weld either and don't own a welder either.
     
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  16. mustbereel

    mustbereel Member

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    GT500KR_vert,

    That looks exceptionally strong. I'm sure many will say that most people who install a MII do not go to the same lengths.

    I will do some tests. I have a 67 coupe shell that I'm about to start working on. I will test torsional rigidity in various configurations. To keep it simple I will measure inches of deflection with a given load. I will support three corners of the car and hang a weight from the forth corner. I will measure how far the frame drops after each mod. It may take a while but I'll start with some baselines this weekend.
     
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  17. 68GT500KR_Vert

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    Wow you must have some free time; I wish I had that kind of time, but I have a full-time job, 4 little kids, going for masters degree, and a wife that wants a lot of stuff done around the house. That's why my car has taken 3 years. Should go to paint in the next month of so.


     
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  18. bnickel

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    there is a guy on the corner-carvers forum named Boss Bill who has done some torsional rigidty stuff on the 65-66 cars already and our own SN-65 has done some as well.

    one of the things i found most surprising was that after installing sub frame connectors (welded in) there wasn't much gain in torsional rigidity. that's not to say that the chassis wasn't stiffened up a bunch, just not much going from the left front to right rear (torsionally)
     
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  19. mikethebike

    mikethebike Member

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    The load is distributed through out the UNI-BODY structure. I think that is why we have triangleulated export braces instead of strut bars.
     
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  20. wicked93gs

    wicked93gs New Member

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    I think the export braces are more due to the fact you cant get a strut bar in there, but they do have triangulation to prevent cowl shake on a guess....carbs and intakes tend to get in the way of stuff like that...I have to say that the more I think about it, the more that it seems as if Reen is right on this...I recently replaced my fender apron in my 66....and that sheet metal is so thin I'm amazed that it can support the battery...much less the weight of the engine...most of the weight has to be on the frame rails from the looks...I mean has there EVER been a documented failure of the frame rails with a MII setup? All i hear are reports of cowl shake...and I'm willing to bet that those reports are due not so much to the shock towers being removed as to the fact that because they are gone so is the export brace, so if you welded in a replacement panel in place of the shock towers of the same gauge metal then made a mount on top of it for some time of export brace/strut bar/monte carlo bar setup...wouldnt that retain all the unibody structure? I just think that Reen is right on this one...even though I'm not going with a MII front suspension for my swap(though it certainly would make things 10 times easier and I am constantly tempted)
     
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