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  1. #1

    Default SN95 Front Control Arms - Bumpsteer?

    Hey guys what is the consensus with running front SN95 control arms on a stock 79-86 k-member. I know that the wheels are pushed outwards 1.25" per side, which is fine. But is there any consensus regarding bumpsteer?
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  2. #2

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    It will be reduced some.
    Jack Hidley
    Maximum Motorsports Tech Support

  3. #3
    FEP Senior Member 854vragtop's Avatar
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    I have slightly MORE bumpsteer with my new '94/'95 spindle conversion over the '87/'93 spindles that I just replaced. It's not terrible, and I'm sure it can be easily corrected with a bump steer kit. So far, it's not bad enough for me to throw a bump steer kit on. Even if I did, it would probably only take one washer to get it back to normal. My '85 convertible is lowered with the lowering springs that came with the Bilstein strut and shock kit. On the plus side, the outside wheel no longer has positive camber like it use to have when the steering wheel is cranked all the way. FYI, I did use MM caster camber plates AND a camber bolt on each side. The camber bolts common to the spindle and strut (one per side) gave me more range so I didn't have to have the top of the struts positioned at the limits of the caster/camber plates.
    '85 Mustang convertible GT, 5 speed, 4V
    Stock bottom end, Comp Cams XE264HR-14, GT-40P heads w/ Alex's springs, Weiand 8124 Street Warrior,
    Summit Racing 600CFM carb, 8.8 Turbo Coupe rear end w/ 3.55 gears, '94/'95 Cobra brakes, '85 Town Car M/C, '93 Cobra booster, MM Panhard Bar, MM Strut Tower Brace, MM 4 point K-member Brace

    '68 Mercury Cougar, w/ '88 5.0L, 4V
    My photo website:
    http://www.twilightphoto.com/

  4. #4

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    Jack what’s preferable for a guy wanting to keep the stock kmember, but plans to run coilovers. Street/strip deal, no road racing. 4cyl kmember with SN95 a-arms or 89-93 V8 k-member with Fox length a-arms?
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  5. #5

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    I would use option #2.

    If you use option #1, the car must be aligned with a lot of negative camber. You must use narrowish wheels and tires 8"/245. The 2.3l/early k-member is heavier and less stiff than the later k-member. Fox swaybar endlinks won't line up correctly with the SN95 FCAs. The only advantages to option #1 is that you get better ball joints to start with and you will end up with a little better bumpsteer curve and less lateral tire scrub . However, these can be swapped into the Fox FCAs.
    Jack Hidley
    Maximum Motorsports Tech Support

  6. #6

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    Quote Originally Posted by Jack Hidley View Post
    I would use option #2.

    If you use option #1, the car must be aligned with a lot of negative camber. You must use narrowish wheels and tires 8"/245. The 2.3l/early k-member is heavier and less stiff than the later k-member. Fox swaybar endlinks won't line up correctly with the SN95 FCAs. The only advantages to option #1 is that you get better ball joints to start with and you will end up with a little better bumpsteer curve and less lateral tire scrub . However, these can be swapped into the Fox FCAs.
    Well let me lay out my plan and you can pick it apart . I'm building a street/ strip car that needs to be friendly on my bad L4/L5 disc. No roundy roundy, it doesn't need to handle any better than a stock 99-04 Cobra. Just needs to ride really really nice so that expansion joints and road imperfections don't force me to sell the car when it's built... The foundation will be a 4-eye of some sort, so it will start with a 4cyl/ early k-member. It's absolutely mandatory that I run a stock a-arm, for road comfort. So that leaves me with a stock k-member, or an AJE/ UPR. I'm building a street car, so fanatical weight savings are not necessary and the tubular offerings from companies other than MM are not 100% confidence inspiring for a street car. So, that leaves me with a stock (welded/ braced) k-member. Here would be the chassis list:

    stock 4cyl k-member welded and Mathis modded (a-arms 1/4" up and 1/4" in)
    MM k-member brace
    SN95 a-arms, holes drilled for fox swaybar
    ?unsure of which swaybar, probably just 85-93 V8
    MM cc plates/ subframes
    94-95 spindles + MM bumpsteer kit
    SN95 steering rack + MM steering shaft
    03-04 Cobra IRS + MM poly bushings

    Springs/ dampeners:
    Bilstein HDs + MM front/ rear coilovers. 225-250in/lb springs up front, unsure of rear.

    Wheels:
    17x8 with 48mm offset (S197 Bullitt wheels) + 245/45/17

    Misc:
    MM STB
    MM 6-point cage

    I won't go into what is powering this vehicle too much, except to say it will be a very lightweight/compact all-motor V8 that will slide backwards 1" and that Hooker has adapter mounts and headers for when using a stock k-member.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  7. #7

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    The information about your back changes things quite a bit.

    I would keep the SN95 FCAs. If you use later SN95 FCAs, they have hydrobushings in the rear, which will reduce impact harshness. Plus you get the better ball joints.

    I would modify a 1985+ k-member as they weight less and are stiffer. Forget AJE/UPS/Griggs for k-members. They are all much less stiff than stock and this will hurt ride quality. If the chassis is flexing, the suspension can't do its job.

    Use an SN95 front swaybar. These are hollow and weigh less. Use some Delrin front swaybar bushings. These will significantly reduce friction, which will reduce impact harshness.

    https://www.ridetech.com/products/co...ay-bar-mounts/

    The bushings above have the Delrin liner slit. The gap between the ends of the liner varies depending on the model. You could use the 1.125" model for a 28-30mm front swaybar and a 1.25" model for a 30mm-32mm swaybar. You can use these in conjunction with a modified MMFSB-51 kit to mount the swaybar to the bottom of the frame rail just like an SN95 car does.

    I didn't know that Hooker makes adapter plates and headers for a Buick/Rover 215 V8.
    Jack Hidley
    Maximum Motorsports Tech Support

  8. #8

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    Excellent information thanks Jack. Let me know if you hear of an IRS assembly pop up on the west coast somewhere. I know you have your ear to the ground in these parts. And your knowledge of GM iron is also impressive.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  9. #9
    FEP Senior Member Patrick Olsen's Avatar
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    Oooooh, those Delrin-lined swaybar bushings/mounts are nice! Never seen those before - thanks for the link, Jack. I could see those coming in handy on a couple of my cars.
    '89 GT convertible - not a four-eye
    '82 Zephyr Z7 - future track car

  10. #10

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    One thing you need to be careful of with the Delrin lines swaybar bushings. For a given diameter swaybar, the metal u-bracket is quite large, so that the center to center bolt spacing is also large.
    Jack Hidley
    Maximum Motorsports Tech Support

  11. #11

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    Jack have you ever heard of someone modifying a MM k-member to use stock stamped steel control arms? I'd imagine a competent fabricator could do it? I'm struggling to understand that with all the variations that MM puts their mind to... lsx swap, coyote, pushrod, sn95, fox, etc etc etc that they've failed to tap into the stock front control arms market. I'd venture to say there are more guys that would like to use stock control arms + coilovers than there are doing coyote swaps. And many of the guys doing coyote or LSX swaps would love to retain OEM rubber bushings in their lower control arms. A real head scratcher for me.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  12. #12

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    It can't be done.

    If you want to make an adequately stiff k-member, there is very little weight savings available when building an aftermarket unit. The majority of the weight savings comes from the coilover conversion. Most of this is in the use of a tubular FCA. With a coilover conversion, the FCA can be made tubular, because it no longer has to handle the huge bending loads of the spring in the middle of it.

    So if you made an aftermarket k-member which accepted a stock control arm, and it was adequately stiff, its main advantage would be that you could improve the geometry. That would at least cut sales in half, compared to one that allows a lower front suspension weight. At least half the customers think that "tubular" means light weight. In reality it doesn't. It really means "easy to fabricate for a company that isn't prepared to invest $5,000,000 in tooling" which in the aftermarket car parts industry, is everyone.

    If you used a different construction technique, it is possible to build a k-member which allows the use of stock FCAs and has adequate stiffness. This will intrude on header fitment a lot and will cost more to manufacture or require tooling expenses that would never make sense for such a low volume product.

    There are tubular k-members out there that allow the use of stock FCAs, but all of the ones I'm aware of, allow this by cantilevering the FCA mounting tabs off into space. This makes the front suspension extremely flexible, especially under cornering and is guaranteed to eventually result in cracking and failure.

    We get very few customers who ever request to use the stock FCAs.
    Jack Hidley
    Maximum Motorsports Tech Support

  13. #13

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    The best riding fox body I ever owned had a stock 4cyl/ early V8 k-member, SN95 a-arms, and Bilstein HD + MM coilovers with 275 in/lb springs. Wish I could do a Coyote motor swap and somehow retain the stock k-member so I could use OEM a-arms. Hooker apparently is enabling this to happen with their engine brackets being released, although the end user is limited to 1 3/4 headers which isn't that big of a deal. Obviously, the whole proposition can easily be achieved when using an LS motor.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  14. #14

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    Christian,

    Did you ever take that car and swap the FCAs to MM ones with polyurethane bushings? That's what you would need to do to isolate the effects on the FCA bushings.
    Jack Hidley
    Maximum Motorsports Tech Support

  15. #15

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    Quote Originally Posted by Jack Hidley View Post
    Christian,

    Did you ever take that car and swap the FCAs to MM ones with polyurethane bushings? That's what you would need to do to isolate the effects on the FCA bushings.
    No, that car was a pretty basic build...82 Capri. Sold it to a guy who does some sort of racing up near Sonoma. But if I do go forward with another Coyote build, I'm pretty much cornered into a MM k-member, and in that case I'm cornered into tubular a-arms so I'll definitely be running poly bushings this time around instead of delrin.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  16. #16

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    We could have some poly bushings made which are softer durometer. These would be for street use only. No hard braking from track use. These would reduce the conducted vibrations some.
    Jack Hidley
    Maximum Motorsports Tech Support

  17. #17

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    Quote Originally Posted by Jack Hidley View Post
    We could have some poly bushings made which are softer durometer. These would be for street use only. No hard braking from track use. These would reduce the conducted vibrations some.
    I like where we're going with this. So far I have the delrin lined swaybar bushings, and now the opportunity for softer durometer poly control arms bushings. Paired with stock-ish coilover spring rates, I may in fact see negligible ride harshness from running tubular arms. Then I don't need to reinvent the wheel suspension-wise.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  18. #18

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    Jack what is your opinion on kmember spacers of say 1” ? I’m reading the 10R80 trans needs a 1” spacer to clear the floor. I see on MM’s website they don’t have kmember spacers that thick, I’d assume there’s a reason for that?
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  19. #19

    Default

    If you install the k-member with 1" of spacer between it and the frame, then install the FCAs in the upper set of holes, the geometry will be as if the FCA pivots were raised 1". This would be ok for a car lowered up to about 1.75" from stock.

    If you use a k-member designed for a modular engine, the big problem is going to be the height of the k-member off of the ground. The main tube is going to be really low. The 10R80 is really big.
    Jack Hidley
    Maximum Motorsports Tech Support

  20. #20

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    Quote Originally Posted by Jack Hidley View Post
    If you install the k-member with 1" of spacer between it and the frame, then install the FCAs in the upper set of holes, the geometry will be as if the FCA pivots were raised 1". This would be ok for a car lowered up to about 1.75" from stock.

    If you use a k-member designed for a modular engine, the big problem is going to be the height of the k-member off of the ground. The main tube is going to be really low. The 10R80 is really big.
    I suppose someone could use the MM k-member designed for 5.0L pushrod, Hooker adapter plates for Coyote, and 1 3/4" headers. Then, the main tube will be a little higher off the ground at least.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  21. #21

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    I think you would also need to use the Holley oilpan.
    Jack Hidley
    Maximum Motorsports Tech Support

  22. #22

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    Hey Jack, do you think on a car that used 1" k-member spacers that IRS could be used? I'm reading that the 10R80 fox bodies are needing a 1" spacer. I know that pinion angle is a consideration when using k-member spacers and obviously there is no way to adjust pinion angle on an IRS car.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  23. #23

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    If you lower the engine 1", then you also need to lower the trans 1". This keeps the angle of the engine/trans the same, so it will keep the driveline angles ok from a vibration standpoint. It will increase the operating angles of both u-joints, so it will reduce the car's safe top speed.
    Jack Hidley
    Maximum Motorsports Tech Support

  24. #24

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    Right, the transmission will lower along with the engine. Generally speaking, when you use k-member spacers you are not using the factory transmission crossmember mounting holes. In this particular conversation, we're talking about a 10R80 trans so the crossmember is moved backwards and a Hooker or Stifflers crossmember is used and new tabs are welded to the subframe/ subframe connectors. Normally on k-member spacer solid axle equipped cars, you would use the upper control arms to dial in pinion angle, or on a torque arm equipped car you'd use spacers/ washers between the torque arm and diff housing. So I'm wondering on an IRS equipped car if there would be a pinion angle issue that could not be corrected if a large 1" k-member spacer was used to allow the 10R80 to clear the floorpan.
    82 Mercury Capri - 11.99 @ 112, AFR headed Mountaineer motor
    86 Mustang LX Coupe - the original Coyote swap 4-eye. Gone but not forgotten!

  25. #25

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    I don't understand.

    If the you move the entire engine and transmission down 1", its angle has not changed, so there is no possibility of vibration

    With the setup you are describing, there is going to be angle adjustment at the tail of the transmission and at the nose of the differential.
    Jack Hidley
    Maximum Motorsports Tech Support

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