Sloppy, Squishy Front End Feel

[1Bad04Mystic]

Ok so the car in question is my 04 Cobra with about 9300 miles on the clock. The car is has a tubular K member and control arms, coilovers with the factory bilsteins, caster camber plates, and a UPR bumpsteer kit installed. I just recently did the bumpsteer kit and had the car realigned. It a helped keep the front end in place over bumps a little better, but the car still feels very sloppy in the front, especially at higher speeds. Anyone have any idea what might be causing this? THe car still has the stock sway bars, as I have thought of throwing a stiffer aftermarket one in the front. Any help would be appreciated, this thing is driving me nuts!

:beer:

 

[shurur]

New swaybar bushings, swaybar endlinks (adjusted to level), solid AL rack bushings and solid steering shaft.....

 

[Bingo13]

What spring rates are in the front? They should be around 375lbs with the stock struts. Assume from the wording of your title that the problem lies in the vertical response of the front end and not the horizontal.

 

[1Bad04Mystic]

300lb spring rate

 

[shurur]

Q: Isn't 300# CO on the front equivalent to the 600# OEM springs in the stock position?
Which should be OK(?)

I thought percentage comparison of Stock spring position to CO was 1/2 on the front
and ~5/8 on the IRS rear springs?

So 350# would be like 700# springs or like H&R Sports...which certainly wouldn't hurt.

I'm just trying to clarify for myself as well...and learn.


If the problem is vertical, maybe the struts are going or gone??

 

[1Bad04Mystic]

Im going to order Maximum motorsports solid swaybar bushings and the shorter endlinks and see what happens. I wouldnt think that the struts would be bad with only 9,300 miles, but who knows they are almost ten years old now lol

 

[pack018]

i have the same issue. My car came with UPR coilovers

 

[Bingo13]

300lb spring rate

Problem number 1, spring rates are much too low. 350 is the minimum on this car and 375 would be recommended depending on the spring rates on the rear of the car, which I assume is also a coil-over setup, if not then another problem is on your plate. Just make sure your struts are still working properly also.

The stock swaybar is fine and fooling with it will only mess up the rear end dynamics. I would also look for loose play in the tie rod ends and steering rack before worrying about bushings and end links.

 

[shurur]

Problem number 1, spring rates are much too low. 350 is the minimum on this car and 375 would be recommended depending on the spring rates on the rear of the car, which I assume is also a coil-over setup, if not then another problem is on your plate. Just make sure your struts are still working properly also.

The stock swaybar is fine and fooling with it will only mess up the rear end dynamics. I would also look for loose play in the tie rod ends and steering rack before worrying about bushings and end links.

He's just changing the bushings on the swaybar. Sounds like he has new MM mods otherwise...so I guess rack would be suspect or steering shaft.

These issues sounds like your area...

Q: So are the standard position 600# springs on the terminator just not up to snuff in the first place?

And is this because of the weigh and nose heaviness of the terminator?

And do I have the "equivalent" ratios for CO correct? 1/2 front, ~5/8 rear?

 

[1Bad04Mystic]

Problem number 1, spring rates are much too low. 350 is the minimum on this car and 375 would be recommended depending on the spring rates on the rear of the car, which I assume is also a coil-over setup, if not then another problem is on your plate. Just make sure your struts are still working properly also.

The stock swaybar is fine and fooling with it will only mess up the rear end dynamics. I would also look for loose play in the tie rod ends and steering rack before worrying about bushings and end links.

The 300lb springs are what came with the aftermarket K-member, and what was listed as the street spring rate from the manufacturer. The only other springs they listed were spring rates for road racing and even lighter spring rates for a drag race set up. The rear still has stock springs, I haven't got around to doing coilovers in the back yer. Im keeping the stock swaybar, just changing the swaybar bushings, and doing shorter endlinks, which should come via UPS today.

 

[Bingo13]

Q: Isn't 300# CO on the front equivalent to the 600# OEM springs in the stock position?
Which should be OK(?)

I thought percentage comparison of Stock spring position to CO was 1/2 on the front
and ~5/8 on the IRS rear springs?

So 350# would be like 700# springs or like H&R Sports...which certainly wouldn't hurt.

I'm just trying to clarify for myself as well...and learn.


If the problem is vertical, maybe the struts are going or gone??

Here is the quick cheat sheet (at MM and a few other places)-
Wheel rate is the effective suspension spring rate as measured at the wheel. Depending upon suspension arrangement and geometry, the wheel rate is usually a fraction of the spring rate. A heavier wheel/tire package increases wheel rate.
A stock '79-'04 Mustang's front wheel rate is 1/4 of the spring rate. A Mustang Cobra independent rear suspension (IRS) has a wheel rate that's 1/3 of the spring rate. For example, a stock '03 Mustang Cobra has 600-lb/in springs front and rear.

Front wheel rate = 600 lb/in x 1/4 = 150 lb/in
Rear wheel rate = 600 lb/in x 1/3 = 200 lb/in
Front coilovers have a wheel rate of 9⁄10 the spring rate. Rear IRS coilovers have a wheel rate that’s 1⁄2 the spring rate. For example, an ’03 Mustang Cobra with coilovers has 400-lb/in front springs and 650-lb/in rear springs.

Front wheel rate = 400 lb/in x 9⁄10 = 360 lb/in
Rear wheel rate = 650 lb/in x 1⁄2 = 325 lb/in.
-----------------------------------------------

I ran either 375/575 or 425/650 depending on the track I visited along with the daily driving duties. The problem with this car is that most people will underspring the front end when switching to coilovers. You end up with a '70's era bounce in the car and will unnecessarily shorten the lifespan of the struts. 350 is the minimum and honestly 375 is where I based my optimal street setup. The difference between 400 to 425 is minimal in ride harshness but 425 seemed to pair better with 650 rears on the technical tracks.

 

[shurur]

Here is the quick cheat sheet (at MM and a few other places)-
Wheel rate is the effective suspension spring rate as measured at the wheel. Depending upon suspension arrangement and geometry, the wheel rate is usually a fraction of the spring rate. A heavier wheel/tire package increases wheel rate.
A stock '79-'04 Mustang's front wheel rate is 1/4 of the spring rate. A Mustang Cobra independent rear suspension (IRS) has a wheel rate that's 1/3 of the spring rate. For example, a stock '03 Mustang Cobra has 600-lb/in springs front and rear.

Front wheel rate = 600 lb/in x 1/4 = 150 lb/in
Rear wheel rate = 600 lb/in x 1/3 = 200 lb/in
Front coilovers have a wheel rate of 9⁄10 the spring rate. Rear IRS coilovers have a wheel rate that’s 1⁄2 the spring rate. For example, an ’03 Mustang Cobra with coilovers has 400-lb/in front springs and 650-lb/in rear springs.

Front wheel rate = 400 lb/in x 9⁄10 = 360 lb/in
Rear wheel rate = 650 lb/in x 1⁄2 = 325 lb/in.
-----------------------------------------------

I ran either 375/575 or 425/650 depending on the track I visited along with the daily driving duties. The problem with this car is that most people will underspring the front end when switching to coilovers. You end up with a '70's era bounce in the car and will unnecessarily shorten the lifespan of the struts. 350 is the minimum and honestly 375 is where I based my optimal street setup. The difference between 400 to 425 is minimal in ride harshness but 425 seemed to pair better with 650 rears on the technical tracks.

I'm starting to cut and paste and link your posts on Mustang suspension, like I have collected NASVTs posts on engine mods.....Thanks Again for another meaty Post/Response!!

Edit: It looks like this spring location/geometry/leverage factor can be calculated for any car.
1. If I know the F/R weight distribution %
2. If I know the OEM spring rates and that effective spring rate is swapped from the F/R weight distribution in order to balance the car.

That is provided the F/R wheels are the same weight and size...

The '99 is 55/45 with springs 500#/470# and the geometry factor 1/4F and ~1/3R comes out in the math.