Car gets unstable around 100mph
- Thread starter WhiteHeat306
- Start date
ram360
Founding Member
crazypete
All my crevices are greased.
Thats about where the aerodynamics start to kick in and airflow starts to have an effect. Something to think about.
My 87 and 91 both shake and rattle like crazy above 90 mph so nothing unusual there. You need to dial some extra toe-in and it will be much more stable at high speeds. Also maximum camber tends to stabalize it more by causing the wheel to want to remain centered. If you go toe-out, it will wander all over the damn place, frighteningly so at high speed.
Your wheel bearings could be crap. If the front tire "wobbles", it will be more noticable at high speeds.
My 87 and 91 both shake and rattle like crazy above 90 mph so nothing unusual there. You need to dial some extra toe-in and it will be much more stable at high speeds. Also maximum camber tends to stabalize it more by causing the wheel to want to remain centered. If you go toe-out, it will wander all over the damn place, frighteningly so at high speed.
Your wheel bearings could be crap. If the front tire "wobbles", it will be more noticable at high speeds.
CrazyCobra
New Member
I have the same problem 
I have not been able to isolate it yet. 
however it got worse when I switched to 17's 245 40's. I use H&R red progressive rate race springs( 2" drop I believe) and tokico shocks. The alignment at rest is not the problem so I am going to try a bump steer kit, it may be the alignment changing as the suspention move up and down at the higher rates of speed?
Try this link and see if this sounds reasonable
http://maximummotorsports.com/mmtierod.asp
I have not been able to isolate it yet. Try this link and see if this sounds reasonable
http://maximummotorsports.com/mmtierod.asp
crazypete said:
If your mustang is shaking and rattling above 90 something isn't happy. Toe in will dampen the effects of steering, which will make the car respond less to your steering _input_ at any speeds. Which if you are shaky at the wheel will stabalize the car at high speeds where small inputs become exaggerated. Camber will help the wheel remain centered because it lifts some of the contact patch of the tire off the road, therefore it will make a wider tire essentially narrower when the car isn't leaning. And as stated before, wider tires will follow imperfections in the road more.
Caster is what truely what stabalizes your wheels at speed. The wheels on the front of a shopping cart are called caster wheels, the caster of the shopping car wheels is what makes them point staight when you push the cart instead of flopping. I'm sure we've all seen a cart with a broken caster wheel that flops around. The caster setting of your front alignment has the same effect.
Bumpsteer only comes into play when the suspension is compressed, or if you lower the car from stock height say 2 inches, you get the same bumpsteer effect a stock mustang would have when the suspension is compressed 2 inches.
The cause of instability can be alignment, wheels out of spec, unevenly worn tires, bad bushings in the control arms, steering rack, shocks, maybe swaybar too but probably not. Bad outer tie rods, bad balljoints, bad steering linkage, bad steering rack, bad bearings, bad spindles.
The list goes on and on.
I do not recommend patching the problem with toe-in (this gives you really really bad ackerman and greatly diminishes turn-in) or heavy amounts of camber (which will decrease already poor braking performance and eats tires)
Find the real problem and get it taken care of, you'll be much happier when you're done.
If you find that the steering response is too twitchy for you at high speeds, you can change to a manual rack, or add a steering dampner.
If the problem does not exist at lower speeds, I would guess aerodynamics.
Did you remove that plastic guard that hangs down a couple of inches below the radiator? This was designed to reduce airflow under the car, thereby reducing lift.
Did you remove that plastic guard that hangs down a couple of inches below the radiator? This was designed to reduce airflow under the car, thereby reducing lift.
crazypete
All my crevices are greased.
Woops, I always mix caster/camber up. Sorry bout that. I wish they made them sound at least marginally different. I found an alignment to greatly reduce these effects for me at least so try that first.
BlackGT89
Member
Yeah, sounds like "lift" is rearing it's ugly head. Wide tires can also hurt aerodynamics (take a look at the skinny tires they use for record runs on the Bonneville Salt Flats). It's not always a popular belief, but for those kind of speeds you are beginning to need front air dams and rear spoilers to keep it pinned to the road.
Sorry man I should have clarified better. It's like the car wants to steer itself, the steering wheel moves back and forth just a little bit, and I feel like I don't have good control of the car. It's not like I whoop ass in the car every day, but the few times before when I was going that fast I really didn't want to stay at that speed for long because I felt like I didn't have control. Plus 100 isn't even that fast.tjm73 said:When you say unstable, what do you mean exactly? Is the car wandering back and forth or does the front of the car kinda feel like it's hoovering around? Define what's happening please.
WhiteHeat306 said:
What everyone said about aerodynamics is true/correct. What you further explain here makes me think sounds like it's more than just that. AS far as a cause goes...man I don't haev any idea. Maybe the alignment gets out of whack as the front of the car rises from the aerodynamic lift.
Check your inner and outer tie rods. Its really easy... grab the sides of the tire and try to rotate it back and forth like you are steering. It shouldn't move at all. If it does, you'll have to look around and figure out where it's loose at. Both inner and outer tie rod ends tend to go bad, espeically with the age and milage of these cars.WhiteHeat306 said:
poneypower89
Now everyone in the world will know I wanna bang t
19865.0 said:sloooooooowwww downnnn
Probably the best advice given so far
My car rides like a dream at 130+ speeds... No shaking, no uncontrollable actions of any kind... Completely stock GT (suspension wise) with a set BFGW Traction T/A's. So i wouldn't blame it on aerodynamics.
BlackGT89
Member
White Heat, I clicked on your "Check Out My Ride" link and I'm going to take back what I said. I notice you have a Saleen type rear wing and a front air dam / spoiler already, so maybe you do need a few new front end parts instead. I'd check the speed rating on those tires as well. Nice ride, BTW !
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