High speed stability

[rob76]

Hello, I recently bought a 1988 5.0 notchback with 60 000 miles on it.
Everything on it is stock and original, original exhaust, shocks, etc.
I have this problem when driving on the highway. The car feels like it wants to turn in on itself around corners. In other cars I've owned the car resists going into a turn. The wheel centers itself when you let it go. In this mustang as you turn the wheel there is no resistance and the car will keep turning by itself, in fact you have to counter steer in some instances because it just wants to keep turning. I think I can feel the back wheels steering straight making the back end steer opposite the front wheels. It becomes noticable above 45mph. It's freakin scary, the other day I was going about 100mph and the car almost went sideways around a gradual curve in the highway. Dry roads and everything, not accelerating.

I checked the camber and toe myself using a piece of 2x4 (meaured with vernier calipers for constant thickness) that fits in my rim and then using a level for the camber and a laser pointer for the toe. I had a helper mark the laser pointer against a wall 125 feet away. The camber appears to be 0 degrees but it's hard to tell since it's hard to find a level surface. It's close to 0 anyway.
The front has 0.68 degrees total toe in.
The rear has 0.11 degrees total toe out.
The only mistake I made when doing the toe measurment was I took the readings after backing the car slowly into position, I should have driven forward slightly to load the steering components in the forward direction instead, not sure how much of a diff it would make though. Front toe might be 0.5 degrees total instead.
Anyway, it's definately not toed out in the front which is what I was expecting given the steering problem.

Anybody have any ideas? The shocks don't seem worn out, the car doesn't bounce over speed bumps. It jiggles when pushed side to side and the back end has side to side jiggle over speed bumps. I think it's just the tires though. I currently have 215/65/15 Blizzak WS-60's on the car for winter. The sidewalls are not as stiff as a summer 50 series tire. I've had these tires on other cars though and did not have any highway driving problems. The only difference I ever had was that the steering isn't as responsive. The car also had this problem with the tires that came with the car which were some crappy 235/60/15's. Could it be those torque struts on the back axle? Maybe they are worn out? Rear control arm and sway bar look ok. I'm out of ideas!

 

[Mustang5L5]

Go have a computerized alignment performed.

Toe is what centers the wheel in a turn, and front toe in is highly undesirable.

 

[rob76]

What are the factory toe numbers?
From what I've read any toe out in front on a RWD car will cause twitchy steering and wandering. Wouldn't a mustang have to have some toe in? The suspension bushings are all stock so it will become even more toed out at highway speed. I'm not an autocrosser so I don't want fast turn in.

 

[white99gt]

HAve it checked on a real alignment machine.

Also even though everything is original and only 60k.The bushings/shocks/struts are pretty much done just because of AGE and they were not that good factory any way..

I redid my complete suspension ,car is TOTALLY different that when it was stock (and ever thing looked ok)..

 

[rob76]

My measurements are accurate to within 0.1 degrees. I'm a physicist so I know how to measure such small angles I'm not going to pay $100 for an alignment if I don't have to.
If I knew the factory Toe angle I would be able to say whether I have to too much or too little toe. The only other clue is that when I accelerate hard off the line the rear end goes out to the right a little and then a little to the left. This is without any wheelspin. I assume this is some kind of torque steer as the axle twists. It just does it a little. Not too much.

The shocks are fine because when you bounce the car up and down it goes back to it's default position without coming back or without any further oscillations. Of course brand new suspension would be tighter but It wouldn't be making the car dangerous to drive. My Neon had original suspension with 150k miles on it and it felt rigid/controlled and tracked great right up to 120mph.

 

[Mustang5L5]

I accelerate hard off the line the rear end goes out to the right a little and then a little to the left. This is without any wheelspin. I assume this is some kind of torque steer as the axle twists. It just does it a little. Not too much..

You should probably be looking for worm bushings or probably torn torque boxes then. The rear end should not do that. When you floor it, it should stay straight if the tires do not spin. A rear end that is shifting left and right without wheelspin is one that has something very loose back there.


Get the rear on jackstands and check for lateral movement of the rear and inspect all bushings and mounts for the control arms.

 

[Pokageek]

A larger front sway bar will also help with oversteer although your issue sounds like somethin aint right backthere. Good luck.

 

[white99gt]

My measurements are accurate to within 0.1 degrees. I'm a physicist so I know how to measure such small angles I'm not going to pay $100 for an alignment if I don't have to.
If I knew the factory Toe angle I would be able to say whether I have to too much or too little toe. The only other clue is that when I accelerate hard off the line the rear end goes out to the right a little and then a little to the left. This is without any wheelspin. I assume this is some kind of torque steer as the axle twists. It just does it a little. Not too much.

The shocks are fine because when you bounce the car up and down it goes back to it's default position without coming back or without any further oscillations. Of course brand new suspension would be tighter but It wouldn't be making the car dangerous to drive. My Neon had original suspension with 150k miles on it and it felt rigid/controlled and tracked great right up to 120mph.

Well because it passed the "bounce" test does not mean they are good..Been wrenching for a living for over 17 years.


Alignments are only around 50.00,but it will not tell you if you have a bushing issue ,which it sounds like you have.

 

[rob76]

Thanks for the tip about the torque boxes, I will definately have to inspect those. When I shake the car side to side at the back the axle doesn't seem to have any obvious play in relation to the body. However maybe it does front to back on one side which could be causing wonky rear end steer.

 

[rob76]

Alignments here in Canada are $100. We get hosed for everything.

 

[white99gt]

You will not be able to see broken diff bushings unless you get real close or take out the control arm...They will cause a shifty rear end..Never saw mine even when i replaced my control arms..Till i stuck a rod through the hole,then they look like they were ready to fall out.

 

[Mustang5L5]

Thanks for the tip about the torque boxes, I will definately have to inspect those. When I shake the car side to side at the back the axle doesn't seem to have any obvious play in relation to the body. However maybe it does front to back on one side which could be causing wonky rear end steer.

Jack up both rear wheels, support it by the body and see if you can move the wheels front to rear...sorta like YAW in an airplane.

 

[rob76]

Haha yeah I'll defiantely have to check that out. Now if it would only stop raining...
I bet the torque box is ripped up. Might get some upgraded steel boxes if that's the case.

 

[mrmustangman357]

the torn bushings wouldnt explain the easy/ no effort steering. I think your caster is set too low positive or even negative. there are sources online you can find out how to set your caster. i think it is: turn the wheel inward 20 degrees. take a reading of your camber. turn your wheel outward 20 degrees from center, take camber reading.

[first number - second number (which should be nagative, so subtracting makes it positive)] X 2.5 = caster.

oh yeah, for the rear end on a solid axle there will be NO toe out/in. what you are measuring is prolly a misaligned rear end, which sometimes happens in these cars. it is called dog legging. as long as the rear end is within .15 degrees of straightness to the front, you are fine. unfortunately there is no really accurate method of measuring this short of a laser alignment system.

 

[skunk21]

the comment you made about the back end helping to steer the car is termed dog tracking, if you could watch your car going down the road it would look more like it was driving at a slight angle vs straight. the effects tire wear, brakings and handling, has you found out. you need to check the rear end bushings on the top of housing for the uppers arms, the uppers arms and mounting area and the same for the lower arms since these are the mounting points for the rearend. check for any prior damage, welding or repairs, go to a body shop or aligments shop and see if you can get some measurements for mounting points in the rear. you need to correct the dock tracking before messing with the front toe since it will very little to help you, you need to get that rear end under control since it's moving around under acceleration. also you may need some big pry bars or pipe to move or flex stuff to see if things will move, sometimes it takes alot of force to move the arms or bushings, think of the forces underway when the car is moving, something could be worn or a bushing hole could be strecthed it just needs more force than your arms to move it to find it.best of luck

 

[rob76]

No doubt, thanks for the advice. I might take it in to the dealership if I can't find the problem.

 

[rob76]

So I lengthened one of my tie rods by about 1/64 of an inch or so, and it now drives great on the highway. I actually went even beyond that and test drove it making about 5 adjustments and trying it out. When it was more toed out (I estimate at around 0 toe) it was just too hairy to drive above 70mph. Taking tight curves felt like I was driving an F1 car or something as it was wanting to dart around which was kinda scary but made for quick steering otherwise. Anyway I toed it back in and now it feels pretty good on the highway. It doesn't randomly change direction and the wind doesn't make it dart about. It sails around curves. I'd estimate the toe on it right now to be about 0.4 degrees total or about 1/16 of an inch each side.
I believe the problem I had originally was I had too much Toe (0.7 degrees) and it didn't want to start turning the car until you had turned the wheel quite a bit at which point it would really pull suddenly to the side. (which was a bit scary at highway speeds!)

It still doesn't want to center the wheel by itself at lower speeds. At highway speeds it kinda wants to center itself now but not otherwise. I think maybe the rack or the ball joints are stiff. How do you test the rack?

 

[rob76]

Also, I think the back end is fine. I think Its just these soft side wall winter tires that have lots of side to side jiggle in them that I'm feeling at times. I don't get any back end steer on the highway even under heavy throttle or deceleration. I just feel it at low speed over rough roads and through intersections and I really think it's the tires. They're like riding on jello. But they stick to the frost at night which is good.

 

[HaynStang]

The wheel not centering itself could be a worn out steering rack, or maybe your alignment settings are still not quite ideal.

The stock range of alignment adjustment isn't that great on these cars. Even on an otherwise stock suspension a set of caster/camber plates will make a big improvement in how the car drives.

 

[PJC Racing]

Toe does help center the wheels, but caster is what primarily centers the wheels. Stock suspension in fox's have very limited to no adjustment for caster and camber, this is why caster camber plates sell like hot cakes.