Twitchy drive/ sensitive steering KR

[GT350AUS]

I put a steering rebuild kit through my KR control valve and made the adjustments to the valve as per spec but I find the car is sensitive on the highway to the slightest roughness in a road.

If there are tyre ruts in the road the car is very twitchy/sensitive and the movement is felt from the front to the back, so much so that my wife complains that it's making her car sick.

As speed builds above 55mph it gets worse.

I've had the wheel alignment done, and new tyres fitted but the problem is still there.

I don't expect it to be like a modern car but my 66 Hertz is more stable as is my 1973 Mach1

Any suggestion as to what could be causing this would be much appreciated.

[Rukiddin]

What type tyres did you install? Belted? They tend to "follow" the lines,crevices in the road. Maybe swap the tires from your '73 and retest.

[KR Convertible]

Sound like you might need some more positive caster.  This helps the car stay straight and the steering to return to center.  If you have crowned roads, you want about 1/2 degree more on the downhill wheel, in the US it would be the right side.

[GT350AUS]

Tyres are Toyo Steel Belted 225 x 60r 15

Can try more castor

[Bob Gaines]

I don't know if this is your cause but those symptoms can be from the power control valve shaft to the drag link getting loose in the socket and requiring a rebuild .

[GT350AUS]

I rebuilt the control valve and have only travelled 300 miles since. Everything went back together fine and the was no slop in the ball socket in the ,valve. Shift was locked in place with no slop.

Is the a way to test what you suggest ?

[Bob Gaines]

I rebuilt the control valve and have only travelled 300 miles since. Everything went back together fine and the was no slop in the ball socket in the ,valve. Shift was locked in place with no slop.

Is the a way to test what you suggest ?

Control valves needing rebuild exhibit those symptoms.  I know that adjustment of the centering spring under the cap can be critical as it pertains to sensitivity of steering. If you followed the shop manual directions in rebuilding and tightening of spring then maybe that part is good.

[GT350AUS]

I'll check the centrering spring adjustment again as the car has been sitting with litle use for the past 3 years.

I've also got the car booked in for a Wheelalignment check again mid next month.

Once I get these done I'll chime bak in with the outcome.

Thanks

[GT350AUS]

Update.

centring spring adjustment made and it has improved but it still is twitchy.

Could it be the steering box needing adjustment?

I have done this in the past but I don't want to over adjust it an ruin it.

[gt350bp]

Is the car lowered. If so, might be a bump steer issue, as the front geometry changes during up and down suspension movement.

Don
gt350bp

[Bob Gaines]

Update.

centring spring adjustment made and it has improved but it still is twitchy.

Could it be the steering box needing adjustment?

I have done this in the past but I don't want to over adjust it an ruin it.

Yes a worn steering box can manifest poor steering symptoms . Sorry to say if the box has never been rebuilt after 53 plus years it definitely needs to be now. The grease inside if never changed has turned to the consistency of clay and not lubricating. The metal to metal contact is destroying the parts inside. Adjustment at this point (tightening clearances)accelerates the wear even more.

[GT350AUS]

With only 32,000 documented miles on the clock I wouldn't have thought the components inside would be worn.

Is there any way of testing for wear?

[Royce Peterson]

Like Bob says the grease gets cooked on FE equipped Shelbys and Mustangs because the steering box is right next to the red hot exhaust manifold all the time. Yours might be OK or not but certainly if you have never replaced the grease there isn't any.

The good news is the steering box can be removed with the engine in the car. Probably the worst part of the job is that there are so many components to remove to make it happen. None of them are hard, it's just that there are so many things.

The box can be refilled with grease without removal but that means the old hard clumps of cooked grease are still in there. Not a great way to do it. Generally removing the box and tearing it apart for inspection and cleaning you will find lots of wear even on low mileage examples.

With only 32,000 documented miles on the clock I wouldn't have thought the components inside would be worn.

Is there any way of testing for wear?

[GT350AUS]

Twitchy steering solved....bad lower control arm ball joints,