Need advice for steering indecisive

[neilmathieu]

Hi,
When I am driving more than 60 MPH , the steering becomes indecisive and handling twitchy and abrupt. I have manual steering from FF5 , IRS , 15¨tires, 9 in. in front , 11 in. rear, 22 psi in front, 24 psi at rear. My aligment made by pros with the numbers from MKIV.com manual. My engine 351W stroked 427 from Engine factory with Tremec TKO 600, 5 speed, 8.8 rear end.
Suggestions, ideas in order ?
Thanks,
Mark IV 066644 running legal on the street since July 19.
__________________
a Quebec-Canadian driver from Saint-Georges-Beauce
FFR Mk4 complete kit with no used parts
351w stroker 427 (538hp), this is the specs of my motor
some pictures HERE

[65 Cobra Dude]

Neil,

My first guess is the pressures are low in the tires. Those pressures are typically for racing/autocrossing. I would put them to 30 PSI all around and if that does not fix it, I would look closely at the front end alignment.

Henry

[Pierre B]

Bonjour Quebec. I have your same steering and tire setup, but with a solid rear axle. For a while now, I have been running 24 psi front, and 28 psi rear, with no stability problems. I too used the FFR alignment recommendations, and I have driven my MKII a bit over 12,000 miles with no problems. My 302 engine is likely quite a bit lighter than yours, but I am not sure how much of an influence that has. Also, I don't know how much of a difference this makes either, but I had the wheels aligned while I was in the car. Bonne chance.

The twitchiest driving car by far that I have ever owned was a 1970 Lotus Europa that I got second hand: very light car with manual steering too. I bought it second hand in 1980, but the car had been bought new in Quebec City, right across the Fleuve from where my mother was born.

[Jeff Kleiner]

It really sounds like an alignment problem. Twitchiness at speed is a classic symptom of too little caster and/or being toed out. Unfortunately giving your alignment guy the specs doesn't necessarially guarantee that is what you got. Specifically, make sure it is set with positive caster (no less than 3 degrees for a manual rack) and 1/16"-1/8 toe in.

Good luck,
Jeff

[Bobasaurus]

I would guess with your weight in the car you have a slight bit of toe out caused by bumpsteer. Just a guess, but toe out will make these cars twitchy.

Bobby