unless you won't give us specific details about the wheel / drivers you use I don't think we can help you a lot.
also you could have a look here: http://www.lfsforum.net/forumdisplay.php?f=14
is the wheel working under windows corectly? You can check it in your control panel -> Gamecontroller. Double click on your wheel and check the settings there, is it calibrated correctly? Are the drivers installed, are it the latest drivers?
start LFS and go to options -> controls -> axes / ff and check if you set the axis corect. (you maybe have to invert some axis).
Have you recalibrated the controller in LFS? Is the "wheel Turn" set? or wheel turn compensation? (default 1.0)
From what you said sounds like a problem i had which was just calibration.
In game go options -> Controls -> Wheels -> buttons/axis (or something like that) then click the little "c" in the bottom right. THen press both pedals fully and turn wheel lock to lock.
Sounds like calibration. In game, go to controls, wheel/FF, calibrate axes. Wind the wheel all the way left to right, stamp on all the pedals, then click calibration lock.