Agree with Andy in relation to CASTER ANGLE. Reading through some of my old Automotive Apprentice training manuals from the mid 70's, I have found the following - I quote - "Excessive caster can make a wheel shimmy at low speeds; after striking an obstruction on an otherwise smooth road, the excessive caster will cause an over-correction of the deflected wheel, causing this to shimmy from side to side. Insufficient caster can cause the vehicle to wander, as the wheels will not trail sufficiently to give forward stability. This may also contribute toward high speed shimmy".
Have been giving a lot of thought to your problem and have added in my little bits along the way but if you look at it this way, you go to the super market and grab a trolley with the caster wheels shimming and it is almost uncontrollable this is due to incorrect caster, may be the same as your truck.
Dave.
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1 x 1955 Austin Champ WN1(restored)
2 x 1956 Austin Champ WN1(restored)
1 x 1955 Humber 4 x 4 GS (restored)
1 x 1945 FMC 1/4 Ton Trailer (restored)
1 x 1942 Bantam 1/4 Ton Trailer (restored)
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