The term "drag link centered" refers to the lateral location of the steering drag link (center link or relay rod) in relation to the chassis frame rails. The drag link should be centered in the chassis as close as possible for proper turning radius and exhaust clearance. Many times the drag link will get shifted to one side or the other when the front end is rebuilt and aligned. This is caused when the left and right inner and outer tie rod ends are not adjusted to the same overall length. If the drag link is offset in the chassis to one side or the other, the pitman arm and idler arm may interfere with the exhaust system. Header manufacturers do their best to build headers that clear everything like the starter, the frame, the steering and clutch linkage, but sometimes things become very tight in the engine compartment of a '55-'57. Many times the steering linkage can be adjusted so the pitman arm and/or idler arm will not make contact with the headers. After spending a small fortune on headers you certainly don't want anything banging into those nice new header tubes!
1/2" Wrench Ratchet 1/2" Socket
When the drag link is properly centered in the chassis the end of the inner tie rod ends will be directly behind the rear lower control arm bushings. This is achieved by adjusting the overall length of the inner and out tie rod end to the exact same length on each side of the car. Many times an alignment shop will turn the steering wheel to straight and then adjust the tie rod ends to set the toe-in and not pay any attention to keeping the drag link centered. What should be done is to center the drag link itself and then set the toe-in. Once the front end is properly aligned, if the steering wheel is not clocked correctly it must be removed and installed properly:
If the drag link is offset in the chassis too far to the left (drivers side) when the car is turned to the left, the idler arm will swing further to the left than it should and may make contact with the header on the passenger side.
If the drag link is offset in the chassis too far to the right (passenger side) when the car is turned to the right the pitman arm will swing further right than it should and may make contact with the header on the drivers side.
With everything set and adjusted properly, the throw of the drag link is limited by th e steering stops on the outer steering arm (knuckles) and the stops on the lower control arms. If the arms and stops become worn the drag link may travel further to the left or right and may also allow the idler arm or pitman to make contact with the headers. Worn steering arms or control arms should be replaced or repaired with a MIG welder.
If the drag link is centered in the chassis and the tie rod ends are adjusted properly and the pitman arm or idler arm is still hitting the header, you can move the drag link off center slightly to correct this problem. If the pitman is hitting the driver's side header, the drag link will need to be moved to the driver's side of the chassis. To do this, the overall leng th of the left inner and outer tie rod ends need to be shorter than the right hand inner and outer tie rod end overall length. If the idler arm is hitting the passenger side header, the drag link will need to be moved to the passenger side of the chassis. To do this, the left hand overall length of the inner and outer tie rod ends will need to be extended and the right hand overall tie rod end length will need to be shortened.
To extend the overall length of the tie rod ends, turn the tie rod end adjusting sleeve counter-clockwise. To shorten the overall length of the tie rod ends, turn the adjusting sleeve clockwise. By extending the overall length of the tie rods one side and shortening the overall length of the tie rods on the other side the same number of turns, the correct toe-in can be maintained.