Understanding Ball Joint Production Changes in the Tri-Five Chevy
Tri-Five Chevys underwent changes to many parts during its reign from 1955 to 1957. Chevy, even made improvement changes to the basic architecture of the frame, suspension, steering, drive train as Chevy’s engineers evaluated and solved construction, maintenance and usage problems. Luckily ,for the Tri-Five Chevy owner and mechanic alike is that the later designed parts will interchange with the earlier design parts.
Today's blog will discuss the upgrades to the lower ball joint.
Beginning with the earliest 1955 model, ball joints went through a series of changes. The first design “lowers” had only four heat-treated rivets on the main face of the control arm.. An additional brace was welded into the arm on the underside to provide support. The ball joint itself did not have any sides. This design was used for only the first few months. Its use was discontinued due to the increased time needed to weld the brace. Later designs have a flange around three sides of the joint, and use six rivets to hold it to the control arm. This design is still used by TRW and MOOG replacement parts.
A special note must be added about the factory lower ball joints. The stud has a loose fit and may have as much as ⅛-inch up and down travel when not installed. The stud did not fully seat in the socket until the pressure of the coil spring was released. Later replacements did not have a much travel and seemed to wear out sooner. Because of these factors, many repair shops replaced the lower ball joint thinking they were worn out, when in fact they were not! Those ball joints have been known to remain usable for at least 35 years.
The upper ball joints from 1955 through 1957, were all riveted to the face of the control arm with heat-treated rivets. The tip of the ball joint resembles a top hat with a rounded dome measuring 1-9/32-inches from the face. The replacements seen today have a very short top measuring ½-inch from the face. Some NOW upper arms have been seen with low-type ball joints riveted to the control arm, though not normally done on assembly line cars. This type of joint was used in 1958, and would have been used for NOS(R) parts. This would not be considered correct on a restored car today.
Factory-installed ball joints were installed on control arms that had already been painted black. Therefore, the ball joint itself was not painted, but left in a oil finish. The rivets are usually black heated-treated but can be natural. The grease cup on the underside of the upper arm was painted black before being riveted in place. Both upper and lower control arm grease fittings are a 90-degree bend style, and point to the front of the car. These should be cadmium plated, The nut is usually heat-treated black, bu may be also be natural; and the cotter pin should be cadmium plated. -By Mike Domoracki, Shop Talk, Bow Times, Volume 1, Number 3, Nov 1992
The BEST way to get a great overview of the changes from year to year can be found in the Historical Brochures-Passenger Car Engineering Achievements for 1955, 56, and 57. These documents address all the technical changes/updates for each new model year...
These documents are found on this site at:
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