Spherical bearings have clearance between the ball and race so the uca will be able to move a little from thrust loading. Cheaper heims tend to have more. As they wear, more clearance is created. There are rubber/metal washers that help to keep dirt out and grease in so they don't wear out as quickly. The further the heims are separated, the less movement there is at the ubj for a given bearing clearance.
Fitting spacers to the sides of heim balls that pivot on the same axis that is parallel to the ground allows for subtle caster adjustment to correct alignment issues from damage or construction errors that can't be found without precise measurement.
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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS
viewtopic.php?f=5&t=13225&p=134742Simple Spring select
viewtopic.php?f=5&t=11815LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12