I only cover some issues using new arms in other threads. More info...
1. GM and other Arm pivot ends have a lot of tension when mounted that should
Not care about such small differences.
Just Try lifting the arm at same distance from spring pivot as the ball end.
Is Why
Lisle 65750 Windshield Wiper Arm Remover is very handy even on Fiero because nail or drill in hole to removal can have problems.
2. OE Fiero and others arm sockets have "notches" to hold the ball that itself isn't smooth and can see as wiper end has to rotate a bit down or up as you mound it on the ball.
In Fact Often can tell when some fool removes the arms for whatever reason because wiper hits the hood and trim or is Parked too high because fool uses 1st try to mount them. That's skipping OE left and right arms are made different even if same length on most models and many put the arms on the wrong side.
Result of 1+2 = issue is 3rd party arms may have no or very small notches and can't hold the ball properly.3. That's completely ignoring rust etc.
Even OE Arms may not fit after removal because arm socket, ball or both have "rust" and changes size of either. Seen it happen a lot like in states w/ high road salt use. Even with arms w/ tapers and nuts to mount them, once removed stirs up the "rust" and taper won't hold.
Many times can "fix" them, often temporary, by shimming them w/ whatever thin metal at hand.
If wiper are on w/ key off after driving then Key On in Winter... can have a lot of problems then just F'd arms as wipers get frozen or jammed by snow.
4. Sorry but Diff of 100th of an inch and More is often cause by the people that measure whatever and more people involved with this "project" means Database is worthless.
Just 3 of many problems:
Most don't buy Starrett and other real Pro Tools and that alone will cause errors.
Even if they buy those High $ tools, most never learn how to use them causing errors.
Exactly where you measure a part can also cause errors.
And that's only measuring the pivot head.
Dorman arms can have different dimension(s) from batch to batch and you can't even say what batch you get/got because may sit in some part store warehouse for years. Dorman like others can have wider tolerance just to make 1 batch to keep Cost to make the parts lower.
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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave
