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Hummer Knowledge Base

The Hummer Knowledge Base


Positive Camber:

Is it possible that if the rear toe in wrong that the rear tires will wear on the edges? Like there are too many shims on the rear control arms. Not sure if this is called caster but looking at my truck from the rear the bottom of the tires look in and the tops tipped out (\ /) enough to notice. Will the toe adjustment fix the problem of wear?

Toe-in could cause the rear tires to wear on the outer sides, but it's more likely that your camber (tire top to bottom orientation--Z axis) is way too positive--as you say "tops tipped out \ /".

In the old days (on rigs like yours and mine) the factory aligned our trucks with the same specs as the HMMWVs (i.e., with substantial positive camber). Presumably this was done because the HMMWVs would be heavily loaded (HLV) more often than not. Heavy loading would cause the HMMWVs to squat a little, and bring the camber back near zero (straight up and down). Because most of us civvies run Lightly Loaded Vehicles (LLV) this is often excessive and in-appropriate. So typically (at least in these parts--Texas) we pull all of the shims out from behind the cup brackets (that attach the upper control arm to the frame), and try to get as near to zero camber as the frame allows (ball joint installation/positioning also impacts camber).

In my tweaking, I was only able to get Lucy down to .5 degrees positive camber and retained thin shims on one side only to equalize between the minimum possible between the left and right. Curiously I've encountered many early owners surprised that the outside of their left rear tire was badly worn on their relatively new trucks... I believe this was evidence of the very positive camber setup (As I recall my left was originally +2.0 and Right was +1.5).

Another curious impact (usually ignored) which can modestly affect camber 'action' is the control arm bushing neutral position. When the upper control arm pivot bolts are released (like when playing with the shims), the wheel spindle center should be positioned at ride height before retightening. Otherwise the bushings may twist upward or downward--at ride height (adding or subtracting a distorting spring component).

Since my last alignment Hunter has revised the alignment specs... Oh and this relates to the earlier discussion about alignment cost. Most shops can adjust toe-in, but a full caster, camber, toe-in job (at least on the Hummers without alignment cams) is a lot of work and should be expensive, probably $350 at minimum...

Regards,
Keri


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