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Short story is I did a 4 wheel alignment on a 2013 Mercedes E250 a few months ago: front/rear toe are still perfect after a recheck due to extreme rear tire inner wear on this sedan. The camber 'seemed' to be too negative but, it calls for -1.6 and, the car's at -2.0 yet, the rear toe's dead on (.35 degrees).

Any ideas here or, is this a quirk on that type of vehicle? Car has less than 100K miles on it, no looseness in the suspension and, we have an unhappy customer.
 

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I tried an alignment on a Mercedes years ago. Many of them require a 'spreader bar' to push the wheels into 'toe-out' while the adjustment is measured and performed. If performed without the spreader which artificially loads the suspension into toe-out, the wheels may be toed-out too far if not using the tool. This toe-out would tend to scrub the rubber away from the tire's inner tread surfaces.
If this tool is required and you don't have access to one, I would suggest that the car goes to a specialty-import or M-B dealer. An example:
https://www.amazon.com/Specialty-Pr...automotive&vehicleId=1&vehicleType=automotive
 

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Odd, it's the rear tires that are wearing badly, the fronts looked fine. That spreader bar is for front alignment only, from what I've been able to find out.
 

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Damn, and I thought Ford twin I-beam trucks were bad. Mine is old enough to have king pins, so no alignment is possible, specs are based on ride height for both caster and camber both of which change as the axles and radius arms move. I had my 1986 F350 aligned by a small independent shop in Gloucester County Virginia nearly 25 years ago, only thing since has been a right inner tie rod and toe-in setting. The shop that did the alignment bent the two I-beams to get things in spec, current front tires were installed 23 December 2014 and are still nice and even on the wear pattern.
 

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Damn, and I thought Ford twin I-beam trucks were bad. Mine is old enough to have king pins, so no alignment is possible, specs are based on ride height for both caster and camber both of which change as the axles and radius arms move. I had my 1986 F350 aligned by a small independent shop in Gloucester County Virginia nearly 25 years ago, only thing since has been a right inner tie rod and toe-in setting. The shop that did the alignment bent the two I-beams to get things in spec, current front tires were installed 23 December 2014 and are still nice and even on the wear pattern.
King pin vehicles don't usually get a camberr adjustment (bending required) but do need caster shimming.
 

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King pin vehicles don't usually get a camberr adjustment (bending required) but do need caster shimming.
In practice: almost any front straight axle can have the total R/L caster adjusted as you pointed out. With lifted Jeep XJ's (1984-01 Cherokee), etc. longer lower front trailing arms many times will bring the caster number back to factory specs
 

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There are no caster shims on a Ford Twin I-beam. The axle halves and the radius arms are in bushings, axle halves pivot and the radius arms are inserted through frame brackets with what look like giant shock absorber mounts. There are some offset radius arm bushings made to raise or lower the rear of the arms for caster changes. Alignment specs on these require ride height and frame angle be determined to arrive at the correct values.
 

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There are no caster shims on a Ford Twin I-beam. The axle halves and the radius arms are in bushings, axle halves pivot and the radius arms are inserted through frame brackets with what look like giant shock absorber mounts. There are some offset radius arm bushings made to raise or lower the rear of the arms for caster changes. Alignment specs on these require ride height and frame angle be determined to arrive at the correct values.
Twin I-Beams has to be at the top of lousy suspensions for the modern era. Alignment and tire wear were always an issue.
 

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Twin I-Beams has to be at the top of lousy suspensions for the modern era. Alignment and tire wear were always an issue.
Ahh, but when you (a) can find someone who knows them and (b) has the tools to do them right, they do not go out of alignment with the king pin version. My king pins are the originals installed at the Oakville Ontario truck line in 1986, they are still snug on clearance after 33 years of being properly greased. They ride much better than leaf springs and are way more suited to a heavy pickup (F350) than car type suspensions. In the 25 years I have owned the truck, I have put one full set of tie rods and one right side (long) inner, two sets of polyurethane radius arm bushings on, no other suspension work. I have had one full alignment in 1994 and two toe adjustments, most recent when the right inner tie rod was replaced. The only other thing done to the front suspension was adding a factory anti-roll bar 3 years ago.
 
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There are no caster shims on a Ford Twin I-beam. The axle halves and the radius arms are in bushings, axle halves pivot and the radius arms are inserted through frame brackets with what look like giant shock absorber mounts. There are some offset radius arm bushings made to raise or lower the rear of the arms for caster changes. Alignment specs on these require ride height and frame angle be determined to arrive at the correct values.
If discussing kingpin vehicles: you're 100% correct. I aligned a 1999 F350 2WD earlier today, Twin I Beam and all, adjusted the camber/caster via the already installed eccentric cams on the upper balljoints, set the toe and, vehicle drove fine.

PS: I used to cold bend the parts in question almost 25 years ago but, even back then, the appropriate equipment was fast disappearing from alignment places.
 
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If discussing kingpin vehicles: you're 100% correct. I aligned a 1999 F350 2WD earlier today, Twin I Beam and all, adjusted the camber/caster via the already installed eccentric cams on the upper balljoints, set the toe and, vehicle drove fine.

PS: I used to cold bend the parts in question almost 25 years ago but, even back then, the appropriate equipment was fast disappearing from alignment places.
I know, my first Twin I-beam truck was a 1977 F150, I was referred to the shop in question by two other Ford truck owners, both of whom very very particular about their vehicles. I gave that truck to my oldest son after I bought the 1986 F350, I drove it with his very pregnant wife and 15 month old daughter to San Antonio where he was in Army medical school. He had to replace the front tires a year later and the tire shop asked him who had aligned the truck and told they had never seen a Twin I-beam with such even tire wear.

The current tires on the F350 are Firestone Transforce that the school buses here use, the fronts were 4 years old Dec 23rd and are just as even a wear pattern as you could want.
 
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And for more irony: I had to correct another shop's 'alignment' earlier today on a 2004 F350, also with Twin I beams. As received: this beast had well over a 3 degree camber split right to left, which neatly explain the hard lead to the left. Short story, to bring the +3 dr's side camber down, I had to remove the aftermarket adjuster and, tossed the original in there. The previous shop tried to make the OEM cam work by grinding down the lock tab, where the pinch bolt passed but, couldn't figure out how to turn the cam. I cleaned up the toe, road tested it and, sent in on its way.
 
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