My understanding of the pre-load or spreader bar is that is simulates the drag of the road on the wheels under motion and is used to adjust toe.

It's not necessary for an alignment, per se, but it helps dial in the handling of the car so it's aligned "at speed" not in a static position on the rack. I would assume that would also affect tire wear, since your car would not have an alignment adjusted for the majority of your driving conditions.

I can't find the reference now, but I recall reading about different recommended settings based on your normal driving speeds; e.g. if you were a mostly highway driver the bar would get more force.

Here's one more opinion from a guy who claims to own the M-B approved bar: http://www.continentalimports.com/ser_ic4232.html

Here are a couple of worthwhile quotes from that article:

"I almost exclusively diagnose M-B cars, but I align everything from Chevy pickups to Ferraris. And no car has more ability for correction, nor is any easier to adjust, than Mercedes-Benz. "

"The spreader bar has always been an issue with me, but I have always had consistent, good results the way I adjust toe-in. Because this issue bothered me, I recently bought the bar from Beissbarth (it came with the M-B# 900 589 01 27 00 on it) and have now used it on two cars. The toe change on one was 1.4 mm and on the other it was 0.9 mm. Since the tolerance of accepted toe is larger than this amount, I assume that is one reason I have had good results without the bar."

I think this is, sadly, one of the largest obstables to getting a proper alignment. I've spent up to 4 hours aligning my Mercedes. But I do mine the old school way with strings and a digital level. (maybe the digital level isn't old school, but you get the idea)

Scott

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Scott
1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
1987 Porsche 911 Coupe 109,000 (sold)
1998 Mercedes E300 TurboDiesel 147,000 (sold)
1985 Mercedes 300D 227,000 (totaled by inattentive driver with no insurance!)
1997 Mercedes E300 Diesel 236,000 (sold)
1995 Ducati 900SS (sold)
1987 VW Jetta GLI 157,000 (sold)
1986 Camaro 125,000 (sold - P.O.S.)
1977 Corvette L82 125,000 (sold)
1965 Pontiac GTO 15,000 restored (sold)

No spreader bar?

I really don't see how any professional can align on of these in less than two hours.......and that's really moving. That would mean a charge of $170. around here........and nobody would pay it.

Therefore, you have a situation where the product will likely never meet the specifications..........and, it doesn't need to meet them because it's a blind article.........the customer will never know in most cases.

I think you're focusing too much on the camber as the source of your tire wear. Several degrees of negative camber are not going to give that wear. I would bet that your front wheels are toed out too much- check the tread for feathering to verify that.

"Several degrees" of negative camber will absolutely cause significant inner edge tire wear.

No need to perpetuate this issue, is there?

For the most part, any car's alignment is best accomplished by following a factory procedure. Shops doing the job for next to nothing are typically adjusting toe in only, even if they take a measurement and find other aspects could use an adjustment. Diddling with caster or camber means diddling with both, which means more time and money. It takes a decent shop and some owner experience to get the job done correctly. The $70 special, 4 wheel alignment is usually not a deal.

As an aside, on the W115 chassis for other than toe-in you had to turn all the adjustment "knobs" to their zero position and then measure alignment, and then plot the "course" to the correct alignment on a chart in the manual. Almost no one followed the procedure and thus you never got a properly aligned car. I went through this in excruciating detail with the local Goodyear "aligned for life" package thirty years ago.

So, while any shop CAN align a MB it is not clear any shop will do it CORRECTLY. There is nothing mysterious about it. It merely requires that someone follow the right procedure. That requires more than the right set of tools, which nearly any shop has.

Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Jim, where would I find this factory procedure?

I have both factory service manuals + two different maintenance manuals . . . I could find it in either. Could it be that I have to go through each replacement part module . . . or are you talking about some manual that would come with a alingment machine . . .

My camber is quite negative . . . I just want to do this right the first time.

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82 240D Manual 277K and still rolling!
02 Volvo S60 AWD For Sale

FWIW I had the same problem, and I adjusted the camber myself using a level. Close enough.

I am on travel for the next few days and can't get to the manual. It has been some time, but I believe the procedure is in the chassis manual for the vehicle. Or it was for my 1975 240D. It involved setting the various adjustment features to a set of alignment marks and then going to a graph to find the caster and camber measurements with the adjusting features in some known position. The graph and procedure show how far to manipulate the adjusting features and in what sequence to get the front end into alignment.

Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Jim,

I have both the chassis & body manuals for 123, I'll have to look again tonight . . . last night I remembered why I want to sell my wifes Volvo, bunch of moron who designed it forgot how big peoples arms and hands are, and that it helps if you can see what your working on! Sure make working on 123's much more fun!

__________________
82 240D Manual 277K and still rolling!
02 Volvo S60 AWD For Sale