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Old 02-09-2008, 03:03 AM   #1
Doktor A (864-623-9110)
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Default Koni Strut ALERT II for 15" 2500 Sprinters

Here's a reprint of Michaels question on Sprintervan yahoo group site regarding Koni shock "bottoming". Koni has superceded 2500 front struts with 3500 front struts, here's a possible clearance problem:

Dok A, You have said that there are differences in the front and rear suspensions between the 15" and 16" wheels. Is the front suspension different and how much height is gained?
I recently got Koni shocks to replace the 1st set of struts #87-2604 with the new version #87-2638 since 1 had failed. Now I get great ride control, but every once in a while, the struts bottom out when you hit a sudden rise in the road surface. Prior to installing the new struts, I had the dealer replace the busted leaf spring and stabilizer bar bushings and the tie rod ends. The ball joints were Ok as well as the control arm bushings. So, all the people I talked with are puzzled as to why these struts bottom out. A very helpful tech at Koni even went so far to call John at Upscale and he said that he never saw this problem. Do you have any insight?

My Reply:
Regarding your Koni dilemma- Your Early 2500 '02(140"/ 158") was originally equipped with 15" wheel. In mid/later '02, marketing/sales pressure forced MBenz to fit 16" wheels and tires to 140"/158" 2500 US Sprinters. Tire availability as well as aesthetics likely forced the issue. In Europe low center of gravity and low loading height is paramount-also 15" load rated tires are everywhere.

When MBenz converted the 2500 mid/long Sprinter to 16" wheels MBenz didn't "just" mount larger wheels. They raised the vehicle about 30mm.

In the rear this was achieved by more extreme "manufactured curvature" of the rear leaf. They also reshaped the wheel well opening and added the plastic wheel well trim.

In the front they added channeling to the front suspension subframe to raise the front roughly the same 30mm. The steering column was lengthened an equal amount and the steering rack was modified(but not dimensionally).

The now raised(in relation to wheel center) upper strut mounting location required longer strut housings and center shafts. This is where your dilemma comes into the picture.

The Koni (3500) F. strut has an almost 11" long strut housing(measured from top of outer housing to center line of upper mounting bolt(chosen as index line). The OEM 3500 strut is about 3/4" shorter(than the Koni) and your original 15" 2500 mid/long strut was about 9 1/4" in length-almost 3" shorter.

Your Koni struts are indeed "bottoming out" but not internally. The top of your Koni strut housing(cylinder) is hitting the upper strut mount steel "washer". This washer is cone shaped and is well below the shaft's threaded section. This bottoming occurs before the internal shaft can damage the adj. mechanism inside the shock housing.

You can check these dimensions by crawling underneath and pulling down the dust cover on the strut. Measure clearance between strut top and that cone shaped seat for upper mount. Compare this dimension to clearance at your suspension arm bump stop.

Hopefully when your spring was replaced they used all the correct spring seat part#'s and didn't complicated that issue as well. Doktor A
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