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Old 01-22-2010, 01:30 PM
The Toecutter's Avatar
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Join Date: Jan 2010
Posts: 20
300 SDL shifting problem

I own a Mercedes 300 SDL. Recently, it began to shift at a much higher RPM than normal. Normally, it shifts up at 2500 rpm or so from 1st to 2nd gear; now, it tends to slip shifting from 1st gear to 2nd gear. At 30% throttle(without even hitting the throttle hard enough to normally activate the kickdown lever), it won't upshift into 2nd gear until ~4,500 rpm. When 2nd gear is finally engaged in the transmission, there is a noticable but brief surge of acceleration, then more slipping if the accelerator is pressed too hard.

A transmission shop took the transmission out of the car(under warranty), ran a few tests on it, and could not find any errors(they may be lying about that). Any indication as to what could be the cause of the problem?

If the transmission is not an issue, perhaps this is a vacuum issue?
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Old 01-22-2010, 06:40 PM
The Toecutter's Avatar
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Join Date: Jan 2010
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I removed Fuse 5; when I apply 50% throttle or so, the car now shifts as it normally would, but it no longer kicks down.

Is this indicitive of a bad kickdown switch, or is the transmission solenoid more likely to be the issue?
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Old 01-22-2010, 07:11 PM
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Join Date: Apr 2007
Posts: 342
Solenoids won't typically "fire" on their own--the spring prevents it. Typical failures are burned/broken windings (electrical failure), broken return spring or dirty/jamming (mechanical failures).

The switch is wonky.
James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
1987 300SDL junker 170k
1982 300SD junker, 265k
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Old 01-23-2010, 06:09 PM
The Toecutter's Avatar
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Join Date: Jan 2010
Posts: 20

Can a kickdown switch be re-built, or does it usually have to be completely replaced?

Once I take care of that issue, I'm going to look into fixing my turbo; I know what the problem is too. A sensor that detects an overboost condition is clogged with soot. I need to replace it, but my air intake manifold gasket is old and corroded(thus I will need a replacement for that too). 0-60 mph acceleration has slowed to 19-20 seconds because of this(times before the kickdown switch went all wonky).

Some of the windows have also gone off track, but that's an easy fix(white nylon tabs need to be replaced).

I've had this car for a year now. Even with the turbo not currently working, it can cruise all day long at 100+ mph, and it feels like a floating couch.

Best $1,200 ever spent.

Once everything is in complete working order engine wise, I'm thinking of taking the ALDA out.
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