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#1
10-20-2005, 10:24 AM
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Boost Switchover Valves - 1987 300D T
Howdy all.
I'm trying to sort out hard shifts on my 1987 300D T and I have questions regarding the 2 switchover valves in the boost pressure circuit. 1. Engine Protection Valve (Y30) - Where/when does electrical signal come from for this valve? My valve is bypassed - Is this a fatal flaw? 2. Vac. Amp. Switchover Valve - What is it's function and where/when does elec signal come from? One would think that this information would be available in the $pendy MB shop manuals. Arrgh.. Thanks Mark
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1987 300D T 1994 Dodge/Cummins 2500 1986 Winnebago Lesharo 1990 Miata 
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#2
10-20-2005, 02:40 PM
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The overboost protection solenoid gets a signal from the pressure switch on the manifold above the IP. That circuit has nothing to do with the transmission.
The vacuum amplifier is more complex. I haven't figured it out but I think the only wires are to a coolant temp sensor. If it shifts hard because it shifts late, you'll have to figure out the vacuum amplifier system if it's not just a bad line to the modulator. If it shifts hard but at the expected rpm then you can adjust the modulator to soften the shifts. If you set the modulator so shifts are imperceptible like in a Lexus or Chrysler you will drastically reduce the useful life of your transmission. The 'normal' shift feel of these transmissions is more akin to a 90s Honda AT. Sixto 87 300SDL
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