vacuum amplifier on '85 722.4
vacuum amplifier on '85 722.4
I still have the vacuum amplifier that controls the transmission and the little tangle of vacuum lines that feed it.
#123 "Vacuum Transducer" or "Vacuum Amplifier"
#125 switchover valve attached to it.
Is this something that's worth simplifying further or does the amplifier have a positive enough affect on drivability to merit keeping?
(thanks to DeliveryValve)
-Christian
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'84 G-Wagen turbodiesel
'75 240D 4-Speed
I simplified the vacuum lines on my '85 617A
I still have the vacuum amplifier that controls the transmission and the little tangle of vacuum lines that feed it.
#123 "Vacuum Transducer" or "Vacuum Amplifier"
#125 switchover valve attached to it.
Is this something that's worth simplifying further or does the amplifier have a positive enough affect on drivability to merit keeping?
(thanks to DeliveryValve)
-Christian
-------------
'84 G-Wagen turbodiesel
'75 240D 4-Speed
The earlier turbo models had basically a direct vacuum source from the main line to the trans vacuum modulator, with a Vacuum Control Valve (VCV) - #65 on the diagram, in the middle to leak down the pressure. A high vacuum pressure around 10-15 Hg leaked towards zero at a different pressed throttle position with a full throttle position at zero Hg.
The vacuum modulator with high vacuum softens the shifts at a low throttle response and a modulator with lower vacuum firms up the shifts with more throttle. This is predicated only on throttle position and no other variables.
On the 1985 models, Mercedes engineered a trans vacuum system that didn’t just rely on throttle position to control the softness or firmness of shifting. It also relies on turbo boost pressure which becomes dependent on engine load and temperature.
The vacuum transducer (#123) works in a system. It works in relation to turbo boost pressure and engine temperature.
Unlike the prior years, the system now starts off at a high vacuum of 12-17 Hg to the modulator. It now leaks down five inches when full throttle travel is given. When the turbo boost pressure goes up, the boost applies an input to the vacuum transducer at connection PRE on the diagram. This produces an upward deflection of the transducer diaphragm, lowering the amount of full vacuum applied to the modulator valve to zero. The hydraulic modulating pressure in the transmission is increased which firms up the shifting.
At a coolant temperature below 50º C, a temperature switch (#20) cuts off vacuum signal from the VCV at a Switchover Valve (#125) on the diagram. The vacuum in the circuit produces a higher vacuum to the transducer from a direct line to the vacuum pump (#76). Then this higher vacuum is sent to the modulator softening the shifts while the engine is cold.
When the coolant temperature rises above 50º C, the switchover valve is powered on and the VCV controls the transducer. The vacuum circuit takes over as describe above which an increase in throttle/power load produces less vacuum to the transmission modulator, thus firming up the shifts.
This is kind of a long winded statement and hopefully it will give some info to make a decision of what direction you want to head towards.
One other note, If you make the vacuum circuit simpler by using the 1981-1984(Fed) model, the modulator will have to be adjusted/tweaked to shift in an acceptable manner.
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Gota love Mercedes Diesels!
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DeliveryValve
01-18-2010, 09:45 AM #2The ’85 transmission vacuum system does have a positive effect on shifting. When properly working, the shifts should be both precisely smooth and firm at varying acceleration conditions compared to the earlier simpler vacuum system.
The earlier turbo models had basically a direct vacuum source from the main line to the trans vacuum modulator, with a Vacuum Control Valve (VCV) - #65 on the diagram, in the middle to leak down the pressure. A high vacuum pressure around 10-15 Hg leaked towards zero at a different pressed throttle position with a full throttle position at zero Hg.
The vacuum modulator with high vacuum softens the shifts at a low throttle response and a modulator with lower vacuum firms up the shifts with more throttle. This is predicated only on throttle position and no other variables.
On the 1985 models, Mercedes engineered a trans vacuum system that didn’t just rely on throttle position to control the softness or firmness of shifting. It also relies on turbo boost pressure which becomes dependent on engine load and temperature.
The vacuum transducer (#123) works in a system. It works in relation to turbo boost pressure and engine temperature.
Unlike the prior years, the system now starts off at a high vacuum of 12-17 Hg to the modulator. It now leaks down five inches when full throttle travel is given. When the turbo boost pressure goes up, the boost applies an input to the vacuum transducer at connection PRE on the diagram. This produces an upward deflection of the transducer diaphragm, lowering the amount of full vacuum applied to the modulator valve to zero. The hydraulic modulating pressure in the transmission is increased which firms up the shifting.
At a coolant temperature below 50º C, a temperature switch (#20) cuts off vacuum signal from the VCV at a Switchover Valve (#125) on the diagram. The vacuum in the circuit produces a higher vacuum to the transducer from a direct line to the vacuum pump (#76). Then this higher vacuum is sent to the modulator softening the shifts while the engine is cold.
When the coolant temperature rises above 50º C, the switchover valve is powered on and the VCV controls the transducer. The vacuum circuit takes over as describe above which an increase in throttle/power load produces less vacuum to the transmission modulator, thus firming up the shifts.
This is kind of a long winded statement and hopefully it will give some info to make a decision of what direction you want to head towards.
One other note, If you make the vacuum circuit simpler by using the 1981-1984(Fed) model, the modulator will have to be adjusted/tweaked to shift in an acceptable manner.
.
.
Gota love Mercedes Diesels!
.
(01-18-2010, 12:44 PM)Syncro_G ... This raises another question - would the '85 vacuum control system be a worthy upgrade for earlier models?
The '85 300sd and 300D came with 722.416 trans for the California version and 722.315 & 722.303 transmission for the Federal version. They then used a version of this vacuum setup on the 603 powered w124 with the 733.4 trans and the 603 powered w126 with 722.3 trans on the later years as well a some other vehicles. So Mercedes thought the improvement was worthwhile to carry it over to the newer models.
With that in mind, theoretically you could use this system on an earlier model and get good results. But only if your able to tweak it to work properly. What you lose is the simplicity of the old system in which more items can now fail over time.
.
Gota love Mercedes Diesels!
.
DeliveryValve
01-18-2010, 02:42 PM #4(01-18-2010, 12:44 PM)Syncro_G ... This raises another question - would the '85 vacuum control system be a worthy upgrade for earlier models?
The '85 300sd and 300D came with 722.416 trans for the California version and 722.315 & 722.303 transmission for the Federal version. They then used a version of this vacuum setup on the 603 powered w124 with the 733.4 trans and the 603 powered w126 with 722.3 trans on the later years as well a some other vehicles. So Mercedes thought the improvement was worthwhile to carry it over to the newer models.
With that in mind, theoretically you could use this system on an earlier model and get good results. But only if your able to tweak it to work properly. What you lose is the simplicity of the old system in which more items can now fail over time.
.
Gota love Mercedes Diesels!
.
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