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#1
07-25-2013, 06:10 PM
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617 - How much Vacuum?
Just wondering how much vacuum the pump should make on my 85 300d. I am seeing 20in/hg at idle. Is this within spec? Just wanted to be sure it was working properly. Thanks.
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1985 300D 296,000 miles - Project "Rusty" 1/4 mile in 19.9 sec @ 71mph. It's almost rust free and water proof! 2006 Dodge/Cummins 6-Speed - 670HP 1159ft/lbs 
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#2
07-26-2013, 12:51 AM
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22-24 in/hg is what many forum Members say is normal. But, that is with no abnormal leaks.
You might unscrew the Check Valve that is in the Vacuum Pump right where the Main Line attaches and do a visual check and clean it out with some WD-40 and see if cleaning it improves the Vacuum.
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84 300D, 82 Volvo 244Gl Diesel
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#3
07-26-2013, 04:45 PM
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I will do that. Thank you.
__________________
1985 300D 296,000 miles - Project "Rusty" 1/4 mile in 19.9 sec @ 71mph. It's almost rust free and water proof! 2006 Dodge/Cummins 6-Speed - 670HP 1159ft/lbs
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#4
07-26-2013, 05:09 PM
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You should have two orifices, one as mentioned the other going to the VCV should be near 12inHg.
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83 SD 84 CD
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#5
07-26-2013, 06:58 PM
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What is a VCV (vacuum control valve?), and where is that located?
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1985 300D 296,000 miles - Project "Rusty" 1/4 mile in 19.9 sec @ 71mph. It's almost rust free and water proof! 2006 Dodge/Cummins 6-Speed - 670HP 1159ft/lbs
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#6
07-26-2013, 08:27 PM
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Toomany MBZ might have a point there. Where are you measuring the Vacuum.
If you are measuring from the first Nipple closest to the Front of the Car on the Main Vacuum Line you will be measuring the total possible Vacuum. The Vacuum Valve is on the Fuel Injection Pump. It is a White Plastic Valve. It regulates the amount of Vacuum that goes to the Automatic Transmission Modulator. On My year and model between the main Vacuum and the Vacuum Valve is a restricted orifice. It is merely a Colored Piece of Plastic with a Hole that is in inserted inside/between the Vacuum Line going to the Vacuum Valve and it reduces the Vacuum to the Vacuum Valve. To know how much it is supposed to reduce that you actually need to have someone read it from the Manual as there is an allowable range of Vacuum. However, on your 1985 there may be a hole bunch of Vacuum control devices. It is better you try to find one of the threads that has a Pic of a Vacuum Diagram for your Year and Mode.
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84 300D, 82 Volvo 244Gl Diesel
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#7
07-26-2013, 09:25 PM
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20" Hg sounds great. I think you only need ~10" Hg for most things to work (door locks, engine shut-off), though the tranny shifting is proportional and fussier. You can rig up tubing to measure only the main tube from the pump, with nothing else connected. That is the best way to check the pump alone. You can easily find info here to remove the EGR controls, as many do, if that is a leak source. Good luck, rebuilt pumps are >$300 and even the simple rebuild kit is $100. I also have an 85 and the CA model. The vacuum controls aren't that complicated once you go thru the diagrams you find here. Main addition in 85 was the vacuum amplifier "blue saucer" that is supposed to improve the transmission shifts.
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#8
07-28-2013, 09:47 PM
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VacuumControlValve sends the proper amount of vacuum to the transmission, here's a video of one off the car.
It's located on top of the InjectionPump. MB VCV operation, part #617 070 02 46.avi - YouTube
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83 SD 84 CD
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