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#1
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W123 Vacuum experts needed!!
I am having late shifting in a 1985 300Dt (CA; 722.416). So there's a modulator [corrected: amplifier] and a vac control valve on the IP.
I have good vac to vac control valve (the valve on the IP). I have good vac to the amplifier, and the amp sucks on the tranny line at about 17" at idle. But when I pull on throttle, pressure only drops to say 14", then jerks around briefly, and even at full throttle I cant get it to drop much below 8-9" (presuming that close to 0 is where I need to be at full throttle). The lack of pressure drop and the jerky pressure needle lead me to believe that my pressure curve to tranny is messed. Now I am trying to figure out whether to purchase a vac control valve or a modulator [correction: amplifier], or maybe neither if I can adjust. AND, I cant figure out if the line coming off the bottom of the vac control valve goes anywhere; cuz it's just hanging there on mine. THANKS. NEED HELP! Last edited by rblookc; 03-08-2005 at 07:03 PM. |
#2
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We need to get the terminology straight, first.
Do you have a round blue device on the driver's side fenderwell? This device takes vacuum from the VCV and sends it to the transmission? When you test the vehicle at "full throttle", do you take it on the road for a drive for this test? |
#3
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the IP control valve is adjustable, sometimes
pop the 'conehead' cap off the side of it there should be a nut- if there is a round collar you cannot adjust but you can open it up and fiddle with it 'till you break it! I'd go to a junkyard and get another one
__________________
'02 BMW 325i '85 300D 450k '93 190E 2.6 170k(killed by tree) '08 Ducati Hypermotard 1100S 6k '06 Ducati S2R800 14k(sold) |
#4
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jaguar424 The trick is tohave 3-4" of vacum going to the modulator from the vacum val
The cure is to have 3-4" of vacum going to modulator from the vacum valve at approx 1/3 throttle opening from stop position this is possible by removing plastic cap on vacum valve and adjusting the two small nuts p.s very sensitive adjustment and can be done remember they did it when they built the valve be patient and take a reading now and log your results to see which way you need to go with the adjustment good luck
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#5
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Brian,
yes I have a blue modulator that vacuums the transmission on the Driver Side. That's where the vac is good from the booster line but sporadic to the transmission when revved while parked, cranking on the throttle arm (not driving). What I dont get about it is the VCV does not seem to be attached to it. The blue modulator gets vac from the booster and delivers it to the tranny. The VCV gets vac from the booster from a different place on the line (right next to where the modulator gets vac). I am trying to figure out if the line coming out of the bottom of the VCV is just the vent line, because it currently connects to nothing. As for VCV adjustment, I have a question: If there are two small nuts behind the cone cap on the VCV, which does what? I cant imagine adjusting the vac regulation without knowing which nut to screw where. Thanks in advance. |
#6
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Quote:
You must make sure that all the connections are hooked up to the VA. There is an input for straight vacuum. There is an input for modulated vacuum from the VCV. There is an input for boost pressure from the manifold. And, finally, there is an output to the transmission. The valve functions in a rather screwy way. It typically provides about 10 inches of vacuum to the transmission under most driving conditions. Then, when you step into the pedal about 2/3 of the way down to about 3/4 or so, the output drops down toward 5 psi. Then, finally, when you get into heavy boost, more than 3/4 pedal, the valve will drop the output from 5 down to about 1.5 or so. You need to connect a proper vacuum gauge to the output of the VA and watch the gauge while you drive the vehicle. See if it performs in a similar manner as described above. In your previous testing, you may have seen proper modulation from the VCV, but, the VA doesn't seem to reflect this modulation. This "appears" to be quite normal as Dave has the same situation on the W124. |
#7
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Right, I dont know why I was calling it the modulator, as the mod. receives vacuum from the amplifier. i guess i lost you with the "Dave" reference. i dont see how it is ok for the amplifier not to reflect proper VCV regulation. None of the literature I have read suggests that I have to drive the car to test for vacuum to the tranny. maybe it's a dumb question, but how do I properly test driving vacuum with the tranny line disconnected? i.e. would I not have to disconnect the tranny vac line to test amplification with a vac gauge while driving?
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#8
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You cannot get a valid test to see what is going to the tranny unless you drive the vehicle and observe the gauge. You can set up a T in the output to the tranny where the gauge fits the T and you run the hose into the cabin to monitor the gauge. Since the tranny vacuum is regulated by boost pressure, you cannot get a proper reading by sitting in your driveway. |
#9
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Ok, thanks. Maybe I will ask him about the lower line on the VCV leading to nowhere. If anyone else has input, please fire away. Thanks Brian.
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#10
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The third line is a vent line and normally leads inside the cabin for fresh air. If it leads to nowhere under the hood, it will pull some contaminated air into the vacuum pump, but is probably not a serious issue. |
#11
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I am confused about this VCV setup you describe (thanks for helping BTW). I have one line that comes from the booster line to the top of the VCV (supply), then I have one that comes off the lower side of the VCV (driver side) that goes to no where (the one I am confused about), and then the only third one I see is the one that comes from behind the VCV (behind being engine side; slightly in the back toward cabin) that goes into the cabin. My fear is that THIS is the vent line, and the one going to nowhere somehow attaches to the amplifier. But I dont see where. I am lost, helpless and losing my mind on this. To boot, I just posted that I snapped the supply nipple off the vacuum booster line.
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#12
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My guidance is based upon the '86 SDL. The function is similar, however, the '85 CA is a unique beast and what I have with this one may differ slightly:
The first photo shows the VCV. Two lines enter the top of the VCV. One line is the supply vacuum and the other is the modulated vacuum for the amplifier (VA). The second photo shows the VCV. Down low on the side is the vent line. It's not very visible in the photo, but, it heads inside the cabin. The third photo is the top of the VA. The central port is supply vacuum. You can see a T just before the port entrance. The supply vacuum continues into the cabin for accessories. The side port is the transmission line. The fourth photo shows the following: Coming from the VCV, the hose splits at the Y: One leg of the VCV output goes into the solenoid. The second leg of the VCV output goes to the bottom of the VA. There are two ports on the bottom of the VA. The port that is offset to the side of the VA, on the bottom, is where this line connects. Going to the bottom of the solenoid is a line from the manifold so the solenoid can receive manifold pressure. Finally, there is a line from the solenoid (horizontal port at the top) to the bottom of the VA. It connects to the port that is dead center on the bottom of the VA. Hopefully, the '85 is similar. Last edited by Brian Carlton; 03-19-2005 at 07:03 PM. |
#13
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Quote:
VCV: The vacuum control valve on the IP VA: The vacuum amplifier (big blue valve in above photos). ALSO: Please describe where you measured the vacuum. I presume that you put a T somewhere, but, I need to know where to determine if what you have makes any sense. My suspicion is that you are referring to the vacuum amplifier. |
#14
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Hey, thanks for following up Brian. My 85 setup is slightly different apparently from yours. I think that although I have a 722.416 transmission, that my vac setup is like this one: www.ultrahot.com/vacuum/722_vacuum_func.jpg
Per your questions ... I am talking about the VA (Amplifier, big blue thing). I disconnected the vac supply line (the one on the top NOT going to the tranny). I attached a Mityvac to the line; no T. It was sucking really inconsistently, sometimes no more than 10", then sometimes it would trickle up over time to 20"ish. Weird part is if I slightly pulled on the throttle, the needle on my Mityvac would jerk down to 10". I think I have read somewhere that the VA should be getting full vac at that point. Also maybe weird: with the vac supply line disconnected, there was vacuum on the VA vac inlet too (where the disconnected hose would attach on top). I wish I knew is this was normal. As we have discussed, I am getting late shifts. My thinking is that the constant pressure to the tranny is ok, but that my VA isnt working right due to either bad boost signal or bad supply vac. The problem is I have an incomplete understanding of vacuum specs on this system. So ... 1) What should the supply vac be to VA? And should it tick down with throttle rev? 2) What is proper boost pressure while underway? (yet to test this; I have to get a T of some sort) 3) And how the heck does my VCV send a signal to the VA in my system. There's a switch over valve of some sort (see jpg). Never ending problem. I am going send KingCake (and cash!!!!??) to whoever solves it, and I'm not even from New Orleans. |
#15
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This system is somewhat different than mine because it relies heavily on the throttles (63a and 63) to control vacuum to the transducer (what I was previously calling the amplifier). If you look at the diagram, you see only one vacuum line going to the VCV. There is no second output line. The only other line leaving the VCV is the vent. So, the way this this one functions is to bleed vacuum via the VCV. If the VCV bleeds off enough vacuum, it will drop the vacuum level to the transducer because the throttles will only let a certain volume of air through them in a given time. So, attempting to test this system with a mityvac between the VCV and the transducer will not be effective because of the nature of the bleeds in the system. To test it properly: Connect a T in the line from the transducer to the transmission and run the gauge up to the cockpit so that you can watch it while you drive. You will probably get a vacuum level of about 10-12 for most operating conditions. When you step into it and get some boost, the vacuum will drop quickly, hopefully getting down to about 2" when under full boost. In answer to your questions: 1) You cannot properly test for the supply vac to the transducer, because it is partially regulated by the bleed. You could monitor it with the vehicle in operation, but, I would suggest to simply connect the gauge to the transmission output line as noted above. 2) Boost pressure, as measured from the manifold, or the line to the ALDA will range from zero under light pedal conditions all the way up to about 11 psi under full boost (full pedal in third or fourth gear above 3,000 rpm). You need to use a proper boost gauge and a T to measure this pressure while the vehicle is moving. 3) The VCV sends a signal to the transducer in one of two ways: a) When the solenoid is closed, the system sends straight vacuum directly to the transducer via one of the throttles. b) When the solenoid is open, the VCV bleeds vacuum off and prevents full vacuum from reaching the transducer. The system is limited by the throttle in how much air will pass, so, the VCV can drop the vacuum quite low if it opens to atmosphere via the vent line. So, in conclusion, it's a pretty sophisticated system that depens on the proper sized throttles (that are clean) to work properly. I'm not convinced that the late shifts have anything to do with this system. Usually, the late shifts are governed by the Bowden cable, which may be set too tight. |
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