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  #16  
Old 05-07-2008, 01:17 PM
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Mike
 
Join Date: Jan 2007
Posts: 63
The 3/2 valve is definitely crucial on my 300td to shifting. I have a weird symptom. I get completely intermittent vacuum. i can get the car to shift perfectly, but only by 'kicking' the throttle a few times-usually in neutral. I thought this was a faulty vacuum control valve, it's spring or internal diaphragm somehow not returning to closed throttle/full vacuum. However, i put a brand new valve on and still problems. If i slightly open or close the 3/2 valve, the vacuum comes back up temporarily. However, with good vacuum at closed valve, when the throttle is applied fully, sometimes the vacuum just drops to zero and won't come back up.

I think the 3/2 valve must be leaking somehow. When the throttle is closed, the valve is completely closed as well, which is what a mercedes mechanic told me is correct--ie, the cam on the 3/2 valve pin should be completely at rest, leaving the valve closed.

Please help!! BTW, it's a brand new valve.

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Vancouver, BC
'79 300td 60k miles!
import from Japan
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  #17  
Old 05-07-2008, 01:27 PM
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mmmmmm Diesel...
 
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Location: Royse City Tx
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How are the rubber connectors?
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70's Southern Pacific #5608 Fairmont A-4 MOW car

06 VW Jetta TDI 133K miles-replaced the other '06 that quit after 300k miles. (did not catch the bad cam in time)

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 195K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #18  
Old 05-07-2008, 02:04 PM
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Mike
 
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i've replaced all the connectors, x + y and all the vacuum lines throughout.
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Vancouver, BC
'79 300td 60k miles!
import from Japan
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  #19  
Old 05-07-2008, 02:08 PM
rrgrassi's Avatar
mmmmmm Diesel...
 
Join Date: Jun 2006
Location: Royse City Tx
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Does the modulator hold vacuum? A lot of time the rubber cap can crack open.
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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

06 VW Jetta TDI 133K miles-replaced the other '06 that quit after 300k miles. (did not catch the bad cam in time)

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 195K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #20  
Old 05-07-2008, 02:09 PM
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Mike
 
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you mean the modulator at the tranny?
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'79 300td 60k miles!
import from Japan
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  #21  
Old 05-07-2008, 02:10 PM
rrgrassi's Avatar
mmmmmm Diesel...
 
Join Date: Jun 2006
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Yes.
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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

06 VW Jetta TDI 133K miles-replaced the other '06 that quit after 300k miles. (did not catch the bad cam in time)

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 195K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #22  
Old 05-07-2008, 02:12 PM
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Mike
 
Join Date: Jan 2007
Posts: 63
Dunno for sure. I've only got a vacuum dial guage, not a mity vac. I can go borrow one today and test it. Then i would assume i'd test the 3/2 valve as well. I' know i've got strong vacuum the other side of the vacuum control valve--to the other consumers, off the brake booster supply, so it's something in the tranny control circuit. Thanks
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Vancouver, BC
'79 300td 60k miles!
import from Japan
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  #23  
Old 05-07-2008, 03:06 PM
rrgrassi's Avatar
mmmmmm Diesel...
 
Join Date: Jun 2006
Location: Royse City Tx
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Sounds like you are on the right path!
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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

06 VW Jetta TDI 133K miles-replaced the other '06 that quit after 300k miles. (did not catch the bad cam in time)

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 195K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #24  
Old 05-07-2008, 07:23 PM
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Mike
 
Join Date: Jan 2007
Posts: 63
Ok, got a mity vac. When the 3/2 valve is fully open (buttom pushed in) it shows vacuum, but it drops off steadily. Does this mean it's leaking, or is it supposed to leak down?

Should the throttle cam have any pressure on the valve lever at idle, or should the 3/2 valve be fully closed?

Thanks
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Vancouver, BC
'79 300td 60k miles!
import from Japan
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  #25  
Old 05-07-2008, 08:12 PM
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Join Date: Aug 2005
Location: USA
Posts: 1,394
Closed at idle or else it will stall.

The earlier models used a 3/2 in transmission vacuum function. From what I've gathered, the transmission received full vacuum until the 3/2 tripped to include the VCV.
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  #26  
Old 05-07-2008, 08:29 PM
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Mike
 
Join Date: Jan 2007
Posts: 63
figured it out. The 3/2 valve is leaking. The plunger pin/rubber seal is in a plastic cap which is just pressure fit into the valve body. This plunger housing is not tight and leaking vacuum! Bad design...time to get a replacement or another...
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Vancouver, BC
'79 300td 60k miles!
import from Japan
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  #27  
Old 05-07-2008, 09:56 PM
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L' Résistance
 
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Quote:
Originally Posted by mgcanuck View Post
figured it out. The 3/2 valve is leaking. The plunger pin/rubber seal is in a plastic cap which is just pressure fit into the valve body. This plunger housing is not tight and leaking vacuum! Bad design...time to get a replacement or another...
Get twice as many as you need. A lot of 'em will leak even when they are brand new.
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  #28  
Old 05-08-2008, 03:45 AM
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Mike
 
Join Date: Jan 2007
Posts: 63
car runs PERFECT now...i seated that sucker as well as possible, and it shuts off too! NExt project, door locks. I pumped up the vacuum at the engine check valve and when i opened the driver door lock, vacuum dropped and i heard a hiss there--no other locks moved, so i bet it's the driver door actuator..

thanks!
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Vancouver, BC
'79 300td 60k miles!
import from Japan
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  #29  
Old 06-13-2008, 04:44 AM
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Mike
 
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Posts: 63
Fixed

Quote:
Originally Posted by Palangi View Post
Get twice as many as you need. A lot of 'em will leak even when they are brand new.
I sealed the 3/2 valve with silicone, sure enough vacuum rose to 12"!!!!

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Mike
Vancouver, BC
'79 300td 60k miles!
import from Japan

Last edited by mgcanuck; 06-13-2008 at 06:55 PM.
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