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Old 11-02-2005, 09:12 PM
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Vacuum leaks narowed down to 3 items, 1982 300D (Pictures)

Hi, everyone.

Well I've tested every darn thing I can for vacuum leaks on my 1982 300D.

I found two things that couldn't hold vacuum, and possibly a third item.

1. The Transmission Vacuum Shift Valve has a slow leak. I take it that it should be holding vacuum?

2. The transmission vacuum lever assembly will not hold vacuum and has a slow leak. The hoses you see in the picture below are hard, and extremely loose. I don't believe they are forming tight seals with the hard plastic. Is this assembly supposed to hold vacuum? (BTW, I replaced the little levers at the left of the assembly...that made a HUGE difference in the transmission shifting).

3. What looks like a green check valve will let you suck and blow air through it. Isn't it only supposed to allow air to be drawn out of it, but not let air into it? Do I have a faulty green check valve?

Thoughts?

Thanks,

Pete.

P.S. All the doors, the trunk, the reservoire, the vacuum pump, the shut-off, the brake booster, etc., hold vacuum.
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Vacuum leaks narowed down to 3 items, 1982 300D (Pictures)-assembly-vaccum-levers.jpg   Vacuum leaks narowed down to 3 items, 1982 300D (Pictures)-check-valve.jpg  
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  #2  
Old 11-02-2005, 09:32 PM
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1. The vacuum valve on the injection pump is supposed to leak.
2. The valves on the valve cover operate the EGR, not the transmission. But when they leak, the loss a vacuum affects the transmission.
3. The green fitting is a damper, not a check valve. It should pass air both ways.

As I told you in your earlier thread, the valves on the valve cover are the most likely source of your problem. You can confirm this by disconnecting the vacuum supply line to those valves (usually a white line) and plugging the supply line. Then drive the car and see how the transmission shifts.
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Old 11-02-2005, 09:37 PM
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Thanks, tangofox007.

I take it then that I'm narrowed down to replacing the valves (or at least the hoses) on the valve cover?

Thanks,

Pete.
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Old 11-02-2005, 09:44 PM
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The 3/2 way valves tend to leak when the get old. If you replace them, I would suggest that you spend the extra money for the OE valves. Other members of the forum have reported problems with the cheaper (MTC) version.
But to confirm that the valves/hoses are indeed the cause of your problem, I would recommend that you disconnect the vacuum to the valves and take the car for a test drive and see how your transmission shifts with the valves out of the picture.
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Old 11-02-2005, 09:49 PM
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Quote:
Originally Posted by tangofox007
The 3/2 way valves tend to leak when the get old. If you replace them, I would suggest that you spend the extra money for the OE valves. Other members of the forum have reported problems with the cheaper (MTC) version.
But to confirm that the valves/hoses are indeed the cause of your problem, I would recommend that you disconnect the vacuum to the valves and take the car for a test drive and see how your transmission shifts with the valves out of the picture.
Thanks, I'll report back.

Much appreciated,

Pete.

P.S. BTW, when I replaced those two levers (which were completely worn down and useless) on the 3/2 way valve assembly on the valve cover, I noticed a really big improvement in my transmission shifting....but you're saying that they don't have anything to do with the transmission...
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Old 11-02-2005, 10:04 PM
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When you go to buy new vacuum valves, take your Mityvac with you and test them before you pay for them. I have seen brand new ones that leaked. Those valves are like single pole double throw switches. One port should hold vacuum in rest position, the other port should hold vacuum when actuated. A good one will have little or no leakage. If it leaks down in 5 or 10 seconds, it is NFG.
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Old 11-02-2005, 10:18 PM
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The valves take vac from the transmission line to operate the EGR. When they leak or have worn levers, it messes up the available vacuum to the transmission therefore modifying the shift characteristics. Under normal working conditions the valves do not have any affect on the transmission.
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Old 11-02-2005, 10:28 PM
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Quote:
Originally Posted by 300DPETE

P.S. BTW, when I replaced those two levers (which were completely worn down and useless) on the 3/2 way valve assembly on the valve cover, I noticed a really big improvement in my transmission shifting....but you're saying that they don't have anything to do with the transmission...
The 3/2 way valves exist to operate the EGR valve. But they share the same vacuum circuit as the transmission modulator. And if they leak, they "steal" some of the vacuum needed by the modulator. Replacing the levers probably altered the characteristics of the leak by allowing the valves to actuate properly.
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Old 11-02-2005, 11:18 PM
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Quote:
Originally Posted by tangofox007
The 3/2 way valves exist to operate the EGR valve. But they share the same vacuum circuit as the transmission modulator. And if they leak, they "steal" some of the vacuum needed by the modulator. Replacing the levers probably altered the characteristics of the leak by allowing the valves to actuate properly.
Ahhh. I feel like "Grasshoper."
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