126 (87 SDL) should vac pump itself hold vac?
 

I am tracking down a hard shifting SDL problem with the vac and can't seem to find an answer to this in any of the posts.

.If I pull a vacuum with MityVac on the single 4mm line that comes off the vacuum pump (and heads to the 5way junction) and it won't hold vacuum, is this diagnostic of anything?


The vacuum just seeps away and I can hear a slight buzzing. This doesn't seem right. The rest of the vac system is tight. I was planning on testing the output of the vacuum pump over lunch hour, hoping that it is between 21 and 23 in, my suspicion is that it may not make the grade...

thanks

On my 603 engine there are check valves on both vacuum lines coming out of the pump. My guess is that they are there because the pump does not always hold a vacuum.

three sources of vacuum leaks
 

So I checked the vac supply and it is delivering 21 psi, so I think that my pump is up to spec. I then noted the following leaks.

1. Vacuum pump to brake booster - leaks 5 psi per minute, apparently at the check valve. This is where I heard the buzzing before. I will take apart tonight, but I suspect that this part will need replacement edit (I ordered the part).

2. Null position of the HVAC pushbutton selector - 5 psi per minute. I pulled a vacuum on the aux line going from the pump to the HVAC system and checked each of the buttons. All held vac except when the O button was pressed. This is not the ultimate source of my hard shifting trans, because when I plugged the distributer to the HVAC, there wasn't any change to the shifting. (edit) I traced this to a main air flap vacuum element that had a ripped diaphram (I ordered the part).

3. Input line to the Vacuum Control Valve on the injection pump. This line will not hold vacuum and it bleeds off really quickly. Could this be the way that it is designed?

Does anyone have any ideas on which of these three leaks are real problems (especially numbers 1 or 3)?

thanks