New tranny with downshift clunk. Too little vac so I am adjusting. Just adjusted the lever on the vcv so the gap is 0.5mm at WOT per Steve Brotherton's article. Now he says to adjust the nut under the plastic dome to get correct amount of vacuum.

Cannot figure out how to remove the plastic dome. See the dome in the pic at the arrow. I assume there is an adjustment nut under it but the dome has not been out since 1981 and I do not want to break it.

Is this just a press fit of plastic dome that gets pried out with a screwdriver or how do I remove it?

Already my vac (per mityvac) is down from 9psi - which was too low- to 6" at idle; due I expect to my adjustment of the lever to 0.5mm. So I really have to make the dome nut adjustment to get more vac. (Some call this entire part the vacuum control valve but I found it in parts listed as injection pump vacuum control.)

Help appreciated; how do I remove the plastic dome?

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Just below that red mark, I believe is a screw, I would think there is another opposite.

You may need to unplug that line on the side.

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83 SD

84 CD

on all the ones that I have messed with, you just pull it off. It has a friction fit.

Try a pair of pliers.


Its possible your model is different... not sure.

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So what the heck does that dome do? Does it secure vacuum for the unit? Therefore do I need to be careful taking it off?

I sent a personal email to Steve Brotherton and am awaiting an answer. Hope he knows how to remove the dome. Someone suggested removing the two screws but I wonder if this would break the seal and if it would be hard to get it resealed. Others have suggested pliers, that the dome is just a pressure fit. I have looked on line for a blow-up schematic to see how it goes together without success.

use a pair of needle nose and twist the cap as you pull out.


I am quite certain it will come out.

It would take alot of intentional force to break it.

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Yes, needle nose pliers did it. Just snag the edge of the dome with the pliers and gently rock it back and forth pulling outward. It will finally release and is just a friction fit. The dome has about a 3/4 inch shroud which fits inside the vcv. The shroud has two square cutouts which must be fitted properly to reinstall. Once the dome comes out, just turn the nut. I asked Steve Brotherton if the nut was just a stop for the copper block which was snugged to it - thinking the copper block needed to be moved then the nut snugged to it again. He said it is only necessary to turn the nut. Maybe the copper block adjusts downward to the nut under presssure; not sure. \\

So turn the nut, check the new vac reading, and push the plastic dome back in after you get the proper inches of vac. 15" in my case.

Would have been much easier if someone had posted this earlier. But this should be helpful to folks in the future.

The tranny shifts quite well not except for a small flare.