main vacuum line ports
 

I believe my main vacuum line, the line from the pump to the booster is clogged.

I replaced the vacuum modulator due to a downshift clunk. All was well but it later returned. I was missing an orifice that was between the main line and the three way to the trans and VCV. I replaced the orifice and that seemed to fix the issue for a day or so.

Yesterday I rearranged the lines coming from the main. The main line has 2 ports the one closest to the pump was going to the shut off, the one closest to the booster was going to the trans/VCV. I switched these and made it where the one closest to the pump went to the trans/VCV and the last one went tot he shut off.

This completely fixed the shifting but now the car shuts off a lot slower.

The brake booster still seems to operate fine. Pressure from the pump is 22lbs.

I tried to clean out the ports.

My theory is the main line is clogged slightly and probably at the second port closest to the booster.

FWIW, I changed the master cylinder and there was no brake fuid in the booster. It was very clean inside.

Should I replace the main line?

It is not that difficult to pull and inspect the main line. I did that when I rebuilt my vacuum pump recently.

I just ran some low pressure air through it, then plugged both ends to pull vacuum upstream and downstream of the check valve. Ops chk good and put it back in.

If there is a problem with it... It will be obvious when you remove and test it.

I'm curious as to what could possible clog the ports or line.

Am I correct in think that any grime/debris would have to come from the booster?

There may be a restriction on one of the nipples for the VCV which, I would think, would clog up first.

Is it okay to take the VCV loose and clean it? Is there a procedure for cleaning the VCV?

^ I don't know and doubt it, but if you find something, let us know.

I have read where some have seen a number of defective booster lines with this problem, but that it was an easy fix to clean out the excess molded plastic. Basically drilling it out.

Also, the line looks fairly new.