Mityvac Not Holding Vacuum

[BSTWAY]

I'm attemping to change my clutch fluid but it's a no go. When I plug the end of the Mityvac hose with my finger it will stay charged up until I release the pressure. But it won't hold vacuum when I attach the hose to the bleeder nipple and pump it up. When I secure (twist wire around hose on nipple (part number: 34 21 2 330 310) like brake bleeding) the hose to the bleeder nipple it slowly loses charge. Bleeder screw is cranked down tight and no apparent way air could escape. Any ideas?

[jm1515]

What happens when you attach the hose to the bleed screw, loosen the screw, and pump the MityVac a few times?
You should get a nice flow of brake fluid into the recovery cup.
If not...you have a bad pump or a leak somewhere

[BSTWAY]

That’s the problem; there’s a leak. I can’t figure out where. During brake bleeding, when the bleeder valve is closed, I can pump the Mityvac up to 25 in.Hg Vac and it will stay there until I crack the valve open. Of course, once the valve is open the fluid flows. Could it be that this BMW bleeder is not seating all of the way and the two holes in the bleeder are causing a leak through the threads?

[BSTWAY]

I’ve been thinking (usually dangerous) not doing anything, when it occurred to me what the problem might be. Unlike brake bleeding when you tighten the bleeder to stop the fluid flow, the clutch bleeder needs to be “opened.” This is because the check valve will stop the flow when the bleeder point is disengaged (opened). So, maybe since I’ve tightened the bleeder screw (check valve open) this allows are to pass through the bleeder threads allowing the vacuum on the Mityvac to escape. I won’t be doing anything until tomorrow evening. So, additional thoughts/comments are still welcome and appreciated. I hate when a simple procedure turns into a royal PITA.

[Twempie]

Every time I used the Mityvac, I would get bubbles in the tube, they were going in the right direction (meaning not back into the system). But I still found the whole process a messy PITA. I have since switched to Speed Bleeders, the fancier stainless type. The Mityvac is now with the rest of the pile of tools that don't get used much, if at all.

[CycleRob]

The vacuum is leaking past the bleeder threads, into the extraction hole on the side bottom of the bleed screw's cone shaped valve. Try a narrow strip of teflon tape, 2 turns around the threads and it won't leak down. A Mityvac is a very useful tool in many vacuum filling or bleeding operations and it's great for removing old fluid from master cylinder reservoirs.

[TicTac50]

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