Let it bleed you nipple!
I’m pretty familiar with brake bleeding procedures, including pressurizing the hydraulics to dissolve the air and using lithium grease and/or Teflon tape to seal the nipple threads from air entrance. The one controversy that seems to perhaps be unresolved is when hooking up a vacuum brake bleeder is air entrance at the nipple thread a problem?
My thinking is as long as the vacuum is held relatively high at all times, air leaching through the nipple threads cannot enter the hydraulic system, and will be pulled away along with the old fluid.
After just having done 3 bikes, it seems that some brake bleed nipples allow air into the threads, no matter if I use lithium grease and/or Teflon tape whereas some nipple threads seal very well without any big fuss.
Of course you get to see air bubbles traveling down the clear vacuum tube along with the fluid with the poorer sealing nipple threads, but so what?
As long as I keep the vacuum high and constant throughout the entire process, is there any chance of air entering the hydraulic system via the nipple threads?
PS: I am sure air entrance is not from a poor fit of the tubing to the nipple or any other part.
Thank you greatly
Jackie Chan's stuntdouble
I can't see the air getting past the nipple threads being an issue. If you are paranoid, you could just finish the job with a bit of old-style bleeding (squeeze brake lever, then open nipple slightly) to get any air out.
Why don't you try putting a gob of heavier grease around the nipple? Lithium greases always seem to be very light.
I've done both things you wisely suggested: finishing the job with a bit of old-style bleeding (while keeping the vacuum via the Miy Vac) and using Vaseline.
Vaseline still permitted air on some nipples, and old-style bleeding (while keeping the vacuum on) was a very, very good thing to purge out the last bit of air on stuborn systems
I do not see any problems with Tefton but *perhaps* if grease gets sucked into the system (past the threads) and does not get pulled back out via vacuum (Mity Vac) it could be an issue if the grease remnants are harmful in some fashion?
Last edited by Chumly; 07-27-2005 at 04:06 PM.