Brake Bleeding air leakage question.

[Orleng]

for all the guys out there who have done brake bleeding yourself.

 

Qn: Do ya'll grease the bleed nipple thread after you loosen it? That's if you don't do the pump-loosen-release fluid-tighten cycle. E.g. if you use an inline check valve or similar (not a speedbleeder nipple), how do you ensure that air does not flow back into the caliper via the loosened nipple threads.

 

From other online sources, it seems that there has been a purported tendency for air to flow past the nipple threads. even a minute amount can affect optimal bleeding i feel.

 

So, basically, I'd like to know, what kinda grease is safe to use in this application of sealing the threads to prevent air ingress. e.g. if the grease contacts the brake fluid, will not form some kinda crud that will jam the threads, making loosening difficult/impossible in the future. and worst-case scenario, contaminate the brake fluid.

 

Any specific grease to use/not to use? Vaseline, axle/bearing grease, caliper grease, heavy engine oil?

[quizesilver]

u use thread locker not grease

[Orleng]

u use thread locker not grease

 

threadlocker? on bleed nipples that are already notoriously prone to seizing? wouldn't there be the potential for threadlocker to contaminate the brake fluid, or accidentally get into the system and seize the pistons?

 

i'm not asking about using grease as an anti-seize if that's what you think i was asking.

we're not talking about keeping a part from moving here. i mean, use it on caliper mounting bolt, yeh, so it won't drop off due to vibes.

 

it's about forming an air tight seal whilst bleeding using a one-way check valve attached to tubing attached to the bleed nipple.

 

when you crank it open, air can get past the threads into the caliper when you release the brake lever without tightening the bleed nipple. sure, maybe it's minute or negligible, but i'd prefer to have an air-free system.

 

have been googling and it seems ppl recommend vaseline and axle grease and other thingmagummys, just asking if anyone else has any other grease they've tried before which is not a potential contaminant.

 

i suppose i could go try find caliper piston seal / dust seal lubes. in that case, anyone knows where to such lubes/grease? i do know that rebuilding, typically just use brake fluid to lube the seals, but there are specific greases/lubes too i believe.

Edited March 15, 2010 by Orleng

[Terrible One]

I pour some brake fluid into the drain bottle and insert the hose in, that helps prevent the air from flowing in. I didn't use any grease so maybe I'm just lucky that the air didn't flow up. Hope u can find a good solution and update us

[Orleng]

I pour some brake fluid into the drain bottle and insert the hose in, that helps prevent the air from flowing in. I didn't use any grease so maybe I'm just lucky that the air didn't flow up. Hope u can find a good solution and update us

aye, i get that, used to do that in the past too. just that this time i decided to use a check valve to achieve the same effect of one-direction flow. thanks for the info though.

 

while doing more research, came across a few threads. they discussed the incidents and possibilities of air going past the threads of the bleed nipple screw, back into the cylinder. it doesn't go in from the drain tube, or the tube-nipple connection. it's the nipple screw thread where it screws into the caliper body itself. it's like if you loosen a screw slightly, you can rattle it a little, there is space between the screw threads. that's where air may reverse into the caliper. you won't be able to see the bubbles when it goes back in cuz it's where the threads disappear into the caliper.

 

so, i guess, the only way to know is if you see small bubbles keep on coming out when you pump. which, i recall, was a problem i had in the past. never-ending small tiny stream of bubbles. couldn't figure out, for the life of me, where they were coming from. now, i guess i sorta know. don't wish to repeat that performance for the next bleed.

 

of course, if i just got a vacuum bleeder and sucked everything out of the caliper bleed nipple, then prolly won't have to worry about air reversing past the threads which can happen when you release the lever during the manual method. but, mo qin buy vacuum bleeder ah! check valve cheap

[spirals]

sometimes is like, when riding through places with higher moisture content, then the vapour tends to be trapped inside.