Brake will not bleed ?

[Medicinal_Motocross]

Having come to the end of my patience with my bike im once again hoping someone can help me

I have today fitted new front master cylinder repair kit it is a aftermarket part and one of the seals seemd excessively bigger than the original, after letting soak in brake fluid for 15minutes a bit of it teared a tiny thin strip as it was not going in for love nor money after the bit came off it went in, have attached a picture of the seal im on about the inner one closest to spring,

Is this the fluid stopper seal? and outer one stop air from being drawn in?

This is the only thing stopping me going in for mot. Air is still bubbling in the master cylinder when pump the brake mostly from the tiniest hole (sewing needle is to big to go into the hole tiny) which i saw on a video is the " return hole"
Judging by how much was coming in from each side and a big bubble every few pumps from the main fluid hole.

A new caliper piston has been fitted with seals, new banjo bolt & washers. How can i pinpoint exactly where the air leaks coming from is there a way?

[Taught2BCauti...]

[robertw95]

Whats said above get the correct oem seal kit brakes aren't something to take chances with
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07 Dt125r, sv650s k8, zx6rr 04

[bikenut]

as above........and make sure the tiny recouperating port is clear.

this is the tiny hole usually at the bottom of the countersunk hole in the bottom of the fluid reservoir.

it is tiny ( less than 0.5mm diameter ) and important.

it is located more towards the "pressure" end of the m/cylinder, rather than the larger hole towards the "open end" of the m/cyl. By open end I mean the end that the piston goes into.

the larger hole, you will see the piston and its movement.

the first movement of the piston makes the "pressure seal" close off the tiny recouperating port so fluid pressurization can commence.

letting the brakes off uncovers the tiny recouperating port allowing the fluid return from the caliper/wheel cyl etc., meaning the brakes can release fully.

if the tiny hole is blocked then brakes cant release fully and bleeding will be problematic.

get the proper seal kit and try again.

I assume you fitted the pressure seal the correct way round and get some red rubber grease.

brakes are safety critical for you and other road users.

check correct fitting with cmsnl exploded views or see the manuals section for your bike on here.
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nuts about bikes

[Medicinal_Motocross]

Right so by the pressure seal which one is that? I was just hoping someone knew if the inner seal on the piston was the air stopper just so I could rule out the master cylinder allowing air in from there, I know it was silly to fit that seal I was contemplating fitting just that one seal off the old master cylinder piston, bad or even worse idea?

Waiting for another kit means paying for my mot again (allowed until wed for free retest) rather than somehow ruling out either the caliper being the issue or m/cyl being the problem..

I fitted new caliper piston and my gut just says its from there somewhere, I don't think its the breather nipple air/fluid doesn't come out when tightened down, these don't go all the way into the caliper as in screw in every thread on the nipple right?

I'm just trying to save myself a little bit of money is all..

[kramdra]

Your almost certainly doing it wrong. Air from the port indicates the system was empty and has not been properly bled.

Get a pic of the actual damaged seal, next to the original seal, if you find yourself taking it apart again.

Inspect the old seal, if its in acceptable condition, swap it onto the new piston. If it is held in a grove, use match sticks as the removal tool, they are unlikely to damage it.

The most fool proof/reliable and quickest way to do a full system fill and bleed is to reverse fill from the calliper bleed nipple:

- Use a syringe with pvc tube to bleed nipple. 60ml is a good size (brake system is usually less than 40ml in total)
- Use PTFE tape on the bleed nipple thread, this stops fluid leaking out the thread, or air getting in while it is open.
- After filling, crack open the master cylinder banjo while pulling the brake lever to bleed. This is the highest point, and should be the only place with air if done corrrectly.

Takes me under 5 mins, I often do not need to bleed anything from callipers, though I usually do it just to be sure.

[Taught2BCauti...]

The bleed nipple has a conical metal-against-metal seal on the bottom - it only needs to be screwed in enough to make a good seal, and nothing to do with how many threads remain exposed.

If there was nothing wrong with the old seal, why change it in the first place?

If the old seal was duff, are you seriously thinking about putting it back?

You probably wouldn't be any worse-off by fitting the old seal, the chances are that the oversized seal you damaged whilst forcing it into the cylinder is now blocking the bleed port.

https://bikeadvice.in/wp-content/uploads/2010/11/MC-6.jpg
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Honda Varadero XL125(V8)
www.TheFutureIsHere.eu

[Medicinal_Motocross]

Ok great, the new cylinder piston feels 100% improved when pumping the lever not sure how to explain but it feels "tighter" ?

Is the bleed port the big or small hole inside the master cyl. ? Like I said air was coming from either hole.

I have one last option which is use either a bit of tube I cut to bleed sat in brake fluid in container or the one man bleed kit and like kramdra said use some tape on the bleed nipple threads can I use any tape?
Its not gonna stay on when undoing / tightening nipple to try bleed right? Also read to turn the caliper upside down incase airs trapped

Was also thinking of trying to cover the caliper piston and seal and bleed nipple while its open to see if its not coming from there or could it come from nooks and crannys in the caliper ?

The old master cyl. Seals don't look to bad or perished at all, just the rubber outer boot was slightly torn & the amount that come off the new seal was so tiny asin probably a cm long of rubber came off would this really stop it sealing and drawing air in?

I was under the impression the outer seal was to stop air being drawn in from lever side(which wasn't damaged at all) and inner one stop fluid leaking out from master cyl ?

[kramdra]

There will not be any air coming from the lever side. None. You have simply failed to bleed the system properly, and are seeing air from your brake lines. Do as I said.

I would rather smear my brakes in shit than use a one man bleed kit or tube in a jar, and probably more effective.

PTFE tape is the only tape you should use and it should only be on the bleed nipple threads, not the sealing taper. Its purpose is only to seal the threads while the nipple is open. Its cheap.

It stays on after bleeding, but is external to the brake system, it only contacts fluid while nipple is open.

Your impression is wrong.

[Medicinal_Motocross]

I am going have to locate some PTFE tape then if none other will seal the same

If your 100% air isnt leaking from the master cylinder side then its coming from the hose or caliper end right?

Could i tape the caliper hose up to guarantee its not from the top end or is this a pointless exercise?

Once i have acquired some ptfe tape i will try your theory and with a bit of luck will end up with no air in the system at all!!

[kramdra]

Yes you should tape up everything, caliper and hose with duct tape. Tape around the pistons, just to be certain.

[Medicinal_Motocross]

[kramdra]

Do not touch your brakes, they will never work again

[barrkel]

[Medicinal_Motocross]

Iv always used a tube into a bottle but this brake is baffling me, with fitting a new caliper piston i am going toward i havent fitted it right or the seal, when taking it off the road the brake was fine only since fitted the piston im encountering these problems.

If i get a foot pump and put the nozzle onto the end of bleed nipple with it being open would it be enough air to push the piston out any? I dont have a air line & iv not once seen it move and iv been trying bleed it for weeks on and off.
Was also under the impression the PTFE tape would disintergrate or tear after turning the bleed nipple a few times to open/lock ?

It is really going be a pain as it took me ages get the caliper seal in correct but i really think i should take the piston out, i could also seal the fluid hole to see if any air is coming from the caliper ?