Bleeding brakes fail

[Rogerborg]

2008 Royal Enfield, joke brand calliper, no brand master cylinder.

Went a bit floppy, wouldn't stiffen up no matter how much I pumped. I have:

Drained down the system.
Cleaned around the pistons.
Replaced the crush washers on both banjos.
Pushed the cylinders fully in (they move smoothly).
Replaced the fluid with fresh, unopened DOT 4, injecting from the bleed nipple, alternating with gentle pumping at the lever.

Plenty of bubbles came out during filling. There are no more bubbles at either end now while pushing fluid in either direction.

Tried:
Tapping the calliper and line, flexing the line.
Removing the calliper and rotating it in various directions while tapping.
Tilting the master cylinder in various directions (so that the banjo is lower than the cylinder).
Leaving for several hours.
Leaving for several hours with the lever clamped to the bars.

There is enough pressure to push fluid out of the nipple, but the lever comes back to the bars without much effort.

Next? Test the master cylinder? Stick a bolt in the outlet?
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[wr6133]

My crappy super cheap Chinese master cylinder I fitted to my ZZR last week had those symptoms. TLDR version I tied the lever back and put a load of kitchen towel on the infill under the m/c, 24 hours later there was some brake fluid on the kitchen towel, so the m/c was leaking a bit.

Managed to bodge old bits from 3 knackered OEM m/c's together now to make one (hopefully) working one just need it to stop raining so I can fit.

In your shoes I'd fork out for new seals I'm sure it won't bankrupt the Exchequer of Borg.

edit - seals at both ends no point rebuilding the M/C and leaving the calliper with old ones

[Islander]

I'd be looking at the master cylinder at this point. You could try blanking the outlet off (or just clamp the hose at a suitable point) to check whether you're loosing pressure there or not.

[arry]

I'd be looking at the master cylinder too.

Years ago I had one rebuilt at a specialist engineering place (rare car, rare cylinder) and the guy was explaining why they tend to go just after bleeding - in effect pushing the rod through past the point of its usual operation, where it's a bit rougher / dirtier. Not sure how much truth there was in it, but having had 2 go like that on cars over the years after replacing brake fluid I'm inclined to think he did know what he was talking about.

[Vincent]

[map]

Isn't there a trick to crack open the master cylinder banjo bolt as might be some air trapped there?

...also found this...

[Rogerborg]

Thanks all, that's the kick up the arse that I needed. I'm not convinced by the pressure at the master cylinder, so a repair kit is on order along with a braided hose for good measure. Stop looking so smug, GS.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Wull]

Did you actually try bleeding at the m/c?
____________________
"Scooters are for men who want to ride motorcycles but prefer to feel the wind on their vaginas"

[Wull]

[Rogerborg]

[weasley]

One last thing - have you pushed-back the pistons with the system all connected up and flushed? Can be a way of forcing any airlocks back towards the m/c or into a bleedable location.
____________________
Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[Wull]

Hhhmmmmm,well after all that lets hope its a fucked m/c.
____________________
"Scooters are for men who want to ride motorcycles but prefer to feel the wind on their vaginas"

[Rogerborg]

£10.19 for a complete kit including new cover, I won't be too upset if it's just a very stubborn air lock. I'd rather have it back on the road.

[Rogerborg]

...nope. Awaiting M/C kit by donkey post from Mumbai.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Bru]

I tend to have old, shit bikes, and prefer to fix what exists, before coughing up for new parts. I found that often, a neglected master cylinder will have some hard deposits in the bore, which will of course do no good to the cup seal.

I have successfully polished these out, using the green side of a generic green/yellow scouring pad (held over a small pair of needle-nose pliers). The green fibre is hard enough to break down the brittle (aluminium oxide?) deposit, but does no harm to the bore. In this way, I have successfully restored manky old dogly master cylinders to full pressure.

It will be worth you squinting down the bore of the m/c before installing your new kit. Sorry if I'm teaching grandma to suck eggs, etc.

[Rogerborg]

[Bru]

Marvellous. Don't be shy when flushing the offending master cylinder out with brake cleaner, either. Be sure to give that pressure relief (pinhole) vent, usually situated quite obviously at the base of the reservoir, a good blast too.

Note: whittle the end of the tube, hopefully-supplied with the brake cleaner aerosol, to a point; this helps wedge it into the vent.

[map]

[Rogerborg]

[Rogerborg]

So, this is going to be one of those tasks. I've got a new piston in the master cylinder, nice and snug, and a braided line ready to go on because pimp, and what does India know about rubber anyway?

Let's just check the caliper again before connecting everything up. Pads are good, pistons are sliding freely.. oh... shouldn't the body be sliding on the bracket pins?

Nope. One pin is locked solid in the body, and I mean solid. Penetrating fluid, tapping the bracket with a little hammer, a rubber mallet, the big mallet, smacking it with the big mallet, nothing. In the vice, grips on the pin, nope, can't budge it 4/1000" in any direction.

It's now sitting on the radiator because, you know, maybe it's just sulking because it's cold. Worth a try.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[331X2]

Try soaking it with plus gas overnight then get the body held steady in a vice, lots of heat from a blowlamp and it should free up with a twisting motion

[Rogerborg]

[331X2]

If you need it out, you need it out. Strip everything that will come off and everything else will have to be replaced, can't make an omelette without breaking eggs...

[Skudd]

[Rogerborg]

Mmm, I can see myself drilling the pin out. Chances of not messing up the caliper, slim to anorexic.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike