Bleeding brakes.

I looked at an old dismantled rear caliper yesterday from a SOSuzuki.
It's clear that the outer bleed nipple is best bled on the sidestand
but the inner one needs the bike to be upright, or preferably leant
to the right a bit.
That might explain why mine has always been spongy.

 

For the life of me, I can't see why it'd make a bit of difference. OK,
in theory air might be prevented from travelling up towards the
nipple, but I've never heard of anyone ever having problems due to how
the bike is placed on a stand. Especially on a rear brake, where the
hose runs are so much shorter. Decent bleeding technique will work[1].

If it worries you, bleed the 'lower' nipple first and then the
'higher' one.

If your brake feels spongey, I seriously doubt it's due to the bleed
nipple positioning.

[1] Happy to be corrected by anyone with first-hand experience of such
a problem, mind.

 

Happy to correct you.
If the vent to the bleed nipple isn't at the highest point of the slave
cylinder,
then you'll never get all the air out.
And it's not always obvious (without dismantling) where the vent joins
the cylinder.

 

So, like I said, bleed them properly.

<Shrug>

I just think you're highlighting a problem that doesn't seem to exist.
Wouldn't be the first time, mind.

 

IME there's a fair amount of swirling around happening inside the
caliper during bleeding, and the fluid is somewhat viscous, so unless
the bleed nipple is actually at the bottom of the cylinder the air will
eventually get carried along by the fluid.

 

Not my experience I'm afraid, but it does seem to be rear brake calipers
that cause the problems. I once spent over an hour trying to bleed one of
my Guzzi's rear brake calipers; clear, bubble free fluid came out but
there was virtually no pressure. I tried a MityVac, I tried pumping it at
the pedal, I tried fast pumps, slow pumps, tapping it to dislodge
bubbles, the lot. Eventually I unbolted it and held it up while tilted so
that the bleed nipple was definitely uppermost, then bled it; clear
within a couple of minutes.

 

How far from the highest point was the bleeder?

 

Hm. My experience has been as Olson's. Oddly, I've found, more than
once, that spongey brakes have been down to worn pads. Yeah, yeah, I
know that hydraulic systems are supposed to be self-adjusting, but it
doesn't seem to work that way, always.

I remember one Suzuki whose brakes I bled and bled, and which remained
spongey, until I changed the rather worn pads. And it felt fine after
that.

 

Odd. I've had spongy brakes from *new* pads, where the calipers and discs
were worn, so the entire pressure was on just a few high points on the
pad surface. As the pads bedded in, the lever firmed up.

 

Not very: the nipple's on top of the caliper at the rear: can't picture
it exactly at the moment but ISTR that the entire caliper is tilted very
slightly down due to the the angle of the swing arm.

 

The perversity of machinery.

 

Indeed.