Gunsons Eezibleed

... and loss of fluid if the bike fell over for any reason.

Many bikes have hydraulic front and mechanical rear (drum) brakes so most the front brake lines are nearly vertical. Saves many issues when bleeding the fronts as the air bubbles tend to rise up naturally. ;-)

The oddest bit though is some of the rear hydraulic systems on bikes where the entire fluid run is about 6" (like on my GPZ550).

Cheers, T i m

I thought that was because it was hygroscopic so absorbs moisture (that eventually turns to water and rusts stuff out from the inside)?

Thinking on Mr C's comments about the bellows you often find in the reservoirs on motorcycle brakes (preventing direct access to the open air) just how easy it is to work on brakes (and most things come to that) on bikes compared with cars.

Not quite so on our 'Jeep' style kitcar as you can get under much of it as it stands, but most cars aren't quite so easy and you can't generally work the brakes manually *and* manage the bleed nipples on your own at the same time. ;-)

Cheers, T i m

[...]

Yebbut motorcycle brakes can be a real bugger to bleed, especially off- road ones. I've had to resort to using a large syringe on the bleed nipple to suck the fluid and air out on many occasions.

Chris

More to do with avoiding weeping of brake guide when cornering.

It does - and where's it get that moisture from? The outside air, via the vent hole...

Ah, not ever had any true 'off-road' bikes so you could well be right. The nearest I got was the XT350 and that was also pretty easy. [1]

Oooerr.

I've had to find the sweet spot where the master cylinder piston was about to cut off the reservoir feed and tickle the lever a bit to get some air up (quicker than if I had just left it) but once it was going it worked as expected etc. I could have just been lucky so far of course. ;-)

Does anyone run a spare (clutch / throttle) cable alongside the active ones any more?

Cheers, T i m

[1] Daughters PW50 and TY80 were all cable braked. ;-)

Yeabut that's nothing to do with the point about 'absorbing air' is it (on a vented system)?

I mean, on a vented system the fluid will absorb moisture over time but won't 'absorb air' in the same way that will cause the same sort of problem as moisture?

Cheers, T i m

Yep. That moisture can't come from anywhere else. It comes in to the reservoir, and migrates through the fluid, so that all the fluid has roughly the same percentage of moisture.

If it stayed localised, then the calipers and cylinders would never get moist fluid, so would never rust out internally. Like what they don't on hydraulic Citroens using LHM, which isn't hygroscopic, yet is circulated (through the suspension) much more thoroughly than DOT.

Yeahbut, wasn't the discussion / issue at that point that of getting air into the system and bleeding, (something the systems can rarely deal with on their own) not the ingress of moisture (which, as you say, the system can deal with to a reasonable level by retaining the moisture within the fluid hygroscopically)?

I'm not disagreeing with your thoughts, just the direction. ;-)

Quite (see above re my comment about dealing with moisture versus trapped air in a braking system).

Ok.

Cheers, T i m

More likely to prevent it spilling if the bike fell over. Cars don't tend to do that. ;-)

Not for 'air' as such, but moisture in the air.

I do feel like it sometimes.

Ah, I see what you mean. Yep, my bad.

tickling the lever as described below is the best way, works on cars too if you can work out the spot (easy on the bench) But I found the way to get that last tiny bit of sponginess out on bikes was to bleed it all as well as you can and then tie the brake lever back to the handlebar as tight as possible with an elastic band made from inner tube, leave over night and in the morning the lever will feel the best it can be.

You want to try it with clipons or ace bars. The brake hose union is above the piston so has a bubble in it. Have to take it off the handlebar and fit on bar that is flat or inclined the other way.

Np.

I took daughters newly re-braked Corsa round the block this morning and think the bite *has* improved somewhat (over some 100+ miles). However, I still don't think the pedal action is quite as sharp as it was previously and I was wondering if this could still be a tiny bit of air somewhere, the fact that the shoes are new and the drums old (so more 'bedding in' to be done) or if you would get that sort of effect with full thickness frictionable material all round (compared with nearly metal to metal on the front pads especially)?

My mate in the garage thought the pedal felt 'about right' so I'm also wondering how much of this is in the mind? It's also difficult if you are jumping between vehicles and especially with one that has as sharp brakes as the Meriva seems to. [1]

I have no idea when the fluid was changed last (she's only had the car a couple of years) so I might take the opportunity to do that and (therefore) fully bleed the system at the same time.

Cheers, T i m

[1] I think it has ABS as well (I inherited it when Dad died this time last year) as I felt some rapid vibration through the pedal when 'testing' the brakes in the snow a bit back. ABS equipped cars don't seem to sport 'ABS' on the rear these days and I don't look for dash lights particularly, just that go out as they should. ;-)

Of course it can but the issue is the time needed for the trapped air to ri se, so that it cannot be drawn into the pipes. The same applies to the flui d in the ez-bleed bottle. Whenever brake fluid is poured, air is drawn into it, much of it in bubbles too small to be visible, and the smaller the bubbles the longer they take to rise. Failure to appreciate that fact leaves many d-i-y mechanics baffle d as to why they can never get a good pedal, and it is why I advocate takin g all precautions to avoid the problem.

Strange I've never had this problem, and I've been working on my own cars for some 50 years.

All of it.

All I can say is that in many years of bleeding braking systems I have

*NEVER* had a problem with using brake fluid 'straight out of the can', either with or without using a pressure bleeding system - must be a case where practice and theory differ greatly.

Funny that, I know several "d-i-y mechanics" who have no trouble in getting a "good pedal" without taking any of the OTT precautions that you are advocating. And I still think you are talking rubbish!