Brake bleeding AIDS - not done. Again

[D O G]

Hi,

At the final stages of my caliper rebuild now.

Have bled the front brake a lot - depress lever, open bleed valve (with tube on, flowing to a bottle with brake fluid in, tube end submerged), close bleed valve, open lever, repeat. I had loadsa bubbles at the start, but now it is just clean, new fluid.

Have even left it for a couple of hours with the lever to the bar, then cracked the nipple, got a few small bubbles.

But the pistons still don't move when I press the lever.

Seriously, I must have pumped it at least 500 times, and pads are not descernably closer to the disc.

Any thoughts on what could be my problem? Or do I just have to keep pumping away?

Thanks![/img]

[Ade]

Once the system is closed, even with a little bit of air in (assuming the worst) the pistons would still move.

There are only really 4 areas that could be causing this:

a) There is a leak in the system - Easy to check.
b) The pistons are seized
c) The master brake cylinder is not operating correctly
d) There is enough air in the system to compress fully without moving the pistons

a+ d are easy to eliminate.

The master cylinder is the part by the brake fluid reservoir. It puts and maintains pressure on the pistons by moving the fluid.

Regards

[D O G]

There is no leak.

If the pistons were seized, there would be pressure when pulling back the lever. There is none, and I have just spend the day stripping and cleaning the caliper, new seals, the lot.

The MC seems to be working ok - I mean it is pumping liquid through, as I have been able to bleed them to this point?

[MarJay]

[D O G]

I will try that in the morning Mr. J.

Turns out that I was simply being a bit of a lazy cock. Went back out, did some more bleedage, still getting air. Got a very large stream of bubbles at one point. Lever improving, and pistons moving, still no way near done tho.

Ran out of fluid (didn't want to put the mankcy stuff back in), so off to Halfrauds in the am to get some more and continue my quest.

[Phoenix]

They have Halfords in Australia?

[Flip]

A good reason to back bleed with a syringe is that you can 'pull' any trapped air out by only filling the syringe about 2 thirds, leaving room in the syringe for the air. Doesn't waste fluid either. (I use 2 30ml syringes and have to pull a small amount of air out that gets caught during the syringe change).

[TheFoxyDuke]

Does the master cylinder have a bleed nipple itself?

I had the same problem a few weeks ago. Mine are Brembo. If not, then +1 to Marjay. Crack that banjo open

FoxyD
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[Kris]

This is the exact reason I use a self-bleed kit (£5 from Halfrauds) with a non-return valve on the end of the plastic tubing.

Put this end in a glass jar - the other on the bleed nipple and undo. Open the reservoir and constantly refill whilst allowing the fluid to empty into the jar. Repeatedly squeeze the brake lever and wiggle all hoses and eventually the air will all be expelled.

Sure, it uses more fluid this way but I've found it's much less hassle.
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[D O G]

Ok. This job has turned into a total nightmare.

A lot of it is my own fault, due to my inadequacies as a ‘mechanic’.

On the first rebuild, I screwed up the installation of the brake pads (yes, I know, ridiculous), I foolishly installed the metal retainer so that it was preventing the pads on the piston side from moving freely.

Essentially it had jammed one edge, causing them to twist. Then the seals started to leak.

I hoped that this leak was due to the uneven pressure on the pistons from the twisted pads, so I stripped the calliper again, and reinstalled everything.

When I came to refill the system (which had run dry), I started by putting it all together, filling the reservoir, tube on the bleed nipple, other end submerged in a bottle of fluid.

Depress lever, open nipple, close nipple, release lever.

Did this, had some bubbles etc, then the fluid started coming through the tube. Still no resistance on the lever at all.

Did the MarJay procedure with the banjo at the reservoir, no air, just fluid.

Continued for at least an hour, with no change.

The lever has no resistance.

There is no leak.

Fluid does come out of the nipple when I open it with the lever depressed.

Fact is, there MUST be a shitload of air still in the system, but it just will not come out.

I need the bike to get to and from work. I thought an entire weekend to complete the small task of cleaning the calliper and putting new seals in would have been enough.

I must have spent around eight hours doing it now, of which only 45minutes was the rebuild, and it is still fucked.

I’ve had to take the car today, leaving the missus and kids without it, and she is going to get me a syringe to try the reverse filling tactic, but tbh I’m so confused about the whole thing I don’t even know if that will work.

I really am at the end of my tether with this one, can someone please give me some advice?

Should really post this in Dear Auntie BCF!

Thanks.

[Mudskipper]

I had similar nightmares, took me weeks to bleed the brakes on the slabby.

Eventually did the back-bleeding with a large syringe on the bleed nipple and a big bottle of fluid from an auto factors.

Do it slowly and gently to avoid a squirt of fluid from your m/c

Once you've forced the system full of as much fluid as it can take from the bottom, do a final normal (RWU) bleed.

I feel your pain, the above worked for me in the end.

ps. as well as the m/c squirt risk, be careful not to let the syringe come off the tube when you're squeezing...I covered myself, a fence and my toolbox in fluid...
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[D O G]

Thanks 'skip.

Did you empty the system again before you went in with the syringe?

[Timmeh]

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[Timmeh]

IMO By far the easiest way is to get some long flexible hose, connect one end to the nipple and stick the other end at the bottom of the res. Fill with fluid and pump away.

Now you're doing reverse and normal bleeding at the same time. And you don't spill or waste any fluid.

Takes 5 minutes, tops.
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[D O G]

[Kickstart]

Hi

First thing, you didn't shake the bottle of brake fluid before use did you? Are they conventional bleed nipples or the bodge fixes with a bleed nipple in the banjo bolt?

Try locating the bars such that any air bubbles have an easy path into the master cylinder. Pull the lever gently and a small amount, and see if any air bubbles come up into the reservior. Similarly check that the bleed nipples are at the highest point in the calipers (ie, no use having the bars to one side so the half of the caliper with the bleed nipple in is lower than the other half of the caliper.

This is on the GS500 I take it? Single caliper, with the caliper being a twin piston sliding caliper. Take it the caliper slides fine (if not if could feel spongy because only the pistons are moving and are just bending the disk).

All the best

Keith
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[Mudskipper]

[D O G]

[D O G]

[Mudskipper]

[Kickstart]

[D O G]

[Kickstart]

Hi

You would think not, but bleeding the brakes is probably giving them a far harder time than they usually get. However if they had gone then possible that there is no air to force out, and the seal can generate very little pressure (before the fluid just leaks round it and back into the reservior).

All the best

Keith
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[D O G]

[Kickstart]

Hi

Not sure, as not sure what would cause a "crack" sound (ie, could just be the lever moving on the top of the piston). There are several seals, but the main important one is the one furthest from the lever.

Is there anyone local who has a spare master cylinder that you can borrow to try out (pretty much any single caliper master cylinder would be OK just to try it out).

All the best

Keith
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