Rear Brake Issues

[LiamHarvison]

Hi all,

I was wondering if someone could help me (sorry if this is a simple issue that I've caused or something silly).

I decided to attempt to rebuild my rear brake calliper this weekend, which all seemed fine. I replaced the seals with OEM ones and greased the calliper parts as per the Haynes manual / recently posted guide on here. It was all seeming good, bled the brakes until no air appeared.

The problem I'm having now is there seems to be no pressure in the system (there is some resistance, but the pedal still goes to the bottom). Moving the bike by hand, the brakes are sticking on quite a bit, so I don't really know what's happening!

Any help would be greatly appreciated.

Cheers,
Liam

[Redmist]

Probably still some air in it. Try bleeding it from the other end of the brake pipe too (Nr the master cylinder), also manipulate the pipe too to get the bubbles to move around.

[LiamHarvison]

Cheers redmist. Is bleeding from the other end as simple as opening the cap on the reservoir and waiting for the air bubbles to appear? Sorry again for the simple questions

[Red Herring]

Rear brakes are always a pain to bleed because the pipe is nearly horizontal and goes up in a loop just by the master cylinder. If you can imagine a bubble of air being pushed out of the master cylinder into the loop and then around into the stretch towards the rear caliper as you close the bleed nipple and bring the pedal back up ready for the next stroke the bubble returns back up the loop but stays there as it can't go down to the master cylinder (air rises), so it just keeps going back and forth.....
The simple solution is to take the caliper off (keep the pipe connected) and hold it up near the seat so that the bleed nipple becomes the highest point in the system. Don't forget to put an old pad or similar between the pads otherwise when you bleed/pump the brake you will push the pistons out.

[Redmist]

Just crack the pipe bolt (Top of the silver cylinder) slightly at the brake pedal assembly end whilst pushing on the pedal and retighten before letting go of the pedal, just like you would when using the caliper bleed nipple.

Once you've got rid of any air from there, go back and bleed from the caliper nipple to be sure.
Hopefully it'll be better at that point anywhere.

Worked for me.

[LiamHarvison]

Thanks very much red herring and redmist! Currently in the garage as we speak so will have a go at both of these methods. Cheers again, Liam

[johnnyrod]

f the brakes are dragging then you may not have pushed the pistons far enough back into the caliper. Before you start with bleeding, do this. They can be pretty stiff and if one starts to go crooked it'll jam. Something like a G clamp is good for this, and often you need something flat to spread the load across the piston face, like a spanner. Don't worry about pushing them in too far, they'll come back out as soon as you have some hydraulic pressure to speak of, they're self-adjusting.

[LiamHarvison]

Hi all, thanks for your help but still no luck :( tried all of the suggestions you said, took it back apart this evening too and checked the piston was straight and all the way in. Held the calliper up next to the seat, bled the top of the brake line next to the master cylinder and manipulated the parts around to move the potential air bubbles. Still don't get it, there aren't any leaks or anything. I don't know what I can have done wrong - I bled the brakes no problem before when I installed HEL braided brake lines.

[maviczap]

Could be similar to nikon70's rear brake problem, his master cylinder was knackered.

[johnnyrod]

So are the brakes dragging (slowing the back wheel when you spin it - even without the chain attached) or is it a lack of pressure? You've mentioned both above. For lack of pressure, it would be odd for the m/c seals to give up just like that (assuming it all worked before), but it'd be the place I'd go next.

[LiamHarvison]

I think I've (embarrassedly) found the problem. I placed an object between the two pads and noticed that it didn't have the problem. So I looked at the calliper in more detail and realised that the front caliper mounting screw (the one that slides) was at a bit of an odd angle
I think I've threaded the screw hole, putting the calliper at such an angle that when compressing the brakes, it allows the whole calliper assembly to move. So basically, new calliper ordered!

[jambo]

Annoying, but good you've found the issue. You may be able to repair the thread in the old one. If I'm thinking of the same hole it's open at the rear, so if you carefully thread a bolt in from the back, and gently work it to and from it can restore the thread as it moves to the front

Jambo

Sent without a real keyboard

[LiamHarvison]

Perfect, cheers Jambo. I will give that a go