Rear disc brake

[PW Cymru]

Just changed the rear disc, hose and pads on the RS.

Now its just like an original f£$kin useless.

Bled it to death, no sponginess, just a solid pedal.

Took it out for a run and tried to get a bit of heat into it but no stopping power at all.

lets hope it matures with age

 

[ollek]

Remove the caliper from its support and attach it to the subframe flange. Bleed the brake with the bleed screw on top of all the circuit by placing a piece of wood at the caliper so the pads will not close.
Caution with rear wheel locks!

 

[PW Cymru]

Been there done that.

It's bled, it just doesn't stop the bike.

I'll give it some time and heat see what it's like.

 

[Redboots]

It's bled, it just doesn't stop the bike.

Shit pads, glazed or the material itself?

John

 

[(RIP) pastyman]

What oil are you using

 

[(RIP) Proff]

What oil are you using

Knowing Paul
Sweet n' sour dot 40...........

 

[PW Cymru]

Dot4 soy source

 

[GEOFFREY DEACON]

Did the old pads wear differently or at all?.

 

[Rob Farmer]

Could be the master cylinder. If the piston isn't going all the way back it doesn't allow more fluid in. I had a similar problem with my RS, it took a lot of fiddling about to strike a balance between it working and getting the travel on the brake lever.

 

[GEOFFREY DEACON]

On its stand, can you turn the wheel when you apply the brake by hand?,
Are both pistons moving when you brake,,?
can both pistons be moved back with finger pressure only?.
are pads moving freely in the caliper and across the pins?.

as Rob says,, CHECK FOR ,master cyl rod adjustment,
and free movement of the brake pedal pivot pin/bush.



let us know?.

 

[PW Cymru]

Could be the master cylinder. If the piston isn't going all the way back it doesn't allow more fluid in. I had a similar problem with my RS, it took a lot of fiddling about to strike a balance between it working and getting the travel on the brake lever.

Hi Rob,
There's definately fluid being pumped out of the MS as it can be seen during the bleed. The pads are also gripping the disc but has no stopping power.

 

[PW Cymru]

On its stand, can you turn the wheel when you apply the brake by hand?,
Are both pistons moving when you brake,,?
can both pistons be moved back with finger pressure only?.
are pads moving freely in the caliper and across the pins?.

as Rob says,, CHECK FOR ,master cyl rod adjustment,
and free movement of the brake pedal pivot pin/bush.



let us know?.

Hi Geoff,

Yes stops the wheel
Both pistons are moving
No, bit too stiff to move by finger pressure only
Pads are free and pins new and well lubed so no sticking evident.

 

[nick.ct]

I dont suppose that in the past someone has changed the master cylinder for one with a larger diameter piston or the caliper for one with smaller pistons?

 

[PW Cymru]

I dont suppose that in the past someone has changed the master cylinder for one with a larger diameter piston or the caliper for one with smaller pistons?

It was previously working reasonably well, however the caliper appears to a front Brembo rather than the original rear one.

 

[fayeslane]

Try pouring hot water over it!

 

[ollek]

Typical symptom of bubbles in the rear brake disc...

 

[PW Cymru]

Typical symptom of bubbles in the rear brake disc...

Why would these symptoms be due to air bubbles in the rear caliper.

I appreciate it's allways possible to have air in the system due to its layout but the pedal is solid with no spongginess.

Caliper has been positioned at all angles during the bleed.

 

[ollek]

The pedal is hard, but also the air is hard to compress.
It is necessary that the caliper is positioned higher than the rest of the circuit and the bleed screew is at the top.
It also helps to release the bubbles knocking with the handle of a screwdriver around the circuit.
I hope that this will be helpful.