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elliotsdaddy
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....yet another stupid AJP brake related question. But please allow me to indulge you.

 

Ok, so, my rear brake is crap...it worked (just) but was pretty pants. So I looked in to the problem, ie made things worse, so now it doesnt work at all!

 

Cue the abuse. Go on I deserve it.

 

So there is nice fresh fluid in the system.

Pads are fine.

Discs are fine.

The system has been bled.....originally back filled via the bleed nipple on the caliper and then today from the resevoir tube (to ensure the master sylinder gets filled) as suggested in another similar post.

The caliper seals are in good condition. No corrosion or debris in the caliper.....but those cheeky pistons just dont seem to want to budge when the pedal is depressed.

I am assuming that the master cylinder is ok due to the fluid being pumped out of the bleed nipple when there is pressure on the brake lever.

 

Am I missing something obvious or does it sound like caliper rebuild time with new pistons?

I noticed earlier that one pad is slightly more worn than the other which suggests a siezed caliper but seems odd that it now fails to work at all.

 

I have learnt my lesson with regards brake systems but please feel free to be sarcastic and judgemental.

 

Regards,

 

Chris.

Edited by elliotsdaddy
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With the seals removed did the pistons move easily (lubricated with brake fluid) in the bores, if not check the surface of the pistons and polish out the bores with fine wire wool.

Is there any corrosion in the seal grooves - you need a dental inspection mirror to check this properly, any corrosion or dirt at all must be polished out.

 

When re fitting the seals dampen them with brake fluid, but leave the groove dry. When fitting the pistons put plenty of brake fluid on the seals and bores, use red rubber grease on the piston. Pistons should push in easily with light to medium finger pressure, if not something is amiss, do not force them in.

 

Put PTFE tape on bleed nipple threads then vacuum bleed, but do not use more too much vacuum. Then bleed normal way by pressing pedal. If that does not work, tie the pedal down and pour boiling water over calliper until it is hot, then continue bleeding.

 

Try standing bike on its back wheel overnight so there are no "up loops" or air traps in hose, any air should move up through master cylinder.

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Thanks for the replies all.

 

I thought that seeing as though I've got to take it apart again, I might as well do it properly, so I have ordered a rebuild kit from SplatShop for the front and rear calipers with nice new pads.  :)

 

If it all goes tits up I will just keep it to myself and hide in a corner until it all goes away.

 

Chris.

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I just went through all this.

 

I had to rebuild my rear caliper and for the life of me still could not get a brake pedal

 

Here is a tip from Ryan young that worked wonders and gave me a brake.

 

With all the lines connected still take the rear master cylinder off and bolt it exactly where it goes but to the OUTSIDE of the frame. ITs like having a 3rd hand.

Take a dull object like a larger phillips screwdriver and push the piston in a few times and hold it. DONT MOVE NOW

Take a wrench and crack the banjo bolt loose on the top of the master cylinder and finish pushing the piston in until it stops. Tighten the banjo bolt and repeat. Do that 4 or 5 times and you will have  a brake. I did mine every which way including back bleeding with a syringe and still could not get a brake pedal. Ryan told me this and it worked instantly

Give it a shot!

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I just went through all this.

 

I had to rebuild my rear caliper and for the life of me still could not get a brake pedal

 

Here is a tip from Ryan young that worked wonders and gave me a brake.

 

With all the lines connected still take the rear master cylinder off and bolt it exactly where it goes but to the OUTSIDE of the frame. ITs like having a 3rd hand.

Take a dull object like a larger phillips screwdriver and push the piston in a few times and hold it. DONT MOVE NOW

Take a wrench and crack the banjo bolt loose on the top of the master cylinder and finish pushing the piston in until it stops. Tighten the banjo bolt and repeat. Do that 4 or 5 times and you will have  a brake. I did mine every which way including back bleeding with a syringe and still could not get a brake pedal. Ryan told me this and it worked instantly

Give it a shot!

 

:thumbup:

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  • 2 weeks later...

Did this last night, the cracking of the banjo bolts helped out a ton. Alas the brakes still never really grabbed very well.

 

I read on here in a what was i think a gas gas topic, to drag the brakes in third gear for a few mins and then pour ice cold clean water on them, it must shrink the piston diameter so it can protrude faster  :rolleyes:   also beds the pad to the rotor for an excellent brake feel.

 

I don't question it anymore, it has worked for me and a few friends. I was about to give up on AJP forever and drop some coin on some braktec.

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Did this last night, the cracking of the banjo bolts helped out a ton. Alas the brakes still never really grabbed very well.

I read on here in a what was i think a gas gas topic, to drag the brakes in third gear for a few mins and then pour ice cold clean water on them, it must shrink the piston diameter so it can protrude faster :rolleyes: also beds the pad to the rotor for an excellent brake feel.

I don't question it anymore, it has worked for me and a few friends. I was about to give up on AJP forever and drop some coin on some braktec.

Ride round till the brakes are really hot then cool the disc with cold water. It can take quite a few heating and coolings to work.

It's always best to put new pads in. Only takes a bit of wear to make it difficult to get a good brake.

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