Brakes help needed

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old git · #1 Post by **old git** » Sat Jun 19, 2010 12:33 pm

OK, stripped everything off the front calipers, cleaned & re-assembled.
Bleeded them for ages, got some lever feel, up the road to test - absolutely useless.
Have now seen that looks like the inner pair (on both sides) pistons are not moving, what little feel I had was outer pistons moving & pressing the disc against the side of the cliper body, obviously causing some scratching.
What the fcuk am I doing wrong>>>Please help I have been at this for over 4 hours already, can't see where i am going wrong.
Ta
Keith

D-Rider · #2 Post by **D-Rider** » Sat Jun 19, 2010 12:43 pm

If you've not got fluid leaking out, I'm betting you've still got air in the lines.

Did you follow KZmille's guide to bleeding?
https://www.ridersite.com/viewtopic.php?t=3763

old git · #3 Post by **old git** » Sat Jun 19, 2010 12:48 pm

Yep, had air out both sides, & from bleeder at the top by the resv.
no more air out, shaken lines to move it around etc. as well.
Why only one side of the pistons moving & not the other>??

D-Rider · #4 Post by **D-Rider** » Sat Jun 19, 2010 12:49 pm

Are you getting the normal level of pressure on the lever when you apply the brakes?

old git · #5 Post by **old git** » Sat Jun 19, 2010 1:06 pm

In truth, no.
I have taken calipers off, put a plate between & pumped as I say, outer pistons move, inner ones stay toatally still.
Obviously once the outers are pressed against the plate & the plate pressed against the other side I am getting lever pressure, but even though I have moved calipers around not getting any more air out nor are the inner pistons moving, I am stummped

D-Rider · #6 Post by **D-Rider** » Sat Jun 19, 2010 1:17 pm

Well I'm still betting on air.

Plenty of fluid in the master cylinder reservoir - diaphragm replaced over the top of the fluid before the cap screwed on .... someone did try to top the fluid up without taking the diaphragm out first.

#7 Post by **Kwackerz** » Sat Jun 19, 2010 1:22 pm

Sounds like there's still air trapped behind the pistons as its on both sides.. I would go for holding them at some other ungodly angle and trying again or else reverse bleeding. It may help as it sounds like you're forward bleeding it (normal bleeding)

**edit**

http://www.rsvzone.com/forums/showthread.php?t=13865

I'll let the RSV boys will explain how..

old git · #8 Post by **old git** » Sat Jun 19, 2010 1:54 pm

Tried reverse bleed as well, just pissed fluid everywhere when the pipe came of the syringe - NO DON'T Laugh I CAN SEE YOU U KNOW!
I guess air is in there as well unless I am doing something really really lame ( & it is quite possible), but dont understand after all the movement, bleeding up down & sideways that it can still be inthere.
If as we suspect air is trapped behind the inner pistons, hence they don't move, how the FCUK do I get it out.

HisNibbs · #9 Post by **HisNibbs** » Sat Jun 19, 2010 2:39 pm

I'd try a wooden lever between the pads to push the cylinders as far back as possible. Then try bleeding again.

old git · #10 Post by **old git** » Sat Jun 19, 2010 2:54 pm

Did that keith, but as I noted only the outer pistons are moving.
I have stripped & cleaned everything so there is no way they are jammed through dirt etc. you could have eaten food off them before my oily shit hands had been all over them.
Do you have to alighn the pads up centrally or something within the caliper body before you re-mount them? so that both inner & outer pistons push on the discs together?

HisNibbs · #11 Post by **HisNibbs** » Sat Jun 19, 2010 3:06 pm

There are different caliper designs and some only have one moving piston that because the caliper floats, apply pressure both sides. However I thought ours had moving pistons both sides. It is possible they've siezed but I'd have thought they'd move given a bit of hydraulic pressure.

If I remember the pads hang off the pins and are contained within the calliper so I doubt they can interfear with the action of the pistons. Maybe if the stationary pistons were pushed right back to start with, the fluid can't get behind them to push out? I'm also of the opinion that there is still air in the system and you need maybe to pump the brake lever a bit more.

anzacinexile · #12 Post by **anzacinexile** » Sat Jun 19, 2010 3:08 pm

Try locking the outer pistons and then pump to get the inner buggers moving. 2 small G-clamps or toolmakers clamps will do the job

If you have pushed the pistons back as far as they go, they can stick pretty hard and the easiest moving piston will do all the moving

EDIT - Our callipers have opposing pistons

#13 Post by **mangocrazy** » Sun Jun 20, 2010 6:40 pm

Have you stripped the calipers down as far as splitting the two halves? There are 4 x M8 socket head bolts holding the two halves together. If you have, there's an outside chance you've mixed the two caliper halves up and put both back on the wrong one.

There's a little drilling between the two halves (with an o-ring to seal it); if you've got them mixed up I guess you could have blocked that drilling off, leading to the symptoms you describe.

Of course it may not be that at all, but if you've had the calipers apart it would be worth checking.

#14 Post by **Kwackerz** » Sun Jun 20, 2010 7:09 pm

old git wrote: NO DON'T Laugh I CAN SEE YOU U KNOW!

Laughing? I was in tears!!!

Willopotomas · #15 Post by **Willopotomas** » Sun Jun 20, 2010 9:22 pm

Is the bleed nipple on the top or bottom of the calliper.. If at the bottom, you'll never get rid of the air trapped in there.. You'll need to take them off and turn them round. Another trick that sometimes works is to strap the lever back to the bar and leave it for a couple of days.. It sometimes works as the air can rise in the lines and escape through the open master cylinder. Least that's the theory.. It's a bit hit-and-miss that one..lol..

Failing that.. Buy an eezibleed kit. Brilliant device and only about £25. If the caps in the box don't fit, you can make one up using another cap for that reservoir.

http://www.gunson.co.uk/item.aspx?item=1818