GSA Brake Pad problem

[Lofty]

I’m frustrated to have to put this up but I’d rather ask for advice before making a potentially expensive mistake.

Simple task in replacing the rear brake pads on my 2012 GSA which are well shot. I have everything to hand and the bike up at height for ease of working and have read the Haynes manual several times so all looking good.

The old pads have come out easily and the caliper has all cleaned up nicely and I have managed to push the pistons back so about 6-7mm of piston is exposed and that’s where it all stops.

I can get them back no further by hand so I've just ordered a spreader tool and will have another go at the weekend. With the new pads in now I am unable to create a gap wide enough to get over the disc – I would say I'm 4 mm short.

My concern is that technically I must have a hydraulic lock as the fluid must need to go back up the way to allow the pistons to move and I’m not certain how the ABS system fits in. The manual helpfully states “push the pistons back till flush” or something along those lines. I have however seen a post on the forum that indicates that by pushing the pistons back on a ABS bike you can rupture a £1300 diaphragm so I'm reluctant to simply force the issue.

Any guidance from the good folk on this parish .. I’ve done this so many time on other bikes but this is the first attempt on the GSA with ABS.

 

[JJH]

Put in old pad on pistons side. Put small tyre lever between pad and disc and gently lever the pad away from disc which should push pistons in. You should have enough room In reservoir unless it's been topped up as pads wear. You can open bleed nipple but I don't see you needing to. JJH

 

[Lofty]

Been there - done that ... I spent a good 45 mins trying to get the pistons back using the old pads and a variety on levers as per the norm but to no avail. That's why I've ordered a proper set of spreaders. I did think about draining off a wee bit of fluid but I was uncertain.

 

[Alan R]

Were your calipers very dirty or corroded? If the sliding surfaces of the pistons are not smooth and clean they could bind with and possibly tear the dust seal and inner pressure seal. Don't force the pistons back unless you are confident that they are clean and smooth. Pump them nearly all the way out, clean again, then smear red rubber grease on the edges with a cotton bud, then push them back making sure that as you push one in, the pressure doesn't pop the other out completely. If the pistons are corroded, then it's likely that replacement is necessary together with the seals.
Alan R

 

[Lofty]

Both pistons were clean and move easily. When I push on one the other comes out and vice Verda. The issue is pushing both back together .. there comes a point at which they won't go any further .. as I said I'm convinced it is because there is nowhere for the fluid to go ... but I could be wrong


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[Steptoe]

Put old pads back in the caliper and the caliper back in place, fit caliper retaining bolts finger tight.

Push the outside of the caliper with your foot while holding onto the rear subframe. The pistons should slide back in place.

Next time you replace the pads do this before removing anything...
Also best to do the "foot push" once a month during the winter as it stops the caliper pins from seizing due to very little movement when in normal use.....remember to operate the rear brake pedal before use

 

[bigtwin]

You have taken the lid of the reservoir haven't you?

Ian

 

[Deleted account 190920001]

I am with bigtwin.

 

[The Grey One]

Been there - done that ... I spent a good 45 mins trying to get the pistons back using the old pads and a variety on levers as per the norm but to no avail. That's why I've ordered a proper set of spreaders. I did think about draining off a wee bit of fluid but I was uncertain.

If the pistons won't push back using old pads and levers then here is a problem that your "proper pair of spreaders" won't solve. In fact using excess force will only make things worse. Are you sure it's not just because the system is too full of fluid. Try cracking the bleed screw and see what happens.

John

 

[RedRick Esq.]

You have taken the lid of the reservoir haven't you?

Ian

I think this is the Answer or is it the question ?

Either way

 

[Lofty]

I haven't because the book didn't say to do it although I felt it was necessary. To be honest that's why I asked the question on here ... I will have another go a the weekend with the reservoir lid off. I was more concerned with how the fluid went back up past the ABS system even if the lid was off ..

 

[RedRick Esq.]

I haven't because the book didn't say to do it although I felt it was necessary. To be honest that's why I asked the question on here ... I will have another go a the weekend with the reservoir lid off. I was more concerned with how the fluid went back up past the ABS system even if the lid was off ..

Take the res lid off and wrap a cloth round it to catch any fluid that spills over the top

It will be fine

 

[alex_rsa]

Those pistons look they have had a tough time, sombody forced them back previously?

I cannot answer for ABS-2 but in the older ABS the caliper is connected to the ABS resevoir and they have overflow pipes so any excess fluid you push back will run out under the bike.

Have you tried cracking the bleed nipple when pushing the pads back?

 

[Steptoe]

Take the res lid off and wrap a cloth round it to catch any fluid that spills over the top

It will be fine

Unclip the reservoir and Pour the brake fluid out before you push the Pistons back in... No mess

 

[RedRick Esq.]

Or you could do as steptoe suggests but what the feck does he know












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[LMiwa]

When you say "Both pistons were clean and move easily. When I push on one the other comes out and vice versa.", do you mean that either piston can be pushed ALL the way back to where it needs to go? If so, that eliminates piston binding as an issue and fluid pressure is the problem.

If you allow one piston to move out, but you can STILL only push the other back to the same 6-7mm of piston exposed, then fluid pressure is not the issue, binding is the problem.

 

[Pukmeister]

Would you like me to pop over and take a look, I can bring my G-clamps, brake cleaner, brake fluid etc. ?

Chances are you have a tiny build up of crud on the piston skirt preventing it fully sealing home, or as already stated you have excess fluid in the rear brake circuit that needs bleeding off.

Drop me a PM if you need help, I'll PM you my phone number, feel free to call.

 

[Lofty]

Thanks to all that have contributed. I'll almost certainly get Adam to have a look over the festive period when I finally get back home.

It's been an interesting debate ..

Cheers,

Mark