Is pushing pistons back in hard?

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Is pushing pistons back in hard?

Postby slarv » Wed May 16, 2012 1:24 pm

Hi BNA,

I got a new set of pads for my Elixir5s. The Avid instruction manual makes it sound very easy but I am having trouble. Just leave the old pads in and use a screw driver to rock back and forth.

I think the pistons have gone back in a little bit but not enough for the disc to fit in between yet. I feel like I am applying a little bit too much pressure but I might just be hesitating. There is a slight squelching in the levers.

1. how much pressure is required?
2. how much rocking back and forth is normal?
3. is a bit of squelching normal or should it be totally silent?
4. does the squelching indicate that air is in the system and it needs to be bled?
5. would a system that needs to be bled prevent the pistons from going back in?

The bike is almost a year old. This its first new set of pads and it and it hasn't been bled before (apart from initial setup). I am planning on taking it to a bike shop for a proper service in about a month (when funds allow).

If all else fails I will attempt to loosen the bleed valve while pushing the pistons back in a bit and hope I don't have to take it for a service early.

Regards,

Slarv
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by BNA » Wed May 16, 2012 1:47 pm

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Re: Is pushing pistons back in hard?

Postby trailgumby » Wed May 16, 2012 1:47 pm

It's best to remove the accumulated sludge off the exposed piston walls with a cotton bud soaked in brake cleaner before pushing them all the way home. If you let it build up, your caliper can develop sticky pistons that don't return properly.

Otherwise, yes, just push back until they are flush with the caliper walls.
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Re: Is pushing pistons back in hard?

Postby rkelsen » Wed May 16, 2012 2:00 pm

Whatever you do, don't open the bleed valves unless you're flushing or bleeding the system.

Pushing pistons back in can take a fair amount of force. The top of the piston should be approximately level with the top of its bore when it is fully home.

The squelching can be ignored, unless the lever is spongy or travels all the way to the handlebar with no effort.

Dunno about rocking back and forth. I'd try to push the piston back in as squarely as possible.

slarv wrote:would a system that needs to be bled prevent the pistons from going back in?

No. In fact, it would be easier to push the pistons back in if the system needed to be bled.
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Re: Is pushing pistons back in hard?

Postby slarv » Wed May 16, 2012 2:26 pm

Good tips. Especially with the cotton tip. I was going to buy some compressed air to try and blow away the brake dust. I tried 4 shops but got the same response: "Not any more". The Avid manual didn't mention cleaning so I figured it would just be going the extra mile.

Does metho count as brake cleaner?
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Re: Is pushing pistons back in hard?

Postby mitzikatzi » Wed May 16, 2012 2:31 pm

slarv wrote:Does metho count as brake cleaner?


It does for me.
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Re: Is pushing pistons back in hard?

Postby trailgumby » Wed May 16, 2012 3:33 pm

The problem with compressed air is that it is too easy to blow dirt in past seals.

When I used to race R/C cars. I used metho to dissolve the fuel lubricant that always coated everything, and **carefully** blow it off with compressed air, being ultra careful to blow across shafts and bearings and **never** blowing **at** them.

Even then, I occasionally had to replace bearings, but they were cheap and readily available so there was a time/dollars trade-off that favoured the compressor.

However, with your brakes, getting rebuild kits can be problematic as some brands don't really design their calipers for servicability and the parts necessary cannot be bought. Juicys used to be fine for rebuild kits, not sure if the practice is current for the Elixir models though. But you still have to do the work yourself or you're up for bike shop labour $$$.

So unless you're prepared to strip and rebuild your brakes yourself, I'd recommend leaving compressed air alone.
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Re: Is pushing pistons back in hard?

Postby alf » Wed May 16, 2012 4:44 pm

Metho should be fine but my preference is isopropyl alcohol

http://www.jaycar.com.au/productView.asp?ID=NA1066

Fantastic to clean the rotors with as well.
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Re: Is pushing pistons back in hard?

Postby slarv » Wed May 16, 2012 11:37 pm

alf wrote:Metho should be fine but my preference is isopropyl alcohol

http://www.jaycar.com.au/productView.asp?ID=NA1066

Fantastic to clean the rotors with as well.


Isopropyl alcohol is another one of those nerdy supplies that is usually out of stock or no longer sold when you need it. I was at a Big W store a few weeks ago and was surprised to see it on a shelf together with a bunch of other useful supplies. They had a shelf full of Diggers brand stuff. Worth remembering for future.

I cleaned things out with the metho and cotton bud.. A fair bit of gunk has come out but I still can't push the pistons all the way back in.
I put the old pads back in, credit card between the pads and squeezed the brake to push the pistons most of the way out. This gave me a good idea of what it feels like to push them back in.

I seem to have pushed them in as far as they are willing to go. However I have noticed when I push on one side, the other side comes out, and then vice versa... seems like a good indication of too much fluid in the system?

I am doing all of this while the bike is upside down, wondering if that is causing the problem? Would adjusting the reach on the levers have any effect? I don't expect either to help but it's worth a shot.
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Re: Is pushing pistons back in hard?

Postby Mulger bill » Thu May 17, 2012 12:50 am

Jeez, I hope my Elixir CRs don't give me this sorta grief when it's time. The old Juicys were easy as.

Did you get a pad spacer block with the brakes? Best tool for piston retraction on the Juicys.
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Re: Is pushing pistons back in hard?

Postby slarv » Thu May 17, 2012 7:23 am

Mulger bill wrote:Jeez, I hope my Elixir CRs don't give me this sorta grief when it's time. The old Juicys were easy as.

Did you get a pad spacer block with the brakes? Best tool for piston retraction on the Juicys.



Nope.. I cheaped out and got 3rd party pads from torpedo7, they didn't come with a spacer. Before you start to blame the pads, the front ones went in fine.. The rear one is being tricky.
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Re: Is pushing pistons back in hard?

Postby trailgumby » Thu May 17, 2012 9:01 am

You need to push both all the way home, simultaneously, to force the fluid back up into the master cylinder. Make sure your bike is upright when you do this, and the master cylinder hatch cover is level (not sure if this last applies to Elixirs :? ).

You can't push one in, and then the other - the free piston will come back out again as you've discovered. This behaviour is actually the system operating as intended, to apply even pressure to the pads on each side of the disc when the brake lever is squeezed.
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Re: Is pushing pistons back in hard?

Postby slarv » Thu May 17, 2012 9:39 am

I think I need to invest in a proper work stand.
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Re: Is pushing pistons back in hard?

Postby slarv » Thu May 17, 2012 10:45 pm

Only took me 3 days to change brake pads. In the end I had no choice but to let some fluid out. I had a trusty assistant to apply a smooth and constant pressure to the pistons while I slowly undid the bleed screw and then did it back up again after the slightest dribble. It made a difference but I had to do this a few times as I didn't want to over do it.

I know I didn't over do it because they both don't go all the way back in at the same time. The only difference is now I have enough space to fit a rotor between them.

I will invest in a bleed kit for the future but for now I think I am safe. To answer my own question. No it shouldn't be that hard to push back the pistons when they behave. Firm pressure but you don't need to force it.

Thanks for all the advice.
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Re: Is pushing pistons back in hard?

Postby Big_Chuck » Fri May 18, 2012 10:55 pm

I've had the same problem with my Elixir 5 brakes. The first time I did most of the above and they still wouldn't move back enough, so I did a full service on the caliper. Cleaning and lubricating the pistons was the best thing I could have done to the Elixirs as it stopped the annoying squeak. The next time I just let a small amount of oil out of the lever as I pushed back. The XT brakes are now waiting to be fitted in the next few weeks.

This photo helped me better understand the Elixirs. http://www.pinkbike.com/photo/4397805/

More info here. http://bmorc.com/node/31889
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