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Hydraulic Disc Help - Should I bleed / refill?

by Scoob_84
Mon, Sep 13, 2021 11:48
3

Hi Folks, 

Apologies if this has been asked dozens of time but i've checked and couldn;t find a similar thread. 

I recently swapped out my front disc pads which had completly worn away. In trying to reset the pistons (push them back in) i found myself playing with the brake lever which the disc out and bike upside down. One of the pistons nearly popped out, but i pushed them back in as far as they'll go. Trouble is, the brake lever now doesnt generate enough pressure to apply any braking force onto the disc. 

Have i broken it or do i just need to bleed the brakes and replace the fluid? 

In normall circumstances, i would leave something like this to the pros, but the workshop is booked up for the next month. 

In case it matters, the brake system is Shimano RS685/805 and i've had the bike for around 4 years and haven't done any maintenance on the brake.

Will someting like this kit do the trick?https://epicbleedsolutions.com/collections/shimano/products/shimano-blee...

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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3 comments

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hawkinspeter | 3 years ago
1 like

Definitely sounds like bleeding it should fix it. That Epic kit should do the trick - I've got a similar one that uses the funnel instead though the description on your link says that the syringe replaces the funnel (it would need to screw into the bleed port on the lever).

Having the bike upside down is likely the problem so you'll need to use a bike stand or similar when you do the bleeding as it'll need to be the right way up. It's quite easy to bleed those brakes - just follow the instructions with the kit or look it up on YouTube.

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kil0ran | 3 years ago
1 like

You probably haven't broken it, it probably just needs a bleed. 

Instructions are here (start on page 26 - https://si.shimano.com/api/publish/storage/pdf/en/dm/BR0008/DM-BR0008-10...)

Get the official Shimano bleed funnel (part number SM-DISC-BP), or a pattern part (Lifeline do one for £2.99)

I haven't used Epic's system but the critical bit is the bleed funnel and the right mineral oil. 

Whilst mineral oil doesn't really degrade you might have introduced contaminants into the system so you could do a full flush and replace, but it's probably not necessary. And also not something to do on your first ever bleed.

Follow the Shimano instructions and you'll be good to go. I'd just add one thing - to get a really good bleed it's useful to get the bike off the ground and to unbolt the caliper from the fork/chainstay so it hangs directly down. Nice straight cable helps bubbles migrate to the bleed funnel. Tapping the caliper with a piece of wood also helps.

It can be a bit messy so it's not one for the kitchen floor, put towels down and make sure you don't pollute the environment. Pay close attention to the bleed tube at the caliper end because it can spring off under pressure. If you've got a willing assistant it's slightly easier, particularly if you have got a repair stand. 

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huntswheelers | 3 years ago
1 like

Personally as I'm on the tools....bleed it...plus a wee trick at the end when you have bled fresh fluid in.... Gentle little "jabs" on the lever, not full pull....bleeds the lever too.... One tip....take your time and be clean/methodical

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