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Dump old brake fluid and refill or flush through?

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slowside
Nova Slayer



Joined: 23 Apr 2019
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PostPosted: 18:49 - 12 Nov 2019    Post subject: Dump old brake fluid and refill or flush through? Reply with quote

The rear caliper on my Sprint is seized, so I'm going to remove and rebuild it.

I'll be replacing the brake fluid afterwards.

My question is:

Should I dump the existing fluid out of the master cylinder and brake line whilst the caliper is off, then refill the lot from dry on refitting the caliper?

Or, should I plug the line when I remove the caliper and bleed the old fluid through and out the caliper with fresh stuff when I refit?

Or does it not matter?
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Nobby the Bastard
Harley Gaydar



Joined: 16 Aug 2013
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PostPosted: 18:51 - 12 Nov 2019    Post subject: Reply with quote

You may as well use it to pump out the caliper and then dump it.
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 19:55 - 12 Nov 2019    Post subject: Re: Dump old brake fluid and refill or flush through? Reply with quote

slowside wrote:


Should I dump the existing fluid out of the master cylinder and brake line whilst the caliper is off, then refill the lot from dry on refitting the caliper?


Yes, then you can give the reservoir and M/C a good clean out while you're at it, there is often a load of sludge and shite in the bottom of it (most likely sitting in the bottom of the hose on a rear).
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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Polarbear
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PostPosted: 00:58 - 13 Nov 2019    Post subject: Reply with quote

It's quiet amazing how much crap can sometimes be found in a brake system. Also brake fluid is hygroscopic so older fluid can have contamination. Edited to add - use brake fluid from a new, unopened can for this reason.

Give everything a good clean then use new fluid and do a flush before bleeding. You only do this job once in a blue moon, do it properly. Thumbs Up
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Pete.
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PostPosted: 11:17 - 13 Nov 2019    Post subject: Reply with quote

I would pump it out through the nipple until the reservoir is just about empty then push the pistons back in and pump it again then once the fluid level is just at the bottom of the reservoir top it up and pump new fluid through until it's coming out clean. If you do it right you'll get out nearly all the old fluid with no need to bleed air bubbles which can be a real bind on some bikes.
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stinkwheel
Bovine Proctologist



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PostPosted: 16:30 - 13 Nov 2019    Post subject: Reply with quote

Pete. wrote:
I would pump it out through the nipple until the reservoir is just about empty then push the pistons back in and pump it again then once the fluid level is just at the bottom of the reservoir top it up and pump new fluid through until it's coming out clean. If you do it right you'll get out nearly all the old fluid with no need to bleed air bubbles which can be a real bind on some bikes.


He's removing the calliper for a rebuild.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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Pete.
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PostPosted: 17:44 - 13 Nov 2019    Post subject: Reply with quote

stinkwheel wrote:
Pete. wrote:
I would pump it out through the nipple until the reservoir is just about empty then push the pistons back in and pump it again then once the fluid level is just at the bottom of the reservoir top it up and pump new fluid through until it's coming out clean. If you do it right you'll get out nearly all the old fluid with no need to bleed air bubbles which can be a real bind on some bikes.


He's removing the calliper for a rebuild.


Oops, reading fail. In that case drain and flush.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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slowside
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PostPosted: 20:46 - 13 Nov 2019    Post subject: Reply with quote

Cheers all. Option 1 it is then.
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Nobby the Bastard
Harley Gaydar



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PostPosted: 20:55 - 13 Nov 2019    Post subject: Reply with quote

How are you planning on getting the piston out?
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slowside
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PostPosted: 23:16 - 13 Nov 2019    Post subject: Reply with quote

Nobby the Bastard wrote:
How are you planning on getting the piston out?


Will push the pistons out before I pull the calliper off and dump the rest of the fluid.

One of them moves freely, the other will just about move if I block the other off and crank the brake, so will have to inch them out bit by bit.

If they don’t pop out I’m hoping I can pull them the rest of the way out with a set of reverse pliers to grip the inside of the piston.

Failing that I’ll hurl the thing across the garden in a rage and start a row with the wife over something seemingly unrelated.
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Grubscrew
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Joined: 23 Dec 2018
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PostPosted: 17:06 - 15 Nov 2019    Post subject: Reply with quote

Great gun works or compressed air in the nipple....ouch, stand clear!
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Old Thread Alert!

The last post was made 4 years, 135 days ago. Instead of replying here, would creating a new thread be more useful?
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