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 Post subject: Spongy brakes
PostPosted: Sat Mar 11, 2017 8:10 pm 
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80 cc

Joined: Tue May 24, 2016 12:30 pm
Posts: 17
Hi I've got a brakes problem I'm hoping someone can help me with please.
I'm new to dirt bikes but I just bought a 2000 drz400 s so I'm on a steep learning curve.
the bike had a new mot when I acquired it but on delivery I find that the front brake is so spongy that the lever comes back to the grip.
First thing I did was bleed the system but still the same. The master didn't seem to be pumping much so the next thing was overhaul the master with new seals etc but still no joy.
So now I'm thinking do I a) change the hose or b) look for a new master.
The master looks ok to me but I'm no expert. It did look as if the threaded bit of the piston had been rubbing in the bore. Is that usual? I saw no scoring inside the bore but obviously it's hard to tell.

The hose looks original so probably 17 years old.
I know unbraided hoses aren't ideal especially old ones but I'm surprised the lever comes so far back and I still can't really feel any pressure.
I guess maybe there is a lot of air in there I haven't bled out??
Thanks.
Richard
(Sorry if this is the wrong section by the way)


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 Post subject: Re: Spongy brakes
PostPosted: Sat Mar 11, 2017 9:59 pm 
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200 cc

Joined: Sun Nov 29, 2009 7:19 pm
Posts: 341
Location: Norton Derbyshire border
Try reverse bleeding by connecting a syringe to the bleed nipple and forcing fluid back to the reservoir. After that if the lever still feels spongey tie the lever with a cable tie to the handlebar overnight, it keeps the system under pressure and seems to remove any small air bubbles from the system. Usually works.


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 Post subject: Re: Spongy brakes
PostPosted: Sat Mar 11, 2017 10:03 pm 
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80 cc

Joined: Tue May 24, 2016 12:30 pm
Posts: 17
Great idea. Thanks.
I'll give those a try.


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 Post subject: Re: Spongy brakes
PostPosted: Sat Mar 11, 2017 11:01 pm 
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125cc

Joined: Mon Feb 22, 2016 6:19 pm
Posts: 145
Don't change any more bits,change your bike n buy a ktm :oops:


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 Post subject: Re: Spongy brakes
PostPosted: Sat Mar 11, 2017 11:21 pm 
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300 cc
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Joined: Mon Apr 22, 2013 7:07 pm
Posts: 570
I assume you've replaced all the fluid with new.

If the hoses are that old then replace it. Should be changed every 3 years according to manual. It should be date marked.

Then Reverse bleed as already said. Remove master cylinder and make sure it's above the loop of the brake line so all the air goes to the highest point.

The main question is, do the brakes actually work. From memory they always felt soft but worked fine. There's also a screw adjuster on the lever to you can get a bigger bite.


Sent from my iPhone using Tapatalk


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 Post subject: Re: Spongy brakes
PostPosted: Sun Mar 12, 2017 10:07 pm 
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650 cc Monster
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Joined: Fri Dec 07, 2012 2:22 pm
Posts: 2439
Location: Romiley
Greetings,

Colleagues have already explained some of the aspects for you to consider.

The standard 'rubberised' hoses are meant to swell a little under pressure but as they age the swelling gets progressively larger and so the lever travels further to give a spongey feel. Conversion to stainless braided hoses which do not 'give' and so limit that spongey feel but they tend to increase the chances of locking the brakes if too much pressure is applied.

Sometimes removing the circlip which retains the master cylinder piston allows the piston to move out along its barrel a little further to aid fluid flow in and out of the reservoir. The piston can be pushed in yet released further rearwards, using a screwdriver with care. Alternatively reverse flushing allows the fluid to pass easier to remove any air with the piston seal slightly further back in the bore.

Take your time and move the piston slowly. Always use fresh new fluid and never shake the container, let it rest on a shelf for an hour before using it to prevent aeration of the new fluid, pour slowly into in the master cylinder.

TTFN

Hugh.

_________________
Please note that I am not a National TRF Officer, any views expressed are my own and may not be in accordance with any official policy.


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 Post subject: Re: Spongy brakes
PostPosted: Mon Mar 13, 2017 12:00 pm 
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80 cc

Joined: Tue May 24, 2016 12:30 pm
Posts: 17
Thanks to all.
I have ordered a new hose and a big syringe.
Found another problem with this bike now so have posted another question.


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