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Front Brakes Keep Losing Pressure


trikpat

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Hey Guys, 

Need some help/advice on my VFR (2011 DCT).

My front brakes keep losing pressure while I'm riding. I've  been bleeding them quite a few times now and it goes back normal for a while but  the next time I ride, If  pull on them they start to lose pressure again.

I can't find any leaks and the brake fluid is staying at the same level. 

I also notice that while riding, If stop at the side of the road for a while and just pump the brake lever hard a few times, the pressure goes back up again.

Any ideas would be help. Thank you.

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I had the same issue with my previous bike.

when the brakepads got thinner, the Tokico calippers pushed the dust-sealings out.

Wedging them between the piston and calipper.

 

Rebuild the calipper completely.

Use special grease thatdoesn't react with the DOT4 brakefluit 

ATE.jpg

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On 2/19/2018 at 9:28 PM, Lampie said:

I had the same issue with my previous bike.

when the brakepads got thinner, the Tokico calippers pushed the dust-sealings out.

Wedging them between the piston and calipper.

 

Rebuild the calipper completely.

Use special grease thatdoesn't react with the DOT4 brakefluit 

ATE.jpg


Thinking of buying 2 sets of kits to rebuild right and left calipers. Hopefully they get fixed.

Do you have any recommendations on where to buy these kits? So far I've only seen one on ebay and nowhere other sites so I have nothing to compare the prices on.

 

On 2/20/2018 at 12:16 AM, andy said:

Apply light pressure as if you were just at a stop light.  If the lever slowly sinks, your master is failing.  If you pump it hard the brake lever will seem normal.


If it's the master, can it be fixed with a rebuild kit? 

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Kits abound on the internet, but as a retired auto mechanic, the usual reason for the seal failure are cuts from corrosion in the master bore.  It’s possible to use a purpose built honing tool or even wet/dry “sand” paper to smooth the bore.  Prevention by replacing the brake fluid  (absorbs water) at least every other year.  Although brake fluid tends to get darker over time, clear/amber brake fluid doesnt’ mean it’s water free.  Fluid from a sealed can is best.

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  • 6 months later...

Update: I tried fixing the issue with a master cylinder rebuild a few weeks back and the problem still persists.

When I first use my bike the pressure is okay but overtime if I pull on the brakes hard (like on sudden stops) the front brakes starts to get a little spongy. Then If pump it a few times the pressure goes back up. I'm thinking there might be a leak somewhere and I can't find it.

I ordered a rebuild kit for the calipers and it's taking a while to arrive.

Any thoughts or suggestions?



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Also - a side note - the brakes are kind of dragging which is weird because I'm losing pressure but the brakes are kind of dragging. (I can a low metal grinding noise)

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  • Member Contributer

If your fluid level stays the same then your master cylinder piston is leaking fluid past it's seals and back

into the reservoir. You may have rebuilt it but that's where the problem lies. OTOH if you're losing brake

fluid and the level is dropping then you have bad slave cylinder seals somewhere.

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The seals on the master are brand new so I'm not sure why it's broken. Could it be a scratch on the master cylinder lining?

I'll check that little hole again when my rebuild kit for the calipers come. I'm going to open up the bike again and do a thorough inspection.


--------------------------

These is brake issues really take the fun out of riding the bike 

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