Spongey front brake - master cylinder?

[smithyithy]

Recently my front brake has gotten quite spongey, in that there is somewhat excessive travel in the lever..

Pads look fine, fluid level also fine, what looks like the master cylinder at the base of the lever does look worn though, like the rubber around where the bottom of the lever pushes in..

Would this be responsible for a spongey feeling and if so is it just a case of replacing that part?

Bike is a 1990 Honda CBR400RR.

Cheers.

[SQL]

Bleed brakes first its cheap and easy and normally the issue

[andym]

I've had this on a couple of bikes (including the current 1), I found replacing all the crush washers and bleeding the brakes sorted it out

[smithyithy]

Bled the brakes with no improvement

What is the crush washer?

[Kickstart]

Hi

The rubber bit you can see around the base of the lever should affect the brakes being spongy in the short term. It is there to protect the rear seals from grit and other rubbish.

If you have bleed the brakes thoroughly with no improvement then hopefully can count that out.

Whip each caliper off and check that they are free to slide on their carriers. If they seize on the sliding pins then the brakes can feel spongy.

How old are the seals in the calipers?

All the best

Keith
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[smithyithy]

Don't know how old the seals are, I've never had the callipers off before, as I say it's only more recently the front has been like this..

I made GIF's of the CBR lever / rubber compared to the Daytona, sorry if they take a bit to load, I did try to reduce the frames per second...

https://farm6.staticflickr.com/5485/14490288952_a2fe6fda02_o.gif

https://farm4.staticflickr.com/3884/14488132471_24246d0252_o.gif

https://farm6.staticflickr.com/5515/14491503445_84a5a9f558_o.gif

[moonzoomer]

[smithyithy]

As far as I know, everything is original, expect pads obviously which have been changed incrementally.

This will become my track bike as soon as I get the 675 on the road, so it'll be having full brake overhaul and everything else serviced, upgraded or properly setup..

Ideally I just need it to tide me over for a 2/3 weeks.. Does that rubber piece look excessively worn? If so I can get a replacement ordered first and foremost..

[moonzoomer]

[Kickstart]

[Itchy]

Bleed the brakes properly?

While you will get massive bubbles to start with, they will decrease in size until they are fizzly drinks bubble size, even then leave it over night with a belt around the brake lever.
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[moonzoomer]

Does your bike have 2 brake lines connected to the master cylinder or just one? If you only have one brake line then there should be a connector which joins the 2 brake lines from each brake caliper, so try bleeding the brakes at this joint as the air bubbles will be rising to the highest point which is this union. The brake line union is usually located around the bottom steering yoke.

[smithyithy]

Yeah the 2 brake lines join then meet the master cylinder as 1.

I've got another day off tomorrow so I'll get the callipers off and inspect everything.

Cheers.

[gavcarter]

check discs for a lip - I went back and forth on this for ages after fitting new pads only to find I had worn discs lol