CBF125 DIY didn't go well - Front brake doesn't work

[Snop Doog]

Earlier I attempted to change my front brake's pads and it has gone very wrong. I did manage to change them successfully but now my front brake barely works; the lever must be pulled all the way in for any useful braking force to occur.

The fluid level is about 90% high with a little air bubble representing the 10%

I did pump the lever a few times (maybe 20/a million?) but it hasn't made any difference.

My local bike shop is about 5 minutes from me so tomorrow morning it looks like I'll be doing a suicidal ride using the engine and the rear brake to slow down...

I assume this is a common noob error and I'd just like to find out what I messed up on and how I can avoid it in the future.

Thanks

Edit: Seems like they need bleeding...

[Robby]

Did you do anything to get air in the system - like opening the bleed nipple - during the pad change?

If not, they probably just need pumping back into contact. Get a cup of tea and go and pump the brake lever while you drink it. It should firm up fairly quickly.

If you did get air in there, same process, but expect to pump it for 15 minutes.

[Snop Doog]

[Robby]

You don't need to worry about air then. You've pushed the pistons back in. You need to pump them back out after fitting new pads to get the pads back in contact with the disk.

If pumping the brake lever doesn't push the pads back in line, then it could be that the sliding pin is worn and the pads are stuck at an angle. If the sliding pins are worn, replace them.

[Snop Doog]

[Ariel Badger]

it is worth bleeding them imho,sounds like air
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[Snop Doog]

[Snod Blatter]

I would guess you have emptied the master cylinder reservoir when pumping the pistons out, and sucked some air into it. When pumping the lever try doing so at full left lock, this puts the master cylinder at a slope and the bubbles can find their way out by rising upwards. Tapping it all with the handle of a screwdriver or something can help, too.

This may be too late though, hope you didn't die??
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[Snop Doog]

Got it sorted today - £20

Turned out I hadn't cleaned the pistons & slider pins enough. The slider pins had seized too.

I don't think I'll be touching the brakes again myself anyway, far too dangerous.

[Robby]

Just learn to do the job properly.

Typically you can only get away with just a pad change two out of three times. Often you will also need to do one or more or the following:

1. Clean all sliding pins, properly clean the caliper.
2. Replace sliding pins.
3. Clean piston (basic clean).
4. Remove piston and seals, scrape out corrosion, remove some corrosion from piston with a finishing pad or light emery paper.
5. Replace piston and seals.

If I'm doing my first brake job on a new to me bike, the caliper will get the works - strip down, remove seals, scrape out corrosion, smooth down piston, new sliding pins, reassemble with new grease in some places and new brake fluid.

Learn to do the full job, then you'll know what needs doing next time you change the pads. Replacing the pads and sliding pins, doing a full clean and replacing the brake fluid is still cheaper than taking it to a shop just to get the pads changed.

[skatefreak]

Hey there.
You just got unlucky.
I've done pads/brake bleeds/rebuilds etc on 125's & 600's and the first few were pretty straightforward/not much to get caught out on.

Its the first step, confidence and learning how to approach a job is as important as experience with that exact part.

It will take time to build experience to be able to deduce how things work/interact and then things will become easier.

Until then, I'd say try to find a service manual for said bike and get some good spanners.

Maintenance can be very therapeutic, save you plenty of cash, a I for one have more confidence hammering around on a bike I know I've had apart and put back together well.
Sounds a bit paranoid I know but *shrugs*.

There is always lots of people here willing to cast their eyes over problems, pictures help a lot as well!

Best regards

[misscrabstick]

It's a horrible possibility that the master cylinder seals decided to fail when you pumped the lever for the first time, the travel of the piston in the cylinder is much longer than usual because the system is trying to get the caliper pistons out against the pads and discs to obtain pressure, this extra travel can knacker the seals, sometimes they tear sometimes they scrape on a bit of rust in a seldom used part of the cylinders bore.

This has happened to me, not often, but had it last year on a rear master cylinder on a Beta Trials bike, Cure is a rebuild kit or a new cylinder.

Also had it happen on cars quite a few times over the years.

[Rogerborg]

[c_dug]

Shame you couldn't have waited a couple of days, looks like I'm a couple of miles from you at most and I'm not too shabby with brakes.
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