Terrible brakes

The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

Picked up my first bike in nearly 5 years today. Great fun on the ride home except overshooting a roundabout a bit. The front brake is terrible. Not really spongy, just terrible.

Am I right in thinking:

Spongy lever = air in the system
Kind of spongy but requires a lot of force to operate = Bad pads/disc?

Any quick things I can try to determine what is the issue?

Beehive Bedlam · World Chat Champion Joined: 28 Oct 2013 Karma :

How much meat is left on the pads?

Also what bike are we talking about?

Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

First check the lever & pivot.
Could be the pivot pin is rusty, or the pin done up too tight.
Also not unknown for the pivot tangs on the master-cyl casting to get dinged and pinch the blade.
Some after-market lever-blades can also be very dire & may have 'cam' that presses on the end of the cylinder that is peculiar.

Next suspect would be the calliper; what state are the pistons in? Are they sticking? If a floating calliper, is the calliper seized on the float pins or sticking.

Drop the calliper & clean

Pull the pads, look for uneven wear - one pad may be down to the backing, opposite not, indicates sticking piston/float

Replace the pads as a matter of course while you're in there.

They could be bad pads, or contaminated or cooked... but basic 'service' aught to sort it.

Probably worth flushing through new fluid & bleeding whilst you are about it.
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The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

Andy_Pagin · World Chat Champion Joined: 08 Nov 2010 Karma :

Personally I'd start with a new set of pads, since it's cheap and easy. If that doesn't help then service the caliper and change the brake fluid which again should be relatively easy on that bike.
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Beehive Bedlam · World Chat Champion Joined: 28 Oct 2013 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Could be a few things. Is it a standard master cylinder (larger bore will make the brakes need more pressure and feel rather dead)? Has the caliper seized on the pins it slides on? Are the pads rubbish?

All the best

Katy
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talkToTheHat · World Chat Champion Joined: 21 Feb 2012 Karma :

Simplest things first: give the disk and pads a clean with come brake cleaner. Buy from a car spares place for about £3, spray liberallly, wipe with clean shop towel (kitchen paper just about works) could just have got a little greasy or a lazy valet could have got wax/soap/sillicone/teflon on your friction surfaces.

If bike is old, your brake lines could be on their way out. manufacturers advise replacing after 4 years. But clean disks, check/replace pads (avoid bargain basement pads), flush old system with new fluid and service calipers if required first. I think i'd describe old brake lines as more vague than anything else, particularly the rear on my bandit which either on or off somewhere across the long pedal travel.
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Howling TerrorOutOfOffice · Super Spammer Joined: 05 Dec 2008 Karma :

Even simpler. Some good firm on-off-on-off braking. Really get those discs hot. So best do it on a quiet carriageway.
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The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

I took the calliper off, the pads looked OK but I cleaned them up with brake cleaner and same for the disc. They are single pot type with a slider. I took the slider out and lubed it all up with copper slip, same with the back of the pads. I pumped the piston out, gave it a wipe and pushed it back in. I had to use a g clamp to push it back in but I think this is fairly normal. It wasn't stuck, I just couldn't do it by hand.

It has made a slight improvement but still not as good as I think it should be. Maybe the pads are impregnated with oil or grease or something.

I don't think this issue is air/lines/fluid related as that would just make them spongy. If I apply as much force as I can on the lever then it should apply a good braking force, regardless of how much travel the lever has.

Islander · World Chat Champion Joined: 05 Aug 2012 Karma :

Copper slip is an anti-seize compound and could attack the rubber boots on the sliders. It's not intended to be a lubricant as such. I always use a rubber friendly lubircant like silicon or red rubber grease on these.

Were the sliders working freely when you checked them?

You may have some corrosion behind the seal if the piston isn't moving freely - thumb pressure is usually enough to get them moving.

The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

rubyhorse2 · Traffic Copper Joined: 03 Mar 2015 Karma :

just bleed them and see if that sorts it. Surely if pads are ok and the piston is moving fine then its something simple as air in the line.

Islander · World Chat Champion Joined: 05 Aug 2012 Karma :

The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

weasley · World Chat Champion Joined: 16 Oct 2010 Karma :

Maybe the disc is glazed? I had a KDX 125 with an awful front brake until I roughed-up the pads and disc with some emery paper and did a few hard stops.
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The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

rubyhorse2 · Traffic Copper Joined: 03 Mar 2015 Karma :

tom_e · Brolly Dolly Joined: 27 Feb 2016 Karma :

Don't forget at the end of the day this is a single piston caliper fitted to a 125 built to a budget, it's never going to stop the world.

Tdibs · Traffic Copper Joined: 16 Jan 2015 Karma :

Was going to say, Dont expect miracles from a single pot disc and fairly small drum. Is the rear brake alright? Are you using brakes in conjunction?
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The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

Front single pot disc. I know not to expect it to stop on a dime but there is definitely something not right with it.

Cheers for the halp. Thumbs Up

The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

https://i.imgur.com/qM0sBbw.jpg

https://i.imgur.com/Vjydx3G.jpg

https://i.imgur.com/HUZeHkb.jpg

When I took the seals out, they were pretty shagged. There were very thin slices of rubber sitting behind the piston. It wasn't leaking before as far as I can tell but I have cleaned the caliper up as best I can and reassembled with new seals and new pads. Haven't had a chance to test but will do tomorrow morning.

New brake fluid as well to satisfy rubyhorse2 Laughing