Soft moped brake

z6vm1dobfnca3x

Hi,

I have an 02 Yamaha Aerox that has a problem with the rear brake. The bike has been laying in my shed for the last year or so, and the rear brake lever feels completely soft and the brake is completely ineffective. I imagine the problem is being caused by something simple such as air caught in the system.

I have tried bleeding the brake manually (without one of those brake bleeding kits), but I haven't had any luck.

Can anyone suggest another solution to the problem? Should I buy a brake bleeding kit?

I want to repair this problem myself as I'm getting ready to sell the bike, so I don't want to hand over my potential profits to a garage.

Thanks in advance,
Hugo.

Wossack

fluid level ok? pads look ok?

if you pump the lever does it eventually get hard (oh matron!) ?

z6vm1dobfnca3x

The fluid level is fine, I topped up the fluid in the cylinder before I started the bleeding process. The pads look fine and were working perfectly before I stopped using the bike. When I pump the lever, it's still staying completely soft.

I don't know if it helps but the cylinder isn't like the cylinder on other bikes. It's like a rectangular basin with a screw in two of the corners. When you open the screws and remove the top cover, there's a rubber lining that is also removable. The lining does not have any holes in it and it covers the bottom and sides of the cylinder. I have been removing the lining while removing the brakes. Could this be the problem?

Wossack

little picture of a typical reservoir, might help - see attached. Yours looks similar enough to that? The lining you speak of, looks sorta like '3' in the pic?


the basin is the reservoir, and is filled with fluid, the bottom of which has a little drain hole, which leads to the actual cylinder
the rubber lining, is called the diaphram, and goes on top. It should be able to concertina, so as to be able to shrink and grow as the level of fluid goes up and down in the reservoir

you can remove the top cover, and the diaphram while bleeding the brakes fine - just try and not let anything (even rain) get into the exposed fluid

Wossack

and just to clarify, the lining/diaphram is removed, and fluid poured directly the reservoir

not insulting - apologies if this is obvious

z6vm1dobfnca3x

Cheers for that info. When I'm bleeding the brakes, the fluid is coming through clear, without any air bubbles so air in the system doesn't seem to be the problem.

It might sound stupid, but do you think maybe the pads have just seized up a bit after laying in the shed for so long. Would that cause the lever to be soft?

If there's anything else you can think of that could be causing this problem, please let me know!

Thanks.

Wossack

how are you bleeding the brake at the moment?

when you say the lever is soft, is it pulling right back to the bar?

z6vm1dobfnca3x

Wossack wrote: »

how are you bleeding the brake at the moment?

when you say the lever is soft, is it pulling right back to the bar?

I'm bleeding it at the moment by opening the nipple on the brake with a spanner, pulling the lever, closing the nipple and then releasing the lever.

Yeah, when I pull the lever it goes right back to the handlebar. There's pretty much no resistance apart from the spring on the lever.

Wossack

so you're getting fluid through the system, but still cant get any pressure to build? assuming theres no leaks, or bulges in the lines etc there must be a fair bit of air still trapped in the system somewhere

bit of a pain

try taking the cap and the diaphram off, pull the lever hard as you can, and replace the cap loosely. Tie the lever to the bars with a rubber band/zip tie so its held pulled. Go round the whole system tapping on the lines, and the caliper, wiggling the lines etc etc. Hopefully give gravity a hand working the bubbles up. Can leave the bike like this overnight (with the cap just loosely on, to keep dirt out of the fluid).

In the morning then, give the lever a few pulls, and hopefully the lever will have a bit of bite to it...

otherwise, have a look into (google/youtube), bleeding from the master cylinder banjo bolt (assuming you dont have a bleed nipple on that end of the system)

Or, try and get a large capacity syringe from a chemist, and use that on the caliper nipple to draw a few reservoir fulls worth of fluid through the system

CJhaughey

I'd say your caliper/master cylinder seals are bad, Brake fluid is hygroscopic in nature, this means it attracts and absorbs moisture.
In a brake system used regularly heat drives a lot of moisture away, when its laid up it corrodes the aluminium in the caliper and behind the seals which leads failure.
If you take the caliper off and pump the lever do the pistons move out of the caliper?
If they don't move then the pistons need to be pumped out and the caliper rebuilt with new seals.
The master cylinder can also seize up.
You need to find out what has failed, the caliper or the master cylinder.

z6vm1dobfnca3x

Thanks a lot for that advice, lads!

Wossack, I'll give the elastic band on the lever trick a go now and if there's still no change by the morning, I'll do what CJ suggested!

I'll let you know how I get on.