I've decided to get back on my mountain bike again after a few years on the roadie. Took the bike out at the weekend, and found half way round my 1 hour loop, the the bite point was moving further and further (they are Deore M615 so non adjustable). It was still solid, but moving closer to the bars each time I braked.
I got home and bled the brake bottom up, it took probably 30ml before any came out of the lever, so I've lost some fluid I think.
But how?! I took them apart, everything is dry, and the brake wasn't howling (so no oil on pads?), no drips on the shed floor, nothing in the back of the car. I don't understand!
The brakes are barely used as I replaced them not long before retiring the bike. Is it worth further investigation or should I just replace them?
Split in hose? Any internal routing?
This is not the infamous 2 part caliper/leaky transfer port/O ring palaver is it? It can be often difficult to tell when you have leaky transfer port O rings but the symptoms are similar. You can get replacements on FleaBay and the repair is very simple.
Is this a bike that's been sat in the shed for months without use? I can always get some air out of my old Zees when the bike with them on has been left hung up unused for a long time. I just do a lever bleed with the funnel. Plenty of places for some slow seepage with some old Shimano I'm afraid. Lever just as likely as the caliper.
Split in hose? Any internal routing?
Hmm I didn't consider the hose actually! It actually quite possible the hose could be damaged as the kids have been dumping their bikes against it.
This is not the infamous 2 part caliper/leaky transfer port/O ring palaver is it? It can be often difficult to tell when you have leaky transfer port O rings but the symptoms are similar. You can get replacements on FleaBay and the repair is very simple.
Would that result in fluid leaking externally or is it 'lost' inside the caliper?
Is this a bike that's been sat in the shed for months without use? I can always get some air out of my old Zees when the bike with them on has been left hung up unused for a long time. I just do a lever bleed with the funnel. Plenty of places for some slow seepage with some old Shimano I'm afraid. Lever just as likely as the caliper.
Yeah it's been sitting for a while 😳 When you do that bleed is that lever downwards you mean? Or calliper upwards with the funnel to catch the oil?
Lever at top. Not opening the caliper end at all. Knock things about to get bubbles up to the lever. By funnel I mean...
https://www.ebay.co.uk/itm/115437011280
Your way probably best to get all the air out, but a lever only bleed is quick and easy... which if you find you're doing it more than once a year makes it less painful.
Had exactly the same. Bled the brake and it failed very shortly after at the lever. Assume something inside has perished and the fluid has been lost internally. Opposite side did the same 6 months later.
also had the leaky calliper on another set. Was minor for lever throw but by god did the brakes not work/ squeal with contamination.
Had exactly the same. Bled the brake and it failed very shortly after at the lever. Assume something inside has perished and the fluid has been lost internally. Opposite side did the same 6 months later.
also had the leaky calliper on another set. Was minor for lever throw but by god did the brakes not work/ squeal with contamination.
Yeah this is what I was worried about. It would make sense with the symptoms.
I've got some fluid on the way, so I may as well do a complete bleed on both. I assume if something is perished, the problem with show up again fairly quickly.
Lever at top. Not opening the caliper end at all. Knock things about to get bubbles up to the lever. By funnel I mean...
https://www.ebay.co.uk/itm/115437011280
Your way probably best to get all the air out, but a lever only bleed is quick and easy... which if you find you're doing it more than once a year makes it less painful.
Understood! Not considered that before!
I got a set of XTs out of a box after 4 or 5 years, they'd gone in working perfectly. The front came out empty. The inside of the box had a few greasy stains, but nothing like the 30 ish ml that was in the system to start with. The rear was still full. Bled both fully and they continued to work for another 3 years until someone (not me) decided that they needed to be "serviced" and destroyed them.
Also had the same with a set of Hopes, but the back had managed to all but empty itself over the 5-6 years they'd been out of service. Still working now after a bleed, Hope Mono M4, bought about 6 months after they were launched. So now 20 years old i think. No sign of anything in the box.
Still no idea where the oil went...
So what we're saying is that disc brakes are actually portals to another dimension, and if you don't use them for a bit the oil gets bored and migrates to the other dimension?
No, just Shimano ones. And it's not usually another dimension the fluid travels to, it's your pads and discs
I think with the issue I raised; leaky transfer ports, the oil can contaminate the pads and discs but it then tends to burn off ('dissappear') when the brakes are in use. It's often difficult to tell you have this issue and I've heard people sprinkle talc etc on their brakes overnight as a telltale for any leakage.
So what we're saying is that disc brakes are actually portals to another dimension, and if you don't use them for a bit the oil gets bored and migrates to the other dimension?
Not sure if it helps? but I took a picture of the rear caliper:
