Fake51

I have an ebike that I just replaced the front calliper on, but it's not braking as well as I expect. The new calliper is a Shimano MT500.

What I did was:

• Took the wheel off
• Took off the old calliper but kept the hose and lever in place
• Cleaned the rotor with brake cleaner then wiped it down
• Installed the new calliper, put the wheel back in place
• Bled the calliper

I had a test run on the bike, and while the brake works, it doesn't brake super well. After driving on it, i tried using the brake when the bike is standing still - no matter how hard I press on the front brake, I can still move the front wheel (only forwards though - if I try backwards the brake stops the wheel). Also, the brake squeals when I engage it - not at first but as the bike slows down.
My rear brake on the other hand, also Shimano, brakes much harder - when I engage that brake, it can lock the wheel.
Is it just a question of breaking the brake in, so to speak? Or is it something else that is wrong?

FBinNY 

Do a search for bedding bicycle disc brakes. Follow the steps involved and see if that helps, before looking for other possible issues.

cxwrench

Sounds like you didn't bleed it properly. Impossible to say without seeing it in person though.

Koyote

It might also help if you tell us why you replaced the caliper; it may be that you have a problem elsewhere in the system, and replacing the caliper didn't address it.

FBinNY 

Not disputing the importance of bleeding. But the problem isn't consistent with air in the line

Bleeding causes excess lever travel and a spongy feel, as the air bubbles compress. But unless that allows the lever to reach the end of its travel range, the actual stopping power is unaffected, because pressure in always equals pressure out.

Fake51

Good point - I replaced the calipers because the front brake wasn't working, and the rotor was getting oily. I had tried to completely clean the rotor and use new discs for the calipers, but it got oily again and there was very little friction. So my best guess at cause was broken pistons

Fake51

Could be the case, but as the other reply points out, i don't have a problem with travel in the lever

Fake51

Thanks I'll do that!

Iride01 

Was the old caliper a BR-MT500?

What diameter are the disc's front and back?

Fake51

No, the old calliper was BR-T615. Couldn't find that anywhere, and BR-MT500 seemed a reasonable substitute - but that probably just shows my ignorance.

I'll update with rotor size when I have a chance to measure later today.

Thanks

Iride01 

Is this an e-bike you just bought within the last year or two? If so I'd really recommend going to the dealer you bought it from and exhaust everything you can get them to do first. E-bikes tend to be very heavy and things like brakes and drivetrain just see way more demands put on them and some regular bike components used on e-bikes might not be up for the demands. Might be some warranty or good graces the shop will do for you to fix this.

You BR-MT500 is probably a good choice. If you have a 180mm rotor on the front then that is the max spec'd for that brake and a 180mm should give more braking power than the smaller 160mm which might be on your rear.

If the front brake has never worked well with either calipers for you then probably something is up besides what you've been concentrating your efforts on. So another reason IMO to let someone else get eyes on it.

Fake51

Sadly it's no longer under warranty. But I'm close to taking it to a mechanic.

Thanks, good to know.

The thing is the front brake did work ok when I bought it, three and half years ago. Then it started losing pressure in the lever - i tried bleeding it, but it just got worse, and it became clear oil was leaking. So I'm trying to replace the calliper now, as oil is leaking onto the rotor, and I can only see this happening from inside the brake

Iride01 

Is the new caliper leaking too?

If it's just that you don't think you are not getting good braking from it, then maybe you've been dinking with it too much and not letting it bed itself in. My disc brakes weren't so great on my new bike, but after about 300 miles they became almost too good at braking.

Fake51

Ah sorry, wasnt being clear. No, the new calliper is not leaking (yet). So hoping that working on the bedding might improve it

Canker

It isn't bedding in the brakes, that will get you the last 5% of braking not 80%. Sounds like to me you have contaminated the pads, that is where the squealing is coming from. You probably didn't get the rotor as clean as you think and contaminated the new pads. Clean the rotor again REALLY well and either replace the pads or get out a propane torch and burn the contaminates off the new pads. Heat those suckers up good and hot and if you really want to be anal sand the surface of the pad a bit. Some people don't like that method but it works and it is cheaper than replacing pads every time you accidentally get a bit of oil on them.

Fake51

Thanks, I'll have a look at that. So far I've been cleaning the rotor while attached so it's possible that didn't do it well enough.

Next problem is figuring out the proper tool to remove the rotor. I believe it's an RT-EM300 160mm center lock, but I can't see any manual specifying which tool to use for it. And Shimano had been very helpful and created a multitude of them ...

Fake51

Found the proper tool, found the actual model of the rotor, got it off, cleaned it again, applied new pads (kept the old to try fixing them later), and reassembled. Front brake now works very nice!

Thanks for the help and the hints, everyone!