[Closed] Rear brake sounds like a choo choo train and barely stops the bike

Dunno, but I'd be chuffing cross if that was my bike

Clean the disc with IPA, sand disc to roughen it up, put new pads in.

It could be leaky seals contaminating the pads, although I'd expect squealing not chuffing.

Get some speed up to try and bed the pads in, contrary to some people's opinion this won't magically transform your pads from cheese that wears out in 5 minutes to the hardest material not even discovered by man yet which will last forever, however it will get the power up after a few stops (hopefully). You need to get a bit of heat in, so go up to 20mph or so, but it doesn't need to be red/smoky hot.

You have covered the likely causes. I've had an issue with Shimano brakes in the past when they were stored for quite a few months without use. The seals can dry out and degrade causing a very slow leak of brake fluid, that constantly contaminates your pads and discs. It is minor enough to be scrubbed off during a ride or by cleaning discs/pads, but the contamination will always come back eventually. Symptoms are as you describe. Solution is a new caliper (new brake basically if Shimano). AFAIK Shimano do not supply user replacement seals. Good job they are so cheap, and otherwise very reliable.

Alignment?

I would suggest the alignment is out slightly. Possibly it has slipped fractionally while you were riding. How tight are the bolts?

Leaking caliper, I've just had the same. Replaced caliper, all good now

Cheers angel and woody... im almost certain you are both correct.

Thanks a million and i think you will have save what little hair i have left. My last maybe 10 rides have been ruined by this so im looking forward to enjoying things again

Are the calipers pretty universal? I was looking at the xt 785?

The current caliper is low spec shimano... i can post a picture or the model if that helps

You'll probably find the 785 has a different (banjo type) fitting to yours, so unless you swap hoses, it's a non starter. Personal (3 calipers in a 2 yr period), and shop experience say that the cheaper Deore and Alivio calipers seem far more reliable.

Thanks.
Ok now im considering buying the full system with lever and hoses

Can i use the slx which are pictured with a centre lock disk? My disks use 6 bolts

Cheers
Christian

The full system generally comes without discs and mounts unless specified, but your old ones will work fine, just be sure you thoroughly degrease them first, and a scuffing with 180 grit wet-or-dry will provide a good key for the new pads to bed in to.

The current caliper is low spec shimano... i can post a picture or the model if that helps

A new calliper won't be much more than the price of a set of pads and will also come with new pads. They're easily available, and easy to change. . Pop a picture up and I'll see if I can find you the part number. 🙂

decided to go with one of these as TBH my levers have seen better days anyway

"Shimano XT M785 Hydraulic Disc Brake - Ispec B Compatible"

https://www.evanscycles.com/shimano-xt-m785-hydraulic-disc-brake-ispec-b-compatible-EV191867

If it doesn't work I can always return it

Clean the disc with IPA

Rumour has it that the sintered pads are less prone to contamination through this slight leakage than resin. Less absorbent or something.