Do I need to bleed my brake? Disc brake newbie..

Bike Forum

Do I need to bleed my brake? Disc brake newbie..

18 posts & 9 voices | Started 4 months ago by dawson | Latest reply from perthmtb

Tags:

No tags yet.

dawson - Member

Hi,

I got a new bike which has Shimano hydraulic disc brakes - the front brake has a nice amount of power, but the rear does virtually nothing.

I really have to pull hard on the lever, it makes a massive squarking noise, and barely has any effect on slowing the bike. I have had several attempts at getting heating into the pads by really squeezing the lever on a steep hill, but it didn't make any difference.

I don't think its dirty/contaminated rotors as I haven't used any cleaning products/lube on the bike yet.

Is it worth swapping the pads from the front to rule out 'bad' pads? (if there is such a thing)

Unfortunately, I didn't buy it from a LBS (I know, I know, else I would have taken it back for them to check!)

Posted 4 months ago #
smell_it - Member

Try some new pads, even if it doesn't sort it you will till have some spare pads for future use. If unresolved bleed the brake. I'll let everyone else keep telling you to take it back or to an lbs.

Posted 4 months ago #
B.A.Nana - Member

a better test might be to swap pads and rotors around. if the problem switches to the front, you know it's def a pad/rotor issue. if the issue is still at the back, then def a rear brake system issue.

Posted 4 months ago #
TandemJeremy - Member

Does the lever come back to the bar or feel softer than the other one? thats air in the system usually

Waht you describe sounds like contaminated brakes for sure

Swapping pads and rotors risks spreading the contamination.

I would remove the pads and sand the surface and give the disc a scrub with detergent and try again

Posted 4 months ago #
dawson - Member

ahh, so would it be better to keep the pads 'paired' to the rotors now that they have been used with a particular rotor?

Is there any way of swapping the bent split pin that is used for holding the pads in for something more straight-forward or is that the normal method of holding the pads in place? (Shimano M445)

Edit:TJ posted while I was typing...

Posted 4 months ago #
dawson - Member

I'll get some pads ordered, but in the meantime I'll try cleaning rotors and sanding pads.

Failing that, it will be a baptism of fire on bleeding brakes - could do with getting it sorted, as I need it for HtN!

Posted 4 months ago #
TandemJeremy - Member

Unless the lever is soft it doe not need bleeding.

Posted 4 months ago #
B.A.Nana - Member

ahh, so would it be better to keep the pads 'paired' to the rotors now that they have been used with a particular rotor?

That's not what I was meaning, swapping around pads to different rotors isn't an issue normally. I was trying to suggest how you could narrow down what your issue is. ie if you just swapped pads over and the rear rotor has some oil on it, then the result will be both pads and rotors become contaminated and you're still not really exactly sure what the problem is. my suggestion would at least tell you for sure whether it was rear brake system or pad/rotor problem.
in most cases rotors are easy to remove with allan key, splinned rotors or nuts with star head need special tools

Posted 4 months ago #
perthmtb - Member

I got a new bike which has Shimano hydraulic disc brakes - the front brake has a nice amount of power, but the rear does virtually nothing

Could it just be the rear hasn't bedded in yet? I've had two new bikes in the last six months with the M445 brakes, and while the front on each has bedded itself in, the rear has needed a little help - cycling up a hill numerous times and hodling the rear brake on all the way down. For a long debate on what bedding-in brakes is all about, see Previous Thread

Would suggest just trying this before removing & scrubbing pads or switching things around - you've nothing to lose!

I agree with TJ that the symptoms you describe do not suggest the need for a bleed.

Edit: Ok just re-read your original post, and seen that you've already tried the hill/bed-in thing

Posted 4 months ago #
Rockhopper - Member

Most likley oil on the rear disk from lubing the chain.

Posted 4 months ago #
ahwiles - Member

I got a new bike which has Shimano hydraulic disc brakes - the front brake has a nice amount of power, but the rear does virtually nothing.

I don't think its dirty/contaminated rotors as I haven't used any cleaning products/lube on the bike yet.

what about before you got it?

sounds to me like someone gave the chain a good dose of spray-lube...

clean the disc with boiling water (from the kettle - pour it all over).

swap the pads (front/back) to confirm, then fit some new pads.

Posted 4 months ago #
dawson - Member

Thanks for the further suggestions.

The chain had just got 'factory grease'- you know the type of lube that only comes on a new chain?

Thinking about it some more, the brake lever doesn't have the same feel as the front brake... so it might need bleeding after all.

I am reluctant to try swapping the front pads for the rear pads, becuase if the rears are contaminated then I'll spread it to the front.

Current plan of attack is to clean the exisiting rotor and sand the pads, I'll get some new pads on order, and I've been looking at some bleed kits on ebay.

Posted 4 months ago #
perthmtb - Member

I'll get some new pads on order, and I've been looking at some bleed kits on ebay.

I've just recently replaced pads and bled a set of M445's. You'll need Shimano B01S resin pads, like these B01S Pads, a shimano bleed kit like this Bleed kit, and a yellow bleed spacer like this Bleed block

Posted 4 months ago #
dawson - Member

@perthmtb - thanks for the links - not sure the bleed spacer is necessary though?

The Park tools page shows the use of a 10mm allen key if you don't have a spacer - http://www.parktool.com/blog/repair-help/shimano-r-hydraulic-brake-service-and-adjustment

this is the bleed kit I've seen - http://www.ebay.co.uk/itm/Epic-Shimano-Brake-Bleed-Kit-Deore-Saint-XT-SLX-XTR-Genuine-Mineral-Oil-/180785723605?pt=UK_Spots_Leisure_Cycling_Tools_RepairKits&hash=item2a17ab38d5

Posted 4 months ago #
Harry_the_Spider - Member

Failing that, it will be a baptism of fire on bleeding brakes - could do with getting it sorted, as I need it for HtN!

Finishing HtN without brakes is not unusual, starting it without them will get you a prize... should you survive.

Posted 4 months ago #
julianwilson - Member

10mm allen key is fine as a spacer, better if you use a rubber band to make sure it stays across the middle of the pistons (possibility they can try and creep 'around' it if the allen key is all the way over to one side.

That epic bleed solutions kit looks fine vfm if you don't have some washer tube and mineral brake fluid to blag off a mate. (you hardly need any!). I would buy the avid one if I hadn't spent £35 on one a few years ago when no one did the brass end thingies

Split pins don't look too pretty and are a faff to change on the trail, but I have never known one fall out (I guess you have to splay the ends out a bit of course), and you don't have the worry of either knackering the thread in the capiler body or spending silly money on a replacement pin if you lose or thread that. In my trail pack I used to carry a tiny leatherman-alike tool from a pound shop with some tiny needle-nose pliers for changing the pads mid-ride.

Posted 4 months ago #
dawson - Member

@julianwilson - pound shop for a cheap leatherman-like tool sounds like a plan! Didn't fancy carrying fully size pliers in my pack.

@Harry - I might bear that in mind if I don't get it fixed.

Posted 4 months ago #
perthmtb - Member

not sure the bleed spacer is necessary though?

You're right, just about anything you can jam in there that keeps the pistons from extending while you pump the levers will do. However, I had a bad experience a few weeks back using a clothes peg, which twisted under the force of the pistons, one of the pistons pushed right out, mineral oil everywhere, and lots of air in the system!

So, for a few quid I decided it was better to get the proper Shimano block, which is exactly the right size, uncompressable, and is held in place by the same split pin that holds the pads - no need for lacky bands!

That bleed kit looks fine - all you really need is the mineral oil, some tube of the right size, and a container to catch the oil. Syringe is necessary if you do the 'bleed from bottom' technique, but I've only done the 'bleed from top' meself...

As for the split pins - never had a problenm with them, they do the job! Just straighten with needle nosed pliers to get them out, and bend with same after re-fitting. Shimano pads sets come with a new split pin if you manage to mangle/lose the original.

Posted 4 months ago #

RSS feed for this topic

Reply

You must log in to post.

Singletrack Mountain Bike Magazine

Bike Forum

Do I need to bleed my brake? Disc brake newbie..

Reply

Don't miss…

Singletrack

Website & Forums

Exits