straightdraw84

The rear brake barely squeezes, is it the pads that need replacement?

Thanks

Pics:
h**ps://i.imgur.com/VFtgWhn.jpg
h**ps://i.imgur.com/VFtgWhn.jpg
h**ps://i.imgur.com/5bkGGcw.jpg

Andrew R Stewart 

Sorry but my poor keyboard skills can't pull up any images so... By "barely squeezes" do you mean that the caliper doesn't move much when the lever is pulled? Or the caliper moves in unison w/ the lever but once the pads contact the rim there's no grip on the rim to slow it down? Or the lever can be pulled so far it contacts the bars before any slowing happens? Or...? Have you looked closely at the condition of the pads? Are they glazed, contaminated/grimy, worn thin, unevenly worn? How about the cable and casing condition? Any rust, kinks, fraying? Since I don't even know what type of brakes you have this is all I can offer for now. Andy

adamrice 

These are hydraulic disc brakes. Based on your description, my first thought is that there's air in the hydraulic lines. If you find that pumping the brakes repeatedly helps pressurize the lines, that's a sign of air in the lines. Re-bleeding the lines is not for the faint of heart—it can be done at home with the right tools, but it's easy to make things worse. I'd take it to a shop.

It's probably not the pads, although you might need to change them too. It's not hard to pull the pads and check (video below). Be careful not to get any oils, including sweat, on the pads. And I'd clean the disc rotors with rubbing alcohol.

straightdraw84

Hi, all you have to do is change the "**" with "tt" and the links will work: h**ps://i.imgur.com/5bkGGcw.jpg

Cheers!

cb400bill

Pic Assist

cb400bill

straightdraw84

Thanks dude, the model is Shimano Deore XT BR-M785

Iride01 

Looks like a fairly new bike. Take it back to the shop you got it at and maybe they'll show you how to bleed the brakes or at least let you watch. New bikes need to go back to the shop for a checkup and adjustment within the first 3 to 6 months anyhow. Many times it's free.

If they do that then buy the little funnel, a bottle of brake fluid and anything else needed for those particular brakes and consider it your cost of education.

jimc101

Unlikely, M785's came out in 2012, so almost 10 years old now, the rotors look pretty worn out (hard to tell from the photo how worn), maybe time for replacement, no images of the pads, so they could be worn out, 10 year old fluids, maybe could do with a change/general service!

Realistically, if you can't easily ID the issue with the bike in front of you; a few photos of only a few bits won't help too much, one for a bike shop that is competent in servicing brakes if you can't bleed them yourself.

Iride01 

Should the banjo fitting on the hydraulic line been a clue for me? I was looking at that as I hadn't seen one in a while.

Any how, the same advice still holds up. But likely won't be free. So the OP should just go to any LBS they trust the mechanic at. And if the mechanic will let them watch, all the better if the OP wants to learn for future DIY.

On an older bike the OP should be worried that they let the pads get too worn and now the piston is too far out and maybe even a little cockeyed and maybe scoring the cylinder. As well once the pad material wears through, the chance of messing up that rotor is greater. So trying to save a dollar by running pads beyond the mfrs recommendation might cost quite a few dollars.

So if the OP doesn't already... they need to learn how to check the pads every so often. Calipers that are good enough for this purpose can be bought for less than 10 dollars.

straightdraw84

Sorry for the late reply, I took out the brake pads:
h**ps://imgur.com/a/z472a01

They're 2mm thick just like the front ones (but the front ones brake perfect)


I do have this grime on the rotors:
h**ps://imgur.com/a/b3ad6d8

I've tried go gone, windex, rubbing alcohol, no luck getting it off.

Iride01 

You only measure the pad thickness. Not the pad and plate they are mounted too. Are you sure the pad is 2 mm?

Pads look like they got badly oil soaked or something. And that is what is building up on the rotor. I might as a last ditch effort soak them in mineral spirits for a while and see if anything leaches out of them. And clean that rotor.... or is the discoloration burned on? Maybe some carburetor cleaner then. Which might also clean those pads.

But if you have to spend money to get all that stuff to clean the pads, then you may as well just get new pads.

https://imgur.com/a/b3ad6d8


https://imgur.com/a/b3ad6d8

Iride01 

I just went out and measured the backing plate on my pads. They are 1.9 mm. So if your measurment included the backing plate then your pads are only about .1 or .2 mm thick.

So you are probably pushing brake fluid out every time you brake and that is what is on the pads and rotor. You need to get new pads and hope the pistons and their seals haven't gotten damaged from being pushed too far out of the brake cylinder.

Maybe let a mechanic at a shop do this for you since hopefully he'll not just push the pistons back in and hope for the best. You may have cost yourself more money than just pads.

straightdraw84

Hi, I measured the pad thickness only, the brown area in the picture here:

h**ps://bikeco.com/wp-content/uploads/2018/11/11-12-18-Magura-Shimano-SRAM-Brake-Pad-Wear-Limits-1024x578.jpg

It was 2mm like the front. (which work fine)

straightdraw84

Anyone?

hokiefyd 

You've been given some great advice regarding a brake bleed. If the problem is a lack of brake pad movement or pressure on the rear rotor (and a glazed brake rotor would support that), then there's likely air in the line that needs to be bled out. Any bike shop should be able to perform this service. You can also find several videos on YouTube that show that process for Shimano brakes.