brake bleeding troubles

violent_keith

Hi I recently decided to bleed my brakes,started with the front and never got to the rear,i followed a video to the letter,a very simple video which i'll leave a link to,but even though iv'e done everything the guy did, twice, my front disc slips through the traction of the pads when i pull it.
I had no air bubbles in the mineral oil after i fed it through the brake cable.
The pads grip but then squeak as the disc slips through and they do clamp tight until there's enough force then it just slips and squeaks. This is my first bleed ever so its quite possible i could have got oil on the pads and disc but thought i'd check here before replacing them or buying isopropyl alcohol to see if it sounds like iv'e just messed up the bleed. Not used to working on bikes so any help would be appreciated.

https://www.youtube.com/watch?v=cS0pBCBT65g

veronese68

If it needs a bleed the lever will be soft and squishy. If you have a firm lever and poor braking it is not the bleed and it is probably contamination. Too late now, but when bleeding it is best to remove the wheel and the pads and use a bleed block so you cannot contaminate anything.

violent_keith

Ok thanks,just been and checked and the front brake lever feels just the same as the rear when i pull it and there's nothing wrong with the rear so i'll invest in some new pads and alcohol and clean the caliper down and the disc and see what happens,will the alcohol clean the disc or will i need a new one? Thanks for the quick reply

veronese68

Disc will clean up fine with IPA. Pads are not so easy, people talk about sanding them or heating them but new is best.
Unlike car or motorcycle brakes, bicycle discs are very sensitive to contamination as they can't burn off anything that shouldn't be there.

uncyclist

Veronese68 wrote:

Disc will clean up fine with IPA. Pads are not so easy, people talk about sanding them or heating them but new is best.
Unlike car or motorcycle brakes, bicycle discs are very sensitive to contamination as they can't burn off anything that shouldn't be there.

Is that because they don't [usually] get hot enough?

veronese68

Usually being the important bit there. I think if they get anything even slightly oily on them they don’t work well enough to generate any heat. If you had a long enough downhill run and the balls to try it you might get them hot enough. I certainly wouldn’t recommend it.
Car brakes have much more weight to stop and are obviously much more powerful so can cope with some contamination. Also car discs are cast iron and will rust very quickly. That’s why car brake cleaners have a light oil content. Although even car brakes can’t cope with a lot of oil.

bobbydigital

Some people, they say putting washing up liquid on a pad then rubbing it against the other pad will clean them up.
Obviously rinse and dry.

I've done it for brakes I've sold but never tried using this method on my own brakes (I did tell the buyers to buy new pads and that mine could be contaminated) but it's worth a shot. The pads always came up very clean afterwards.

I don't know why but I always have issues with hydraulic brakes squealing and not stopping very well, only good set were my avid elixirs 1 and they were crap to bleed but would be solid for 6 months and performed well enough for me, so now I run semi metal pads in my brakes and it seems to be a lot better.

cooldad

Pads are porous, so cleaning them is pointless. Just replace, cheap, and probably safer.

The Rookie

I agree with CD, but while waiting for new pads have had some success by soaking them for 24 hours in alcohol and then putting them in the oven on Max for about 30 minutes, not perfect but at least usable, I then mark the back of the pads and keep them as spares.

cooldad

I always have a spare set or two lying around. Learnt my lesson on a muddy trip to Wales getting gouged £40 for a set from a bike shop.