Front disc brake driving me mad

[Maccuk44]

Hi guys,

I am just looking for some advice. I have a giant Defy advanced 2 2018 and the front brake disc brake just doesn't have much power especially on steeper decent. I have cleaned it with brake disc cleaner to no avail.

I am wondering if I would be better off upgrading the disc and or pads.

Can I use any 140mm 6 bolt disc? In terms of pads i assume I don't need to use giant ones? Am thinking a shimano sintered pad would work but not sure.

Any advice much appreciated.

Thanks
Paul

 

[JhnBssll]

Disc brakes need to be properly bedded in and the disc and pads clean to work properly. Cleaning the disc alone won't necessarily help if the pads are also contaminated. Replacing discs and pads is an option but I would try first sanding the disc and pads back and bedding them in again. You need to sand the disc with a medium grit until both sides are nicely scratched up and you can't see any of the circular wear pattern anymore. Then take a clean bit of sand paper and place it on a flat surface and lightly sand each pad until the shiny top surface has gone. Then take the bike out and bed them in. I tend to ride to the top of a local hill for this. You want to get some speed up and apply firm pressure to get some heat in to the pads but don't completely stop - ease off the brakes before you come to a rest. Repeat this for a while then leave the brake to cool off for a few mins and try it. It should now work normally.

If the brake is working as it should but still not powerful enough you should consider a larger diameter disc and an adapter to reposition the caliper. 140mm discs are just about the smallest available, I run 160's on the front of my road bikes.

 

[cosmicbike]

What @JhnBssll said. I just fitted a new dynamo hub wheel and disc to my commuter, even with used pads it took a week to bed in nicely. 140mm is a small disc, even my commuter has 160mm front and rear

 

[iLB]

Is the pull of the lever ok or does it feel spongy and reach the bars?

 

[JhnBssll]

Is the pull of the lever ok or does it feel spongy and reach the bars?

Good point. I'd assumed it was a) hydraulic and b) properly bled but that may not be the case

 

[iLB]

Good point. I'd assumed it was a) hydraulic and b) properly bled but that may not be the case

Looks like bike comes specced with 105 levers but an in house caliper from Giant, sometimes these things do need to be bled out of the box unfortunately.

How long have you had the bike Paul?

 

[Drago]

Clean the disc and go through the bedding in procedure. If there's the slightest doubt about lad cleanliness then replace them before doing so.

 

[SpokeyDokey]

Hi guys,

I am just looking for some advice. I have a giant Defy advanced 2 2018 and the front brake disc brake just doesn't have much power especially on steeper decent. I have cleaned it with brake disc cleaner to no avail.

I am wondering if I would be better off upgrading the disc and or pads.

Can I use any 140mm 6 bolt disc? In terms of pads i assume I don't need to use giant ones? Am thinking a shimano sintered pad would work but not sure.

Any advice much appreciated.

Thanks
Paul

Ask your dealer to take a look at it - AFAIK these giant cable actuated hydraulic brakes are a bit of a faff to set up.

Giant have a bit of a thing going on with 140mm front and rear discs on their road bikes. Nonetheless they should be adequately powerful to stop you on a steep descent.

I don't know if Shimano pads will fit - I think Tektro did the development work for Giant.

I'd leave disc changes out of it until you have had the brake set-up checked plus usual checks for pad/disc contamination.

 

[Globalti]

If the brake judders and sqwawks as the bike rolls to a stop the brake is contaminated with oil.

 

[confusedcyclist]

Once you've sanded down your discs, providing they are still true (if not, true or replace) you'll need new pads for bedding in procedure, because they come with a thin layer that transfers to the disc to smooth it off. Don't be tempted to use part worn pads or you'll have to sand down the discs again. Without doing it properly you'll get sub optimal performance and a healthy dose of disc squeal.

 

[Globalti]

I don't think this is right! Pads don't come with a layer, what happens is that some pad material transfers to the disc under hot braking. On a mountain bike frequent use doused in gritty water will take this material away.

 

[berty bassett]

i am a new comer to disc brakes and i have to say i am not all that impressed with them ! i have them on a cannondale synapse and although the front brake is brilliant , the back brake just does not work . i have taken it all to bits and cleaned with solvent set it all back together many times ( with youtubes help ) , took front one to bits and copied exactly how it goes back together . the discs have plenty left on them . set up tighter than the front brakes but still they won't even lock the wheel when unloaded . tried new cable and now just think they are more hassle than they are worth

 

[SpokeyDokey]

i am a new comer to disc brakes and i have to say i am not all that impressed with them ! i have them on a cannondale synapse and although the front brake is brilliant , the back brake just does not work . i have taken it all to bits and cleaned with solvent set it all back together many times ( with youtubes help ) , took front one to bits and copied exactly how it goes back together . the discs have plenty left on them . set up tighter than the front brakes but still they won't even lock the wheel when unloaded . tried new cable and now just think they are more hassle than they are worth

Which brake system are they. I've found that rear discs tend to lock up very (too) easily and there is a period of adjustment to get used to this when you get a new bike and/or change systems.

 

[socks0101]

I have Giant Defy 2 2019 with a Conduct SL (Brake converter system from cable to hydraulics) The Rear brake is a bit spongy does anybody know how to adjust as I can't find any useful PDF's . The only manual I have found does not mention it and does not mention how to bleed the conduct SL. (I have attached to the post). Thanks.

 

[Slick]

This

The last thing you want is unclean lads

I've met a few who.......nah, forget it.