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So I’ve just bought a Giant TCX advanced SX and I noticed the front disk brakes didn’t work very well ( after breaking in screeching and lack of power, not being able to lift the back wheel in full force braking) I took it back to the shop where they replaced them with new (different) ones. These also don’t seem to work very well and are also screeching. I am very new to disk brakes as I’ve came from a race bike with rim brakes although I have ridden disks before and been very impressed with the power. What could be causing this? (bearing in mind they are hydraulic disk brakes)

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mike the bike [1082 posts] 2 months ago
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A little more detail needed Harry, before I focus my forensic investigative powers on your problem and very likely come up with the wrong diagnosis.

 

Which model of brakes are they?

Are the noisy discs from the same manufacturer?

If you have ridden discs before you would know if there was excess travel at the lever?

Does pumping the lever improve things at all?

Is the rear brake as bad as the front?

Did the shop replace just the callipers, or the pads or the levers too?

Any signs of brake fluid leaking anywhere on the bike?

Is the fluid level OK in the reservoir?

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Itf_harry.s [2 posts] 2 months ago
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mike the bike wrote:

 

A little more detail needed Harry, before I focus my forensic investigative powers on your problem and very likely come up with the wrong diagnosis.

 

Which model of brakes are they?

Are the noisy discs from the same manufacturer?

If you have ridden discs before you would know if there was excess travel at the lever?

Does pumping the lever improve things at all?

Is the rear brake as bad as the front?

Did the shop replace just the callipers, or the pads or the levers too?

Any signs of brake fluid leaking anywhere on the bike?

Is the fluid level OK in the reservoir?

 

 

Thanks for the reply Mike 

 

1, SRAM Apex

2, Yes

3, not sure 

4, not at all (tried)

5, rear brake locks up extremely easy 

6, replaced with non OEM pads only 

7, no signs of leaking 

8, I assume so 

To make matters worse I crashed today when a lady walked out infront of me, I had already applied my brakes before she stepped into the cycle path but the front brake it so weak I ended up swerving her and colliding  with a trafic light post instead. Bearing in mind I had alreadry told the bike shop on multiple occasions that these ‘amazingly powerful’ disk brakes are dangerous.

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Bob F [47 posts] 2 months ago
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I'm not a huge lover of Sram brakes, mainly because living in the tropics the hygroscopic nature of DOT fluid causes early corrosion. My MTB's all run Shimano with its mineral oil fluid.

Having said that, my most recent road build has SRAM Red HRD brakes [I wanted the eTap] which are performing faultlessly with easy set up.

Sorry it doesn't help much Itf_Harry s. , but the SRAM Apex should work equally as well. Mike will probably come up with a more correct diagnosis than I.

In the meantime I'd be looking at the front disc for possible contamination. Give it and the pads a clean up with isopropyl alcohol and give the pads a light buff with 120grit paper. Confirm that the bite point of the lever is similar to the rear brake and that the pads move equally with lever movement. Try a few stops from moderate speed to re-bed the surfaces again. If still weak braking then you may need to bleed the fluid to rid any trapped air, or you have faulty component mechanical issues. I'm a little surprised your LBS hasn't sorted it easily. Have a pleasant but firm chat with them.

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philhubbard [144 posts] 2 months ago
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Ask the shop to bleed the brakes. With new pads you will need to do a few quick stops to bed the pads in before riding. It sounds like the fluid could do with topping up.

 

 

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mike the bike [1082 posts] 2 months ago
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Mmm.  A strange one this, particularly as the shop hasn't succeeded in improving things.  

My next step would be to look at the fluid level in the reservoir.  A quick visit to YouTube should show a dozen videos offering advice.  If the level is good (full to the brim) it may still require bleeding, but unless you have the kit* it's easier to ask the shop to do this.

A sensible next step would be to whip out the pads, very carefully apply a little pressure to the brake lever and check that both pistons are moving.  It is not uncommon for one to stick and this will ruin brake performance, giving symptoms similar to yours.  

For goodness sake don't move the lever too much or the pistons may end up on the shed floor and this, I promise, will wreck your day.  If necessary the pistons can be gently levered back into their original position using a blunt screwdriver.

Best of luck.

 

* D-I-Y kits are cheap at Epic Bleed Solutions and work really well.  Their quick bleed takes five minutes and corrects most problems.

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don simon [2327 posts] 2 months ago
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Have a read of this.

http://reviews.mtbr.com/how-to-bedding-in-new-disc-brake-pads

My initial thoughts are either contaminated discs or not bedding correctly.

 

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Itf_harry.s [2 posts] 2 months ago
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Thank you for the help everyone. I had another very near miss today (Oxford drivers).  Subsequently I took the bike back to the shop and explained to them that the brakes are extremely dangerous and if this was a car ( I work as a tech for BMW) and a customer returned their new car because the brakes weren’t working (to a suitable degree) and we tell them it’s fine and just to ‘come back at the end of the week’. If that car then gets into an accident because it can’t slow down quick enough and the driver gets killed the technician that signed off that car as ‘okay’ can be prosecuted.  

I was ‘sightly’ annoyed  no

The shop then just said to me ‘we’ll get in contact with Giant’ 

 

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IanEdward [199 posts] 2 months ago
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I'm not too familiar with other models of SRAM brakes, but my experience with some SRAM Level brakes (an MTB brake, but I was using it almost entirely on road on a slick tyred commuter) was pretty poor. Initially they were great in the dry, but horribly screechy in the wet. Changing pads to sintered (at the shop's advice) made them screech in the dry too... Changing rotors to Magura Storm SL and pads to Uberbike Kevlar made them screech slightly less in the wet, but still screeched quite badly.

Eventually gave up and changed for TRP Spyres, which still screech in the wet... new Shimano rotors and Swisstop Green pads on the way!

Sorry I can't give any more constructive advice than that. Your problem (if screeching in both wet and dry conditions) definitely sounds like a manufacturing or warranty issue, but be warned, a lot of people, including shops, will tell you that screeching is normal for disc brakes and you should just accept it as a trade-off for better braking...

 

 

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MoutonDeMontagne [108 posts] 2 months ago
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Had a similar experience when i first bought my commuter fitted with Sram Apex HDR. Like you I'm an experienced disc user from the knobbly tyred world and like you i (nearly) hit somethign as the lever pulled to the bar and nothing.  Sadly, like you, the shop's answer was something along the lines of 'well you bought it'. 

I tired:

1. leave it over night with the Lever pulled all the way back to the bar and secured with a laccy band/string/strap.

2. if that helps but then goes dead straght away again, I'd probably bite the bullet and just blead them. Mine took 3 bleeds from new until they stopped getting air in the system.

3. if the above done help, take a can of lighter fluid and a lighter to the pads and disc to burn off any contamination. Takes the pads and wheel out first though.