Disc rubbing - SRAM Rival hydraulic brakes - Looks faulty?

daniel_b

Hello there,

recently took delivery of a Cannondale Synapse with a full Rival groupset.

The front one seems fine, but the rear one was pretty draggy.

I found this video guide on installation, and have followed the process to the letter 4 times, but if anything the drag is worse than before :?

https://www.youtube.com/watch?v=r5bHJzJFo6U

The rotor appears to be fitted squarerly, so am wondering if this might suggest a bigger issue, or possibly even a faulty brake unit.

Is anyone aware of any other adjustments I can make to them before I have to contact Evans.

I can see an allen key accessible from the opposite side of the bike, but am not sure if I should be tampering with it, as it doesn't get a mention on the video at all.

imatfaal

Is it a permanent drag or an intermittent touch ? is the mounting loose enough to move when you are doing the five times etc and you are keeping the brake on whilst you make the adjustment?

daniel_b

It seemed to be intermittent when the bike arrived, but bad enough to be not minor if that makes sense.

Now it is a permanent drag!

Yep, I loosened off the calliper's two bolts a half turn, which was plenty for it to move in and out as desired.

I then pumped the brake 4 times, and then held it on tight whilst doing up the bolts to where they originally were tightened too.

I have read elsewhere about taking the wheel out and pushing the pistons back in with a tyre lever for example, but am wondering if this should be required on a brand new pair of brakes - ie I am happy to have a go, but wonder if it suggests a bigger problem.

I've e-mailed Evans so it is logged anyway, and worst case if I can't fix it (Which I would MUCH rather do) I will have to take it in - 40 mile round trip.

imatfaal

I just set up a new pair of shimanos a month or so back - did basically what was in the video you showed (but via one of shimano's huge instruction sheets) and was ready to rock'n'roll.

That was the case for the set before as well. I have a set of hi-end Sram mtb that I had on for a weekend before being removed and set aside for my new build - and did exactly the same and had no trouble. Sram's disc brakes did have a rep for being finickity and difficult to keep from touching - but that was the old X-series MTB disc brakes. The new hydrau disc brakes are (similar to new G-series and revamped Avid X series ) supposedly much better and I hear good things.

You didn't remove the spring as well as the red bleeding spacer?

kajjal

The loosen the caliper bolts, pull brake on and tighten method often doesn't work as the calipers are rarely completely symetrical with identical piston action.

The best aporoach is to set the brakes up by eye. Loosen the caliper and look down the pads and disc. Adjust the caliper so the pads are the same distance from the disc either side. Then carefully tighten making sure the gap stays the same. Hop on the bike and try the brake few times. If it is still rubbing check the gap again and also see if one pad moves in slightly faster than the other. If it does adjust slightly to copensate. You should then be good to go.

Main thing is take your time, keep calm and it may take a few attempts to get it right the first time you do it.

(Make sure the wheel is in firmly and straight, also the disc bolts are done up properly and there is nothing stuck in the pads / caliper. If it still rubs take it back to the shop.)

daniel_b

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19745347#p19745347]imatfaal[/url] wrote:

You didn't remove the spring as well as the red bleeding spacer?

Hiya - no I didn't remove anything, and actually looking more closely, the nut that I thought was an adjustment nut is actually what you are talking about I think, ie the safety mechanism that holds the pads in.

Kajjal - thanks for that very helpful reply, if I look down the side of the bike, I can see the kerb side is touching the disc.

I'll try your method first of attempting it by eye, and go from there I think - most strange!

I'll update with various failures I expect

The Rookie

Light touching (rubbing) is perfectly normal, drag isn't, make sure you really have an issue!

daniel_b

Thanks for the help guys.

I found a pdf of how to remove the pads to get to the pistons.

I measured the gap between the pads - all be it slightly approximately with callipers, and it seemed to be 1.6mm - I removed the pads, and pushed the pistons (is that the right term?) back into the housing with a tyre lever, and popped the pads back in, this then increased the gap to 2.6mm.

However on refitting, although it was better, it still was rubbing like a bugger - I basically got it back to how it was when it came from the shop, perhaps 10% better, but a rub for 50% of the rotation.

The holding the brake thing hard on did definitely not work for these set of brakes by the way, it did for the rear nut, but I saw the unit move towards the wheel when I tightened the front nut up, even with my hand HARD on the brake - so I got around this by tightening up the rear, taking my hand off the brake, and then bracing the brake unit whilst I tightened it - this is what gave me the back to the out of the box situation.

So I think this would suggest that pistons are not retracting properly?

I popped them out again, and they were proud again, and the gap down to 1.6mm - I tried the process again, with the same results, so unfortuantely it looks like a trip to Evans to see if they can sort and or replace :-(
And if I do have to go this route, would you fess up and say what you have tried, or play dumb and just say the brake is rubbing and ytou can't ride it?

Unless anyone has any whizzy ideas?

First two pics - either piston, proud from the surrounding housing - this is as they were when I first took them out:




And this is one piston only (The other picture blurred) showing you it flush after I had pushed it in - compare with the pic immediately above for a comparison:

daniel_b

Any comments guys?

imatfaal

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19749193#p19749193]Daniel B[/url] wrote:

Any comments guys?

If you have done the basic remedial stuff (and it seems you have done so to fullest extent) AND it is new - then put it back in Evans Lap.

The Rookie

The pad needs to stay out close to the disc or you end up with no braking as the pad wears (obvious innit), so if the disc is 1.6mm thick, then that is what the gap should be!

Rubbing is PERFECTLY NORMAL, so it it rubbing or actually dragging?

Sometimes you have to centre the calliper on the disc by eye, especially if a pad has worn off square, holding the brake on will just align it askew again!

If the calliper uses CPS washers you have to be very careful how to do them up as the bolt torque can twist the calliper, this is less likely without the CPS washers but still possible, hence checking by eye.

Its possible one piston is a bit grubby, you can clean it by removing the pads and advancing the piston out A SMALL AMOUNT (don't pop it right out), clean round it with some brake fluid on a cotton bud, push back and then repeat (to pull any crud out of the gap between piston and calliper), clean away all excess fluid before refitting the pads!

6wheels

Are the calipers tilted at all (from top to bottom), just had to pack mine on the one side?

daniel_b

Thanks for the replies chaps,

I booked it in, and took it to Evans in Reading on Saturday morning, really helpful and enthusiastic bike people in there, an impressive start - one of the chaps raced, and was more than happy ot talk bikes.

They took it in, and thought it would only take them 10 minutes, but it was apparently a bit of a bugger, as it ended up takin gmore like 40 minutes.

They agreed that the 'grip the lever hard 5 time, hold and tighten the unit' was not the be all and end all, and that they only used that as a starting point, before fine tuning by hand and eye.

I was in the shop all that time, so could see it did indeed take all that time to get it sorted, and he admitted they are a bit of a pain to setup, but once in the right place, should never need moving.

At least I know if they do, it's going to take me some time.

They were also very complimentary of my vinyl wrap I had applied on the frame in certain places, saying they couldn't tell it was aftermarket - nice to know :-)

Now just need to to decide whether to fit Shimano SPD-SL or my favoured Look pedals (I have both in a cupboard), and actually go for a ride!

imatfaal

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19752040#p19752040]Daniel B[/url] wrote:

Thanks for the replies chaps,

I booked it in, and took it to Evans in Reading on Saturday morning, really helpful and enthusiastic bike people in there, an impressive start - one of the chaps raced, and was more than happy ot talk bikes.

They took it in, and thought it would only take them 10 minutes, but it was apparently a bit of a bugger, as it ended up takin gmore like 40 minutes.

They agreed that the 'grip the lever hard 5 time, hold and tighten the unit' was not the be all and end all, and that they only used that as a starting point, before fine tuning by hand and eye.

I was in the shop all that time, so could see it did indeed take all that time to get it sorted, and he admitted they are a bit of a pain to setup, but once in the right place, should never need moving.

At least I know if they do, it's going to take me some time.

They were also very complimentary of my vinyl wrap I had applied on the frame in certain places, saying they couldn't tell it was aftermarket - nice to know :-)

Now just need to to decide whether to fit Shimano SPD-SL or my favoured Look pedals (I have both in a cupboard), and actually go for a ride!

Glad after a few attempts you actually have a rideable bike - stick the favourite pedals on it and have a blast