Front bake Grabbing on and off under braking.

ukroadster

Hi

Had my Focus cayo team for a week now and its a great bike.

However, on the very first ride i noticed that when you aply the front brake it appears to grab and let go grab and let go. Doing a 30 mph decent it was quite worrying and impossible to regulate the front brake as it is pulsing on and off with a constant lever pressure.

When i got back i centred the brake action so the the pads were equally braking the rim at the same time and not pushing the wheel rim slightly from one side. I recentered the blocks perfectly in line with the rim and was confident this would fix it but it hasnt.

Ive checked the rim and it is perfectly true horizontally and vertically so im at a complete loss as its quite bad when braking moderately hard. Its like the wheel is bucled and the brakes grab and then let go but the wheel appears perfectly straight.

Anyone got any ideas or suggestions. The brakes are sram force and the wheels are DT Swiss r1900. The rear brake is perfeectly smooth, its just the front.

Thanks

challengedavid

are the rims dirty, contaminated?

Monty Dog

As well as rim - pads might be contaminated too - try running a file across the face of the pad to remove any 'glaze' - or change to a better quality pad

lfcquin

Are the brake blocks catching on the tyre? Make sure they are aligned properly with the rim.

Other option with a week old bike is to send it back I guess?

ukroadster

Thanks for the responses.

The pads are definately not touching the tyres. Ill check for contamination today to see if thats an issue.

On very close inspection the right pad seems perfectly parallel with the rim front to back wheras the left pad seems to toe in slightly at the front and this pad seems slightly behind the right pad when you look from above. I donnt think there is much front to back adjustment though.

Ive just tried spinning the wheel and lightly applying the brake and you can definately hear/feel the pads contact on and off like a buckled wheel. Checking the wheel alignment the wheel could be minutely out but we are talking far less than 1mm. could this be the issue? The wheel seems within tolerance to me.

Ill ring Wiggle today to see what they say. i love the bike and dont want too return it but i do want this issue resolving. Seems mad to return for something that must be fixable. If i have to exchange it though i will.

keef66

The on / off nature of the problem suggests something wrong with the wheel, which rotates, rather than the brakes, which don't.

Sounds like the simplest thing would be for Wiggle to send you a new wheel and you send the original back to them. You can get on with your cycling and they can investigate the duff wheel at their leisure.

The alternative of sending the complete bike back would seem to be overkill to me.

Wamas

Do you have another front wheel handy, or a mate that could give you a loan of one to try.
If it does this with their wheel, the problem is with the brakes, otherwise the problem is the wheel.

Possibly there is some play in the bearings, they may not have been set up correctly.

ukroadster

Thanks again for the replies.

yes, I agree it does have to be the wheel, not the brakes.

Unfortunately do not have another wheel to swap out so have rung Wiggle.

Spoke to a Wiggle mechanic who believes the wheel rim may have hot spots due to being machined incorrectly. i.e although the wheel is true the rim itself may have thicker and thinner sections causing this situation.

Sounds the most feasible cause to me and have discovered that the wheel will repeatedly stop at the same point on the rim with a light brake applied sugesting a high spot at that point. I actually think there are 2 high spots on the rim with one more pronounced than the other.

Wiggle are sending me a new wheel today to exchange and return my original. ive asked them to check the new rim before sending so hopefully this will cure it.

I cant think of anything else to be honest, the nature of the grabbing on and off means it has to be the wheel rim really.

Thanks for the help Ill report back once the new wheel is fitted. Disadvantage of not buying from an LBS i suppose but wiggle have been really good.

keef66

Sounds like the sensible approach.

Hope it fixes it.

fnegroni

Two other things I would check:
1) Is the QR skewer tightened properly?
2) Is the headset correctly adjusted? With bike standing still, if you grab the front brake lever only and pull tight, and then push bike forward and back, is there excessive play in the headset (i.e. bike rocks back and fore)?

ukroadster

Hi

Skewer is fully tightened and headset is correctly adjusted. No play at all but not so tight as to restrict turning.

ukroadster

Hi All

Sorry for the late update , been away over the bank holiday.

Wiggle delivered a new front wheel the next morning (good service). Swapped the tyre and skewer over and took it for a quick spin. All seemed ok but wanted to wait until i completed a longer ride which i did today.

The new wheel has fully cured the problem, now got smooth, progressive powerful braking performance

So look like i had a dodgy rim with hot spots (wider and narrower sections) which were causing the pulsing.

Thanks for everyones input and good service from Wiggle too!