8 replies to this topic

[dmmsta]

On the way home front work last night i became aware of a speed linked bump/wobble.

 

I hd a temp repair on the front tyre last week, which is still a little proud on the tyre surface but I'm not conveinced its that.  Though it does feel like a swell on the tyre.

 

At the same time my front brake has decided to go up the swaney.  With this I can get pressure on the lever and it all feels good, but then within 30sec's the lever is soft, and pulls all the way in.  A few pumps and it's tight again, but then 30sec's and soft.

 

I took the calipers off this morning, and checked pads, and pistons - all seems ok.  1 slightly seized pistion, but it's still moving.

All pads have life in them.

 

While the calipers were off I checked wheel rotation & play, and couldn't feel anything untoward, which points me back to the puncture repair...however this doesn't account for the brake issue, which started at the same time.

 

Any thoughts / diagnosis tips?

[celticbiker]

Do the brakes do this when stationary or only when moving?

[Wildbill]

If the lever is going soft at standstill; air is in the system.

Has the level been low or the bike laid at a severe angle ?

 

Now more probably; if this is when riding.

 

A disc may be distorted.

This will push the caliper piston back further than normal and will need the lever to be pumped

to get pressure back.

A few wheel revolutions later, the pistons are pushed back into the calipers too far.

This may also account for the wobble at speed.

 

Does the brake lever pulse if lightly applied  when riding?

Remove both calipers and spin the wheel again ;checking for disc run out.

[dmmsta]

So in answer to the above - it doesn't go soft/slack when standing, only when moving.

 

Stripped calipers to allow free spin on the wheel, and couldn't see any discernible warping on the disc, but whilst I was there I checked axle movement again, and there it was...collapsed wheel bearing.

 

No idea why I didn't spot it this morning - assume I didn't have the bars strapped tight enough so they were soaking up the movement, and I didn't spot it.

 

Have a feeling it was a sudden breakdown as I've not noticed anything over the last few rides to indicate it was on its way out.

 

Anyway - I'm off to check local suppliers to see if anyone has them on the shelf as I really need the bike for the rest of the week.

[poldark]

If you can't source locally these guys are really good, carry good stock and have inclusive next day delivery - http://simplybearings.co.uk/shop/

[dmmsta]

Thanks Poldark.

 

Have managed to get some from an eBay seller who is local(ish), so no delivery costs (a friend drives past on way to work so don't even have to worry about fuel)

 

£21.99 inc seals.

[Toydepartment]

Sounds like master cylinder problem, If you pump the lever and you get a good brake, then leave it for a minute and pull the lever in very slowly and it comes into the bars, ive always changed the master cylinder or put a kit in and it has cured the problem.

[wicklamulla]

Sounds like master cylinder problem, If you pump the lever and you get a good brake, then leave it for a minute and pull the lever in very slowly and it comes into the bars, ive always changed the master cylinder or put a kit in and it has cured the problem.

you need to read all the other posts above yours !    collapsed wheel bearing makes sense. 

[Toydepartment]

Ahhh  Bugger!