Rear brake issue?

[Dodgy69]

Had new tyre's fitted to loose wheels on Thursday. Now, rear brake lever has far too much movement and is hitting the stop. Pads are grabbing disc, not sure how effective whilst riding though. Never noticed this much lever travel before.

What's gone wrong.???

[KungFooBob]

Have you tried pumping the lever a bit?

The piston will have been pushed in a bit, give it a load of pumps and it should firm up again... unless the disk is warped and pushes the piston back in.

[Dodgy69]

Done lots of pumps but not stiffening up. Might take wheel off again and make sure it's all fitted proper. Was rushing a bit on Thursday and the caliper carrier was a right faff to get back. There's also a fair bit of caliper movement when pumping.

[Tricky]

Both pads on one side of the disc?

[Skub]

Was rushing a bit on Thursday and the caliper carrier was a right faff to get back. There's also a fair bit of caliper movement when pumping.

I don't know what the setup is on your bike,but most I've had,I take the rear caliper off from the mount (usually 2 bolts) before wheel removal,then put the wheel back in again and fit the caliper last.

Saves footering about with the spindle and caliper,while needing an extra hand.

[Dodgy69]

Well, took wheel and caliper off again, checked spacers, refitted, all looks good, but brake the same. Surely it doesn't need bleeding, no fluid loss. ?

[Le_Fromage_Grande]

Sounds like there's air in it, could have been there already and you've moved it to somewhere it's affecting the brake

[Skub]

I'd bleed it anyway,only takes a minute or two.

[David]

Make sure the bleed nipple is at the top.

[Dodgy69]

Well, bled it through and still no good resistance building up. Gonna take to a mate whose got some fancy thing. Cheers guys.

[Dodgy69]

Well, had a lamb dinner break and looked again. These bike's brake line's go into some kind of servo thing under the seat, then out from there to caliper. Do all bike's have these, these days, I don't know ? I wonder if the fault lies there. Front brakes all working fine.

Gonna ring dealer tomorrow.

[Le_Fromage_Grande]

It's the ABS unit for the rear brake, you have refitted the ABS sensor for the back wheel and ridden it far enough for the ABS to calibrate itself?

The ABS light goes out once it's happy.

[KungFooBob]

If there's air in the ABS valve block you either need the dealer diag tools to cycle it... or take it out and try to make the ABS kick in.

[ChrisW]

Strap the lever down, keep it pressurised overnight then give the bleed another go tomorrow.

[A_morti]

When you push the piston back (I'll assume you did when taking the wheels out or to ease refitting), you do a few things that don't happen in normal use.

The piston goes further than usual, which can mean any dirt or rust pits on it can get into the seals. This can stop it moving and returning correctly. Your best indicator would be to take the caliper off and look for dirt or pitting on the piston face.

The fluid in the caliper, which may have rust or alloy corrosion in it, can be pushed up the line. Usually into the master cylinder, but I guess maybe into the ABS unit too. I have no idea how you'd check that.

When you pump the pedal to re-engage the brake, the master cylinder piston slides in parts of its bore which it doesn't usually see. This can leave the piston sliding against dirt or corrosion inside the bore. If you hold the pedal down, or if you have to pump it a few times, does it hold pressure? My first guess is it won't, which indicates a master cylinder rebuild is required. I've never bled ABS yet, so I don't know how it would go if you had to bleed the brake from dry.

[A_morti]

All that said - is it a sliding caliper? If so, pop the sliding pins out, they should slide easy.

[Dodgy69]

I'll look again tomorrow but it seems there is an order of bolting up caliper. Forward most bolt fit first, but not tight, then rear bolt, then tighten both. Apparently it's to make sure the caliper is lined up nicely with the disc. I do currently have caliper movement on applying brake so maybe it's out of line a bit.

[Big Red]

Have you checked the brake disc isn't buckled??
You say you had tyres fitted to loose wheels and also brake is dragging.
The tyre place hasn't buckled a brake disc when changing the tyres.
Most brake discs sit very close to the tyre machine when breaking the bead and it is quite easy to catch the disc on the side if the machine when breaking the bead if you are not carefull.

[Dodgy69]

Spoke to Yamaha tech today. First thing to try is take bolts out and let the caliper just sit there loose and see if the lever now pulls normal and pads grip normally. He thinks it should as I may have damaged thread in caliper bracket, he asked if it was a tight bolt and it was first time so may have cross threaded.

On mt forums its common and easily done. Cross threading resulting in caliper out of line. Gonna have a look later.

[weeksy]

why was the caliper unbolted ?