hope mono m4 brake issues

tsenior

ok, go easy on me; am new to hydraulics!

there was an unacceptable level of rub on the rear brake on my ebay marin AND the lever depresses a long way and is 'spongey (and makes loud creaking noise :shock: ', I looked at the parktools blog referenced here and the maunal so:

1st tried realigning the caliper: no difference.
2nd took wheel out and pushed the pistons back in: 2 of them (not opposing) rebounded a little (~0.5mm), more so when the other one was held in.
3rd (as experiment) partially depressed the lever without the disc in: the 2 with the rebound came out much more than the others, one of which did not move.

pushed pistons back in (still slight rebound) refitted the wheel, and pumping the lever has improved the rubbing somewhat but still too much lever movement and still spongey

any ideas on what to try next? to my tiny mind it seems like 2 pistons are jammed in resulting in excess pressure on the other 2 keeping them out but would this not result in less movement at the lever not more??

thanks!

bennett_346

time for a bleed.

tsenior

i was afraid someone would say that

http://www.youtube.com/watch?v=E6EltEsGIGg

looks fairly sttaightforward

but how does this explain the pistons not retracing i would have thought this would be due to too much pressure in the system , not too little?

bennett_346

Might be sticking, if you rebleed them with the pistons pushed back and the pad spacer block in it then it cant be overfilled, so if it continues to not return them during normal use then theyre sticking.

tsenior

so:

do the bleed as per video whilst keeping the pistons pushed fully back.

if all 4 pistons dont move following this then what; are we talking strip down and clean time?

'precciate you taking the time btw, as said i'm new to these beasts.

allthegearnoidea

as above, best give them a good bleed, when youve got the pads out, open up the spring for the pads a bit! helps push the pads back a little more,
best to bleed them from the caliper too, tried it both ways on mine, and whilst is a little messy to do it that way (wrap a rag around the lever end to catch the fluid) is easier than nipple open, lever to bar hold, nipple closed, release lever and repeat!

alitodd

I'd go to the nearest bike shop and have them do it if you're inexperienced... Bleeds can be quite fiddly (although Hope are quite simple) - its only £15ish...

tsenior

ok will pick up some dot 5.1 and give it a go. as i dont know when they were last done probably a good idea anyway.

will report back here when i get stuck!

stu8975

Which version of M4? older black/gold or newer silver/black? older ones can be harder to align due having to shim the caliper (I.S. fitting).

Easiest way I used to do the old style ones is to loosen the caliper bolts and press the brake a few times, keep it pressed and note where the rotor is sitting in the caliper, if its centred, note the gap between the caliper and tabs on the frame (if any), if there is then you need to shim the caliper to take up the gap.

tsenior

they're the old black/gold ones, pretty sure the alighment is ok as the disc looks central in the caliper but i'll double check using that method, ta.

my boss suggested just pumping with the reservoir open but as its second hand i'll change the fluid (might be the original!) and follow the instructions as per the video and this:

http://www.bikeradar.com/gear/article/w ... akes-21609

if its sticky pistons and i cant free them after bleeding: LBS time!

nicklouse

before starting pull the lever and watch the disc.

if it moves then alignment or sticky piston is the main issue.

tsenior

will do nick

cheers people i'll get a couple of tins in and have a crack it it tonight.

tsenior

Update in case someone with simlar issues searches this: all fine now 8) .

checked the disc movement as per nick: none, lever still spongey

removed pads and one much more worn than the other, so:

bled brakes as per the linked guidance above
centred caliper by swapping shims about
new pads

everything fine now apart from the creaking noise at the lever, no previous experience with hydraulics at all: so dont be afraid newbies!!

allthegearnoidea

creaking at the lever is just a dry joint between the lever blade and the lever body! drop of lube will stop it or unbolt it, clean it and a light covering in grease helps!! mine do it quite frequently!!