Spongy brakes (front)

[mick_dundee]

Seems to be an ongoing issue with this bike, get the brakes bled and soon enough they become spongy again, ie I can pull the lever right to the grip. Brakes work, just not a massive fan of that much travel, put braided lines on this beast about 6 months ago or so, song remains the same, could I have an air leak somewhere??

[Smitty]

Mick

you got any fluid loss? level of fluid in master cyl dropping?
unusual to have an air leak without fluid loss ( I assume the system is standard 'cept for the braided lines)

if normal bleeding dont' work...there are 2 other ways
force bleeding (where they cap the top of the m/cyl and force fluid thru and out caliper)
and delayed bleeding
bleed as per normal, seal off system as usual then tie brake lever to bar with occy strap or similar
and leave overnite (this gets air bubbles out)


hth

[mick_dundee]

Done the cable tie thing Smitty, doesn't make any diff, firm for 5 minutes and spongy again, no fluid loss which makes it all the more puzzling, do know this bike seems to have a few idiosyncrasies, perhaps this is one

[Strika]

Mick, why worry, brakes only slow you down anyway!!

Knowing the pristine condition and meticulous maintanance schedules you operate under Mick, I'd suggest replacing the brake fluid. I know it's a large investment for not a lot of percieved gains, but it's worth the $13 it costs. Honest!!!

[matt6]

If you haven't already done it, try bleeding at the banjo connection at the master cylinder - air can get stuck here sometimes. Also depending on how long since the calipers have been rebuilt a build up of shmoota on the caliper pistons can give dodgy bleeding results. Quick fix is a good blast of brake cleaner but proper fix is pull all the pistons out and give them a good clean.

[mick_dundee]

Fluid has been replaced about 3 times in the last 6 months, therein lies NOT the problem, as Matt suggested, perhaps time to just pull the lot apart, give it a good clean and refluid/rebleed cos tried every other fucking thing..

[Slow and wobbly]

Done all of the above mentioned to Micks brakes.
Fluid has been flushed and replaced. Bled as per normal. Bled from bango fittings. Lever tied back to bars. Lever pumped continuously for over 5 mins with no air appearing in reservoir. Vaccum / suctioned through system.
Still they refuse to give a firm lever.
At this point I am thinking a MC overhaul since everything else has failed to produce results.

[tim]

Another master cylinder available to swap out to check?

[mick_dundee]

No but spose I could visit Vic bike wreckers and grab another easily enough..

[Rossi]

Mick,

As I understand it, the spongey feeling from the brakes comes from the seals deteriorating due to the dirt and shit that gets into the callipers and grabbing at the pistons, when you release your brake the seals pull the pistons back into the caliper ever so slightly which means you have that extra bit of travel when you apply the brakes again before they actually compress the pads onto the disc which gives you that shitty spongey feeling.

after hearing the problems of getting the pistons out of the calipers thought i would give this piece of advice.
only do one at a time

1 take off your calipers from fork legs
2 remove brake pads
3 find a good solid peice of wood to fit in the slot of the calipers where the pads where
4 pump your break lever so the pistons push into the wood
5 keep pumping till they are all out (this might take some time if they have noy been looked after ) (JOESHOEY)
6 LEAVE THE WOOD IN PLACE
7 now do the same to the other caliper

NOW GIVE THEM A BLOODY GOOD CLEAN AND KEEP ON TOP OF THEM

If that does not work then


Remove caliper bolts, slip the calipers off the discs, take the pads out, slip them back on the discs and pump the pistons out to their fullest extension. remove calipers.
Sit at the kitchen table with them on a tray, an old toothbrush, some brake fluid and a can of brake cleaner.
Liberally douse the pistons with brake fluid and set to them with the toothbrush until EVERY blemish has disappeared, spray with brake cleaner and then attack with dry cloths until shiny (all the way round EVERY piston), finally lubricate each piston lightly with brake fluid and push them back into the caliper bodies fully, cleaning off excess fluid with kitchen paper.

Put back on bike, bleed through in the usual fashion and THEN, half close the nipple and bleed through another resevoir or two full (the extra pressure created by this method seems to help).

Re-fill the resevoir and put the cap on then start pumping that lever, as hard back to the lever as you can about 50 times.
Voila, you have decent lever travel / feel for..oooh...days.
I'm not a great fan of leaving resevoirs open (or caps off of brake fluid bottles) because brake fluid is excellent at dragging moisture out of the air and you don't want that.

Just go out to the bike now and pump the lever as hard as you can about 50-60 times (hard, not neccessarily super fast) I bet it improves markedly (a sign of the top pistons being sticky).

tieing back the lever actually closes off the system, it doesn't allow air to get back to the master cylinder (actually prevents it) but the constant preasure on the brake pistons of tieing it back over night can allow any pistons that are stuck to the seals (causing them to retract too far giving long spongy lever travel) to slip through the seal thus reducing the lever travel..

If you've tried all ideas and didnt quite get it as good as you want then Rossi's tip of the day is........ Undo the four bolts that hold caliper together, pump the brake then do them back up

[mick_dundee]

Alright, thanks Val, will be a project for another day though, no light in garage and work tomorrow and Sunday. Best I read up on the workshop manual so I don't completely fuck it up..

[IsleofNinja]

Isn't this the same bike that had wobbles stumped for days Mick - or was this 1 the 'lets everyone learn about MC maintenance' bike (Cos this blue bastard definitely needs some lovin )???

Have to agree with the 'Rossi theory' re cable tie trick. Yes it gets results but I don't think it due to air bleeding back into the resavoir...Tried it myself on the 95 and sorta worked ..... for about 10 seconds!? maybe it just temporarily expands the seals or something

Mine not so bad by the sounds but makes the Gumby lever feel rock solid!? Doing the caliper overhaul thing this weekend also - 14 years old I think she's earn't a birthday.
Might even pull the M/C apart and give it a clean / check over.
Lever goes about halfway on pos#4 (stock lever-and yeah I'm anal ) - If the overhaul doesn't help things I'm sure SB supplies can help out with some less flexible levers.

[Bussa]

do know this bike seems to have a few idiosyncrasies, perhaps this is one

Hi Mick, read all the posts, valuable input,makes me wonder if the master cylinder could be a little undersized,causing low overall pressure load and low holding power over the 2 discs, thus the need to apply more lever application.

[seiko1]

Solution is so bloody simple!!!!!!!!!
Mix Viagra with the fluid dumbarses

[Rossi]

do know this bike seems to have a few idiosyncrasies, perhaps this is one

Hi Mick, read all the posts, valuable input,makes me wonder if the master cylinder could be a little undersized,causing low overall pressure load and low holding power over the 2 discs, thus the need to apply more lever application.

Unlikely, as Mick's is stock....... However, I have been thinking about the master cylinder...............
Check the mastercylinder and clean out the 'refill' hole in the top of it where it gets fluid from the resovoir, even a tiny bit of shit in there will cause it to retract fluid from the system rather than from the reservoir and that will give you so much travel before 'bite' that you will have a shit lever and can pull it back to the bar with ease.