Spongey front brake........any one had this happen ?

[johny brando]

Hi any idea's please on a Spongey front brake lever ??????
Z900 master Cylinder working with GPZ1100 b2 front end fitted to my 900 ....which includes forks- calipers, disc's , wheel . These all worked fine together prior to a very, very long lay-up. So I stripped the Calipers ....& Pistons were OK , but fitted new seals also I put a rebuild kit through the Master Cylinder as this had been leaking during the lay-up period ( piston cylinder bore was fine )......the Kit included all new seals , piston , spring etc. I then filled the system best I could with DOT 4 ...then I inverted the master cylinder & bleed it ,then inverted the brake line splitter & bleed that ...caliper bleed nipples are fixed at @ 12 o,clock position and they bleed through oK BUT the brake lever remained spongey & instead of a good pressure with lever compressed ( i.e.lever tip pulled in ) about 20mm , well... it will not pressure right up until it's travelled in about 40mm =half way to the handlebars !!!
I bleed & re-bleed the system a few times ensuring that no air is being drawn in during this but still the same ! I cant find the culprit , however , if I retain the front brake lever under pressure by cable tieing in, for say 24-48 hours it,s then is fine....with instant good pressure ( works great too ) but over a couple of days it returns to it's old spongey ways. It seems to pull air in some where and then appears to be trapping it in the brake hose spitter ........but there's no visable leakage sign,s anywhere .....all the bango washers , brake light switch,bleed nipples etc are Bone dry.
I'm running out of idea's besides changing all the bango washers "but" I've never had to do that in my life ! you'll normally find & see a leak under pressure aye ! If any one has any ideas , I'm keen to hear them . THANKS.

[KWACKERZ1]

like you say its got to be sucking in air.
Re the washers though if they are copper ones you can re aneal them by taking them off and heating them to cherry red.

Personally I tend to use new ones as they are pennies, but they can be re-used after annealing.

Also re-check your seals its very easy to get them the wrong way around if they are tapered.

[PAULJAC47]

H,i Are you using an old brake line? may be bulging under pressure,get some hose clamps and clamp after the Mc, isolates where the prob is mc or caliper or hose etc.good luck Zed brakes are a pain..Paul J,oh and make sure the little return hole in the mc plunger is clear!

[jimmock]

I would "SPLIT BLEED" your system.

ALWAYS works a treat.

[Al]

Its not the new caliper seals sucking the pistons back in is it?
Banjo bolts bottoming out in the splitter? Mine were, i ditched the splitter and fitted two full length hoses off the MC!

AL

[johny brando]

like you say its got to be sucking in air.
Re the washers though if they are copper ones you can re aneal them by taking them off and heating them to cherry red.

Personally I tend to use new ones as they are pennies, but they can be re-used after annealing.

Also re-check your seals its very easy to get them the wrong way around if they are tapered.

I appreciate your good input. I had NO idea about the caliper seals being tapered !!!!!Guess I'll have to pull em apart now have look......I hope I will be able to identify any taper ,as I expect it will be a sutle one ! & then will be a good time to change out all the original Banjo sealing washers for Copper one's. Thanks again.

[johny brando]

I would "SPLIT BLEED" your system.

ALWAYS works a treat.

Thanks for that........... Do you mean ...clamp off or blank one side out of the Brake hose spliter........ then bleed the side that's still on line. Then do the same to the other side ? If so I can see the value in that..... if say one side then shows air while bleeding i.e. it's an indicator of the problem side after the Spliter & narrows down the search a bit......Or am I missing another angle here altogether that your putting across ??
Thanks Jimmock.

[johny brando]

Its not the new caliper seals sucking the pistons back in is it?
Banjo bolts bottoming out in the splitter? Mine were, i ditched the splitter and fitted two full length hoses off the MC!

AL

Thanks for your help here. But I don't really understand what your saying about a sucking action ?? I'm guuna pull the calipers apart again now, as it's been pointed out to me that the Piston Seals are Tapered !!! & that was bit of a shock & news to me and as such there's a possibility that I may not have installed em right ! I must say too that I'm not aware of Pistons being sucked in either ? .......... I believed the Pistons are retracted by the reversed action of the twisting affect of the exposed head of the square shaped seal when the piston is forced forward a tiny ammount within the caliper body ...it then reverts back to it's normal resting position in doing so pulling the Piston back that small forward ammount it's travelled.
I take on board & get the 2 New full lengh hose's that you pointed out but I don't really want to do that as ...it's too expensive & look a bit "hows ya father " plus ......brake light switch will then be out of play then too.
Thanks for your good input...I appreciate that.

[johny brando]

H,i Are you using an old brake line? may be bulging under pressure,get some hose clamps and clamp after the Mc, isolates where the prob is mc or caliper or hose etc.good luck Zed brakes are a pain..Paul J,oh and make sure the little return hole in the mc plunger is clear!

Hi Paul ...yeh I'm using original hoses & thats a good idea about clamping off the hose's to find the problem ( at least it will narrow down the problem area ).......Can they actually be sqaushed/clamped to that degree without damaging them ????? if so I''l definately give that a try as it would help identify where the problem source lays !
I'm sure it's air ingress though not hose bulge .....as when they are held pressured up for say a day or two ...the lever pressure & brake is absolutely fine for a couple of days ....then, it gradually reverts back to where it was & seems to get air back in the system somehow.
When I stripped the MC I was aware about the 2 very tiny drillings in the MC body that you refered i.e......1/ to fill the primary delivery side chamber in the MC piston & 2/ To release the down stream pressured side of the system back into the MC......so yeh there fine & thats a good point which is often over-looked aye.
Thanks for your constructive input......much appreciated.

[PAULJAC47]

Yes i have clamped hoses with mole grips lined with soft wood no probs,though you can get special tools to do the same job,have you checked the caliper bleed nipples?might be getting air in through the threads!

[jimmock]

I would "SPLIT BLEED" your system.

ALWAYS works a treat.

Thanks for that........... Do you mean ...clamp off or blank one side out of the Brake hose spliter........ then bleed the side that's still on line. Then do the same to the other side ? If so I can see the value in that..... if say one side then shows air while bleeding i.e. it's an indicator of the problem side after the Spliter & narrows down the search a bit......Or am I missing another angle here altogether that your putting across ??
Thanks Jimmock.

Johny,

Bleed the system to the banjo at the master cylinder.
Then bleed to the inlet side of the splitter.
Then bleed to ONE caliper.
Then bleed to the other caliper.

I've NEVER had a problem after this procedure.

Let me know how you get on.

[johny brando]

Yes i have clamped hoses with mole grips lined with soft wood no probs,though you can get special tools to do the same job,have you checked the caliper bleed nipples?might be getting air in through the threads!

Thats good Paul......thanks & yes I thought I might run a couple of turns of PTFE tape on the bleed nipple threads... Cheers.

[johny brando]

I would "SPLIT BLEED" your system.

ALWAYS works a treat.

Thanks for that........... Do you mean ...clamp off or blank one side out of the Brake hose spliter........ then bleed the side that's still on line. Then do the same to the other side ? If so I can see the value in that..... if say one side then shows air while bleeding i.e. it's an indicator of the problem side after the Spliter & narrows down the search a bit......Or am I missing another angle here altogether that your putting across ??
Thanks Jimmock.

Johny,

Bleed the system to the banjo at the master cylinder.
Then bleed to the inlet side of the splitter.
Then bleed to ONE caliper.
Then bleed to the other caliper.

I've NEVER had a problem after this procedure.

Let me know how you get on.

Thanks Jimmock.....I'll do that -it's gunna get messy aye !!!! I'll keep ya posted. Cheers.

[ADE]

Might be a stupid question.Did you clean the grooves out where the seals go.A little corrosion and they won`t fit in the grooves as they should.Pistons go out but struggle to go back as they are sticking to the seal
Ade

[Pigford]

Its not the new caliper seals sucking the pistons back in is it?
Banjo bolts bottoming out in the splitter? Mine were, i ditched the splitter and fitted two full length hoses off the MC!

AL

Thanks for your help here. But I don't really understand what your saying about a sucking action ??

The pistons don't actually slide in the seals when being used.
When braking, the pistons stretch the rubber seals as they only move a tiddly bit, then when released, the seals spring back, pulling the piston away from the disc.