Z1OwnersClub GB

I have a small issue with my front brakes I hope you guys can shed some light on. I recently fitted new pistons and seals to the calipers, new braided hose and pads fitted and also fitted a piston and seal kit to the master cylinder so in a nutshell everything but the allly caliper bodies and master cylinder body is new. I have bled probably a litre and half of new fluid through and I am no longer bleeding any air out of the system. I can still pull the lever pretty much all the way back to the grip. There are no leaks anywhere. Is it possible that the seals in the master cylinder are allowing fluid to leak past the main seal and back into the reservoir (hence no external leak) ? It does not get any worse or any better always the same amount of travel even if the bike is left for a week or two. If the master cylinder is the likely culprit does anyone have a good one from a 1000 J they would like to sell.
Thanks guys.

Sounds like you still have air trapped in there somewhere, fluid can pass this and give you the impression that all the air is gone but its still there
popular haunts for these evil little air bubbles are in the splitter, in the hose if the hose is routed horizontilly anywhere and in the top of the caliper if the bleed nipple is bellow the highest piont of the caliper. You can also try cable tying the lever to the bar once you have pressure and leaving it for a day or too, with the piston pushed in and the air under pressure often the bubbles rise through the system into the resevoir and out. Solved this problem for me many a time, and a cable tie is a lot cheaper than another master cylinder. worth a try and might save you a few quid. Regards, Steve

Pasc,
I had a similar problem (which resulted in me removing one of me 2 x front calipers - much to everyones mirth ) and it took me a few litres of fluid & a whole week of evenings
One of the calipers was not quite square with the disc, so it opened a caliper up more than the 'throw' of the master cylinder could cope with. This made the lever VERY spongy. Bleed many times, NO AIR visible.
Even took whole brake system off bike, stretched out, hung from garage roof beams to bleed. Only when putting calipers back did I notice that when applying brakes, one caliper was moving a disc slightly. The disc was acting like a big spring washer, pushing the pads back deeper into caliper
Suppose I could have shimmed it up TRUE, but, looks better with one

Cheers for the replies guys. Steve, I've bled the system with the calipers off the legs so that the bleed nipple was at 12 oclock and I also unbolted the splitter from the frame so that I had a small amount of movement to allow any air to make its way up. I must also add that I have had this problem since I bled them about 6 weeks ago and the bike has not been out of the garage since. I did try the cable tie on the lever trick but only left it overnight. Maybe I'll put another one on today and leave it for a few days.
Thanks again.

Have just replaced the brake hoses on mine,put a new service kit in the master cylinder so all was new.It was taking ages to move any fluid down the lines and there was no pressure at the lever at all.
Ended up sucking the air and fluid through from the calliper with a hose tie wrapped to the nipple (stop sucking when it gets to your lips!) this got all the air out and now the lever is fine.
Only thing I have noticed is the calliper halves flexing with the brake applied,any one else had this?
Good luck with yours.

Steve, while I was bleeding the brakes I had a piece of tube attatched to the caliper nipple and a syringe attatched to the tube. This allowed me to draw air out whilst bleeding (dunno if it had any real benefit but it did help get the fluid flowing initially).
The caliper halves will flex under lever pressure, all of my 80's era kwaks flex.

Use the banjo bolts as bleed nipples as there is usually air trapped in them. If you have the splitter/brake switch holder rotate and tap it while bleeding to free any air bubbles.
The only way I have found to do a dry system without hassle is to take it all off, have the calipers suspended from the garage roof at the top and the m/c at the bottom and bleed all the air up through the systam.

Rich wrote: take it all off, have the calipers suspended from the garage roof at the top and the m/c at the bottom and bleed all the air up through the systam.

That's pretty much the only thing I have'nt tried yet. I'll give it a go.

As Rich said bleed them fromevery banjo from lever downwards this has always worked for me

I had the same problem on my J. New M/C kit, new lines caliper pistons the works. Bled It so many times to no avail I finally took it to a brake specialist. Reverse bleeding the works; No joy there either.

The I thought back to when the problem arose. This was during some "routine" maintenance when I greased the slider pins with Never Seize. So I decided to look here further and I had the devil of a job getting the the slider pins out of their bores.

It was as though there was a vacuum pulling them in. With some mighty tugging managed to get the pins out. The most troublesome were the ones with the plastic anti rattle sleeves on them. With these in particular there was real difficulty getting the pins out.

I suspect the never seize had caused these to swell, binding in the slider bores, and thereby pulling the caliper piston away from the disc. Replacing these plastic sleeves (part still obtainable) and removing all trace of lubricant solved the spongy leverproblem. I would not say brake performance is exactly sparkling, but spongy lever back has gone.

I had the same problem with my J. In the end I got rid of the compensator and put on two lines from the master cyl straight to the calipers. Then vacuum bled. The only thing was I needed to put an adjustable lever on of a s***** to take up any slack. Check out any threads from a couple of months ago. Good luck, mine was a nightmare. PS look at projects koolasaki to see results.

A couple of things to consider:

1, Make sure there is free play in the lever or the piston will not be returning all the way to bleed the air.

2, Get a pice of cardboard and some mole grips and starting from the middle of the upper pipe clamp it tight (after wrapping the cardboard around it) and see how firm the lever is, it should be virtually rock hard at the first clamp - work your way down and se where it starts to lose the pressure.