ZZR600 Brakes

[Kickstart]

Hi

Having problems with the ZZR600 brakes.

I have rebuilt the calipers with new seals and pistons. Fitted new braided steel brake lines. Rebuilt the master cylinder.

I still cannot get them to bleed through and give a firm lever.

If you leave the bike for a short while then pull the lever it comes straight back to the bars with no effort. Pump them a few times and it builds up some resistance (such that a reasonable pull results in the lever stopping about 1cm from the bar). Keep the brake lever pulled and it doesn't loose pressure. Release the lever and leave it for a short while and it is straight back to the bar.

This might show what I mean:-

https://www.alfa-pages.co.uk/temppicture/zzr_brakes.mpg

Any suggestions? Only thing I can see if that the pistons seem to retract when you release the lever as far as they come out when you pull the lever. Pushing the pistons back into the caliper means it takes ages to pump them back out again (even with new pads so they do not have to move far).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[finpos]

I once had exactly the same problem with a car master cylinder (a 105 series alfa romeo, oddly enough). rebuilt the master cylinder twice, still could not get it to keep any pressure. In the end, I replaced the whole thing at hideous expense, and that fixed it.

Can only assume that one or more of the mechanical parts were worn/damaged past the point where replacing the seals made any difference - everything looked ok, but I guess not!

EDIT - Scratch that, I just read your post properly!
If you can actually see the pistons retracting when you release the lever, I reckon they are pulling back too far - which would imply the new pistons and or seals in the calipers were not the correct match (they need to be a pretty exact tollerence, as I'm sure you know)

finpos.

[Kickstart]

Hi

Could be. Odd thing is the brakes are worse that when I started out, and having major master cylinder failure at the same time would be too much of a coincidence.

Looks almost like the pistons are being pulled back too far.

By the way, got some 105 series workshop manuals around I think.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[finpos]

See edited post...

Got lots of 105 manuals and spares myself, but sold the car!

finpos.

[Kickstart]

Hi

They are pattern pistons and seals from Wemoto. Not sure if anyone else has had problems with them.

Going to Alfa Day?

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[finpos]

I've grown deeply suspicious of pattern parts over the last 2-3 years, I reckon a lot of them are coming from the far east and aren't all that clever. They seem to be made poorly from either very hard rubber or very soft metal. A number of times I've binned the new bits and restored the 30-year old ones. Appologies to Wemoto if they do not fall into this category.

Might possibly make alfa day, but I live in the northern wilds and my current transport choices have a combined top speed of about 75 mph. Also I have promised myself I'm not buying any more rusty old motors for a couple of years - I might not be able to resist the temptation. Maybe just one more rusty bike.

finpos.

[Kickstart]

Hi

Often have the same feeling about pattern parts, but Wemoto normally seem to have a good reputation.

Old pistons are fairly wrecked.

Should be at Alfa Day. Probably buying a load of spare parts as usual. Chances of finding any of the unavailable bits for a 33 P4 are pretty slim though.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing