SOHC.co.uk Forums > CB750

Front brake lever travel

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steff750:
 ;) hi have you bled the system? or changed any brake pipes ,check that the rubber pipes don't swell when you pull the lever, if that is the case they will need replacing, although you live in OZ . you might well have moisture in the brake fluid
 it does sound like there is air in the system, you can try the old way and back bleed the system remove the master cylinder cap and using little short pulls of the lever you are checking for bubbles coming back up into the master cylinder BEWARE any long pulls will send a jet of brake fluid over you nice paint work so keep some rags handy
the best way is to replace all the brake fluid with a power bleeder and if they are as hard as a cb750 to bleed that may well be your only solution good luck with that

Moorey:
What I have know happen in hydraulic hoses is a fault to develops in the inside of a hose and as you increase the pressure fluid is forced between the braiding in the hose and the lining. the lining then closes down effectively sealing off the hose so no more pressure can get through to where you want it, ie the calliper, but this very rarely happens. If you were to blow through the hose everything would seem fine also no bulging of the hose occurs as the braiding is intact.

Lobo:
Thanks Steff... the stuff you describe would surely manifest as a spongy brake lever... mine is the opposite - after about 1” of travel is rock hard. Regardless, it was bled (tho’ not fresh fluid) a few months ago.)
Moorey - your explanation certainly best describes what I’m experiencing, and changing the hoses might be the best way to go. (though these were all new about 5 yrs ago when I restored the bike). I’ll have a good gander today & see if I can notec any bulgings under pressure. Thanks.
Simon

flatfour:
The same happens with my CB750 K2. The front brake lever has a very short travel, whereas on my CB500 K1, the lever travel is around a third of the total available, with a much gentler "bite". I believe that the reason is that the CB750 has a DS replacement master cylinder on it, whereas the 500 has the original still fitted. The DS master cylinder has flutes in the reservoir, the original is a smooth finish.

Pads are the same in both bikes, DS replacements for the originals.

Lobo:
... thanks flatfour, this could be the answer as the master cylinder does have a newish look about it. Moorey... I pumped the lines hard, and couldn’t detect any ballooning at all. Given the hoses are only 5yo / no bad weather / low mileage / adorned / moly coddled etc I can’t really believe they’re failing. Dang... and maybe an evening on eBay, though who knows what you’d be buying.

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