SOHC.co.uk Forums > CB750

TROUBLE BLEEDING FRONT BRAKE

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Gromitdog:
Please could anyone shed any light why it is so difficult to bleed the front brake system on a CB750 K8 use import  :( :(   ?

I  have on Graham and Julies advice brought a S/Steel piston, new master seal kit, new s/steel braided hose which on my model is one piece which is 80cm in length   ALL THE SEALS are genuine Honda seals using Dot 4  fluid put in new crush washers at the master cylinder banjo joint
1)    I have tried bleeding it by the normal std method of opening and closing the lower  bleed nipple
2)   Using a syringe I have back bleed it by pushing the build towards the master cylinder
3)   Using a syringe I have bled it by sucking the fluid through from the master cylinder
4)   Without out the lower bled nipple being open & with constant small movement of the brake lever for 20 minutes.

Comparing the movement of the front brake lever with my CB550K3 My 550 moves back less than half way and then unable to pull it back any further ........ With my 750 I am able to pull back the brake lever back to within 1 finger thickness of the handle bar most times  And if i really pull the brake lever hard I can get it back to the handle bar
which i am not happy with ( Not got the confidence in it stopping me )

Any help or guidance why I am having so much trouble with this simple task

JezzaPeach:
On my 500 I use a one way bleed tube that I’ve had for decades which I think helps. That may not be the issue but are you using a one way tube from the nipple to the low level container?
Also I didn’t need to but I wonder about putting the bike on the side stand and turning the bars to the left to create a slope to maybe help bubbles up to the master cylinder.

MrDavo:
Something I learned when having trouble bleeding my CB750 front brake was that pulling the lever all the way back to the bar is very wrong, as your taking the piston to where it wasn't ever meant to go.

Either my shop manual or a service bulletin has a picture of something around the size of a matchbox taped to the bar to limit the travel.

You may already know this, but worth pointing out.

Spitfire:
I do mine the same ways as Jeremy with the bike on the side stand and the bars in the highest position, mine is also fitted with speed bleeders.

Cheers

Dennis

hairygit:
Before panicking further, I assume you have adjusted the caliper correctly, as in a 6 thou clearance between the fixed pad and the disc,,? If not, excess clearance there will have you chasing your tail forever.

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