Topic: Front brake adjustment question

[cookindaddy]

I just finished rebuilding the master cylinder and the front brake caliper on my 78 cb750.

It works REALLY nicely now. New seals and new brakelines from pampadori.

I have a question about the adjustment of the screw in the picture. I can't seem to find anything about it in the Honda shop manual. It seems to be a limit on how far the arm can swing but I am not sure why it is necessary or how to adjust it since I don't know it's purpose.

[HondanutRider]

Here's a copy from my CB35F Shop Manual that describes the procedure.

[cookindaddy]

Thanks!

I understand, but am having trouble seeing the picture well enough to see which is pad B. Is it the inner or the outer?

[spitcrazy]

It sets the inner 'dead' pad. When the live pad moves in to the disc, I assume the pivot arm deflects and the pads grip the disc.

[HondanutRider]

It sets the inner 'dead' pad. When the live pad moves in to the disc, I assume the pivot arm deflects and the pads grip the disc.

Pad "B" as shown in the diagram, is the inner "dead" pad as described above.

Here's a bigger picture that may be clearer to see.

[cookindaddy]

I see.
Would the function be to keep the caliper from swinging too far inward and perhaps hitting spokes?

[mystic_1]

The brake arm would never swing that far anyway unless something was broke, cause the caliper would hold things in place.  Some guys run without the adjustment screw entirely.


When you let go of the brake lever, the only thing that retracts the pad into the caliper is the caliper piston seal.  This deforms when you squeeze the brake lever and the piston moves out, then it retracts when you let go and retracts the piston.

The amount of "spring back" from the piston seal is very small.  Call this distance X.  The idea is to set the adjustment screw so that the inner (dead) pad moves X/2 (half of X) distance before contacting the rotor.  That way, when you let go of the lever, BOTH pads retract from the rotor, the live pad because of seal retraction, the dead pad due to spring pressure.  End result: neither pad touches the rotor when the brakes are released.

mystic_1

[MCRider]

The brake arm would never swing that far anyway unless something was broke, cause the caliper would hold things in place.  Some guys run without the adjustment screw entirely.


When you let go of the brake lever, the only thing that retracts the pad into the caliper is the caliper piston seal.  This deforms when you squeeze the brake lever and the piston moves out, then it retracts when you let go and retracts the piston.

The amount of "spring back" from the piston seal is very small.  Call this distance X.  The idea is to set the adjustment screw so that the inner (dead) pad moves X/2 (half of X) distance before contacting the rotor.  That way, when you let go of the lever, BOTH pads retract from the rotor, the live pad because of seal retraction, the dead pad due to spring pressure.  End result: neither pad touches the rotor when the brakes are released.

mystic_1

Right o.

The problem with running without the screw adjustment is that as you go down the road, vibrations and bumpity bump can cause the A pad to retract even a little more, and as it does, so does the B pad causing an excessive amount of clearance between the pads and the disc.. This condition can get so extreme that one has to pull the brake lever twice, or maybe at least much further than normal to get the pads back where they are supposed to be, putting a delay in the braking action at a time when such delay could be dangerous.

[cookindaddy]

Ah!
Ok then.
I'll adjust it carefully.
Thanks!

[SanDogDewey]

Get the front wheel off the ground. Turn the screw till the inner pad touches the rotor and the wheel won't spin. Back it off until the wheel spins freely. Set the lock nut.

[Big Cobra]

I gotta question...I just finished re-sealing my forks(74 cb750) and I'm trying to get my front brake adjusted so that the brake pads don't touch the rotor while driving (causing wobbly steering).  So I got the front end off the ground--when I have it adjusted so the wheel spins freely the adjustment screw is not tight/or seated at all...this feels wrong to me.  I can use the lock not to keep it tight, it just looks and feels wrong....I've tried and will keep trying bigger tougher springs to see if I can push the brake medially...ANY SUGGESTIONS WOULD BE APPRECIATED.

[TwoTired]

If I may add to the already good info here...
The piston side pad will sometimes fail to retract (dirty or pitted piston usually, or is  could be a blocked relief hole in the master)
 Anyway, to adjust the fixed pad to the .006 inch clearance, you can push the piston pad back into the caliper before setting the fixed pad clearance.
If you set the clearance too close, you can get brake drag.  If you set it too loose, you get excessive lever travel on application of brake.

Cheers,

[MCRider]

I gotta question...I just finished re-sealing my forks(74 cb750) and I'm trying to get my front brake adjusted so that the brake pads don't touch the rotor while driving (causing wobbly steering).  So I got the front end off the ground--when I have it adjusted so the wheel spins freely the adjustment screw is not tight/or seated at all...this feels wrong to me.  I can use the lock not to keep it tight, it just looks and feels wrong....I've tried and will keep trying bigger tougher springs to see if I can push the brake medially...ANY SUGGESTIONS WOULD BE APPRECIATED.

Per Sandog...:
When you back the screw off to achieve the 6thou clearance it won't be tight to anything. THat's what the lock nut is for.  The arm that holds the caliper floats on the slack the "loose" screw provides.

[cookindaddy]

All excellent advice!
I will set it up tomorrow.
Thanks