Vintage brake adjustment Shimano BB300 - 600

[Ray_72]

Hello

Hope you can advise. I am currently fitting a pair of Shimano 600
brake calipers and I am unsure what adjustment is needed to the double bolts in front of the fork.

On the front caliper it is clear they need to be tightened as the arms are all over the place. So I tighten the front bolt up but then the caliper doesn't move as expected, so I back them off a bit until the arms move freely but then the whole assembly including the front bolts move with the arms and lose adjustment very quickly.

Whereas on the back caliper the arms move smoothly and the bolts remains in their position.

Is this purely an adjustment device and a lock nut? I am assuming the bolts when set should remain in a fixed position? Maybe just clean and regrease?

Thanks, Ray

 

[Old Ned]

Strip them down for a good clean and a light greasing. The adjustment is more or less as you say with the 2 nuts locked together with very little or no play. Are there any washers between the nuts and the front of the stirrup? Get the stirrups to move as you want then hold the front nut while you back off the inner nut a tad to lock them. You really need a pair of suitable size spanners for this.

 

[Ray_72]

Re:

Thanks for your reply, that is sorted now.

However, I now find that when the calipers are cabled up only one side springs back when the lever is released. - what is causing that?

Ray

 

[Nob]

Maybe they are missing a brass type shim washer?

 

[ZG862]

Re: Re:

Thanks for your reply, that is sorted now.

However, I now find that when the calipers are cabled up only one side springs back when the lever is released. - what is causing that?

Ray

The other thing that might cause this is the spring being biased to one side. Indeed, the ability to adjust this precisely is the defining of the various black-capped Weinmann brakes, in which a tool can be inserted to control the position of the central bolt (which carries the spring) whilst its nut is tightened to hold it in position. In the absence of such a feature, you need to get a little bit clever with holding the lock nuts that you have been adjusting. If when tightened you can get them to align (or offset by 30 degrees), you should be able to slip a ring spanner over both simultaneously and thus rotate the bolt at will, allowing you to control the position of the spring and thus the relative force that it applies to each arm and then lock this position with the back nut. Of course, the spring may be corroded or dragging where it loops or where it acts on the arm, so Old Ned's lubrication advice is spot on, but also the random fitting of extra washers in the system can mean that the bolt is never stationary as intended. Some designs have a star washer in front of the nut to help it bind into the frame and this can become worn out too.

 

[Ray_72]

Re:

Thanks for your replies.

I took the whole assembly apart this morning, cleaned, re-greased and remounted. Its works well now but it took a while to get the right amount of balance between the front arm adjustment bolts and the rear caliper mounting bolt. Too tight and the whole thing would bind, backing off slightly allowed the arms to move with very minimal fore-aft play.

I think I am used to modern calipers where everything is rock solid - these needed "fettling" which you dont need to do these days.

thanks once again, Ray

 

[droppedout]

Be careful with cable lengths as too long or too short will tend to pull the caliper to one side or the other.