Topic: 1972 CB750K rear brake

[Beav068]

Hello, I hope somebody can help with a problem I am having with my old girl. I just picked up this bike from the original owner with 15k miles on her. I purchased tires, tubes and rim strips straight away, and had it all installed professionally. Shortly thereafter I tried to take a friend to pick up his 75 CB750k and discovered that with the added weight, the rear brake was locked by movement in the linkage.

Help me! Is this just an adjustment problem or was something possibly put back together wrong?  I did not try to double up before the tire job, so I have no comparison to make.

Thank you!

Tim

[eldar]

I would say it is either an adjustment issue or when the suspension gets compressed, something looks up the brake arm.
The brake rod is on the right side, you will see it just follow from the brake pedal. Turn the adjust nut out a ways and the brake pedal should go down about 2 inches or so and the tire should about lock up. You can also put the bike on the center stand and remove the shocks and lift the tire and see if the brake locks.

[Beav068]

I CAN adjust the brake back when I add the extra weight.  However, I am thinking that there should be a built-in feature that maintains the brake travel when the extra weight is added.  Is this not the case?

Tim

[dusterdude]

the weight should not be an issue,check the brake anchor rod and make sure its not loose.been there done that.

[Beav068]

Not to be a pain, but I'm kinda new to this bike.  Where is the anchor rod?  On the drum, the frame or what?  The rod I see is the "linkage" that pulls the activator arm on the drum.

Thanks,

Tim

[dusterdude]

you have a rod that runs from the brake backing plate to the frame up under the swingarm.check and make sure its not loose.

[Bodi]

There's no compensation for the slight change in brake pedal travel as the suspension compresses. The brake pedal should have about 1/2 inch minimum free travel with your weight on the bike. Setting a small free travel can lead to the brake locking up as the shoes expand from heating.
The torque arm attaching holes can get worn to ovals and allow some slop too. If you roll back and jam on the brake and then find the brake grabbing hard the next time you go forward that's probably happened.

[Beav068]

Bodi - thanks for the clarification.  I was told by the PO (original) that there was no compensation and that I needed to adjust the brake travel when I had a passenger, but that didn't make sense to me.  I guess that's the price you pay for having an early model bike. :-)

You were probably right about the limited travel hypothesis - I have re-installed the original 4-4 exhaust (looks awesome!!) and now have much more travel in the rear brake pedal, which allowed me to back off the adjustment nut a bit, so hopefully that will be sufficient so that I don't have to readjust for double up riding.

Thanks to all for your help!!

Tim