Topic: Brake pad clearance issue

[Dream750]

For starters, the 1977-78 caliper is not correct for your K5, this mismatch may be causing your binding problem. The correct factory stock caliper looks like the one in the pic below.
 
Here’s how the owners manual shows caliper adjustment. Also note the orientation of the caliper arm to the rotor. There is a distinct offset is present between the caliper arm and rotor when correctly assembled and adjusted.
 
Lastly, the fender brace mounts on the outside of the caliper arm parts, otherwise binding will occur. Ask me how I know this.

[eelliiss]

For starters, the 1977-78 caliper is not correct for your K5, this mismatch may be causing your binding problem. The correct factory stock caliper looks like the one in the pic below.
 
Here’s how the owners manual shows caliper adjustment. Also note the orientation of the caliper arm to the rotor. There is a distinct offset is present between the caliper arm and rotor when correctly assembled and adjusted.
 
Lastly, the fender brace mounts on the outside of the caliper arm parts, otherwise binding will occur. Ask me how I know this.

This may have been addressed in this post:

The K7-K8 arm is thicker in the area where the caliper mounts. In the attached pic, a K7 caliper with a K1 arm is on the left, and a K1 caliper with a K7 arm is on the right. I suspect you have an earlier arm. BTW, all the 750K discs are the same.

I do believe that I have the correct arm though.  A 77-78 caliper on a 69-76 arm does not look like it would allow a rotor in with even only one pad installed.

I think that I will try to sand the outer edges of the active pad to see if it will further set into the caliper.  If this does not help, I will machine down the pad.

[chickenman_26]

I think that I will try to sand the outer edges of the active pad to see if it will further set into the caliper.  If this does not help, I will machine down the pad.

The mating surfaces of the rotor and hub must be completely free of powdercoat (and anything else), and perfectly flat. I suggest you do that before machining down anything else to compensate. You can easily remove the powdercoat with a rag soaked in acetone or even brake cleaner. Just be sure to mask off any areas you don't want to clean.

Stu

[madmtnmotors]

 You need to at least post some picts before "machining down" the brake pad. Something is not right.

[eelliiss]

It'll be this weekend before I get the bike again. It's at a friend's garage about 35 minutes away. I'll take pics then.

[ekpent]

I will say that if the piston is pushed in all the way in the caliper the new brake puck should easily fall in there where the brake material is flush to the outside and not protruding out.As you bleed the system the piston will regulate that aspect.

[eelliiss]

I will say that if the piston is pushed in all the way in the caliper the new brake puck should easily fall in there where the brake material is flush to the outside and not protruding out.As you bleed the system the piston will regulate that aspect.

Thanks for addressing this. It was one of my biggest concerns. Mine sits out a little bit.

[camelman]

I'm totally spitballing here, but installing the axle nut backwards on a 350/400f causes this exact symptom. I am not familiar enough with the 750 setup to know if it might be an issue. Anyone with 750 knowledge want to chime in?

Edit: just looked up the 750 axle and it is similar in design to the 350/400. I think the nut is correctly positioned with the flats inboard.

Camelman

[70CB750]

Do you mean the cylindrical nut on the front axle?  And what is the wrong way installing it? 

[scottly]

With the caliper unbolted from the fork legs, will it slip easily over the disc? If yes, this indicates an alignment issue. If no, then the pads are too thick, or are not seating fully in the caliper. Do you have the nylon ring that fits between the piston and pad properly in place? If it is not centered on the piston, it can push the active pad outwards by about 2 mm.

[MCRider]

Do you mean the cylindrical nut on the front axle?  And what is the wrong way installing it?

1. The axle nut goes on opposite side of speedo drive and 2. the nut goes on the axle hex inboard.

I've seen both errors made and the owners actually rode it.

[eelliiss]

Definitely gives me more things to work with when I get back to the bike. I'll report back soon, duder mcdudersons.

[totty]

I think that I will try to sand the outer edges of the active pad to see if it will further set into the caliper.  If this does not help, I will machine down the pad.

The mating surfaces of the rotor and hub must be completely free of powdercoat (and anything else), and perfectly flat. I suggest you do that before machining down anything else to compensate. You can easily remove the powdercoat with a rag soaked in acetone or even brake cleaner. Just be sure to mask off any areas you don't want to clean.

Stu

I doubt this is the reason for the brake binding, but I agree 100% regarding the mating surfaces. I've had a disk work loose on another bike with painted mating surfaces.

[70CB750]

Do you mean the cylindrical nut on the front axle?  And what is the wrong way installing it?

1. The axle nut goes on opposite side of speedo drive and 2. the nut goes on the axle hex inboard.

I've seen both errors made and the owners actually rode it.

I see, some people just don't have it, do they:)  - while I am quietly correcting mine 

[chickenman_26]

I'm totally spitballing here, but installing the axle nut backwards on a 350/400f causes this exact symptom. Camelman

That's a great example of thinking outside the box, while the rest of us are focusing on the items the poster is discussing. You're correct, and I have to admit I once created the same issue on my CB500 when not paying attention and installing that nut with the flats outboard.

Stu

[eelliiss]

Maybe a silly question, but which way does the piston go into the caliper?

[flybox1]

Hollow side towards the pad

[eelliiss]

Hollow side towards the pad

I don't have a hollow side, per se. 

[MCRider]

There is a metal cap with a convex roundness to it that covers the hollowness of the piston. Your cap may be stuck on?

[eelliiss]

There is a metal cap with a convex roundness to it that covers the hollowness of the piston. Your cap may be stuck on?

Got it.  Very helpful. 

Should the cap come off with relative ease?  I've sanded some of the pitting a few weeks ago, and never realized that the piston is two separate  pieces. 

[eelliiss]

Also, if this is the case, I have the piston in incorrectly.  Maybe this will help me resolve some of the issues right now with the binding?

[MCRider]

Yes, the cap should fall off from gravity.

[eelliiss]

Yes, the cap should fall off from gravity.

Is this something that I will need to absolutely take care of?

[scottly]

The K7-K8 piston does not have the rounded removable cap. It has a piece pressed into the pad end. The piston itself is a cup, and the bottom of the cup goes into the caliper.

[eelliiss]

So in the following pic, the smaller portion of the piston on the right side of the groove should completely come off?