Topic: Brake pad clearance issue

[eelliiss]

I am reassembling my 75 CB750K and in the last stages of completion.  Last night, for the second time, I tried to put the caliper together with new pads.  The first time, I realized that I didn't have the same year caliper for my specific bike.  It turned out to be a 77-78 caliper, so I had to order new parts such as the pistion seal, bleeder screw, and pads.  Parts arrived yesterday, and once it was all together on the bracket and over the disk, the wheel would not spin freely.  To illustrate how tightly the pads are on the rotor, I wasn't able to push the bike around.  The forks just compressed when I tried to move the bike forward. 

The inside of my rotor and my entire hub are powdercoated.  I actually had to use a dremel to get the powdercoat off the inner lip of the rotor so that it would sit flush on the hub.  I'm wondering if the additional layers of powdercoat between the two components is pushing the rotor out and causing it to sit too tightly on the active pad.  I also wonder if the rotor is mismatched to the caliper.

With this info, what would you guys do?  It's been suggested to me by a mechanic to either machine down active pad or to add some sort of shim on the bracket. 

Also, how much should the active pad be sticking out of the caliper?  Should it be completely flush with nothing sticking out or should there be about 1/8th of an inch protruding?  I have Daido pads if that makes any difference.

[MCRider]

i can't address all your questions, not up on later model parts. Of course the pads need to be free to move etc. But a solid lock up you have may mean something else.  You need to eliminate this common problem from the list.

If your Master Cylinder is pumping but not releasing you get the symptom you describe. If you loosen the brake line at some point, like the bleeder valve, then tighten. And the pads release their grip, then the problem is the MC. Put a rag over the bleeder because the fluid will come out under pressure and squirt everywhere.

try that test and if it passes, report back and we'll discuss the master cylinder problem. Very common problem.

[eelliiss]

i can't address all your questions, not up on later model parts. But you need to eliminate this common problem.

If your Master Cylinder is pumping but not releasing you get the symptom you describe. If you loosen the brake line at some point, like the bleeder valve, then tighten. And the pads relaese their grip, then the problem is the MC. Put a rag over it because the fluid will come out under pressure and squirt everywhere.

try that test and if it passes, report back and we'll discuss the master cylinder problem. Very common problem.

Correct me if I'm wrong, but there are no lines connected to the caliper at this point and no fluid in the systems because of this.  This experiment wouldn't work then, no?

[MCRider]

i can't address all your questions, not up on later model parts. But you need to eliminate this common problem.

If your Master Cylinder is pumping but not releasing you get the symptom you describe. If you loosen the brake line at some point, like the bleeder valve, then tighten. And the pads relaese their grip, then the problem is the MC. Put a rag over it because the fluid will come out under pressure and squirt everywhere.

try that test and if it passes, report back and we'll discuss the master cylinder problem. Very common problem.

Correct me if I'm wrong, but there are no lines connected to the caliper at this point and no fluid in the systems because of this.  This experiment wouldn't not work then, no?

Uh, ... never mind.

[eelliiss]

I truly do thank you, though, MC.  You've always been a tremendous help!

[eelliiss]

MC, would you think machining down the pad ever so slightly would be a viable option?  One part of me thinks that it would be an ok "fix" since the pads are designed to wear, but another part of me thinks it is a little too easy of a fix.

Thoughts?

[MCRider]

MC, would you think machining down the pad ever so slightly would be a viable option?  One part of me thinks that it would be an ok "fix" since the pads are designed to wear, but another part of me thinks it is a little too easy of a fix.

Thoughts?

I can't think how that would further the situation. The A pad is designed to go into the caliper, that shouldn't offer any resistance to the rotor turning. Of course it needs its circumference to be free to allow the A pad to travel in its cavity. But that should be obvious.

As I mentioned I'm not up on the later parts. My first hand experience stops with K2. But...

The B pad is on the "swinging gate" adjuster. If the adjuster screw is too tight it draws the B pad into the rotor. Whether the A pad is even in the caliper or not, if the B pad is adjusted too tight, you have resistance. There sb 5thou clearance between the B pad and the rotor, via the adjuster.

[eelliiss]

MC, would you think machining down the pad ever so slightly would be a viable option?  One part of me thinks that it would be an ok "fix" since the pads are designed to wear, but another part of me thinks it is a little too easy of a fix.

Thoughts?

I can't think how that would further the situation. The A pad is designed to go into the caliper, that shouldn't offer any resistance to the rotor turning. Of course it needs its circumference to be free to allow the A pad to travel in its cavity. But that should be obvious.

As I mentioned I'm not up on the later parts. My first hand experience stops with K2. But...

The B pad is on the "swinging gate" adjuster. If the adjuster screw is too tight it draws the B pad into the rotor. Whether the A pad is even in the caliper or not, if the B pad is adjusted too tight, you have resistance. There sb 5thou clearance between the B pad and the rotor, via the adjuster.

The wheel will not turn even when the adjuster screw is not in the bracket.  Again, I think that the new, additional layers of powdercoat between the hub and the inner rotor possibly "push" the rotor out enough that it is pressed up against the A pad to prevent rotation.  I'm not the most mechanically inclined, but that is the only thing I can think of outside of the possibility of the rotor being too thick for the caliper since they may be potentially mismatched.

[ekpent]

Does the new pad slide in and out of the caliper recess easily without sticking or getting hung up. On some new pads I have had to sand and dress up the outside edge of the round brake pad to properly fit in the caliper without hanging up. Also there should not really be any powdercoat in the area either if I am reading this correctly ?

[MCRider]

The A pad should go into the caliper to the point where the rotor is hitting the caliper. (At least in my minds eye)  In other words the A pad should offer no resistance. Esp since there is no fluid in the system.

With the adjuster screw out, the B pad should not be in contact with the rotor. is it?

[eelliiss]

Does the new pad slide in and out of the caliper recess easily without sticking or getting hung up. On some new pads I have had to sand and dress up the outside edge of the round brake pad to properly fit in the caliper without hanging up. Also there should not really be any powdercoat in the area either if I am reading this correctly ?

The both pads take the slightest pressure to get it in there, but remove easily.  There is no powdercoat on the inside of either parts the caliper.

[MCRider]

Does the new pad slide in and out of the caliper recess easily without sticking or getting hung up. On some new pads I have had to sand and dress up the outside edge of the round brake pad to properly fit in the caliper without hanging up. Also there should not really be any powdercoat in the area either if I am reading this correctly ?

Yes this is true, I did not say it as well.

The powdercoat, at least as I read it, was on the hub of the rotor. This would space the rotor away from the wheel hub by the thickness of the powder. This should be absorbable by the caliper adjuster I'd think.

[eelliiss]

The A pad should go into the caliper to the point where the rotor is hitting the caliper. (At least in my minds eye)  In other words the A pad should offer no resistance. Esp since there is no fluid in the system.

With the adjuster screw out, the B pad should not be in contact with the rotor. is it?

The active pad ever so slightly sticks out of the caliper, meaning the actual pad is not completely level with the outside of the caliper.  Maybe 1/8th of an inch.  I feel like it has bottomed out, and is sitting where it should be.  Someone chime in if this is not correct. 

I think that there is contact with the rotor, but I didn't try to slide anything in there to make sure.

[70CB750]

The pad on the piston side should have sides sanded, polished and lubed to make it move easily in the caliper.

As somebody here wrote here while ago -  the pad should fall out on it's own when you turn the caliper sideways.

[scottly]

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.

[eelliiss]

Thanks for all the help, dudes.

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.

^^^^^^

This is an extremely helpful post!

[MCRider]

Wow! I did not know that. Glad I recused myself from knowing about K2+ parts.

[eelliiss]

What does that whole arm look like from the K7?

Anyone have one??

[70CB750]

I think I do - bought it by mistake when shopping for my dual disc setup.  I will measure it and take a picture for you tonight.

[eelliiss]

Actually, now that I'm looking at the diagram on Hondaparts-direct and examining the attached pic in scottly's post, I think I may have the correct one.  There is much more clearance between the two pads than his pic.  It doesn't look like a rotor would even fit with the arm/caliper combo on the left.

[eelliiss]

Also, my caliper components line up to the arm much better than what is pictured in scottly's post.

[bjbuchanan]

I know that ebc brakes somerimea need some sanding on the pad material. My shoea i basically had to contour to fit the hub. Its not much material that comes off but its an important amount. Its only takes a little to grab tight. If the caliper functions right i would take a new clean sheet of sandpaper and take a little material off

[eelliiss]

Should the active pad immersed within its socket with no pad showing?  In the above picture, this looks to be the case.  If so, this might be the problem. 

[scottly]

The active pad is not installed in that pic...

[eelliiss]

Does anyone have a pic of a new active pad fully set into the caliper?  Maybe that would be a good starting point.