75 CB750 Brake Question

[Harper.]

I just bought a 75 Honda CB 750, and as a pre-emptive apology I'd like to say up front that this is my first bike and I'm very new to motorcycling, so please excuse any bone-headed questions.

On my first ride I noticed a problem with the front brake. There was a constant squeal and pressure seemed to be building up in the brake line until there was almost no play in the lever and the caliper was constantly engaged. The rotor was sizzling hot and the wheel could not turn freely. At home I dissembled the caliper and cleaned inside with brake cleaner and soft cloth, applied brake quiet behind the pads, reassembled, and refreshed the brake fluid. Now the brake is serviceable (but relatively weak and still squeaky), but I want to replace parts because the pads are worn and the piston is pitted. My question is: can I use 1976 parts interchangeably on a 1975 motorcycle (OEM parts are available online from Powers Edge.com for 76 but not 75, and there are other parts on the bike that need to be replaced, so it would be great if I could just order specific parts online, rather then looking on ebay or gettinf a parts bike), or would it be possible (better?) to get an entire new brake assembly from some other company that would be more powerful. And, if I could get a modern brake system, how can I find one that fits?

Thanks so much for your help

[Tech78]

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[Re-run]

I would put up a brake write up but there is no way to sticky it or faq it. On the K bikes, the calipers are all the same for most purposes, the 77/78 F calipers are different. The lines on the K bikes are all the same or at least all interchangeable. They all end in the hard line. Anyways, as long as the parts are K, then you should be good.

A newer system is not really an option without mods as far as the caliper goes. Here is what you do.
remove the whole brake system. remove the piston and remove the hose, basically pull the whole system apart. Remove the bleed screw and get a speed bleeder. Inside the caliper there is a rubber ring, remove it. Use a brass brush such as a dremel attachment. Clean all around the inside of the caliper, especially the area where the rubber ring sits. Now put the piston back in and set it aside.

Now you do not need it, but a cir-clip pliers will make it easier. Remove the clip inside the barrel of the master. This allows you to pull out the piston there and clean it all up and remove the corrosion there. You may need to replace some of the seals there. Put it all back together and attach the hoses.
Remember to clean and grease the pivot pin for the caliper arm, if cant move smoothly, it will bind.

Put it all back on and start filling the master and bleeding it down. Here is where the speedbleeder saves you a lot of time. Hook a hose to it and open it about 1/4 turn and pump away, just make sure the master does not drain. Squeeze the lever slowly though or you will shoot the roof of your garage with brake fluid!

Get it all bled and it will work good. A braided brake line will seriously improve your stopping. I am mixed on the drilled rotors though. On one hand, it cools better and can help in the rain, on the other  hand, you are removing material used for stopping and the rotor does heat up faster. If you do get one, just make sure it does not have too many holes or the rotor could crack.

[Tech78]

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[Myumi-2]

Re-run's cleaning procedure is on my regular servicing list.

Another option, everytime you stop and the caliper is binding, kick the outside of the caliper, this forces the piston back into the caliper by pressing it against the disc.  This might not be in the Honda repair manual but it makes me feel better.
 

[Re-run]

The housing though is purely cosmetic, the rest is the same. As for the pressure switch, most people get rid of them anyways, it is not required in any way you just get the 77/78 master which most feel works better anyways but even if you do not dump the switch, you can still use a 77/78 caliper and it will bolt right on.

[Harper.]

Thank you everybody for the replies, this is incredibly helpful.
I have a few follow up questions:

1) Is there any authoritative source for parts for these bikes (where I could get a "high quality set of pads" or a new rotor)?
2) Stupid question, but I'd rather know than make a mistake: what do I use to grease parts like the pivot pin for the caliper, or bolts so that they don't stick?
3) If there's pitting on the piston in the caliper, does it need to be replaced?

Thanks for the advice

[Re-run]

Pitting is common when people use DOT3 fluid. It attracts moisture. If a piston does NOT have pitting, it wasn't used! Some mild pitting is no big deal, if the pits cover most of the surface or are really deep, then replace it.

I used regular grease on the pivot pin, works fine. What bolts do you refer to? The caliper bolts? I would actually use blue loctite on those but the lock washers should hold them fine.

David siver spares can hook you up with a rotor. You can still get pads from honda and many other sites carry them.

I have a list of places but again, no sticky or faq area here.

[Harper.]

Great, thanks, I get to work on the bike today (finally) so I'll check all this out.
Actually, I was referring to the pin that the caliper assembly pivots on, the one that you can adjust with that spring-loaded screw. I think someone mentioned that if the caliper can't pivot freely there it can cause sticking.

Thanks again

[Re-run]

That was me. And regular grease is fine, just a light coat is all you need.

[Steve w/'74 Honda CB750]

The problem with increasing pressure is the master cylinder.  There's a tiny port that is likely clogged.  Rebuild the master

[Re-run]

Excellent observation Steve. The return hole is certainly a possible option. That hole is tiny and clogs easily. I know other who have had it clog. it is also a fun hole to have when you squeeze the brake lever and the cap is not on!