Upgrading and modifying my '79 KZ650 brakes?

My '79 KZ650 has the stock single caliper and original 40 year old rubber lines.

I wish to purchase a new MC (14mm would be correct no?) from ebay that also has the wiring for the brake switch.

That would allow me to run one single new braided stainless steel line from the MC to my caliper.

This would bypass the front brake light switch and with one singe brake line give me a more solid feel?

Any issues or problems that might arise ? How are these generic ebay MC units? I'd actually prefer a cup reservoir version truth be told. Any advantage to going for a 16mm MC instead? Less lever travel in theory?

I don't have a manual for your bike but it's customary for single disc bikes to use a 14mm bore master cylinder. Using a larger bore master like 16mm or 5/8" will result in a firmer feeling lever which will take more force for equivalent braking power. Master cylinders are simple devices so buying a new generic unit off ebay poses low risk. If you mount a mirror to the master be sure to look for that feature, and pay attention to the thread size.

In terms of the brake line, running a one piece line will be cheaper and simpler, but don't expect it to firm up the lever. If you buy a Teflon/stainless line you will enjoy a firmer lever all else being equal. I'm a fan of homebuilt lines using Earl's parts but that's just my point of view. There are lots of options for brake lines these days.

Lastly, installing some nice brake pads such as Ferodo Platinum's wouldn't be a bad idea, and of course, pop out the piston in your caliper to make sure it's all corrosion free inside. Replace the piston if it's pitted and consider new OEM Kawasaki caliper seals. Beware of aftermarket caliper seals, particularly from K&L since, in my experience, they are inferior to OEM in terms of fit.

Good luck

The stock master cylinder on my motorcycle is embossed with 1/2 & the piston measures 12.5mm (1/2" = 12.5mm).
I installed a good used Fr brake mc from a Honda CBR500. It's an oem Nissin brand made in Japan & it also has 1/2 cast into it.
For the brake lines I went with Goodridge lines & fittings from Z1Enterprises.com. upper line & lower line.
I got the Fr br wire lead from a KZ1000P police bike. same wire colors. matching terminals.
My motorcycle is 1981 KZ650 w single disk Fr br & rear drum. If the age of the Rr brake shoes is unknown, replace them.

In the XS650 world we swap our MCs for a smaller diameter (from 14mm to 11mm) to firm the lever. Apparently European XS650s have dual disk brakes while the NA 650's have a single disk but they kept the larger MC. The other alternative is to add another caliper and disk to the front and keep the stock MC. Of course this adds unsprung weight so you have to choose your poison. In any case, I would avoid the eBay MCs and try to adapt a stock Japanese MC if you go that route.

ThatGPzGuy wrote: In the XS650 world we swap our MCs for a smaller diameter (from 14mm to 11mm) to firm the lever.

Going to a smaller diameter will have the opposite effect of firming the lever.

Nessism wrote: Going to a smaller diameter will have the opposite effect of firming the lever.

Odd. It's a common modification in the XS world and one of the first modifications recommended. I know it worked for me but then I also replaced the rubber brake lines with a single SS line at the same time.

No eBay APP ID and/or Cert ID defined in Kunena configurationOkay, I spent a little time looking at the parts fishe and factory manuals and according to Partzilla the master cylinder piston/cup assembly is used on a wide range of bikes including single disk brake KZ550's, 750 twins, 440's, and the KZ650 B2-B3, (plus others) www.partzilla.com/product/kawasaki/43020...731ecad49de27beda452

Looking up the service info in the factory manual for the 550 shows that the single disc bikes used a 14mm piston master (dual gets 16mm.)

ThatGPzGuy wrote:

Nessism wrote: Going to a smaller diameter will have the opposite effect of firming the lever.

Odd. It's a common modification in the XS world and one of the first modifications recommended. I know it worked for me but then I also replaced the rubber brake lines with a single SS line at the same time.

To visualize what's happening realize that in order to create a specific amount of braking force the caliper piston must move out of it's bore by a certain amount (call it X.)

To move the caliper piston X amount we need a specific volume of fluid pumping through the system.

If the master bore is made smaller than the original size that means that in order to pump that specific volume of fluid the master piston needs to travel further then before.

So in the end, using a smaller bore master will require more lever travel, the lever force will be lower though so it's a trade off. Less travel required but more force OR, more travel and a mushier handle feel. That's the trade off.