Seca 750 Master Cylinder Transplant

Those liking aesthetically pleasing modifications may want to avoid reading the rest of this write-up. The XJ750 is ugly enough, but this has turned it in to a sort of Frankenbike of hideous proportions.

As you all know, the front brakes on the Seca 750 are an exercise in horrible design. I decided to remove the cable-actuated master cylinder and replace it with a bar mounted one, and running both brake lines directly from the new cylinder. The cylinder I used was from a CBR 600 F3. I was worried that because the F3 weighed about 100 lbs less than the Seca, the volume displaced by the F3’s piston might be smaller. Then I read that the F3 has dual twin-piston calipers and rationalized that the volume must be more.

The first step is to cut off the brake lever mounting bracket from the right control pod. I used a combination of a hacksaw and a Dremel cutting disc. The end result is not pretty but if you’re feeling up to it, you could always sand it down and paint. You should also at this point disconnect the cable from the brake lever, and the brake light switch leads.



At this point I realized that metal shavings were falling on to the fork dust seals, which could eat away at the fork seals below. Don’t make this mistake. Cover up your dust boots. I used wet paper towels and medical tape.




Next, remove the screws holding in the turn signal stalks, and the screws holding in the headlight and foglight. You need to pull the headlight housing out far enough to remove the two screws holding the master cylinder to the forks (in red). You also may want to remove the brake line going from the master cylinder to the splitter. It makes removing the MC much easier, as it is a tight space. I couldn’t get the fittings to budge so I just cut the line with the Dremel tool. You’l also have to snip the level indicator leads from the MC. If your new MC doesn’t have them (mine doesn’t) just splice them together and solder. It will complete the circuit and prevent your “BRAKE” idiot light from illuminating.





Next, install your new master cylinder and route your new brake lines. Be sure to use new crush washers wherever there is a mating surface. Also, connect the brake switch leads to your new MC. Polarity does not matter. After all the lines are hooked up, bleed, road test, then bleed again.

There is a huge increase in front braking ability, as well as modulation and feel. The lever from the CBR is much longer and thicker. Grabbing the stock lever felt like I was riding a mountain bike.





For those interested in cost, I paid about $40 on Ebay for the MC and lever, $50 for the hoses, and $40 for the banjo fittings. A container of DOT4 was around $7.









I bought the lines and fittings from Z1 Enterprises. You can order any length and the prices aren’t that bad.

 

Hi and thanks for the info.
Did you take off your anti-dive lines? Would be necesary?

Thanks & greetings!

 

you did yours pretty much identical to mine, just a bit messier lol

 

Or, you could do what a PO apparently did on my 750J -- jumper wire with two male bullet ends in the headlight bucket.

 

I collecting all the neccessary parts to switch mine over too. Only I think I will run one brake line from the master cylinder to a T fitting to split into two lines instead. I think it will look cleaner than having two lines coming off the master cylinder. Just a thought.
Yes, I agree the Seca is one butt ugly bike in it's stock form. I sure didn't buy mine for its looks, that's for sure. And that front brake system is not one of Yamahas better ideas at all. I can't wait to get mine switched over.