750 Seca Master Cylinder

Finally was able to remove the master cylinder on the 82 750 Seca (I envy you Maxim Owners). There are many threads about the tiny hole that must be cleaned in the MC. I believe this hole is on the Maxim MC which is mounted on the bars near the right controls. My Seca MC is a completely different design. Am I correct in that my Seca MC does not have this hole? I cannot see where there would be one.

 

Carl, I believe you are correct. The "tiny hole" in question is in the reservoir on all of the bikes that have the reservoir integral with the brake 'perch' on the right bar. Your bike has a remote reservoir which probably does have its own "version" of the little hole but it's not the one in all the posts.

 

Thanks Fitz. The reservoir only contacts the master cylinder pump tube casting in one location where the reservoir supplies it with fluid. The Seca MC must do what the small hole in the Maxim MC does by some other method.

I got the MC back on the bike and ready to bleed, but the game started.

 

The Seca Master Cylinder does have the same hole.
This picture is blurry but you can still see it just above the main hole.
I suffered for years with bizarre brake problems before finding this site and learning about the "hole"

The hole is behind where the plastic resivour meets the master cylinder, be very careful separating them as the grommet that seals the connection is unavailable as far as I know.

 

Ok, I'll bite. What's the story with this tiny hole? What happens if any debris gets in there?

 

Sushi, if it works the same as on my xj650 master cyl. it will cause sponge to no breaks at all. Depends on how blocked. the little hole allows the fluid to transfer back from the caliper & brake line. If it is blocked you won't get the pressure to actuate the caliper suffieciently. It has to be clean for the brake to function to its capability.

 

My experiance was brakes that worked good but would also seem to come on by themselves, or in hindsight probably not release entirely, pretty scarry experiance when blasting down the free way in traffic.

I rebuilt the master and calipers but the symptoms persisted, even my local Yamaha shop was clueless, most people suggested a line collapse.
Searching for an answer to this is actually what lead me to this site and the wealth of knowledge contained herein.

When I read about the tiny hole I pulled my master back apart, I was sure there wasn't a hole there but it was. It is hidden in a depression that looks like an unused part of the casting. I think moisture in the fluid collected there and oxidized the opening shut over time. That's one reason why we are supposed to change the brake fluid at regular intervals, if you haven't done it, do it soon and avoid these kinds of problems.

 

Got it, thanks.