Slabby rear master cylinder

[yyt]

As usual I'm always trying to fix everything without thinking its easier and cheaper to buy a new part.

I'm fixing my 30 years old original Rear Master Cylinder and because at the rear the oil has never been changed it damaged the cylinder bore with pits at the center.

I got a honing bit in order to smooth the pits.

The 1/2" diameter - 12.7mm got to 13.3mm to eliminate completely the pits at the bore.

Any one here knows if its OK?

Should i hone to 14mm and find a 14mm (same length) replacement piston?

Is the original hopeless to fix and i must replace it?

I want to keep the original set-up, is there a newer bike equivalent  to this master cylinder?

I saw a Chinese set-up which looks very close which i can fit for 10$.. are the Chinese stuff any good?

Any Recommendations? I'm stuck at this point..

 

[Swiss Toni]

You could get the cylinder bored out, and sleeved back to original size?

[yyt]

Guess  most just buy new or just don't look down that hole/ bore ..

Anyone knows what kind of oil/grease is best for the internal rubbers of the braking parts?

It will take a while (some months) before I will connect all the braking components and fill the system with DOT4 fluid.

 

[SiBag]

Red rubber grease.

[crow]

I don't think a 0.5mm oversize bore will seal properly, that's a pretty big clearance for the seals to take up.

Boring out to14mm will change the hydraulic ratio & make the pedal feel firmer but reduce power. If you go down that route, it might be difficult to get the bore the right size to work correctly, the original will have been machined to precise tolerances to work with the piston & seals. I would just replace it.

I use brake fluid on master cylinder seals and red rubber grease on caliper seals

[yyt]

Its about time I update..

Well, I got  a rear master cylinder from China. didn't have any specs, bot I saw in the picture: the "1/2" and the overall size looked like it will fit, so I bought it for some 10$.

Its amazing that all these parts are 10$. It looked great and needed only minor changes to fit.

I opened it up and found its 14mm!! (although on the body casting there is a "1/2")

So, trashed it aside..

 

[Dorkburger]

Another thing I've heard about those Chinese remote reservoir M/Cs is that the hose is garbage, not resistant to brake fluid and eventually fails. 

[bluedog59]

One thing regarding m/cylinders and calipers, The front brake on my DR650 was never up to much, more a speed adjuster than a brake, cleaned them both out and serviced everything but to no avail. I was just about to look at a caliper swap when I decided to give them one last chance and dropped them in the ultrasonic tank,

Bingo, I have a brake. 

[Dezza]

On 3/22/2018 at 9:20 PM, yyt said:

Its about time I update..

Well, I got  a rear master cylinder from China. didn't have any specs, bot I saw in the picture: the "1/2" and the overall size looked like it will fit, so I bought it for some 10$.

Its amazing that all these parts are 10$. It looked great and needed only minor changes to fit.

I opened it up and found its 14mm!! (although on the body casting there is a "1/2")

So, trashed it aside..

 

Do the new internals from the Chinese MC fit in the (now 14mm) original body? Also, why is the 14mm Chinese mc not worth trying out, or am I missing something here? It would be fairly straightforward to change the hose and any other bits if interchangeable with the original unit. <1mm difference in the mc bore diameter isn't going to make much of a difference to the feel of the rear brake, and it's the rear brake anyway. Hill starts, more use when it starts raining......

[yyt]

Sorry..

I was  in the middle of continuing the epic when I was distracted and had no time through the weekend.

I didn't want to put the 14mm internal piston (which looked just as good as the Suzuki original replacement part) as to not to change the relationship between the piston/leverage/force of the original Suzuki engineers.

Anyway..

I ordered from USA a used  1995 Suzuki GSX750F for about 9$ with shipping 25$, and still less than half the price I could (not) find locally.

Had to make slight upgrades to make it fit and the rear bracket to connect, painted it and it was perfect.

Drowned it  with red rubber grease n put i away..

 

 

[yyt]

Thanks to Swiss Toni

On 12/12/2017 at 11:33 PM, Swiss Toni said:

You could get the cylinder bored out, and sleeved back to original size?

I made a sleeve : OD-14mm, ID-12.7mm

 

Glued the sleeve with 3M Scotch-Weld structural adhesive.

I also just in case, tested the strength and resistance to brake dot3 fluid by gluing 2 bolts together and let it stay submerged in brake fluid ( after 2 months up to now, its perfect).

Got all assembled and was really pleased with the result.. 

 

 

 

 

[Swiss Toni]

Good! Looks like you did an ok job too!