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Front Master Cylinder - Rebuild or Replace?

  • Thread starter Thread starter srg
  • Start date Start date
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srg

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I took my front braking system apart on a whim today just to see what's inside. I'm glad I did. It was pretty bad.

mc_gunk.png


mc_cleaned.png


Anyway, apparently there's only certain parts still available from Suzuki. I can't get the base assembly thing, cap, or the screw holding the reservoir on. I can get a new reservoir, seals, and piston.

Is it worth it to get those OEM parts (costing roughly $70) or should I just get a whole new master cylinder?
 
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I just bought a master cylinder from Ebay, one of those cheap Chinese jobs. Came in a few days, works fine, comes with a rebuild kit should I ever need it, and it costs less than half of your $70.

There are better ones and cheaper ones, but they mostly all work.
 
Yep, as Tom says, those cheap Chinese MCs work just fine and they're cheaper than the repair parts. It remains to be seen whether they'll last 30 plus years but my oldest one is 7 or 8 years old and fine.
 
I had good results with an MC from Mike's XS. They have several different ones, with different bores, and most have a new brake light switch, which is an improvement over the GS one.
 
Ok, I think I'll replace the whole master cylinder. I always disliked the look of the reservoir anyway. Should I be looking for a specific size or compatibility?

I'm also gonna build my own brake lines with new adapters. Is http://www.anplumbing.com/ still the best place?

On my bike, the front brake line is split into two hoses. The joint is pictured below (that's the front of my forks, looking up - Left side goes to MC, right goes down to caliper.). What's the point of this? In my opinion, another hose fitting joint just adds two more potential points of failure. Can I just run a single line from the MC down to the caliper?

front_brake_line_joint.png
 
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Yes you can, commonly done that way.

Are you planning to stay with the one front brake or go with dual brakes?
 
tkent02 said:
I just bought a master cylinder from Ebay, one of those cheap Chinese jobs. Came in a few days, works fine, comes with a rebuild kit should I ever need it, and it costs less than half of your $70.

There are better ones and cheaper ones, but they mostly all work.
Click to expand...

Link?......
 
Anyone know what piston bore I should be getting for a single caliper brake? Would I need a different bore if I later upgrade to a twin-pot brake (single disk, just twin-pots)?
 
srg said:
Anyone know what piston bore I should be getting for a single caliper brake? Would I need a different bore if I later upgrade to a twin-pot brake (single disk, just twin-pots)?
Click to expand...

Sometimes they work, sometimes they don't. Not sure why. On a few bikes like the '79 750 I did with the 1000 engine, dual brakes worked perfectly with the single disc master cylinder. On the 550 I'm working with now, it didn't work very well at all. I don't have any idea why. You got some braking, but it didn't really come on all that hard.

That's OK, my brakes are sweet now!
 
srg said:
Anyone know what piston bore I should be getting for a single caliper brake? Would I need a different bore if I later upgrade to a twin-pot brake (single disk, just twin-pots)?
Click to expand...

If you want to be dead accurate about it, you need to work out the hydraulic leverage involved, but generally, a 16mm / 5/8th" will happily do a pair of 1980-on calipers and for the older, '79 smaller calipers, a 14mm or even 13mm will do fine.
However - there's one big proviso - that's not taking the wear and tear of old caliper mounts into account. High-mileage worn mounts will sometimes knock back the pistons a touch if the front rattles on bumps and if you have to do any sudden braking, you find yourself with some lost motion on the lever before anything happens. A situation best avoided.

If you go too small, you get a good feeling lever that runs out of room before you brake enough to avoid hitting something, and if you go too big, you get a wooden lever that you have to heave on to stop any time soon.
Google for brake hydraulic leverage - it'll tell you all you need to know.
 
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Thank you Grimly, that's exactly the information I was looking for. I like to be dead accurate about it ;-) I'll do some research on Google.
 
For dual caliper bikes Suzuki used a 5/8" master cylinder. I'd look for one of those 16mm jobbies off ebay. If you go with a 14mm master the hand lever will feel spongy compared to larger master, and more hand lever movement will be required. Don't be surprised if the lever comes almost all the way back to the grip during heavy braking.
 
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