Author Topic: Aftermarket Rear Master Cylinder Replacement Guide $10-$25  (Read 25110 times)

Offline lmiklosy

  • One Less Car
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  • Posts: 67
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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #100 on: January 30, 2019, 07:21:00 PM »
Rear MC rebuild update:    I rebuilt my MC using a piece of tough silicone rubber brakeline.  Slid the brakeline on a mandrel chucked in a drill, sanded the contour to a piston seal shape and installed the seal on the piston with some Brembo silicone grease.   This fix cost $0 and works, no leaks since 2017.   My Chinese brake cylinder remains in a box  as a spare.    :twothumbsupp
  • Laguna Beach, CA
  • 1993 K75S-Mystic, 1981 R100RS-RedBaron, 1991 K75S-Marrakesh

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #101 on: March 10, 2019, 05:07:08 PM »
Update as of March 10, 2019:

I have now done the retrofit on a total of four bricks.  Two 1994 K75's with ABS and two K100RS 16V. 

First off, there appears to be two ways the rear brake line is attached to the master cylinder.  Either with a banjo fitting or by screwing a threaded hose end fitting into the end of the master cylinder.  The banjo fitting is the easiest, just use the bolt that comes with the new master cylinder.

The brake line that screws into the end of the master cylinder will raise problems as the Chinese master cylinder has a different thread.  In order to connect the rear brake line you need to get a new one with a banjo fitting so you can use the bolt and washers that come with the new master cylinder.  Another option(that I haven't tried) is to have a new hose made with a fitting with the correct thread.  Either way, you need a new brake line.  If the existing line is original, you probably need a new one anyway.  Even if you are replacing a newer line, you are still ahead of the game with the money you save with the Chinese master cylinder.

Second, Instead of trying to splice the new supply line to the old one, I just go to the auto parts store and buy 3 feet of rubber vacuum line.  A couple inches of 1/4" i.d. clear vinyl tubing from the hardware store is also needed.  Total cost should be under $3.

Take the fabric covered hose off the bike's reservoir.  You need to open the clamp to do it.  Be careful not to break the hose barb on the reservoir.  Push the 1/4" vinyl tube onto the barb, and cut it off even with the end of the barb.  Spread a small drop of liquid  soap on the tube, and push the 5/16" vacuum line over it.  With the tube and hose I get, the fit is so tight no clamp is necessary to hold it together.  Feed the hose down and connect it to the new master cylinder using the clamp that came with the cylinder.

The bonus here is that the 5/16" vacuum line allows the fluid to flow more easily to the master cylinder, making the bleeding and flushing of the rear brake incredibly easy compared to doing it with the old 6mm OEM line.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE
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Online Martin

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  • Posts: 3872
Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #102 on: August 18, 2019, 09:05:02 PM »
Master cylinder update, over two years on Chinese master cylinder with no problems. I had one as a backup but I kept of having to sell them.  One was mate of a mate and has not reported any problems with his after a year of use. I just ordered another spare $14.05 Au slightly up in price from $13.33Au. However this time I used a different supplier and it comes in black so worth the extra .72 cents. I would never bother going back to an OEM cylinder or a kit. It's a lot easier and quicker to just replace it with another Chicom one.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline lmiklosy

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #103 on: August 19, 2019, 12:37:08 AM »
Same here, piston seal fix still holding no worries. Spare Chinese MC remains in box.   :bmwsmile
  • Laguna Beach, CA
  • 1993 K75S-Mystic, 1981 R100RS-RedBaron, 1991 K75S-Marrakesh

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #104 on: August 19, 2019, 07:13:43 AM »
I've installed them on three bikes now.  Total mileage on the three master cylinders is over 20,000 miles with no problems.  The modifications necessary to install them are fairly straightforward to me now and are easier than doing a rebuild(and with a lot better results).

The only thing you need to be careful of is the brake line fitting on the cylinder.  Some of our bikes have the line attached with a banjo fitting, and others have the line threaded into the master cylinder.  You may have to use a new line with a banjo fitting.  No big deal because even with a new line it's still cheaper than buying a rebuild kit.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Online Martin

  • ^ Quintessential Motobricker
  • Posts: 3872
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline tannerman917

  • Curious
  • Posts: 6
Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #106 on: September 17, 2019, 11:28:43 PM »
Just mounted up my new RMS... I didn't like how little travel I was getting with the piston threaded directly into the pedal, so I made a second joint for the piston that I'm gonna try.  I rounded off the threads on the end of the stem and drilled out a cap screw with a ball end mill so it rotates freely.  We'll see how it works once I get a new brake line for it.
  • USA
  • '85 K100 RT

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