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Replacement front master cylinder

  • Thread starter Thread starter Bennys78
  • Start date Start date
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Bennys78

Guest
Hi, My 78 GS750 is to the point where it's all going back together. One thing definitely needs replacing is the Master Cylinder. Rebuilding is not an option and I'd prefer not to have a remote reservoir. Bike is twin disc.

My first thought was a DL-650 master cylinder from prior 2007 (or DL-1000 post 2007). The piston is marginally bigger than the GS, it carries a mirror mount and fits 7/8 handlebars. The only difference is the pitch in the banjo bolt, 1.0 Vs 1.25. Given how often banjo bolts are replaced, I can live with that.

A potential option is the Radial Master Cylinder from a B-King, It has the same banjo bolt thread size + the mirror mount and fits the bars. Problem is I know nothing about radial master cylinders.

Common sense says if it stop something as ugly as a B-King that has a heavier dry weight than a stock GS750 and 8 caliper pistons then it will be good for the GS750 without being too harsh. Making my GS 0.7% B-King is kind of a turn-on as well.

Any thoughts or knowledge around this?
Suggestions around a modern replacement for the rear master cylinder that bolts straight on (I've been at this bike for a year, I'm all about easy at the moment) may also give you good karma.
Cheers.
 
Going for a later master cylinder is a good idea. Check that the window is still useful for keeping an eye on the brake fluid level.

Important: Take it apart before fitting and clean out and replace any rubber parts if required.

This is the most important component on your bike and your life could depend on it!!!

If you have a single front disk a master cylinder piston diameter of about 13mm or 1/2" would be good enough and give good travel on the lever and finger stopping. The DL650 sounds good.

If you use one from a bike with double disks and piston size 16mm or 5/8" or larger, and maybe multiple pistons, you may find that it will require too little pressure on the lever to stop and you may find it too powerful.

The banjo bolt is no problem as long as you have a good one and have proper sealing washers on each side.

You must also ensure that you already have or can use the front brake switch on the new master cylinder or get a new one.
 
Radial is nice another possibly cheaper more readily available alternative that I use is the GSXR1100 (93-95) master cylinder. You can mix and match the GS mirror mounting top bracket with the GSXR lower to still use a mirror.
 
You can replace the mechanical piece of crap brake light switch with a hydraulic one that goes under the banjo bolt as well and you don't have to worry about whether it works with that or not.
 
On a tangent . . . has anyone successfully adapted a newer generation rear master cylinder to a GS1000?
 
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