Master Cylinders for dummies... '80 550L

[MatBirch]

Hey gang,
Rebuilding an '80 550L for my wife, and the front m/c is in really rough shape, both inside and out. I did some research before, and there evidently no rebuild kits for these bikes. Even if there was, the outside is trashed as well. Short of ponying up the coin for NOS, what are my limitations on just picking up an aftermarket unit? Ebay is of course full of really fancy looking chrome, and skulls, and what not, but just a clean looking, functional m/c should be easy enough, right? Does anyone have experience with any of these? One concern is the NEXT rebuild... What then? Seems I'd have a part with no support for rebuild kits and such again, right???
If I stay with factory parts, and look toward other, newer bikes, what do I need to keep in mind with respect to piston size, etc.? Why isn't a master cylinder a master cylinder???

BTW- my apologies, but this not a stock restoration... Not a shatbobb, but not stock either. I don't need factory parts if there is a suitable, more affordable part.

Thanks !!!

[cowboyup3371]

Others can tell you the exact type you can use but I will say I have a Kawasaki MC with Kawasaki twinpot brakes on my bike. The point is, you can use other MCs from other bikes as long as they are the correct bore for the brake style you have.

The single brake MCs have a 14mm bore while the duals ran 5/8" bores. Look for a MC from a bike with a setup similar to what you have (I had an 850 MC on my bike at one point).

[tkent02]

You can run the smaller single caliper bore with dual calipers, it increases braking pressure slightly for a given finger pressure… I prefer one finger brakes to two or more. You must have a tight system to do this, as the smaller cylinder moves less volume of fluid. Must have no air in the system, etc. Nice new braided brake lines would help to.

[derickson104]

I ran into the same thing rebuilding my 79 GS550 - MC rebuild kits were not an option. I actually went with an 08 KLR650 MC from ebay since the 14mm piston bore, single disk, mirror mount and handlebar attachment (7/8'') all matched. The mirror threaded right in, banjos were no issue and it works great - all for a fraction of an oem or aftermarket part (no salesmanship intended). Just remember that if you're planning the double-disk upgrade you'll need a different MC and banjos to accommodate that. I would recommend the self-bleeders from Z1 if you're rebuilding, makes life much easier.

Below is some stuff I collected from other threads on the GS Res. about fitting MCs from other models, good luck:

"GS Brake Cylinder Sizes
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" (.625) 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.
16mm is the inner diameter of the piston bore. 16mm is stock of a 550 with dual discs – not sure about your 1100.

If you go with a 14mm bore master cylinder the lever will have a more spongy feel but you will have reduced lever force for any given amount of braking force. 16mm will have a firmer lever feel but you will have to squeeze harder. Again, not sure what the stock size is so you need to do some research.

The proper size master for a single disc front brake is 14mm.

The first MC you linked to is a 12.7mm (1/2”) bore. It would fit your bike (would have to modify the brake switch connection) but probably isn’t what you want if you have dual front calipers. IIRC Suzuki used 14mm MCs for single and 5/8” (15.875mm) for dual caliper.
GS handlebars are 7/8". 1" is a Harley size, plus some of the modern big metric crusiers have adopted it as well.

Single disc brake master cylinders are 14 mm, whereas dual disc GS masters are 5/8" which is larger. You can use a 5/8" master on a single disc bike but the hand pressure required to use the brake will increase. One side benefit of the large bore master is the lever will have a firm feel with less sponginess than a 14 mm master."

[GSXR7ED]

I'm rebuilding mine...problem I'm having is getting the "piston & cup set" out.



I pretty much damaged the piston twisting it off with pliers. I was planning on buying replacement parts anyway since I don't have any other way to remove it. She came out...now I just need to soak the caliper in solvent.



I'm interested in buying another type of MC is I can't get this piston/cup set out without damaging the MC.


Ed

[MatBirch]

Thanks for info! It helps a lot. I'm planning on picking up something different. I don't believe my current one is original anyway. In looking at everything, it seems different. The tank is trapezoid shaped. It is also sinfully ugly! The lever is HUGE! Lol

[Spiff]

lots of clean and nice looking brakemastercylinders here, complete with all you need

http://www.dimecitycycles.com/cafe-racer-parts/suzuki/vintage-suzuki-gs-caferacer-cafe-racer-motorcycle-parts/suzuki-gs-caferacer-motorcycle-brakes/suzuki-gs550-gs650-caferacer-brakes.html

[GSXR7ED]

Mc

lots of clean and nice looking brakemastercylinders here, complete with all you need
http://www.dimecitycycles.com/cafe-r...er-brakes.html

Thanks for the heads up!

I wanna keep this original MC but if I break it while disassembling, it's good to know where I can procure another.


Ed