Marko's Workshop: August 2021

Monday, 2 August 2021

'73 Suzuki GT250 - Part 17 - Front brake system

To finish the front brake system I had to find a master cylinder and a caliper for it. Flat brake disc design doesn't allow much space near the wheel spokes so multi piston calipers with pistons on both sides were out of the question. I ended up going with front brake parts from a 1991 Kawasaki KX80. Master cylinder has 11 mm bore and brake caliper 30 mm bore.

Both front master cylinder and brake caliper required refurbishing. After disassembling both of them I stripped black paint out of master cylinder with paint stripper and soda blasted both of them. Aluminum pieces got a quick polish. I bought a new lever made by Motion Pro (#14-9318) and a rebuild kit made by ProX (#37.910001) for the master cylinder. I replaced old fasteners with DIN 912 hexagon socket head cap screws where I could. For the brake caliper I bought standard brake pads made by EBC Brakes (#SFA083) and sealing kit made by TourmaX (#ACK-451). Assembly vaseline delivered with the sealing kit turned out handy when putting both assemblies together and avoiding scratching new seals.

Polished front master cylinder parts

Parts of master cylinder rebuild kit

Details

Parts of master cylinder rebuild kit

Piston and new spring and seals

Piston assembled

Washer, stopper and cover seal for piston

Front brake lever

Black oxide fasteners replaced with zinc plated

Fasteners and return spring for front brake lever

Holder and fasteners M6x20 DIN 912

Diaphragm, cap and fasteners

Front brake caliper polished

Brake caliper sealing kit and pads

Piston, breather, spring and parts
from brake caliper sealing kit

New parts installed to front brake caliper

To get KX80 brake caliper to work with the brake disc I made for GT550 front fork and wheel I had to design a new bracket for it. I used the OEM KX80 front caliper bracket and CAD models which I created earlier for brake disc, front suspension and wheel as reference to get the geometry right for the new bracket. Once I was happy with the design I cut and machined parts for it which were then welded together. Before painting the bracket with primer and matte black I chamfered screw holes and tapped them for M10x1,5 thread.

I turned separate spacers (10x20x4) for the bracket out of aluminum. I wasn't 100 % sure how far bracket has to be from the brake disc so additional spacers give me some room to work with if I need change the distance.

Welding assembly of
front brake caliper bracket

Dimensions for plate

Dimensions for pins

Dimensions for spacers

Parts of front brake caliper bracket

Welding instructions

Welds of spacers

Welds of pins

Front brake caliper bracket
painted with primer and matte black

Guide on one side

Bracket and pads installed to front brake caliper

Other side

Hexagon socket head cap screws
M10x45 DIN 912

Dimensions for spacers

Spacers, 10x22x4

I ordered a custom stainless braided brake hose from HEL Performance. I carefully measured length for it after installing both brake master cylinder and brake caliper on the bike. I decided to go with straight fitting on the master cylinder side and with 20 degree angle fitting on the brake caliper side which made brake hose to run in a better angle in my opinion. I fixed the brake hose with M10x1,25 banjo bolts and put aluminum washers on both sides of the fittings. To keep brake hose from moving around I made a custom clamp out of stainless steel sheet. I added piece of heat shrink tubing to the round section of it to avoid chafing.