'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.

Specifications of custom brake hose

Stainless steel braided brake hose

Close up of the straight fitting

M10x1,25 banjo bolts and washers for brake hose

Master cylinder

Clamp for fixing brake hose to the bottom yoke

Brake caliper

'73 Suzuki GT250 - Part 11 - GT550 front fork swap - 1/2 - Rebuilding front shock absorbers

Some of you might remember me purchasing a set of Suzuki GT550 front forks quite a long time ago. At the time I wasn't sure what to do with them until I got my GT250K project going. First I was thinking of rebuilding GT250 forks for this project but the set I have was in worse condition than these ones. Good thing about these are that they are more rigid than GT250 front forks. Main difference is that stanchions have 35 mm diameter compared to 32 mm ones in GT250. Otherwise main dimensions like spindle diameter and steering bearings are the same so it's easy to swap them. I will feature triple trees and mock up more detailed on next part. This part will cover rebuild process of front shocks.

Suzuki GT550
front forks

Below is a picture of steps how to assembly Suzuki GT250 & GT550 front shocks (left to right). Same process applies also for disassembly but from right to left. I disassembled my forks long time ago I didn't unfortunately take pictures of that process.

Steps of assembling GT550 front shock absorbers

Upper parts of old stanchions were very pitted and rusty most likely due to moisture accumulating inside headlight brackets. Since I wasn't going to use original headlight brackets and wanted to leave them exposed I went ahead and bought myself a new pair of stanchions from eBay instead trying to do anything with the old ones. I cleaned sliders and circlips, which attach to bottom of the stanchions, and installed them to the new ones.

New stanchions for Suzuki GT550 front forks

Unboxed

Comparison of new and old stanchion

Sliders and circlips in order

I decided to shave off ears from outer tubes which the stock front fender attaches to since I didn't have any use off them anymore. I started by cleaning outer surfaces of them with soda blasting gun. After that I removed most of material with a saw and an angle grinder. Since there were still a lot of excess material to be removed I used a file next. I tried to be careful and not remove too much or making too deep scratches while filing so I marked a spot with a red marker pen to indicate when to stop and move on to sanding. I used normal sand paper for rough and wet sand paper for finer sanding. Last step was to polish them with buffing wheel and polishing paste. I purchased new hardware for inner tubes and axle holders and screwed them back on.

Outer surface of outer tubes cleaned with soda blasting

Ear sawed off

I marked an area which I wanted to file flat
with a red marker pen

After rough sanding...

...and finer wet sanding

Buffing wheels and Autosol polishing paste

Outer tubes and axle holders after polishing

New M8x27 hexagon socket head screws
with low head (#51147-48130) and copper washers

Rebuilding outer tubes

Non-serrated M8 flanged nyloc nuts DIN 6926 for axle holders

After getting stanchions and outer tubes back together it was time to mate them together. I started by sliding the rebuild stanchion inside the outer tube. Before installing a new oil seal I made sure that the upper slider was inside the outer tube. Otherwise it would have been a nightmare to get the oil seal out to get it back inside. For this project I chose fork seals made by Pyramid Parts (#FOS 013) just like I did with my CBR600F. After knocking oil seal in place I put on a washer on top of it and installed circlip with circlip pliers.

Pyramid Parts fork oil seals #FOS 013

Box comes with a pair of 35x48x11 mm oil seals,
seal buddy tool, lubricate and a sticker

Slider, oil seal, washer and circlip

...and order how to put them back together

Circlip installed with circlip pliers 

Last step was to install new fork dust seals, slide in springs, add fork oil and screw on caps to top of stanchions. Since these forks originally had boots instead of dust seals I wasn't sure if I was able to find a suitable pair for them. I ended up ordering a set of Pyramid Parts fork dust seals (#DB10) which seemed to work decently well with them. I got myself a one liter bottle of 15W Motul fork oil and measured 2.35 deciliters for each shock. Caps were little bit pitted as well so I took a small piece of aluminum foil and brushed rusty spots with it under a running water. That's an easy trick to get rid off small rusty spots from old steel parts which are chrome plated. Off course it's not a permanent fix but a lot cheaper than new parts or chrome plating. I replaced old O-rings with new ones (#51181-31030) before screwing them back on.

Outer tube dimensions

Pyramid Parts fork dust seals #DB10

Springs, caps and set of dust seals

Fork inner tube caps and O-rings (#51181-31030)

Motul SAE 15W Expert Medium Heavy fork oil (#101138)

Measured roughly 2.35 decilitres of fork oil
for each shock

Rebuild Suzuki GT550 front shocks

Check out also part 2 where I complete this swap after refurbishing top and bottom yokes and fitting it to my GT250K 😎