[goodoltup]

Now that I've finished with the CD175 engine upgrade project (CB200 cylinders and bottom end with a CD175 head, see also CD175 upgrade to 200cc, 12V, electric start, 5 speed gearbox ) I can move on to another project I've been looking forward to, putting a disc brake on the CD175. (I call it the CD200 now).

The CD175 stops "okay" with the small, single leading shoe front brake it came with. But, in some panic situations you feel like you're about to snap the cable. It takes a LOT of force. A twin leading shoe brake would be an improvement. The mechanical CB200 caliper and disc would be an improvement. But also why not go crazy and put a modern disc and caliper on?

Thoughts going into this:

I'll try to use a CB200 wheel and hub first. It has a higher likelihood of the axle diameter matching up, and the speedo drive being the same.​

I'd like to convert the CD175 to 18" wheels anyway, so the CB200 wheels would be a good fit. I'll do the rear wheel as well.​

I might use a remote master cylinder so I can retain the CD175 handlebar controls. I might have to tuck this behind the headlight shell or maybe under the battery or somewhere.​

I'll plan on welding mounting lugs on the fork leg, not trying to use CB200 forks or similar. I want to retain the CD175 chrome fork covers.​

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Some risks:

Speedo drive might not fit up properly. I'd rather not use an electronic speedo or anything, I'd like to keep it original. If I move to an 18" front wheel then the speedo will definitely be off a little. I might repaint the dial if it is too far off.​

Welding lugs on the fork leg might be a disaster. I won't do, I know a coded welder that I have used on other projects.​

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Bike is still up on the table from the engine project and I won't be riding it in the UK cold, so now is a good time.

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[goodoltup]

State of the front end in the initial state. In order to use the CB200 speedo drive, the disc will have to be on the left hand side of the bike. I'd like to mount the caliper behind the fork leg, in the space between the fork leg and lower fender stay.

 

[goodoltup]

CB200 front wheel has been sourced for mockup purposes. The rim will need to be replaced, and the spokes, and the speedo drive. But the wheel was only £60 pounds delivered, with the tyre and disc and spindle etc. A bare hub would cost almost £50, so for an extra tenner I've got some temporary parts for mock up.

 

[goodoltup]

After a cleanup I put the wheel in the forks. Immediately you can see that the 18" rim and tyre fit nicely. The disc will probably not be used, but it's good to see it on there for reference.

 

[goodoltup]

The CB200 fork spacing must be narrower, because the spindle is shorter and there is 12mm total gap between the hub and spacer stack and the forks. I will take the CB175 wheel spacer and part it off in the lathe to create two 6mm spacers for either side. Then I will use the original CD175 spindle and nut. So far so good. The drum brake mounting boss will have to be cut off the forks.

 

[goodoltup]

I'll order these parts for mock up and see how it goes. The disc is from a Yamaha TZ125. It's 267mm OD, so about the same size as the CB200 disc. It's flat, so I can make an adapter plate/spacer on the lathe and the disc will still have the same offset. The ID and bolt PCD are also convenient. The caliper is a copy of a Suzuki EN125. I like it because it's twin piston, relatively small, and is meant to be behind the fork leg on the left hand side. It also has a steel adapter plate, so if I need to modify it to fit I can cut and re-weld if needed.

 

[Boomer343]

I had a mounting bracket broken in shipping on a GL1800 lower leg. Took it to a specialty welder for repair. Asked him if he wanted me to take everything apart and he declined saying it would be better to weld it with the parts assembled. Doing it that way he had no concerns with the tube going out of round inside where the fork tube moves.
Since he was also the welder who repaired the frame on the bike for a factory recall I was already trusting his abilities. All worked out.

 

[goodoltup]

I had a mounting bracket broken in shipping on a GL1800 lower leg. Took it to a specialty welder for repair. Asked him if he wanted me to take everything apart and he declined saying it would be better to weld it with the parts assembled. Doing it that way he had no concerns with the tube going out of round inside where the fork tube moves.
Since he was also the welder who repaired the frame on the bike for a factory recall I was already trusting his abilities. All worked out.

Hi Boomer, thanks it's good to know it's not a crazy idea. I figure there is a fair chance that the fork leg will be so contaminated with oil that it will never get a clean weld. My welder has not replied yet, I hope he has some recommendations about the aluminium alloy that will weld best so I can get some stock to make the lugs.

 

[goodoltup]

Small side project. I've had some aftermarket stainless fork sleeves waiting to be put on, now seemed like a good time. I removed the legs fully and replaced the sleeves, and staked them on. Reassembled, they look great. The old chrome ones were quite bad looking. I intend to keep the patina on the painted parts of the bike, but these just looked too crap. I fully reassembled the front end, that's where it is now.

 

[goodoltup]

The master cylinder has arrived. It is much bigger and uglier than I thought. I can use it for now, but I don't like it. I may use a more traditional type from a CB400 or something. I can always change it later.

 

[goodoltup]

The disc arrived. It had some flaking paint on it so I cleaned it up and offered it up to the hub. I now have all the dimensions I need to make the spacer/adapter. I'll post a picture of the STP file when I do the CAD at work on Tuesday.

 

[goodoltup]

Wheel spacer CAD. Getting quotes now.

 

[goodoltup]

The TZR125 disc has about 35mm of useable friction diameter. The EN125 caliper I originally planned (two piston) for leaves a good amount of unswept area. I got a GS125 caliper (single piston) and it covers a lot more area. There is still around 8mm of unswept area, but I think I'll live with that.

 

[goodoltup]

From eBay I got a new speedo drive, as the original one had a perished rubber bushing. I also took some time to remove the bearing retainer from the hub and give it a quick clean and inspect.
Next, I'll mock it all up and hopefully order the spacer.

 

[goodoltup]

Disc spacer has been ordered. It was around £130. Delivery two or three weeks.

 

[goodoltup]

Disc spacer arrived. It is beautiful.

 

[goodoltup]

Here it is on the CB200 hub, with the TZR125 disc on it.

 

[goodoltup]

I ordered the spacer with the M8 holes simply drilled, not tapped. This was because at the time of ordering I hadn't decided on the bolts yet, so they could have been coarse or fine thread. The bolts have been chosen now (M8 x 1.25) so I tapped the holes to suit.

 

[goodoltup]

I had to enlarge the bolt holes on the disc to 10mm, to accommodate a shoulder on the new disc bolts. I felt better having a shoulder bolt than having the disc ride on the threads.

 

[goodoltup]

Had to remove the drum brake boss on the forks to clear the new disc. No going back now.