Rear disc brake conversion - question

[OliverB]

I have acquired most of the parts (rear mag w/rotor, swing arm, caliper, hose and MC, brake pedal shaft) to add a rear disc brake to my 1980 but have one question. I know the rear master cylinder bolts to ears on the frame but, of course, my bike does not have those ears. What have others done to be able to secure the MC? I know tabs could be welded to the frame. Is that what most do and is it the best/safest bet? I would like to hear from others who have converted a newer XS400 (post '79) to a rear disc. I good close-up pic of the exact MC location with a measurement would be of great help, too. Thanks!

Any other comments about such a conversion are also welcome.

 

[crush1776]

I am doing the same thing, I can't imagine trusting the mc any other way than a welded bracket. What size/ brand tire are you going to run? If I get around to doing mine before you tackle it I'll make an extra bracket and share my process/ pain.

Good luck!

 

[OliverB]

I am doing the same thing, I can't imagine trusting the mc any other way than a welded bracket. What size/ brand tire are you going to run? If I get around to doing mine before you tackle it I'll make an extra bracket and share my process/ pain.

Good luck!

Yeah, I think a welded bracket is probably the safest way to go. I just installed a new set of IRC Durotour RS310 tires last week. They are classified as a "Sport Touring" tire. Bought them last Winter before I thought of this mod so if I do it soon, I will have to buy another new tire!! May actually put if off for now and use the time to rebuild/refurbish all the parts then get into it next Winter. Haven't decided for certain. There is a 110/90x18 as well as a 120/90x18 IRC Durotour RS310 available for the rear. My preference for the rear is the 120/90 size. From what we have learned recently, a tube should be put in the tire for this vintage rim.

Have you thought about tire type you want? My son is running Dunlop 404s and they are very much like the IRC tires I just bought. Whatever you do, get a matched set for best handling. I had my bike out on a 55 mph road in some gusty wind conditions today. Of course, a cycle will always be affected by wind gusts but with the set of IRCs, the bike was noticeable less twitchy in the wind than the mismatched set of Chinese tires that were on the bike when I got it - two different manufacturers and two different styles of tires.

Weren't you searching for rebuild kits for the rear MC and caliper? What did you come up with?

I would welcome input and help, too.

 

[scoutnaround]

weld the bracket on (or have it welded) here's mine

 

[OliverB]

weld the bracket on (or have it welded) here's mine

Hey, thanks! Great pic showing location and bracket design. Since I posted this thread, my son got a '79 with front & rear disc brakes so I will be restoring that over the Winter. Will leave my '80 as it came from the factory.