Disc brakes.

[Dickytee]

Howdy all,
TX650A 1975.
I’m playing around with installing an extra disc up front. In my search for a good match for the current disc I’ve noticed a variation in how they mount. See photos. In photo 1 the disc appears to have a bearing and I can’t get my head around how it works. I’m after the disc in the second photo. I’m in Sydney.
TIA.
Dickytee.

 

[GLJ]

The first disk is for a XS2. One year only. You have to have a 72 hub/spool to use it and 72 fork legs.
If you look at the back side of it you will 2 rectangular areas 180 apart from each other cast into it. The hub has 2 corresponding lugs on it that fit into them.

 

[Dickytee]

Thanks. Are all other types compatible?

 

[GLJ]

I think 73,74,75 and 76 are the same. Not sure after that.
Hopefully a more knowledgeable person will chime in.

 

[jetmechmarty]

For sure, the '77 and later brakes are altogether different.

 

[JJames]

Others may weigh in, I'm just not sure how much is to be gained by adding a second disc. Especially a heavy old xs disc. It's your bike. Hopefully someone who has done this conversion will comment. Welcome to the forum.

 

[drgonzo]

Others may weigh in, I'm just not sure how much is to be gained by adding a second disc. Especially a heavy old xs disc. It's your bike. Hopefully someone who has done this conversion will comment. Welcome to the forum.

I agree, a well set up single disc can get the job done quite nicely. Drilled disc, good pads, braided line, correct master cylinder ratio, etc. But then, I've not done a dual disc conversion.

 

[GLJ]

I also agree dual disks are generally not needed for normal riding. Especially if you have the 76 and earlier caliper. I do know there are people that can utilize and at times have a need for the stopping power of a dual set up. I do not ride fast enough to really need duels. But with that being said I am building a 72 with dual front brakes. I have to use a 73 front end to do it. I'm mainly doing it for the looks.

 

[motormike]

I had duals on my 77'... took a disc and caliper off a 750 Yamaha triple... bolt on... used the 650 master.. no problems. The bikes in Europe came with dual disc.

 

[Jim]

I added the dual disk to my '80 SG. It looks cool. Yes... I know all about the unsprung weight I added. I don't care. Doesn't bother the ride much at all... at least not the way I run nowadays.... but it looks cool.

I know that a smaller master would have cured the wooden feel... but the duals look way cooler than a smaller master nobody would notice.

Yes, getting rid of the wooden feel was my main reason. Love the new feel. Another reason was more stopping power... I seem to be a magnet for phone users in cars. It has that in spades. Know what else it has in spades?... Pizazz. It just screams "look at me!!"

...and that's all the reason I need.

 

[bosco659]

My ‘76 has dual discs but not stock. I love the braking capability and modulation. I had a ‘79 with a single disc and hated the wooden feel. I agree with @Jim about how cool dual discs look.

 

[XSTime]

To me that left fork leg having empty mount holes is just not right.
Adding the left side disc and caliper does immediately improve the braking and feel of the stock master cylinder.
Some guys really go negative about the added weight but having done most of my fast riding on an FJ1200 which has a very heavy front end, that planted front wheel feels just fine.

 

[Dickytee]

Thanks all. I’m aware of the unsprung weight factor. Especially with those old 70s discs that could double as a bbq plate. The brake as is feels wooden and it doesn’t pull up as quickly as I’d like. And I’ve always liked the balanced look of twin discs. Also I love tinkering around in my shed.

 

[Its been a long time]

Thanks all. I’m aware of the unsprung weight factor. Especially with those old 70s discs that could double as a bbq plate. The brake as is feels wooden and it doesn’t pull up as quickly as I’d like. And I’ve always liked the balanced look of twin discs. Also I love tinkering around in my shed.

I had a 76 XS650C in the UK, they had dual discs. Stoppies were easy. It was a very good front brake for the time. Back then though when it rained you'd better be careful. The Japanese factories hadn't worked out yet how to get brakes working with wet discs.

For my recently acquired 650D (US spec) I'm recommissioning it with the stock single disc front end. But I have a complete custom built dual disc front end to bolt on to it later.

 

[arcticXS]

My Euro 77 XS650D had dual discs from the factory, 267 mm diameter. And frankly, those brakes were piss poor and stupidly heavy. So into a cardboard box with the stock discs, calipers, hoses and master cylinder. A custom made 320 mm disc from ISR in Sweden a 34 mm 4 piston Brembo caliper, and a 13 mm Brembo MC transformed the brakes to purely 2 finger operation, and reduced unsprung weight by around 5 kg, which is a lot, also improving suspension noticeably.
So I would definitely not recommend adding a second disc, from a function perspective. Especially not on a US bike with the 298 mm discs.

 

[gggGary]

To get a dual as mentioned a fork from a 77-79 XS750 Standard NOT a special will give you everything BUT you will need to transfer the steering stem from an XS650 triple to the 750 triple, not all that hard.
Next in line is a later (78 up) xs650 fork complete. The LH caliper is available aftermarket. To keep weight down use rotors from later Yamaha sport bikes with spacer collars.
When I got my 79 special

Same bike now.

An 18" rim with a 110/80 /18 modern tire to match the brakes stopping ability. And a fork brace to reduce shaking under that hard braking.
Like everyone else here, it's more show than go (stop)

 

[jetmechmarty]

To get a dual as mentioned a fork from a 77-79 XS750 Standard NOT a special will give you everything BUT you will need to transfer the steering stem from an XS650 triple to the 750 triple not all that hard.
Next in line is a later (78 up) xs650 fork complete the LH caliper is available aftermarket to keep weight down use rotors from later yamaha sport bikes with spacer collars.
When I got my 79 special
View attachment 260112
Same bike now.
View attachment 260113
An 18" rim with a 110/80 /18 modern tire to match the brakes stopping ability. And a fork brace to reduce shaking under that hard braking.
Like everyone else here, it's more show than go (stop)

Those lighter weight rotors don't hurt a bit.

 

[Bountiful]

My Euro 77 XS650D had dual discs from the factory, 267 mm diameter. And frankly, those brakes were piss poor and stupidly heavy. So into a cardboard box with the stock discs, calipers, hoses and master cylinder. A custom made 320 mm disc from ISR in Sweden a 34 mm 4 piston Brembo caliper, and a 13 mm Brembo MC transformed the brakes to purely 2 finger operation, and reduced unsprung weight by around 5 kg, which is a lot, also improving suspension noticeably.
So I would definitely not recommend adding a second disc, from a function perspective. Especially not on a US bike with the 298 mm discs.

Hey arctic, this is a modification that I seriously want to consider on my ‘77 D this year. I’ve been doing some research and I’ve found so many options however I’m just not certain on what’s best for the bike with the least amount of messing around. My bike came with dual 298’s, those and the calipers are so heavy it’s ridiculous. I got a quote to cnc my discs down from 7mm to 5 with holes drilled -£550! lol surely I could get a better set up at a fraction of that?! I don’t want something OTT just a set up that’s realistic in weight, safe, that I can rely on. Could you share some more information about your set up? I’m thinking of changing out my front 19” for a 2.15 18” would this complicate my choice of brake set up? Kind regards Kev