Dual disk upgrade for USA spec 1975 650B

AlanW

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Apologies if this is already covered in the forums - but I’m interested in upgrading my single front disk to twin setup.
so.. is the upgrade worth doing, if yes, can someone please point me in the direction for parts, what to look out for etc..
Thanks.
 
Morn'n Griz! One advantage of dual discs if you use lighter rotors is it reduces fork twist.
plus they are just pretty! ;^)
front rotors.jpg
 
https://www.xs650.com/threads/xs650...workshop-manuals-and-other-information.30569/

Being in the UK it will be hard to source the US twin disk set up unless you are lucky. Calipers are the same. Although they do have a left and right caliper, 2 left or 2 right can be made to fit the other side buy changing the bolts around. RD's and TX/X500's and TX750's also had the same caliper as the XS/TX650, 73-76

US and UK/Euro 75's and later standards had different front forks and rotors. Read the link above and it has pics in the 75/76/77 that show the difference. Best read in light mode not dark
 
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Thanks for all the replies. I will stick with the original single disk and just try to remember I’m riding with 47 year old technology when I squeeze that lever!!
 
I agree with @grizld1 that a second disc adds unnecessary weight and complexity. IMHO the best upgrade to your front brake is a braided line and a master cylinder with a smaller piston. Did those changes, plus a perforated disc, on my 1978 Special and the front brake is transformed from kinda-works-but-feels-horrible to works well and plenty feel for what's happening. I no longer feel the need to allow for 44 year old brakes.
 
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Thanks for all the replies. I will stick with the original single disk and just try to remember I’m riding with 47 year old technology when I squeeze that lever!!
If you still would like to reduce unsprung weight, an alloy reproduction caliper from Economy Cycle will be an improvement:
https://www.economycycle.com/shop/y...er-front-rd250all350all40076-78-reproduction/
I have had that caliper on my RD 350 for years, and it has worked flawlessly (with a Brembo 13 mm master cylinder) The weight savings may not be quite 2 lbs, more like 1.5 lbs.
Also, ISR brakes in Sweden make custom discs, either for the OEM disc hub, or as a proper full floating disc with an alloy hub. ISR use a much better material than OEM, and disc thickness is 5 mm, not 7.
So with an alloy caliper, a more modern 12-13 mm master cylinder, and a disc from ISR, you would save a total of around 3 lbs and have a much better brake as well.
 
I just pulled out 2 discs, one completely stock 267 mm one piece from my Euro XS 650D, and a custom made ISR 298 mm, 5 mm thick on a stock 73-76 alloy hub.
The stock, smaller diameter "boat anchor" weighs 2580 g, while the larger 2 piece custom setup weighs 2058 g. This disc was planned for my RD 350, but I may abandon that plan. It is most likely overkill for a street RD.....
 

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thanks wideawake but my fork lowers are totally different. Pretty looking setup though.
 
Most collectors of the XS in the UK would really like a UK Spec XS650B.
The trouble is most of the original ones rotted out years ago and ended up in bike breakers (wrecking yards).
At one point spares for these bikes had a very low value here, and in the mid '80's I'd bet a lot of it was weighed in as scrap metal by dealers who just couldn't find buyers.
So you end up buying a US Spec 650B then try to retromod it back to UK Spec.
Nowt wrong with that if it gives you the looks and style you want.
Sure the unsprung weight will go up, braking will of course be better.
Yes there are obviously loads of performance options out there, but people are buying these bikes for a nostalgia trip, not to go fast
 
Grewth, you’re spot on. I bought the bike because the black 1975 B model was one I wanted. Coming from the US it has no rot issues and this one is really low mileage. But because I like tinkering I just thought it might be easy to bolt on another disk and calliper…. I’m now inclined to leave well alone and just enjoy it for what it is.
 
Grewth, you’re spot on. I bought the bike because the black 1975 B model was one I wanted. Coming from the US it has no rot issues and this one is really low mileage. But because I like tinkering I just thought it might be easy to bolt on another disk and calliper…. I’m now inclined to leave well alone and just enjoy it for what it is.
If your bike has the large 298 mm US market disc, a good set of SBS or EBC pads, a light resurfacing of the disc (if required), a braided hose from Venhill or Goodridge, and a 12 or 13 mm master cylinder, you will have all the brake your front tyre can take. Without altering the stock appearance much at all.
 
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