XS2 Front Disc Brake - what fails ?

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Grewth

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I've almost got enough rolling chassis parts to build up a complete XS2 now.
But one thing puzzles me.
I can't work out why Yamaha designed that weird "floating disc" arrangement for '72, and then felt the need to rework it all for the TX650 in '73.
That suggests to me that the '72 set up didn't work out too well.
The guy who sold me all the XS2 bits described the front brake design as "crap", but didn't care to elaborate on exactly why.
Looks like he had trouble with the weird spigot arrangement that connected the disc to the wheel.
So what actually goes wrong or causes trouble ?
A bad design or just poor maintenance ?
 
Jim said:
Our XS2 experts that spring to mind...

@Mailman
@GLJ
Click to expand...


The only reason I can think of is that the factory simply improved / simplified the design. The XS2 front disc had a lot of fiddly bits, including rubber parts that will crush over time. The newer designs had far fewer pieces in the design.
As for performance, my XS2 stopped every bit as well as my ‘77 XS650.

If you are getting into your front brake, I have a media album just for the front brake with a lot of detail photos, you might find useful for reference .
-Bob
https://www.xs650.com/media/albums/xs2-disc-brake-detail-photos.3096/
 
Mailman said:
The only reason I can think of is that the factory simply improved / simplified the design. The XS2 front disc had a lot of fiddly bits, including rubber parts that will crush over time. The newer designs had far fewer pieces in the design.
Click to expand...
Good point. I know '73 was the first year Yamaha put a disc on the RD350. So I'm pretty sure the '72 XS was the very first disc design from Yamaha. Stands to reason they'd improve it the second year out.
 
Courtesy of @TwoManyXS1Bs
XS2 Service Bulletin directions for installing a service/upgrade kit from Yamaha. I have never seen this kit anywhere.
1714093783721.png
 
Grewth said:
I've almost got enough rolling chassis parts to build up a complete XS2 now.
But one thing puzzles me.
I can't work out why Yamaha designed that weird "floating disc" arrangement for '72, and then felt the need to rework it all for the TX650 in '73.
That suggests to me that the '72 set up didn't work out too well.
The guy who sold me all the XS2 bits described the front brake design as "crap", but didn't care to elaborate on exactly why.
Looks like he had trouble with the weird spigot arrangement that connected the disc to the wheel.
So what actually goes wrong or causes trouble ?
A bad design or just poor maintenance ?
Click to expand...
If it makes you feel any better, the first year Honda front disc brake on my 1973 Honda CB350G feels like absolute wood compared to my early Yamahas...it really is terrible, despite being 100% rebuilt/refurbished by me. It looks good and is a great idea in theory but it works very, very poorly.

1714146046424.png
 
The '73 RD350 had a very similar front to the XS2. Some bits might have even been swappable. It was the first bike I had with a disc. For it's day, it was an incredible stopper. I recall that Cycle World's road test from that year said it was the most powerful disc they ever tested.
 
Vincenthdfan said:
If it makes you feel any better, the first year Honda front disc brake on my 1973 Honda CB350G feels like absolute wood compared to my early Yamahas...it really is terrible, despite being 100% rebuilt/refurbished by me. It looks good and is a great idea in theory but it works very, very poorly.

View attachment 324127
Click to expand...

My 69 cb750 stops great.

I believe Honda was first of the Japanese with disc and I believe used the same design on all cb/cl bikes without real change through all of production.
 
Vincenthdfan said:
Sure doesnt on my 350G (first year disc for that model). I've done everything to try to get better feel....wooden.
Click to expand...
ive had an olive green 350g. Although about 20 years ago. Brakes worked pretty good.

Maybe a caliper change?

or lines if they are old.

I also have a gold 71 with a drum front that works just fine too

I have nor have I ever had a modern bike to reference any of my options against. I did ride some rg500s years ago but it was just flat out on an open strip/drag so stopping was always gradual and kinda just slowing down.
 
WideAWAKE said:
ive had an olive green 350g. Although about 20 years ago. Brakes worked pretty good.

Maybe a caliper change?

or lines if they are old.

I also have a gold 71 with a drum front that works just fine too

I have nor have I ever had a modern bike to reference any of my options against. I did ride some rg500s years ago but it was just flat out on an open strip/drag so stopping was always gradual and kinda just slowing down.
Click to expand...
All new
 
The front bake on the XS2 is unique in the respect that you remove the wheel and the caliper and rotor stay on the bike. As far as how it works, it works very well, very good stopping power. It has a 2 piston caliper whats not to like. It's downfall was for a few reasons. One is all the extra parts needed. 2 more bearings, a seal and the hollow shaft and extra nut that were needed. I would bet that all the extra parts were deemed a unnecessary expense. Another expense would have been the extra labor assembling all the parts. The biggest problem was the rubber dampers used as a cushion between the rotor carrier and the hub. They just didn't hold up. When they deteriorated enough the rotor would get loose and the bike would develop a clunk sound whenever you used the brake. The brakes still functioned just fine, just had a clunky sound. I'm sure if you rode it long enough with it loose you could break the rotor carrier or hub.
What I have done on my XS2s is use strapping in place of the rubber cushion pieces. The strapping material (plastic) being harder than rubber they last quite awhile. I do have to replace them every couple of years. Not a big deal as I usually pull the wheel ever year for cleaning.
 
Many thanks for all the replies folks !
Well, there's nothing here that would really put me off using the standard XS2 front end that I already have.
I've got a front wheel with good chrome on the rim and nice clean shiny spokes, the forks I've got have minor pitting but that's only to be expected after fifty years.
Point taken about the rubber cushions between the disc and hub, looks like the P.O. had tried silicon sealant as a substitute - not a very clever solution IMHO.
I was seriously considering converting to the '73 front end if the '72 was going to cause issues, but that would seem like a lot of unnecessary expense now.
BTW, I had quite a few 1970's Hondas with the first generation disc brake, CB250G5 (x3) CB360G, CB400F.
Never had a problem with the brake feeling wooden, just the usual problems with wet weather, when the disc would lack power
then suddenly grab as the rotor/pads warmed up.
The 360G was a lovely little bike, but I was pleased to see the back of the gutless 400 Four that everyone raved about so much.
 
Grewth said:
but I was pleased to see the back of the gutless 400 Four that everyone raved about so much.
Click to expand...
I loved my 400F. Yeah, didn't have an excess of power.... if you want to be kind about it, but the sound of that 4 into 1 at 10 grand would put a grin on my face every time.
 

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