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Old 02-03-2009, 12:07 PM   #1
One Less Harley OP
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adding another disc to a R80 G/S

I've been looking at BMW forks and brake set ups, now why isn't it possible to just add another disc to the left wheel hub? As some other BMW's (R100RT) have what appears to be the same fork sliders as on the G/S as the calipers mount to the rear of the fork. Wouldn't it be possible to add a disc to the left side w/ a thinner disc brake mount hub(?) and just buy the left caliper.
Parts needed
1) left caliper (mounts to rear of fork)
2) bake hose and "T" to connect the two calipers
3) possible different bore to the MC (13,14,or 15mm??)
4) brake disc and carrier

Any thoughts??? why this would or wouldn't work??
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Old 02-03-2009, 01:23 PM   #2
Wirespokes
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Yeah, in theory it should be easy.

Except it turns into a much bigger project than you'd think.

I've looked at this too, but there are some problems. It's hard to say what's really going on since the forks really do appear to be the same as the 81-4 road-going models. The only differences I've seen are internally and flat spots machined to allow clearance for the disc rivets.

I don't recall if the triple trees are the same, I did measure and compare at one time but don't recall the conclusion. I think they are the same, which makes it confusing, since in that case the only difference is the hub.

I tried mounting another disc on my hub and the wheel wouldn't fit - the discs stuck out too far and rubbed the sliders. I think if a millimeter or so were milled off the backside of each disc it would fit. And then the spokes would have to be adjusted to center the rim on the hub (offset removed). Finally new axle spacers would need to be found or made to locate the wheel.

There might be more, but that seems to me what would be necessary, which doesn't seem like a whole lot. I have heard of guys dual-discing the G/S and spending 40 hours and mucho bucks to accomplish - and they were BMW knowledgeable - so there may be much more to this than appears.
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Old 02-03-2009, 01:31 PM   #3
SOLO LOBO
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TEXASYETI's G/S came to him with dual discs... let's see what he can add to this discussion

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Old 02-03-2009, 02:03 PM   #4
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"TEXASYETI's G/S came to him with dual discs... let's see what he can add to this discussion", yeah but no caliper on the left yet!!!

I was looking at the R80 Rt and there was a double disc retro kit available for the 84-87, it had different part numbers for the left and right disc (possibly one is offset more?)), and the calipers mount to the front of the fork. also specs out a 15mm Master cylinder.

But there are left and right calipers on the 82-84 RT and I did notice the spacing on the hub is favored to one side on the G/S.

P/N 34111241555 left caliper RT
P/N 34111241556 rt caliper RT
p/n 34111236566 disc same left and right Rt

p/n 34111458384 G/S left caliper
p/n 34111236005 disc

It seems doable, by sourcing out the RT calipers and disc and reshiming the axle to be more centered.
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Old 02-03-2009, 02:36 PM   #5
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Quote:
Originally Posted by SOLO LOBO
TEXASYETI's G/S came to him with dual discs... let's see what he can add to this discussion

It has its own apartment .

I looked at double discing my g/s and it got too expensive for my cheapness. Just replacing the existing disc is a few hundred.
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Old 02-03-2009, 02:56 PM   #6
England-Kev
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Motorworks here in the UK do a bigger disk option.
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Old 02-03-2009, 02:58 PM   #7
elmoreman
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Quote:
Originally Posted by One Less Harley
I've been looking at BMW forks and brake set ups, now why isn't it possible to just add another disc to the left wheel hub? As some other BMW's (R100RT) have what appears to be the same fork sliders as on the G/S as the calipers mount to the rear of the fork. Wouldn't it be possible to add a disc to the left side w/ a thinner disc brake mount hub(?) and just buy the left caliper.
Parts needed
1) left caliper (mounts to rear of fork)
2) bake hose and "T" to connect the two calipers
3) possible different bore to the MC (13,14,or 15mm??)
4) brake disc and carrier

Any thoughts??? why this would or wouldn't work??
I believe it would be easier to change the whole front end...ask me how I know
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Old 02-03-2009, 03:17 PM   #8
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Man I think I need to get to work, to much free time.

Doesn't look that bad, but I'd have to see an R80 RT w/ the dual setup and take some measurements.
I've ordered the 320mm disc conversion , but you know how these things go. Probably don't need two disc as the 320 mm may work just fine.

http://www.siebenrock.com/index1.php?sprache=en
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One Less Harley screwed with this post 02-03-2009 at 05:39 PM
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Old 02-03-2009, 03:20 PM   #9
bmwblake
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i noticed a good improvement by going to a braided line. bleeding the system is always a good start, and a louder horn.
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Old 02-03-2009, 03:32 PM   #10
bgoodsoil
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Quote:
I believe it would be easier to change the whole front end...ask me how I know
A big benefit of the new front end I put on my bike was the massive brake rotor and dual piston caliper that came with it. $600 for forks, triple clamps, front wheel, fender and brake system and I paid a bit of a premium for that so I could get it all off the same bike. I'm sure a deal will present itself on eBay if you wait and you can get it for even cheaper. For little more than the cost of new brakes and a decent top triple clamp I got the whole shooting match.
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Old 02-03-2009, 03:42 PM   #11
One Less Harley OP
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I've got the braided line, but was really working the brakes and my right hand on a spirited road ride chasing a 650GS. The stock brakes work...kind of, but the fun is improving these things.
You won't believe how scary it is going from ridding the G/S back to the R1150RS, especially when I've been off the RS for a while. The RS will scare the p#$@ out of me if I just hop on a go.
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Old 02-03-2009, 03:48 PM   #12
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Quote:
the fun is improving these things.
yep!
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Old 02-03-2009, 03:51 PM   #13
bmwblake
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i used to have an rs. i know the exact feeling you're talking about.


Quote:
Originally Posted by One Less Harley
I've got the braided line, but was really working the brakes and my right hand on a spirited road ride chasing a 650GS. The stock brakes work...kind of, but the fun is improving these things.
You won't believe how scary it is going from ridding the G/S back to the R1150RS, especially when I've been off the RS for a while. The RS will scare the p#$@ out of me if I just hop on a go.
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Old 02-03-2009, 04:08 PM   #14
TEXASYETI
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When I got the g/s pictured above, the PO had two calipers powdercoated blue and ready to go on. I ended up going with tha single disc and will tell you that with a new master cylinder, a rebuild caliper, and a nice stainless line it stops reeeeaaaaaallllllllyyyyyyy nice!

IIRC, the disc on the left side uses a shallower carrier. Not sure why but when I get home I'll take a gander and see whats up!

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Old 02-03-2009, 04:08 PM   #15
Caddy82rats
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There is a SEMC Brembo kit



But you can deal with the OEM disc
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