Brazing 990 mounts, over or under?

!Jones said:

I'm getting ready to light the torch; I have built my brazing fixture
and have the 990 ("U-brake"😉 bosses.

I think that, if all else were equal, I'd put them under the seat
stays as opposed to on top. Can anyone think of any reason not to do
that? As I recall, there was once a fad wherein they were mounted
under the chain stays behind the BB. It seems like the only issue I
heard was that they collected dirt quickly when mounted thus.

Jones

you should probably let whatever will give you best the routing
determine it

!Jones said:

I'm getting ready to light the torch; I have built my brazing fixture
and have the 990 ("U-brake"😉 bosses.

I think that, if all else were equal, I'd put them under the seat
stays as opposed to on top. Can anyone think of any reason not to do
that? As I recall, there was once a fad wherein they were mounted
under the chain stays behind the BB. It seems like the only issue I
heard was that they collected dirt quickly when mounted thus.

Jones

Make sure that your straddle cable clears. I can see it acting as a
wire saw on the seatstays.

forgive but i don't know a 900 from a ...
and off course a dirt deflector or two works if not stylish but who
notices?
the idea is factory design wise liability or high level comp or down
the rockies is the wheel rotation backs the assembly into the mount
not carrries the assembly away from the mount.

datakoll said:

forgive but i don't know a 900 from a ...
and off course a dirt deflector or two works if not stylish but who
notices?
the idea is factory design wise liability or high level comp or down
the rockies is the wheel rotation backs the assembly into the mount
not carrries the assembly away from the mount.

pour some linseed in there after brazing or the tube will rust out.
allow drying, 3-4 weeks in warmth, then coat agin with walmart white
rusto gloss.

in rec.bicycles.tech datakoll said:

the idea is factory design wise liability or high level comp or down
the rockies is the wheel rotation backs the assembly into the mount
not carrries the assembly away from the mount.

I think you're putting your finger on the question... is there a
structural difference? I don't think that it makes any difference
which direction the wheel rotates, but I'm not sure. The under the
stay mount is cosmetic; I could put the bosses on either side.

Jones

It's hard to see how you would run the cable and housing with the, er,
brazed on center-pull, underneath the seat stays...

JG

JG said:

It's hard to see how you would run the cable and housing with the, er,
brazed on center-pull, underneath the seat stays...

JG

this is by far the most common design used on current frames

in rec.bicycles.tech JG said:

It's hard to see how you would run the cable and housing with the, er,
brazed on center-pull, underneath the seat stays...

JG

Assume it's an... err... somewhat oddball frame and that the cable
routing will be fine if not better. Will there be any reason not to
do it that way that would go to the functionality of the brakes?

Jones

Hank Wirtz said:

!Jones said:

I'm getting ready to light the torch; I have built my brazing fixture
and have the 990 ("U-brake"😉 bosses.

Quoted message said:

I think that, if all else were equal, I'd put them under the seat
stays as opposed to on top. Can anyone think of any reason not to do
that? As I recall, there was once a fad wherein they were mounted
under the chain stays behind the BB. It seems like the only issue I
heard was that they collected dirt quickly when mounted thus.

Quoted message said:

Jones

Make sure that your straddle cable clears. I can see it acting as a
wire saw on the seatstays.

An old Haro bmx frame I have runs a 990 on the chainstays. The cable
runs through a pierced seat tube.

The rationale on the BMX frame was for trick riding. Moving the brake
caliper south and out of the way lets you do certain tricks where your
foot wedges between frame and tire.

There were some old MTB frames that used this method. GT comes to
mind. Something about the brake being in a more advantageous position
for power, but it didn't seem like much more than a gimmick.

/s

I take it they are linear pull these days?

I suppose it might be a bit easier to work on if they are on top.

JG

!Jones said:

On Tue, 18 Sep 2007 21:54:31 -0700, in rec.bicycles.tech JG

Quoted message said:

It's hard to see how you would run the cable and housing with the, er,
brazed on center-pull, underneath the seat stays...

Quoted message said:

JG

Assume it's an... err... somewhat oddball frame and that the cable
routing will be fine if not better. Will there be any reason not to
do it that way that would go to the functionality of the brakes?

Jones

There's the question of whether the cable carrier will be able to be
in a spot that gives good mechanical advantage (presuming the routing
setup would use a carrier as opposed to dual cables, and I'm also
assuming this would be a typical setup where the carrier is in front
of the seattube and the straddle is going around the tube). Lower
tends to be better. I wish I knew how to quantify it accurately, but
if the cable carrier's nut is gonna be more than about 4 inches way
from the cable anchor points, braking will probably suffer. That 4
inches is a fudged number but i think it's about right. This could
definitely be a problem if the frame has a long-ish rear end. If it
seems like it's going to be too far away, and you still want to do
under-ss mounting (ie, for the sake of getting the best routing), then
you could just run the main cable through the seattube somehow,
allowing you to get the straddle nice and low. I'm not totally
confident on this, but I kinda suspect that there are millions of BMX
frames that really should have been built this way.

You also need to make sure that the chosen position provides clearance
from the rider and other parts of the bike.

It might also be worth mentioning that the alignment/symmetry of 990
bosses is important because it doesn't take much to cause some brake
arms to rub on each other.

in rec.bicycles.tech Nate Knutson said:

There's the question of whether the cable carrier will be able to be
in a spot that gives good mechanical advantage (presuming the routing
setup would use a carrier as opposed to dual cables, and I'm also
assuming this would be a typical setup where the carrier is in front
of the seattube and the straddle is going around the tube). Lower
tends to be better. I wish I knew how to quantify it accurately, but
if the cable carrier's nut is gonna be more than about 4 inches way
from the cable anchor points, braking will probably suffer. That 4
inches is a fudged number but i think it's about right. This could
definitely be a problem if the frame has a long-ish rear end. If it
seems like it's going to be too far away, and you still want to do
under-ss mounting (ie, for the sake of getting the best routing), then
you could just run the main cable through the seattube somehow,
allowing you to get the straddle nice and low. I'm not totally
confident on this, but I kinda suspect that there are millions of BMX
frames that really should have been built this way.

You also need to make sure that the chosen position provides clearance
from the rider and other parts of the bike.

It might also be worth mentioning that the alignment/symmetry of 990
bosses is important because it doesn't take much to cause some brake
arms to rub on each other.

I have plenty of room and can locate the cable stop in an optimal
position on either side of the ss... if cable routing is my only
issue, then I don't have an issue. I have run cables through the seat
tube in the past (and seat post by milling a slot) but try to avoid it
because I didn't have a positive experience with that idea.

I spent a good deal of effort building the fixture to locate and align
the bosses. I'm putting them at 9.125" from the center of a mandrel
through the dropouts. I was real fussy about building the fixture to
be square. I think I'm something like 3.9" apart on the bosses and
that's wide, but that's where the stays are. Someone on the frame
builder's listserv said 80mm spacing was optimal, but I'd have to make
a flange to offset them and I plan to use the widest rim I can get.

Here goes! Pardon me while I light the torch.

Jones

in rec.bicycles.tech Scott Gordo said:

The rationale on the BMX frame was for trick riding. Moving the brake
caliper south and out of the way lets you do certain tricks where your
foot wedges between frame and tire.

Sounds like fun!!! Would you teach me to do that?

Jones

!Jones said:

On Wed, 19 Sep 2007 13:13:49 -0000, in rec.bicycles.tech Scott Gordo

Quoted message said:

The rationale on the BMX frame was for trick riding. Moving the brake
caliper south and out of the way lets you do certain tricks where your
foot wedges between frame and tire.

Sounds like fun!!! Would you teach me to do that?

Jones

Just read your post about the BMX tandem. I take it that you're
building a BMX frame?

If it helps, the Haro had the posts mounted on the bottom of the
stays.

BTW: I started looking around for old GT MTB frames with a U-brake,
and stumbled upon this very sweet, 1985 GT "Timberline". My friend
Jeff had that exact frame. In fact, I think it was the first MTB I'd
seen, back when I thought gears were for sissies.

Have fun!

/s

in rec.bicycles.tech Scott Gordo said:

Quoted message said:

Sounds like fun!!! Would you teach me to do that?

Jones

Just read your post about the BMX tandem. I take it that you're
building a BMX frame?

I was joking. I'm a geriatric professor, machinist, and frame builder
taking on an interesting project... and learning the history of BMX as
I go. I just learned that Gary Littlejohn did "Billy's" fall in *Easy
Rider*. Wow!

I'll *ride* the damn thing when I finish it, of course... and my wife
and life-long stoker will go, also... but the half-round is out of the
question, I'm afraid. I wonder how it'll handle? I'm used to our
early Paramount, so I positively cringe at the very thought!!! I
mean... can one apply that concept to a BMX? And a tandem to boot?
What I need is a real side hack! Wouldn't that be kinky? A couple of
60-somethings in a Littlejohn tandem side hack!!!

Jones

!Jones said:

On Wed, 19 Sep 2007 14:32:43 -0700, in rec.bicycles.tech Scott Gordo

Quoted message said:

Quoted message said:

Sounds like fun!!! Would you teach me to do that?

Quoted message said:

Quoted message said:

Jones

Quoted message said:

Just read your post about the BMX tandem. I take it that you're
building a BMX frame?

I was joking. I'm a geriatric professor, machinist, and frame builder
taking on an interesting project... and learning the history of BMX as
I go. I just learned that Gary Littlejohn did "Billy's" fall in *Easy
Rider*. Wow!

I'll *ride* the damn thing when I finish it, of course... and my wife
and life-long stoker will go, also... but the half-round is out of the
question, I'm afraid. I wonder how it'll handle? I'm used to our
early Paramount, so I positively cringe at the very thought!!! I
mean... can one apply that concept to a BMX?

The concept of caring about handling? Yes, why wouldn't it apply? Look
at what a skilled flatlander can do; of course they're sensitive to
how their stuff handles. Look at racing; there's any number of
variables that need to be considered to design a bike that handles
aggressively but controllably enough.

No idea at all how to make your tandem handle well though, of course.