Retrobike Forum Index

It is currently Sat Dec 10, 2016 2:00 pm

* Login   * Register * Search  * FAQ



Post new topic Reply to topic  [ 19 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: Sat Feb 11, 2012 1:21 am 
Old School Grand Master
User avatar

Joined: Sun Aug 21, 2011 11:57 pm
Posts: 4074
Location: Antwerp, Belgium
I installed a pair of Hope disks on my bike today, and am having a few issues.

Firstly, they are out of true by ... ermm ... I think somewhere around 0.5mm. Unfortunately there simply isn't enough space between the pads to compensate for this, so you can hear them touch with every revolution.
I'm quite good at straightening wheels on sight alone, so I'm fairly confident that with a lot of patience (and a good working stand, gotta get me one of those), I can bend the disks a bit in the right places to get them to within 0.1mm.
However I was wondering if anyone has any tips that could make things easier.

Secondly, and this is the bit that bugs me most, the cooling holes have really rough edges.
when the pads touch them, they make the same sound as when you slowly turn the wheel and let something run against the spokes.
I guess it's just a matter of crude machining. They probably did the braking surface first, and then punched/cut the holes, leaving rough edges on the braking surface.

Can I sand the braking surface or is that taboo? I could just sand the edges of the holes to smooth things up a bit, but that would involve a massive amount of work.
There's 54 holes on each disk's braking surface alone, and both disks need to be sanded on both sides. That's 216 holes to sand, which would take half a day at least.

Any tips are welcome.


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 1:28 am 
Gold Trader / rb Rider / Special
Gold Trader / rb Rider / Special
User avatar

Joined: Mon Aug 31, 2009 12:26 am
Posts: 16165
Location: Rurally close.
Go for it on the sanding! Just dont take too much off.

You can use an adjustable spanner to true the rotors in much a similar way as you would a wheel. Remember little bits at a time as its easier to correct a small mistake.

Is what i do is:

Spin rotor until it is centred, then grab where it begins to go to either side. Then keep spinning until it is back in the centre again. This is the bit that will need trueing so put the spanner on and bend to either side. Dont use too much force but not too little either. You will get better at this in time. Then repeat until its as straight as you think you can get it in as many points as possible.

Hope that makes sense.


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 8:57 am 
Retro Guru
User avatar

Joined: Sat Jul 18, 2009 8:52 pm
Posts: 793
Location: Costa-del-Oldham
If they are new, phone Hope up, explain your issues & i bet they will send you a new set out.

They are VERY good with warranty issues


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 8:59 am 
Old School Hero

Joined: Wed Dec 14, 2011 9:57 am
Posts: 183
You can get a tool to true brake rotors, but an adjustable spanner will work as cyfa says.

Sanding isn't a problem, just don't sand them to a super smooth high polish.


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 9:00 am 
Old School Grand Master

Joined: Sun Jun 27, 2010 9:37 am
Posts: 3976
To save sanding the pads, if the calliper are post mount with adaptors just use a thin washer to spac the calliper from the spacer.


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 9:21 am 
Old School Grand Master
User avatar

Joined: Tue Oct 04, 2011 4:15 pm
Posts: 3499
Location: Behind you with the duct tape pulled out.
The holes are there to clean the pads so smoothing the holes would reduce there effectiveness. But if it really is doing your head in then use either a countersink or a large drill bit to just chamfer the holes slightly.


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 10:57 am 
Old School Grand Master
User avatar

Joined: Sun Aug 21, 2011 11:57 pm
Posts: 4074
Location: Antwerp, Belgium
Thanks for the replies, guys.

The disks are new indeed. I'm suspecting that the wobble is within tolerances, but the Formula RX calipers simply don't have enough clearance. They were a pain to align on the original disks, and on these ones they're playing up as well. Once they are set up properly, they're brilliant, but it takes a long time to get to that point.
I considered getting a set of Tech M4 brakes, but they are not available in any colour that suits the rest of the bike. If Hope did a black with anodized red version, I'd buy it right away and ditch the Formulas.

The adjustable spanner is a good idea. So far I've been doing it by hand.
Yes, I'm aware of the grease problems, but I plan on cleaning the disks and sanding the pads anyway.

Never thought about the holes' function. I always assumed they were there to help dissipate the heat and give the water somewhere to go. But cleaning purposes make sense.
Then again, the bike is built to be the ultimate tool for city traffic, so it doesn't get to see much dirt. I think I'll just give the braking surfaces a quick once-over with 240 grit sandpaper, and we'll see from there.

Anyway, I'll be off to get a proper work stand this afternoon, so I can get both wheels off the ground when I'm working on the bike.


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 12:56 pm 
Old School Grand Master
User avatar

Joined: Mon Jun 14, 2010 9:06 pm
Posts: 4448
Location: Herts UK
no point in sanding the holes because as the discs get worn by the pads, the holes will regain the sharp edge.

you should grip the disc in two places - at the spoke and keep that still and at the braking surface which you move to bend the disc. If you do not do that, then you are stessing the mounting hole in the hub so risk snapping it.


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 1:40 pm 
Old School Grand Master
User avatar

Joined: Sun Aug 21, 2011 11:57 pm
Posts: 4074
Location: Antwerp, Belgium
02gf74 wrote:
no point in sanding the holes because as the discs get worn by the pads, the holes will regain the sharp edge.

you should grip the disc in two places - at the spoke and keep that still and at the braking surface which you move to bend the disc. If you do not do that, then you are stessing the mounting hole in the hub so risk snapping it.


I think I'm not explaining myself correctly. It's not just the edges that are sharp. There are very small but really sharp burrs sticking out. (I actually spent half an hour googling until I found the word burr, as I had no idea hat they were called in English)
Looks like these disks simply weren't finished properly.

Thanks for the tip on holding it in 2 places though, I'll be careful. Looks like the 6 rings are taking up most of the movement while the center piece of the rotor stays straight. however I'm sure there are some forces being transmitted all the way to the mounting holes.

Here's the Hope Saw disc I'm referring to. Mine have a black center though.

Image


Top
 Profile  
 
 Post subject:
PostPosted: Sat Feb 11, 2012 3:57 pm 
Gold Trader / rb Rider / Special
Gold Trader / rb Rider / Special
User avatar

Joined: Mon Aug 31, 2009 12:26 am
Posts: 16165
Location: Rurally close.
If theyre floaters as i did suspect, you can see if they will maybe bed in but in my opinion you should send them back. Or at least ask what theyre tolerances are. I reckon they should be straight.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 19 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: keitht and 19 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  

About Us

Follow Retrobike

Other cool stuff

All content © 2005-2015 Retrobike unless otherwise stated.
Cookies Policy.
bikedeals - the best bike deals in one place
FatCOGS - Fat Chance Owner's Group

Powered by phpBB® Forum Software © phpBB Group