BMC Time Machine rear brake issues
So I've been have a few wee problems with the rear brake on my TM02 (same as TM01, by the way).
The arms are not returning properly and this seems to be because the brake cable cannot move freely through the metal hook 'thing' that guides the cable in it's 90 degree turn as it meets the arms. It was hard enough getting the cable through this metal hook thing in the first place, no wonder it won't move freely! The problem is exacerbated by quite weak spring tension in the brake arm springs (well certainly weak compared to a standard road caliper).
I am wondering if anyone else has had this problem and if so how did you solve it? I'm thinking of putting a small spring on the cable to push the arms apart? Or maybe I can get a thinner brake cable that will move through the guide better? Or maybe I could try and unbend the metal guide hook thing a bit so the turn isn't quite so sharp?
Surely this can't be a problem for a bike that's straight out of the factory? (I've only ridden it twice) Am I missing something....
The arms are not returning properly and this seems to be because the brake cable cannot move freely through the metal hook 'thing' that guides the cable in it's 90 degree turn as it meets the arms. It was hard enough getting the cable through this metal hook thing in the first place, no wonder it won't move freely! The problem is exacerbated by quite weak spring tension in the brake arm springs (well certainly weak compared to a standard road caliper).
I am wondering if anyone else has had this problem and if so how did you solve it? I'm thinking of putting a small spring on the cable to push the arms apart? Or maybe I can get a thinner brake cable that will move through the guide better? Or maybe I could try and unbend the metal guide hook thing a bit so the turn isn't quite so sharp?
Surely this can't be a problem for a bike that's straight out of the factory? (I've only ridden it twice) Am I missing something....
0
Comments
-
Firstly, if it's only 2 rides old, the place you bought it should really be fixing the problem.
I'm unfamiliar with your rear brake, but am I right in thinking it's a direct mount thing just behind the BB?
Your description of the "metal hook" makes it sound like the noodle on a v-brake? Had them on my last MTB (which tells you how long ago that was) and never experienced any issues despite the mud and water. The return springs on those weren't particularly fierce.
You sure it's that tube causing the drag? If so you could try a V-brake noodle? Google for pictures of them, make sure I'm not talking rubbish again...0 -
http://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F1/Official_BMC_Time_Machine_Owners_Thread_P4363884/
Have a read. You are not alone. Noodle it is.0 -
There's always the option to take it back but there's nothing they can do that I can't and I'd go further and say there's probably actually less they can do (this is Evans Cycles we're talking about!) and I want to fix the problem myself.
Ah ha so its called a noodle! That piece of info makes like easier. And it looks like I can order a flexible one, or one with less bend which might just do the trick...
Thank's for the link to that thread - look very useful, I'll dig in.0 -
I thought I would post up my solution, just incase anyone searches the same problem in the future.
I bought a small length of compression spring off eBay, about 25mm long with a 5.8mm outer diameter. Probably wouldn't go any bigger than this as the brake cable is only thin and the spring will be flexing a lot. I chose 5.8mm because particular gauge of spring wire had the strongest resistance compared to many others and I thought it would be good compromise between spring size and resistance - seems to be fine, surprisingly firm actually.
I threaded the spring onto the brake cable, as pictured.
I haven't ridden the bike yet but this seams to have fixed the problem. The arms now return fully and the brake functions as you would expect. We'll have to see how the little spring holds up but it's a very easy job to replace should it wear out. I'll probably make a couple of little wooden seats out of some dowel when I'm home just to stop it rubbing the metal.
0 -
Ingenious! Top fettling!0
-
Jrich you absolute beauty. Man of the year award!
I have the TMR02 and was actually looking to sell due to this issue. I replaced the 105 on it with dura-ace and ever since I took it apart, I have cursed BMC constantly. I've actually hardly used the bike as I didn't have confidence in the rear brake.
The design is poor to be frank, but this little spring could solve most bad things about it. Has it worked well with you since putting it on? Ive got 4-5 different springs on order from ebay so lets see what happens!0 -
Jrich could you post another pic on how you've done it having the same issue
0 -
Alright Gb89.
I've relativity recently rebuilt the rear brake on mine...and this time didn’t install the springs like jrich did.
I had never taken off the brake arms from the frame since I purchased it. Good job I did this time, as I found a lot of dust and grime hidden in there. A good clean and lots of new lub and they provide good resistance now. I got a new inner cable noodle from evans as my BMC one had perished (google 'evans cycling noodle'), I had to trim it down as that inner tube is too long for the BMC.
I’m still with the opinion that the rear brake has too tight an angle for it to function like normal calliper brake's. I haven’t put many miles in my bike this summer as I’ve been busy but I can tell that to keep it running in top form needs more maintenance work than any other brake type.0
