Thorn Cycles Forum
Technical => Wheels, Tyres and Brakes => Topic started by: Matt2matt2002 on July 31, 2016, 08:15:28 pm
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While way on tour I noticed my front XTR brake not retracting fully on the right side, where the cable connects.
While riding I could reach down and nudge one side so that the pads didn't rub.
Today I removed the front wheel and took a good look at the set up.
I dusted it down and then used a tooth brush and soapy water to clean things up.
The none brake cable side definitely sprung back fully and easily. I presume this is the function of the small ' internal' coiled spring?
The other side did not retract and return to the same degree. I could see why one side would be rubbing.
I then removed both brakes from their spindles and oiled the moving hinges/ moving parts. I also greased the spindles before replacing the brakes.
On inspection the coiled springs looked OK but can these fail or loose their tension?
Both were hooked up fine.
Reassembled I still had the same/ original problem. On releasing the brake lever, one pad still rubs the rim.
I can see it not retracting. So I don't think it's an untrue wheel rim.
Any thoughts folks?
Matt
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My guess...
While your bike was in transport with the front wheel out -- and the box being dragged along the tarmac with enough force to bend your forks(!) -- something probably pressed in on that one brake arm enough to deform the spring, causing it to ride closer to the rim.
Yes, the linear springs on v-brakes are quite elastic and can be bent in this way. I have yet to receive a pair from the Shimano factory with equal spring tension and set mine up with the spring-tension adjusting screws backed out equally, then set the tension by bending the springs lightly. I once ran into a Shimano rep at a MTB race and he confirmed this was his own preferred method for initial setup.
The springs are not coils in the strictest sense, more like one coil and the rest laid out in a line. Simply use a fingernail to unhook the end from the peg that holds it, then pull gently out a bit under tension, then rehook it under its mount and try again. Normal function should be restored quickly. If not, you can try again. The tension-adjustment screws that bear on the lower spring ends can be used for fine adjustment.
Hope this helps.
All the best,
Dan.
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Thanks Dan.
Bedtime here in UK but will try your suggestions tomorrow
Matt
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... The tension-adjustment screws that bear on the lower spring ends can be used for fine adjustment.
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I would start with the screws as that may be all the adjustment you need. If the screws can't do the adjustment, then try bending the springs.
The screws thread in to tighten the springs, thus tighten the screw on the side with the rubbing pad first, the tighter spring then pushes the pad out further.
If that is insufficient, you may need to loosen the screw on the other side. I am assuming both sides of the brake have the screws, some cheaper models have only one screw on one side.
I find that I am adjusting these little screws more often than any other adjustment on my bike. I think that V brakes are more sensitive to adjustment than cantilever brakes.
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Rather than bend the spring I would try the spring in the upper of the three holes on the brake boss on the arm that's sluggish, that will increase the tension on that arm
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Rather than bend the spring I would try the spring in the upper of the three holes on the brake boss on the arm that's sluggish, that will increase the tension on that arm
Good idea, and make sure the pivot is well lubricated.
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Rather than bend the spring I would try the spring in the upper of the three holes on the brake boss on the arm that's sluggish, that will increase the tension on that arm
It surely will and is functional, but the brakes will end up with a base tension that is unequal.
I've surely been disappointed to find *all* my new Shimano v-brakes came from the factory with such wildly varying spring tension, which headed me in the direction of gentle spring-bending. Once the spring tension was equalized, they've stayed nicely centered ever since. With the linear springs, it takes surprisingly little -- and gentle! -- force on the ends (after unhooking from their perches) to equalize the tension over their length.
If you do this, be mindful to use a thumb and forefinger, so the bending forces don't impinge on the base plastic covers.
All the best,
Dan.
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Ah! I see from personal correspondence, we are talking about different springs, Matt. Your problem is not with the linear springs, so my advice does not apply.
All the best,
Dan.
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Thanks Dan.
Linear spring. The long ' straight ' thin one?
What is the other one called?
This is the one that concerns me.
Is it removable/ adjustable?
One is definitely weaker than the other.
Matt
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Pretty sure there is only one spring in a v brake arm and it looks like this
http://www.ilovebike.it/en/parts-brake/spring-brake-v-brake-right-left/ (http://www.ilovebike.it/en/parts-brake/spring-brake-v-brake-right-left/)
Try the top hole as I said earlier
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Thanks Bill.
I know the one your link shows but I appear to have another one.
I'll post pix asap tomoz
Matt
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XTRs are odd brakes. Hard to photograph, too - really needs manual focus, which my camera does have, if I could just remember which knobs... Anyway, maybe this is the spring of concern:
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I previously suggested starting with the spring adjustment screws. Without being there to see why that is not the best option, my advice is the same as before.
They have lots of models, not sure which you have.
http://si.shimano.com/php/download.php?file=pdf/ev/EV-BR-M960-2141.pdf
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seems I have the m970 which sure looks like the m960! No idea what Matt has. For sure with my brakes, the adjustment screws have always handled what imbalance has arisen.
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here somebody says the 960 and 970 are mechanically identical: http://forums.mtbr.com/brake-time/difference-between-shimano-xtr-br-m960-br-m970-998583.html
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XTRs are odd brakes. Hard to photograph, too - really needs manual focus, which my camera does have, if I could just remember which knobs... Anyway, maybe this is the spring of concern:
Yep!!
That's the spring.
I don't think I could photography it any better.
One side is definitely weaker. And I don't see how it can be removed and retensioned.
I'll strip down again and follow instructions offered above.
Many thanks folks.
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Yes - I have the M970
I found the paperwork that came with the bike.
(https://lh3.googleusercontent.com/-agK79mHM0lg/V6ITuxl7ExI/AAAAAAAALtk/vXZj4fbfN0okgWZ9r0OFaMXqYxjj1U4xwCL0B/w530-d-h398-p-rw/DSC00305.jpg)
And here is that internal spring I was going on about.
It's not shown on the paperwork diagram and I don't see how it can be removed.
(https://lh3.googleusercontent.com/-8EwOVWMIVnM/V6IUdPHxD3I/AAAAAAAALuE/8ZILhZOKgvkh9pPLWdetLLR2-pPhLGimgCL0B/w530-d-h398-p-rw/DSC00307.jpg)
There is a zip tie end pointing to it.
Well folks, many many thanks for all your hints and tips.
After another strip down and clean, I put things back together and by tweaking the 2 adjusting screws things are much much better.
Now to clean up the rear brakes....!
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Time clean the Xtrs.
Running blue Swisstops on CSS rims.
Had a squealing front brake for some time and needed to clean off accumulated dust/ muck.
Please refer to my last picture showing the instructions from Shimano. Middle diagram showing pad, washers and nut.
On removing all parts I realised that the washers on the ' spindle' had not been assembled correctly.
They sit within each other and allow toeing in.
Things greatly improved once cleaned up and refitted.
However.....
On the last set I cleaned up I noticed the the ' spindle' that goes into the ' bracket' that holds the pad, was wobbly.
I had removed the pad and found a little dust underneath. Nothing serious. Just wanted to be thorough.
All 3 other units had a snug fit of the spindle into the pad bracket. They just pull out. No nut or fixing mechanism.
So..... I have a squealing from the back brake. The one with the wobbly spindle.
Could this be the cause of the sequel?
Or maybe I need to do a little more toeing in?
I've been out on a 10 mile hilly run to bed things in. And still the squeal.
Also.....
On the rear left brake the gear shift mechanism located.
I didn't remove this.
Played safe.
Any tips for removing it and getting it back on in the same position?
Please excuse incorrect terminology.
Thanks folks
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Matt,
Pad squeal usually comes as a result of oscillation of the pad material against the rim sidewall under braking -- the pad catches, slips, and catches again. This cycle is usually what results in noise (though occasionally it can be caused by a poor match of pad surface to rim...old MAFAC 4-spot and even 5-spot black pads were notorious for the squeal even when used on other brakes).
Toeing the pads in reduces oscillation and noise. If your brake arms are worn or already flexible by default, then more toe-in is called for.
If one of your pads is held less securely, that is where I would look first to find a source of squeal. Look carefully for any mismatch in size or for something that is keeping the assembly from tightening fully. Worse comes to worst, you may have to add a bit more toe-in on that one brake to reduce noise, but I'm betting the most likely cause is a loose fitting, based on what you've told us.
Yes, the spherical washers have to be mirrored as shown in the instructions to get the full range of toe-in. On the rear left brake the gear shift mechanism located.
I didn't remove this.
Played safe.
Any tips for removing it and getting it back on in the same position?
When faced with a similar situation, I look for the gap in the clamp and mark its location with a piece of tape stuck to the handlebar right next to it. That way, when reinstalling, the clamp and assembly not only slides on the same distance, it has the same orientation. When finished, I just peel off the tape and all is as it was before.
All the best,
Dan. (...who appreciates the photo of the elusive spring)
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This link might be helpful to you, Matt:
http://www.myra-simon.com/bike/vbrakes.html
Best,
Dan.
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Great link Dan.
I'll run the bike a few more days and then take another shot at the rear brakes.