Truly Awful Brake Performance

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Boogaloo
Posts: 63
Joined: 25 Nov 2016, 12:54pm
Location: Sunny Suffolk

Truly Awful Brake Performance

Postby Boogaloo » 11 Mar 2019, 2:02pm

I recently put an old but sound front wheel in my Cinelli and am puzzled as to why the braking is so poor.
The wheel is a used Veloce / Mavic MA3 which I had kept in the hope of finding a home for it and it would be perfect for this bike.
I fitted a tyre and rode it only to find the front brake was now hopeless.
The bike has Tektro RL340 levers and Veloce calipers with new pad inserts. Both have new cables and the rear is fully enclosed and works a treat on the new Kinlin rim I built up.

So my question is why is the front so bad? Having read a recent thread on a similar theme I have replaced the outer cable with some much stiffer casing and carefully filed the ends and ensured snug fitting.I rubbed the MA3 rim with wire wool and then alcohol. No better!

I then tried 2 other wheels ( CXP21 rim and TB-14 rims) and they are both much better.

The braking surface of the MA3 is marked but not particularly worn and certainly not concave but does have signs of light scoring.

My assumption is that there is something wrong with the braking surface of the MA3 but what can I do to improve it?

Any thought?

Thanks

Paul

Samuel D
Posts: 2699
Joined: 8 Mar 2015, 11:05pm
Location: Paris

Re: Truly Awful Brake Performance

Postby Samuel D » 11 Mar 2019, 2:07pm

If the pads are new and the brake track is deeply scored or concave, it may take a while before the pads wear to the matching shape.

You’ve done what I would have done to eliminate problems: new cables, carefully prepared, new pads, and cleaned the rim. There isn’t much left!

Brucey
Posts: 34239
Joined: 4 Jan 2012, 6:25pm

Re: Truly Awful Brake Performance

Postby Brucey » 11 Mar 2019, 2:25pm

the rim hasn't got an anodised braking surface, has it?

FWIW it usually takes one wet ride for the brakes to bed in. New brake blocks can have mould release compound on them , which could now be transferred onto the MA3 rim. If you then tried the same brake blocks on other rims, the brake blocks would be cleaner and could therefore work better.

I'd suggest cleaning the rims with some fairly powerful solvent, like acetone.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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horizon
Posts: 9211
Joined: 9 Jan 2007, 11:24am
Location: Cornwall

Re: Truly Awful Brake Performance

Postby horizon » 11 Mar 2019, 2:43pm

Interesting that you switched from "Brake" performance in your thread title to "braking" performance in your text. Obviously I'm being very pedantic here :D but isn't that at the heart of so many discussions about brakes? It isn't the brakes (or type of brake) per se but the whole environment that they operate in from cables and rims to adjustment and cleaning.
I have two doctors, my left leg and my right leg. (G. M. Trevelyan)
PS I always wondered why the YHA HQ was called Trevelyan House. :)

Boogaloo
Posts: 63
Joined: 25 Nov 2016, 12:54pm
Location: Sunny Suffolk

Re: Truly Awful Brake Performance

Postby Boogaloo » 11 Mar 2019, 4:06pm

I was wondering about whether the pads might 'bed in' to these rims after a few hours. That may be what I end up doing as I really want to use this wheel.

Rims are not anodised. Just plain old alu surface. Interesting about the mould release. I think these blocks were used on another rim first but that was a cheap painted (?) rim braking surface that was gradually wearing away so maybe the mould release wasn't removed by the 'painted' rim??. Stopped pretty well though.

I will see if I can get some acetone.

Thanks

Boogaloo
Posts: 63
Joined: 25 Nov 2016, 12:54pm
Location: Sunny Suffolk

Re: Truly Awful Brake Performance

Postby Boogaloo » 11 Mar 2019, 4:08pm

horizon wrote:Interesting that you switched from "Brake" performance in your thread title to "braking" performance in your text. Obviously I'm being very pedantic here :D but isn't that at the heart of so many discussions about brakes? It isn't the brakes (or type of brake) per se but the whole environment that they operate in from cables and rims to adjustment and cleaning.

Agreed but the only variable here AFAIK is rims.

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kylecycler
Posts: 617
Joined: 12 Aug 2013, 4:09pm
Location: Kyle, Ayrshire

Re: Truly Awful Brake Performance

Postby kylecycler » 11 Mar 2019, 5:16pm

Boogaloo wrote:I will see if I can get some acetone.

Or you could try this stuff - Halfords Electrical Contact cleaner - only £3.99 a can:

https://www.halfords.com/motoring/engin ... aner-500ml

I think it might well contain acetone but it's powerful stuff. I bought a can to revive a scroller on an old phone - a few squirts worked a treat but that left me with the rest of the can unused. So I used it to clean brake disc rotors. Not only did it work exceptionally well but it's about half the price of actual bicycle disc brake cleaner.

Question for Brucey, though: When you 'bed in' brake pads I believe you're supposed to leave a 'transfer layer' of pad material on the rotor's surface (out of interest, does that also apply to rims?). I've wondered if the Electrical Contact Cleaner might be so powerful that it removes that layer. Lately I've gone back to using proper disc brake cleaner, which I think might just be isopropyl alcohol, and I don't think there's much difference either way. What do you think?

Footnote: I cleaned my disc rotors just before heading out on a club run recently, using 'regular' brake cleaner. I'd run out of paper towels so used Kleenex-type tissues. Got to the first junction and nearly didn't get stopped - had to turn back and fix it. Used toilet paper instead. Hadn't realised that the Kleenex tissues are coated with balsam, hence the pants-wetting 'issue' at the junction!

(WARNING: don't use Electrical Contact Cleaner to clean chewing gum off car upholstery - it melts the upholstery. Guess how I know. :oops: )

Brucey
Posts: 34239
Joined: 4 Jan 2012, 6:25pm

Re: Truly Awful Brake Performance

Postby Brucey » 11 Mar 2019, 6:11pm

cheapest source of acetone in small quantities is to buy a small container of nail varnish remover. A quid in the pound shop.

Disc brakes work differently to rim brakes, but in either case if you do clean the braking surface completely part of the bedding-in process usually needs to be repeated.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

james01
Posts: 2026
Joined: 6 Aug 2007, 4:48am

Re: Truly Awful Brake Performance

Postby james01 » 11 Mar 2019, 6:20pm

Another possibilty: is the rim significantly wider or narrower than the others?

Brucey
Posts: 34239
Joined: 4 Jan 2012, 6:25pm

Re: Truly Awful Brake Performance

Postby Brucey » 11 Mar 2019, 6:27pm

I meant to say earlier, take a look at the brake blocks. If they are only worn in small areas, the brakes are not bedded in properly yet. If only a small part of the brake block touches the rim, this tends to overheat easily and the brake feels pretty useless.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~