Juddering brakes

[niggle]

Hi Mick, you probably remember my old 1980s Overbury's 531 frame touring bike. That bike developed similar brake juddering at the front after a heavy impact with a pothole. The effect was of pulsing felt at the brake lever, fluctuation in braking effect and also the fork was straightening and flexing slightly at the same time. The fork was a lovely compliant steel thing which could also be witnessed flexing a bit as it went over bumps in the road surface, hence the nice ride it gave.

My first diagnosis was an out of true rim, as it appeared to be when I span the wheel in the fork with one brake block adjusted very close, because there was a point where it would rub the brake block. I trued the wheel patiently taking my time to get it as good as I reasonably could with quarter turns of the spoke nipples, but on test riding the problem was still there. By adjusting both brake blocks really close I found that there was now a point where the brake block on the other side was catching, and in fact there was no corresponding depression on the first side, in other words the rim now had a slightly thicker section.

The rims were old single wall type Wolber Champions and I think the rim was slightly flared outwards by the pothole impact.

I measured the rim all round just like you have, but with a micrometer. The rim was about 0.2mm wider at the point where the problem was. I tried to remedy by some judicious squeezing of the problem section in a vice, and did get the width difference down to about 0.1mm, but the problem was only partially alleviated and I did not want to apply any more pressure to it with the vice. When I sold the bike I mentioned front brake judder in the advert, advising that it probably needed a new front rim.

Anyway the point is that I can quite believe that you are getting the symptoms you describe with the degree of width variation in your rim that you are reporting. It is not the same as the rim being out of true, in that case the brake may compensate slightly by swinging from side to side, as where the rim is closer to one brake block it is further away from the other. In the case of varying rim width the rim gets closer to both brake blocks at once, so the brake is pushed open, which will be felt at the lever as pulsing, as well as juddering in the braking action on the bike as a whole. Also a compliant fork, such as I imagine your Mercian has, may actually accentuate the problem as compared to something more rigid.

[Mick F]

Spot on!

Eventually, the rim MAY get parallel, but I'm not hopeful for a while yet.

Busy today and tomorrow, but I can get out on Tuesday - and rain is forecast, so I may get some wear going yet!

[MikewsMITH2]

I've only ever scrubbed the rims and (removed) blocks with hot soapy water. I usually use a stainless steel pan scourer. Rinse off and allow to dry.
Clean as a whistle.

I've never needed to chamfer or toe brake blocks. I'm not about to start now as the problem is the rim, not the brakes.

Soapy water is not very good at removing many contaminants. I would try the brake cleaner. It sounds like good stuff. Having trained as an engineer and spent many hours tracing faults. I have learned you can't always assume one component of the system is at fault. It is often an interaction between 2 or more parts, You may have a long wait if you are hoping the fault will disappear with time. My daughters bike has still got noisy rear brakes after 19 years! I tried everything when she first had it: solvents, toe in and various adjustments to no avail. She only rides occasionally now she has left home so it's not top of the list, but I will buy some brake cleaner when I am Halfords next.

[Mick F]

Soapy water - plus fresh water rinsing - has served me well for as many years as I care to remember.

Alu rims wear away in use, so the only "contaminants" will be rubber and alu. There could be oil deposits from hands and maintenance, but not on this rim. Spick and span. However, a brake cleaner sounds a good buy as it could be easier and quicker than washing. I'll keep my eye out for some.

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I took a couple of photographs of an old rim and a new rim. I said earlier that these new Rigida Chrina rims are different. It's difficult to describe the difference as the profile and size is the same, but the finish is different. Also the markings:

This one is of an old Chrina rim. Note the engravings and the name "Rigida".

This one is of a new Chrina rim. Note the etchings and the fact that it doesn't say Rigida. Obviously there are stickers on the rim, and these are identical to the old rims, however, this is where I smell a rat.

I just wonder that this rim isn't made by Rigida themselves, but contracted out to another firm to produce, then the Rigida stickers put on afterwards? This would explain the differences.

The old style of engraving was on all my old Chrina rims, and it's only this new pair that are like this.

Please click the photographs for clearer views. I had to play around with exposure and lighting to get the details as clear as this.

[MikewsMITH2]

Youve no idea what lubricants etc are flying around in the factory. They won't wear off they'll just get impregnated into the brake blocks.
Soapy water (if you mean soap not detergent) will only wash away water soluble contaminants or animal fats not mineral oil based products. Have you tried just washing your dirty hands with soap and water after working on the car? You have to use Swarfega. You don't actually know it's just the rim unless you substitute a brand new brake calliper and brake blocks. It's very unlikely to be that but you don't actually know.

[Mick F]

Sorry, I don't mean "soap", I mean washing up liquid. That and a pan scourer and brush. If they can get a frying pan clean, they can do my wheels.

I say again, though, that these rims aren't the first new rims or wheels I've had, and this is the very first time this has happened. My first alu wheels were back in the 1970s.

[ferrit worrier]

Hi Mick

I've just got home from Rachels and I've been looking at the old and new rims I've got the same "Etchings" on my new ones too, also the valve hole is in a different place to te stickers not that it should make any difference. I've been doing some more measuring and will be back later with the findings.

Malc

[Edwards]

Youve no idea what lubricants etc are flying around in the factory. They won't wear off they'll just get impregnated into the brake blocks.

That is the type of contamination that I was getting at no amount of scrubbing with washing up liquid got the grease out of the Alloy rim but brake cleaner did.

Mick do you feel a pulsing in the brake lever if you apply the brake very lightly? If it is being caused by the rim being wider at a certain point you should be able to slowly apply the brakes so that the brake blocks catch at the wider part and do no touch in other places.
Sorry for stating the obvious but I do not recall you writing about the lever pulsing.

[ferrit worrier]

Right here we go a few interesting things here!

the old Chrina rim dia is 632 mm

the new Chrina rim dia is 634 mm

from memory the old Alex rim was 630

I measured the depth of the well in the three rims My original Alex rim (DA22) the old and the new Chrinas.

Because the well is curved I placed a steel ball inthe well held in place with a dab of grease, then using a depth mic measured from the top of the ball to the top of the rim.

The dia of the ball is 6.345mm the measurment from the old rim was Ball plus 1.79 mm total depth 8.135mm

repeat with the new rim, Ball plus 1.675mm total depth 8.02 mm

This now gives the well dia's as old 632 - 2x well depth = 632- 16.27 = 615.73

repeat with the new .................634 - 2x well depth = 634- 16.04 = 617.96 an increase of 2.23 mm in dia

The old Alex rim had a well depth of 8.625

so well dia of the old Alex rim is 2x8.625 = 17.25 take that off the dia of 630 = well dia of 612.75 mm

(The Alex rim well is flat so there was no need to use the steel ball that was a straight measurment)

so the well circumference of the rims is as follows old Chrina 1934.62 new Chrina 1941.63 compared to 1925.26 of the old Alex rim

The last two pics show the difference in the stickers and the alignment of the joint in the new and the old Chrina rims

With 16.37 mm difference in circumference of the well it's not surprising it's hard getting tyres on and off.

Anybody want a new Chrina rim, one owner never raced or rallied.

Malc

[Mick F]

Thanks FW,
Very informative.

I too have noticed that the stickers are in a different position. In fact, I'm positive that Rigida Chrina rims aren't the same as they were. Be it diameter, width, design or quality. Luckily, mine are the same overall diameter as before, but if you read my thread from a few weeks ago, you'll see that the Effective Rim Diameter can be different even in Old Chrina days.

Actually, the tyres are difficult to fit now. They are tight and hurt my thumbs, but previously the Chrina rims were easy to fit. It's not the end of the world with tyre fitting, but it is definitely annoying. I reckon I will not be buying Rigida Rims in the future, which is sad, because these are my third set and they will be my last set.

Further to my wheel re-building and spoke ordering and the fact that these new Rigida rims are "different" ..........

I've just made up the front wheel with the new rim - retaining the old DB spokes. The trouble is, threads are showing!

I've spent the last hour measuring and taking notes, and it seems these are the facts:
New front rim has an ERD of 605mm
Old front rim has an ERD of 602mm
This is why threads are showing.

New rear rim has an ERD of 605mm
Old rear rim has an ERD of 605mm too!

Front rims are 32h, and rear rims are 36h.

When I originally built up my Rigida/Campag Chorus wheels, I measured up and recorded 603.5mm. However, these rims and spokes were wrecked in my spectacular crash in 2008, so I bought new rims and a complete set of spokes as per the original measurements. I never measured again until today.

So, I need to order a set of spokes 2mm longer for the front, and I may as well buy the LH set for the rear wheel whilst I'm at it.

Why is nothing simple?

[foxy12]

I had juddering brakes when I put new wheels on my bike. It was caused by the anodising on the braking surface of the rims. When it wore off the brakes stopped juddering.

[The Mechanic]

I am a bit worried. Last week I ordered a Chrina rim, with spokes and hub, from Spa for my first ever wheel builing project. I hope it goes OK. They have not arrived yet but I will check the measurements and let you know.

[niggle]

I had juddering brakes when I put new wheels on my bike. It was caused by the anodising on the braking surface of the rims. When it wore off the brakes stopped juddering.

Interesting, how would you feel if you bought a complete new bike and it had the same symptoms?

[531colin]

I am a bit worried. Last week I ordered a Chrina rim, with spokes and hub, from Spa for my first ever wheel builing project. I hope it goes OK. They have not arrived yet but I will check the measurements and let you know.

Relax. There are 4 of us building wheels at the shop. Not all at the same time, but somebody is building wheels all day. 3 pairs a day is sort of average. They aren't all Chrinas, obviously, but all our own audax bikes go out with Chrinas, so do any Sabbath Septembers, all our audax test bikes have Chrinas, we build lots of Chrinas to post out to customers.
There are 2 reasons people send wheels back, the most common is they have ordered the wrong OLN (135 not 130, etc), second most common is the carriers have run a fork lift truck into the box.

My thoughts on wheelbuilding are laid out here http://forum.ctc.org.uk/viewtopic.php?f=5&t=49702&hilit=spokes&start=30
A relatively narrow rim like a Chrina will be more sensitive to half a turn of the nipple than a big strong Sputnik, obviously.
Just post on here if you get stuck, I'll do my best. For your first wheel, take your time, build up tension relatively gradually, keeping the wheel more or less true, round, and centred.....when you can do 3 pairs a day, you can wind up the tension quickly to begin with!

In case anybody is puzzled as to why tyres are getting tighter, it goes like this......
If the tyres are tight, people start whining on internet forums like this one.
If somebody puts 150psi in the tyre, goes for a ride, the tyre blows off and puts them in hospital, they are looking for somebody to sue.

[Mick F]

Mick do you feel a pulsing in the brake lever if you apply the brake very lightly? If it is being caused by the rim being wider at a certain point you should be able to slowly apply the brakes so that the brake blocks catch at the wider part and do no touch in other places.
Sorry for stating the obvious but I do not recall you writing about the lever pulsing.

Sorry, I forgot to answer this.

If I squeeze the brake gently I cannot feel anything through the brake lever. I don't know if that means anything or not, but it's when I feel the bike and the way I'm slowing down that I notice it. The pulses are at wheel rate, and I'm fairly sure there's two or even three pulses per rev. At higher speeds, it appears as a judder - hence my OP title.

The bike "pulses" and the front forks twitch back at the same time as the pulse. There's no tell-tale at the lever, but I think that may have to do with the brake design system: Campag Ergo with dual pivot front brake.

The brakes callipers are fairly new, as are the blocks. The cables have about 1,500miles on them and the whole brake system is perfectly set up and adjusted. If I fit my spare front wheel, and the nothing else, the front brake is totally smooth as it should be.

I'll be out on the bike tomorrow, and I understand we're due some rain, so I'll fit the mudguards and take my Goretex and hope I get a soaking. This always wears rims and blocks more than dry weather, so hopefully this problem will slowly disappear.

I repeat - I have never had this before: on wheels I've built, brand new wheels, or on any shop-bought bike. This is the very first time in my whole cycling life. It's that new to me, hence my investigations into the rim width and Chrina rim quality.

Actually, thinking about it, before the Rigida website was taken off air, the Chrina rims were listed as "Chrisna". Whether this means anything or not, I don't know. Perhaps they are "Chrina" spelt differently in Dutch? Or perhaps they are different rims - as I expect - but using the old Chrina stickers for us Brits.