Siezed dual pivot calipers

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Siezed dual pivot calipers

Postby PT1029 » 9 Feb 2019, 2:56pm

On the "Is there a perfect bike for commuting?" thread on here, I posted to not use dual pivot brakes without mud guards, as they always sieze up (water + winter road salt).
I had the best case yet this week at work, Campag Veloce, front and rear calipers siezed (pads sort of just about rubbed rims when off, 1 brake sort of slowed a bit when applied). Unlike the usual siezed dual pivots, not only were the pivots seized but one arm was so corroded along the metal grain boundaries that it had split down the middle, thus exerting so much pressure on the other (outer) arm that it had cracked near its pivot.

Split/corroded arm

Interestingly, I showed the upper photo to my local bike shop, who said he recognised the bike, and was glad the owner had been taking it to me because it was so knackered. Bike in question is a 653 road bike with, er, good patina!
Image Attachments
Fractured arm (near the pivot)

Samuel D
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Re: Siezed dual pivot calipers

Postby Samuel D » 9 Feb 2019, 3:40pm

That is quite something.

I find interesting that the spring does not appear to be severely corroded despite the “good patina” and wholesale failure elsewhere. My Shimano BR-R650 springs are badly corroded despite the rest of the brakes appearing to be in fairly good nick. Perhaps Campagnolo buys springs with better plating.

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Re: Siezed dual pivot calipers

Postby Brucey » 9 Feb 2019, 4:32pm

if you take a high strength aluminium alloy, forge it, and then anodise it, you have a pretty typical (expensive) bike part. Unfortunately such aluminium alloys are more susceptible to certain types of corrosion too. You can get intergranular corrosion, SCC, you name it. In the case of a drop forged part there are often internal stresses which are high enough to drive a corrosion-related failure. Spraying everything with salty water hastens things along at many times the normal rate.

The brake arm in question appears to be a forged part that has suffered intergranular corrosion. It may have been faulty in some way but I have seen numerous failures of this sort over the years, in high strength forged parts, usually driven by road salt, sometimes driven by corrosion from sweat etc.

The weird thing is that often the use of high strength materials has little or no real benefit; the parts are commonly limited (by design) by factors such as stiffness not strength, and there is little or nothing to be gained from using a higher strength material.

Cheaper brakes use cast arms (which are not full of locked in stresses) and/or use materials which are inherently more corrosion resistant. Such parts are considerably less likely to suffer a corrosion related failure when subjected to all-weather use.

Quite a lot of cyclists have for decades used expensive equipment for their summer bike and less expensive equipment for their winter bike. This is exactly as it should be; often the posh kit is a lot less durable in winter conditions.


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Re: Siezed dual pivot calipers

Postby foxyrider » 9 Feb 2019, 5:40pm

Glad i'm not the only one whose winter 'hack' is a basket case! :lol:
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!

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Re: Siezed dual pivot calipers

Postby londonbikerider » 11 Feb 2019, 8:06am

I wonder how is the rest of the bike, if corrosion has split the metal of the brakes how is going to be inside the frame, which I assume is steel?