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Atlas front brake.

Submitted by neil_waterton on Sun, 09/09/2018
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Heavy Twins

My '68 Atlas is fitted with a 2LS front brake. Having just renewed the bushes throughout the front forks, and bolted all back together nicely, I find the front wheel spindle is tightening up onto the brake plate and making the shoes bind in the drum. Have I inadvertently left out a spacer or washer? It seems that the forks are pulled together (inwards towards each other) by about an eighth of an inch when the last couplet of turns of the spindle nut are done up, and something seems to be pulling out of line. Looked on exploded views of brakes/wheel/hub drawings, and nothing seems missing. Should I slacken off the stanchion pinch bolts on the lower yoke and give it a few bounces to re align anything.

Help and comments much appreciated.

Neil

Submitted by barry_carson on Sun, 09/09/2018

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not atlas, but i had a similar thing with a Norton tls brake binding. if you can raise the front wheel off the ground safely then slacken the pinch bolt plus the wheel spindle so it turns freely in the forks. turn the spindle and just observe the top of the wheel and see if it moves from side to side while turning the spindle if it does the spindle is bent. more than likely the pinch bolt side.

Barry

Submitted by ian_soady on Sun, 09/09/2018

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The left hand end of the spindle should be a sliding fit in the fork end until the pinch bolt is tightened, so I can't quite understand how the fork leg is being pulled in unless you're tightening the spindle nut without slackening the pinch bolt.

The bouncing is usually done with the pinch bolt slack to let the fork sliders align.

And of course we all know not to overtighten the pinch bolt don't we!

Submitted by robert_tuck on Sun, 09/09/2018

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It could be that your mudguard is a bit wide and is spacing the forks?. Also have you renewed the linings? or different shoes?, I have some rear wheel replacement shoes from rgm that needed some fettling with an angle grinder as when the brake cam spindle is tightened it tipped the shoes sideways and then when the axle was tightened the brake locked. Otherwise very happy with the RGM shoes as the linings were FULL thickness and give good grip. Not like other suppliers. Check also the shoes are not too wide and rub the back of the drum.

Submitted by jonathan_soons on Sun, 09/09/2018

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If you suspect the mudguard is exerting any pressure inwards or outwards you should remove it until the wheel is properly installed. Your pinch bolt should be completely loose at this stage and the spindle rotating freely in the fork end. That is why there is a hole in the spindle for a tommy bar. The pinch bolt is the LAST thing you tighten when installing the front wheel (unless you removed the mudguard in which case the mudguard can then go back on).

Submitted by neil_waterton on Mon, 10/09/2018

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No mudguards fitted yet. Ground up build.

Have had another look at the 2LS back plate. As stated previously, the refurb was started by the previous owner, and he evidently bought a load of aftermarket stuff such as stainless wheel spindles and nuts, stainless yoke bolts and steering head nut etc etc. The brakes have never been applied in anger and the backplate alloy casting, shoes springs etc are brand spanking new. Now I have stripped the backplate back to a bare singular part. If you stand it on a flat surface with the inner workings upwards, it doesn't sit flat,horizontal. The small 'nub' cast into the centre,sitting next to the fork leg that the whole thing is sitting on is, I think, not machined square with the plate surface. Hence when the last couple of turns on the spindle nut are tightened, it kicks the back plate out of square and locks the shoes onto the drum. Seems the most logical reason at the moment. Comments and views always most welcome.

Neil

Submitted by robert_tuck on Mon, 10/09/2018

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That would do it, I have a similar issue with another bike. The machined surface (on both sides of the plate) needs to be at 90 degrees to the fitted shoe linings, the bore in the brake plate is not really relevant as its usually a bit loose anyway.(less so on TLS)

Submitted by neil_waterton on Tue, 11/09/2018

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I had a good look at the plate stripped back and then assembled. The shoes were within a few thou of touching the cast-in weather strip on the inner edge of the plate. I added four shims between the cams and the plate and the shoe fulcrom posts to push the assembled shoes 30 thou (thickness of a washer) further into the drum., andaway from that weather strip shape cast into the inner edge of the back-plate. Well what a transformation! everything lines up perfectly, the wheel runs for ever when jacked up in the air, and no hint of lining binding on the drum edge. Nut and spindle does up perfectly tight before nipping up the spindle clamp. Result. Just took me 2 weeks to fathom it out. Hey Ho norton ownership. Lucky i have the hours to ponder the irritations that seem to be endlessly coming over the hill. (sic) Hope this may help someone with a similar prob.

Thanks for all contributions. Neil

 


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