Broken rear hub - Mike Norris - LL

[John Wakefield]

Interested to hear Mikes problems with TWO broken British Hub rear brake plates, in fact this problem is not just with scramblers but road bikes also.
This thread concerns the same problem 'dibgreeves' had with an East Coaster road bike http://www.greeves-riders.org.uk/for...ht=Broken+rear
Looks like metal fatigue is probably the main factor here, 50 year old alloy castings showing their age. These brake plates are not very thick section & the stress & strain of a long period looks to be the cause. Maybe time to get some new ones cast.

[Phil Hyde]

I like the idea of a replacement brake plate. A couple of solutions come to mind:- a new casting, or, CNC item. The fly in the ointment, so to speak, is product liability. Designing and making a reliable product is dead easy, likewise marketing.

So, the exam question is who wants one, and how much would you pay

Comments please.....

[John Wakefield]

I took a look at the brake plate on my 25DCE today, when pressure is put on the rear brake pedal the brake plate deflects quite noticeably, the more the pedal pressure the greater deflection, so given time the metal gets stressed. The fact that on these hubs the brake actuating lever is cranked outwards thus putting more stress on the brake plate does not help matters. Looking at my bike there is no need for a cranked lever & a straight one would put less sideways stress on the brake plate.
This looks to be an ongoing problem, & buying a second hand replacement brake plate is not really the answer as this is likely to have had a lot of use & stress over the years, particularly if from a comp. bike.
As Phil says the answer is newly manufactured plates either cast, or NC machined from solid billet, the second option would be the best but at what cost? New castings would need to have strict quality control & made from the correct spec alloy. This is a serious safety matter & I think all breakages should be recorded by the club so we can see how far reaching this problem is.

[scott151]

Interesting thread this

But... I have to admit that having heard of two of these breaking out off all the motoloy hubs sold is hardly a huge need for concern?

I've known of a couple of alloy beams breaking over the years but I'm not too worried about mine..

Adrian moss used to sell replica amc alloy brake plates for £25 or £30 I think but I'm unsure.. I would have thought £30 for peace of mind would not be unreasonable... But il change my Anglian one when or if it breaks?

Scott

[John Wakefield]

But... I have to admit that having heard of two of these breaking out off all the motoloy hubs sold is hardly a huge need for concern?

I've known of a couple of alloy beams breaking over the years but I'm not too worried about mine..

Adrian moss used to sell replica amc alloy brake plates for £25 or £30 I think but I'm unsure.. I would have thought £30 for peace of mind would not be unreasonable... But il change my Anglian one when or if it breaks?

Scott

Yes but is it just the 3 we know about, has there been a history of the hub plate braking in the past. It may not be a huge problem on a scramble bike on grass, but a road bike doing maybe 50 or 60 mph on tarmac & in close proximity of other vehicles could spell disaster. 'dibgreeves' had a nasty moment when his broke.

[KevinLS]

This isn't directly related but circa 1976 I had British Hub 8 inch front brake plate on my Silverstone catastrophically fail on the way into Druids at Brands Hatch. The result was a triple Salchow followed by an impressive face-plant on the tarmac. At the time the rumour was that "they had a history of doing that", although I never saw another example. I'm now rebuilding my Greeves and looking at a couple of similar brake plates rather sceptically and leaning towards putting something different in. Mind you, a decent drum brake costs a bob or two nowadays.

[mikerwt]

broken rear hub

If some one takes up the challenge of casting new back plates it is a fine opportunity to improve the design ie bigger radii thicker walls were appropriate and perhaps a different spec ally this is not rocket science there are small foundries that could sand cast in small batches leaving some basic machining to finish. the main cost is the pattern and as you will all know ally shrinks an old brake plate could be improved and used as a pattern. good luck

[John Wakefield]

I have spoken to Paul Powell (Cotton Villiers Spares http://www.cottonvilliersspares.co.uk/ ) about this problem & he says
he is aware of the problem & has seen it before, he may consider getting some new ones cast & will be at the agm if anyone wants to discuss it with him.

[gribley]

For competition use bikes or road bikes that are mainly for riding, there are many Japanese and Italian hubs that can be used and don't look very out of place.
My MDS sprint bike has a Royal Enfield (Indian) front brake

[John Wakefield]

Would the answer be heat treatment? this article make interesting reading http://www.heat-treat-doctor.com/doc...20Castings.pdf
Particularly the paragraph entitled Stress Relief & Annealing - TS Condition.

[hawkie197]

Axle nut torque figures

It’s an interesting article written by Mike Norris, and the fact that it has happened to him twice is all the more interesting.

The part that concerns me is "When I tighten up the wheel nuts, I use a long ring spanner and put all my weight into doing it up", when you look at both photos the backing plates have fractures through or radiating from the hole for the axle.

I use a similar technique to tighten up crankpin nuts to the required 200-400 ft-lbs torque.

I think that 50 ft-lbs should be more than adequate for axle nuts, maybe someone can quote an actual figure from the relevant service sheets.

Maybe Mike should invest in a tension (torque) wrench.

Cheers Pete from the Antipodes

[Rob]

They can't be that fragile as Dangerous Dick hasn't managed to break any of his yet to my knowledge! It can't be too many pies either!

I just wonder if the hub has an incorrect spacer or something else that is putting the plate under stress? I have never heard of any others breaking.

Regarding the front brake and Druids at Brands, my brake plate operating arm somehow got caught up under the loop during braking and when I let go of the brake it stayed on and I went straight on! I know the feeling Kevin!

[John Wakefield]

I have never heard of any others breaking.

I spoke to Paul Powell (Paul trials, the Cotton man) about this & he knows of lots that have broken, & as mentioned on an earlier thread one broke on a roadster.
Paul agreed with me that its fatigue in 40 old year old castings. He is considering getting some re cast.

[dave higgins]

I spoke to Paul Powell (Paul trials, the Cotton man) about this & he knows of lots that have broken, & as mentioned on an earlier thread one broke on a roadster.
Paul agreed with me that its fatigue in 40 old year old castings. He is considering getting some re cast.

Waffle...waffle waffle......most hubs are put under stress, by an imbalance of brake shoe contact area.
When one shoe touches the drum first, it puts strain on the pivot pin /cam, as it does not have force acting on it from both sides.
Both shoes must centralise & operate with equal pressure against the drum to allieviate strain on the the cam & prevent stress fractures & eventual material failure. .
So many people take a pair of new shoes out of the box, & just fit them, or mix & match old shoes ( that have a bit of meat left on them ) without checking the shoe height.
Quite often, you will see a variation of lining material thickness on a pair of matching shoes, so its always pays to check.
To overcome this, some companies fitted a floating pivot, which when lossened allowed the shoes to be centralised, then tightened back up
On the vintage racecars, we always remove the hub assemblies complete & turn them in a lathe till they are perfectly round, just a few thou under their operating position.
Extreme, but it works well & some of these alloy back plates are close to a 90 yrs old,

[John Wakefield]

Not all waffle. Whilst an imbalance in brake shoe contact can also be a contributing factor, the outward force via the cranked brake lever also causes a bending motion to the brake plate which is very thin section. This bending motion sets up a stress line which coupled with the work hardening of the aluminium eventually causes fracture. If Paul (or anyone else) has new castings made then extra strengthening ribs need to be added. It would also help matters if the brake lever was changed for a straight one.