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Brake Drum Cracked.


Well Known and Active Website User
VOC Member
My Rapide front right brake drum cracked so bad that there was only 1 inch of brake surface holding it in one peice. The nuts were all very tight except one which was at the crack and it wasn't exactly loose. I removed it then hit it with a hammer and it shattered. Any ideas what could have caused it to crack so bad?
Peter Sprot


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Vic Youel

Well Known and Active Website User
Non-VOC Member

Would anyone care to state whether there any failure details available for current drums supplied by Vintech and the VOC spares company? Have current suppliers solved the problem? Has the VOC drawings project researched the issue and imlemented solutions? I am sure all Vincent riders would appreciate more information on this potential safety hazard. Cannot recall ever reading about this in MPH although I have not checked FYO.

Assuming the drawings project has solved the potential problem, are the VOC spares company brake drums manufactured in accordance with the new drawings?

I found one rear drum cracked on my Rapide twin...... must look at my Comet now!!


Comet Rider

Well Known and Active Website User
VOC Member
Cracked Drums

Having seen a couple of failures within the last year, they seem to fall into 2 distinct groups.
1/ the crack that radiates out from one of the bolt holes
2/ this was seen on a Shadow drum, where the whole mounting flange broke away. The crack started from one of the drain holes and spread right arround the drive face.


ray vinmad

VOC Drawings Manager
VOC Member
I had a rear drum break up into 16 bits at the Dolomites Rally ten years ago, it was only the sprocket holding it together! I've got an old steel one on the back now, they don't seem to suffer the same fate.
As for new drums, I've got a pair of new(ish) Shadow drums on the front now, the old Rapide cast ones had cracks across the face.
As for how long they will last in comparison to the originals, hopefully I will have to wait another fifty years to find out.


Roger Barton

Active Website User
VOC Member
Cracked drums

I had one explode on my Rapide on the M25 at 70 mph all that was left was on piece 2 " long still bolted to the rear sprocket this was an original which I checked before fitting and had no cracks. I have now replace all four with New shadow ones as I found that both front ones had cracks. I will be replacing my Comet ones as soon as possible and will not be fitting any more original ones as I feel that it may be age related stess / fatigue.

Tom Gaynor

Well Known and Active Website User
VOC Member
Cracked drums

I found one of my original rear shadow drums cracked. God knows how long it had been like that. The crack however started on the braking surface and had grown towards the outer edge. I thought it was probably a casting fault - difficult to imagine what else it could have been.

Tom Gaynor

Well Known and Active Website User
VOC Member
Cracked drums

Should have said this earlier. Steel and cast iron do not fatigue with age. They only begin the fatigue process if the stress applied exceeds about half the yield stress (which is called the endurance limit). If the stress is below that, then it'll last forever. Or for 120 years and counting like the Forth Bridge and many other steel and cast iron Victorian structures. The Tay Bridge fell down because flaws in the castings were filled with silly putty. So don't repair cracks in your front hubs with plastic padding.........
If you want to crack detect them, a pretty good job can be done with "simple household materials". Clean the paint off, immerse them in hot paraffin, take them out, wait until the paraffin has evaporated off the surface, then dust them with talc and blow the excess off. The talc sticks to the cracks because the cracks still hold unevaporated paraffin.
It is safe to conclude that if there are no cracks then the fatigue process (caused by alternating stress above the endurance limit) hasn't started yet.
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Well Known and Active Website User
Non-VOC Member
More than cracked drum.

Does this one come into the 'beyond the endurance limit' category?
Too late for the kero & talc method! That has always been the 'field' method for suspect breech blocks, it works as well.


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