Brake Drum Cracked.

[Shadowman]

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

 

[clevtrev]

From experience, I would say 70 % of brakedrums out there are cracked. That is to say, original ones.

 

[Vic Youel]

70%......wow!

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!!

Vic

 

[Comet Rider]

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.

Neil

 

[ray vinmad]

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.

Ray

 

[Roger Barton]

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.

 

[nkt267]

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.

I'm the same age as my Comet.....HELP!!!!

 

[Tom Gaynor]

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]

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.

 

[piggywig]

More than cracked drum.

Tom,
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.
Col.

 

[Shadowman]

Getting ready for my next adventure I thought I'd give myself a sporting chance and get the brakes working better as they still were not so good after renewing all the shoes. I did the test of holding the drum on a wire from the centre and tap it with a hammer. If it rings like a bell it should be okay. One drum from the front and one from the rear did not ring true and sure enough I found both to be cracked. So that is three out of four drums replaced because of cracks. I have replaced them with new shadow drums.

 

[Albervin]

Getting ready for my next adventure I thought I'd give myself a sporting chance and get the brakes working better as they still were not so good after renewing all the shoes. I did the test of holding the drum on a wire from the centre and tap it with a hammer. If it rings like a bell it should be okay. One drum from the front and one from the rear did not ring true and sure enough I found both to be cracked. So that is three out of four drums replaced because of cracks. I have replaced them with new shadow drums.

That is a 75% failure rate which is right up there with Trevor's statement. I would like to know whether there is a greater failure of rear or front drums & why that may be so. I thought that if there was an alignment problem with the front or rear suspension that could be a cause??

 

[indianken]

Fellows,

Seeing all of these dead drums, I'm even more happy with the front disc
brakes I installed on my Rapide.

(I can here the knives being sharpened now by the Origionalists )

Ken Smith

That is a 75% failure rate which is right up there with Trevor's statement. I would like to know whether there is a greater failure of rear or front drums & why that may be so. I thought that if there was an alignment problem with the front or rear suspension that could be a cause??

 

[nkt267]

(I can here the knives being sharpened now by the Origionalists )

Put a disc on the rear,put the bike on it's rear stand and with engine running and in gear we can sharpen them on the disc.

 

[Tom Gaynor]

Cracked drums

I replaced a rear nearside drum which had a piece come out of it. I was told it wasn't uncommon, and some Vincent drums weren't up to much being made from "plumber's cast iron". (I don't know if that is true.) It wasn't obvious why it broke, no impact damage, so I concluded it was a casting flaw and had always been there. It wasn't a fatigue crack - I know what those look like - but it was a bit disconcerting to see that the piece, like a section from a pie-crust about 2" per side was fully rusted and had evidently been held in place largely by paint.

 

[Len Matthews]

If the drum rings when tapped (like a bell) it's probably OK.

 

[Vincent Brake]

Cast drums crack

Hi Guys, they are cracking as you bolt them on the hub.
1s there is the unevenness in bolting torking them down.
2nd there is unevenness as you tighten it down to the spokes (where the 90deg bend is) and couse a great offsett force on them.
3rd surface on pressed steel spoke flange isnt flat but uneven.
4 its mostly ****y material (GG 25)

This all is also the case why hubs (cast ones) are cracking also

The srongest part is the steel soke flange as it gives way (mostly) without giving in

so take care and have them bolting down as they have contact under the bolting surfrace and not beside it, as it creates a bending force on the drums, cousing the crack.

Best regards

Vincent Speet Brake

 

[VinParts]

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.

Try 50 years of use Tom.

 

[Len Matthews]

Another thought; be sure when fitting a new drum, be sure that clearance exists between drum and spokes. I've had some where the drum casting has to be machined to achieve this. Failure to observe this point means the drum does not bolt up flush with the spoke flange.

 

[Robert Watson]

I have a drum in my garage at the moment (of totally unknown parentage!) that had been bolted up to a hub, (I would say blindly but I know the perpatrator lurks amongst these lofty walls and I wouldn't want to cast a shadow on his fine reputation!) and brought to me to turn the new linings up to suit. There are I think about 9 substantial cracks in it. 6 of them run through the sprocket mounting holes and through the face of the drum, and others in the same manner except not at a sprocket bolt hole. We replaced it with another of unknown parentage, but one that rings a nice c#.

Wondering how fragile it might be I threw it on the concrete floor several times, and yet it remains in one piece. I know it can't be used as a dinner bell, so it off goes to cast iron heaven.

Robert