Brake Drum Cracked.

[Peter Holmes]

Alf and Jack

Whilst having some wheels built up years ago by Furness and Searle I was surprised to see Alf, just prior to tapping in the brake drum bolts with hammer and drift, run a drill of the correct diameter through each hole, I guess that removes any stresses that could be caused by slight discrepanciesin manufacture. Drill the first hole and tap in bolt, drill opposing hole and tap in bolt then just drill the rest.

 

[The VOC Spares Company Limited]

Spoke flanges

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.

Note that there are at least 2 different patterns of spoke flange (ok 3 counting Series A) (ok 4 with 10 hole) the difference is the depth of the offset, I believe the this was deepened when the thicker cast iron drums replaced the pressed steel. The part no was not revised for this change.
Identifying the part nos. is always an interesting game,
H2 – Series A (smaller inside dia.)
H2/1 – Series B on wards, 5 hole
H2/2 – ‘Racing’ and Black Shadow 10 hole (but the D Spares Diag M0106 shows H2/2 as a 5 hole on the rear wheel only)
H2/3 – not listed
H2/4 - D Spares Diag M0106 has H2/2 as a 10 hole
But as there are many errors in the D lists these are not to be trusted.

 

[bmetcalf]

When I laced on a 21" rim a year ago, I did the drilling and thought it was a bodge that I should never admit. Now, it turns out I did the right thing! Maybe a wee dram tonight to celebrate?

Did I make sure that the spokes didn't touch the drum? The concept seems familiar, so probably. I'll see if I can slip paper between at each spot, if it isn't a visual check.

Whilst having some wheels built up years ago by Furness and Searle I was surprised to see Alf, just prior to tapping in the brake drum bolts with hammer and drift, run a drill of the correct diameter through each hole, I guess that removes any stresses that could be caused by slight discrepanciesin manufacture. Drill the first hole and tap in bolt, drill opposing hole and tap in bolt then just drill the rest.

 

[Tom Gaynor]

Gosh: just cracked another one...

On Friday, the drive side drum (ribbed) parted right round the wide groove that takes the sprocket nuts. There was no indication that trouble was brewing until about a second before it brewed. CRUNCH! Whoops, wossat... No great damage done, and an hour later, having scrounged some 6 mm nuts and bolts from a car dealership and put the sprocket on the other drum, I rode the 70 miles home. I did have to promise that if I ever bought a Skoda, I'd buy it in Burrelton.

It was my second original rear drum letting go but I am pretty sure the cause was the slackening of the sprocket bolts. I was left with five rather battered 1/4" BSF setscrews and never a nut to be seen. Wonder how long it's been like that? I Fitted the sprocket 10,000 miles ago. Doesn't bear thinking about... Memo to self: use locknuts and/or Loctite next time, and use 10 bolts, not 5.
The new drum is in place. What a ****** of a job it is to take the drum off the hub. Eventually I made a screw-jack and jacked the bolts out, so successful that I re-used them. It also helped to fit a 3/8" drive 5/16" BSF socket to a 1/4" drive ratchet (smaller head). That way taking the ten nuts off, each clinging to the bolts to the last thread took only took an entire afternoon.
I had two new bolts, bought as spares when I replaced the other drum. Those dropped straight in. The original Vincent eccentric headed ones had to be driven in.

 

[lindie]

justifiably so i realize, but you're all getting me rather paranoid. might have a good closer look at my drums next weekend.

 

[Tom Gaynor]

Cracked drums - aftermath

At least check that the sprocket bolts are tight...

In the end I used 7 x 6 mm stainless capscrews and nylocs (cheap as chips, but second choice because no first-choice 1/4" UNF caps available) and put three 1/4" stainless dowels in to prevent "hammering". So far, so good...


QUOTE=lindie;9527]justifiably so i realize, but you're all getting me rather paranoid. might have a good closer look at my drums next weekend.[/QUOTE]

 

[ossie]

securing bolts

its better the thread doesnt go right up to the shoulder then the sprocket and drum will be driven by the bolts diameter and not relying on the nut to pinch it together and the drive will also be just on the crest of bolt thread.

 

[bmetcalf]

its better the thread doesnt go right up to the shoulder then the sprocket and drum will be driven by the bolts diameter and not relying on the nut to pinch it together and the drive will also be just on the crest of bolt thread.

Different application, but we were taught in school that auto flywheels are secured to the crank end by bolts in tension causing friction between the faces of the parts, not the bolts in shear. This is because of the difficulty in drilling the holes and controlling the bolt diameters to have each bolt equally loaded. However, I assume our drums put the bolts in shear and the theoretical unequal loading isn't that bad.

 

[Alan J]

I spent some time last year at the "Dutch" moving sprockets and drums about, much to the amusement of all and sundry-it's not the best design in the world and you need a tame monkey to get at the bolts!!

 

[Vic Youel]

Cracked Brake Drums

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

Sadly nobody adressed my original questions in this long running thread; I tried "ringing bell" (good idea Len) with some of my spare drums but was unsure of the result. So how good are current spares (Rapide or Shadow......are they made to the technical commitees's drawings? what materialis used etc etc ??? Have they been properly tested ....... let's have some decent information please

Vic