Brake shoe return springs

[ranton_rambler]

Anyone else have problems with brake shoe return springs?
I have never broken one of these on any other vehicle but the rear brake on my 175 has now had 2 failures.
The first one broke while I was riding and the broken bits briefly locked the wheel which was slightly scary.
The second one I detected while pushing the bike back into the garage after a short ride this week - I could hear it clonking round inside the hub.
This is the smaller brake used on some bikes up to around 1960. Drum diameter 136mm I think. No spares left now, but I have found out that this brake is also used on Guzzi Stornello.

[double diamond]

I’ve had two rear brake shoe springs break recently. One discovered at the track when the rear brake was dragging (and getting very hot!), the other discovered when the rear wheel was removed to replace the tire. Both springs were in excellent condition when installed.

[LaceyDucati]

Broken springs are quite a common issue on race bikes, I always wired the springs through the middle, just in case, to stop the large part causing havoc in the drum. It's a known issue, don't know far back, but throughout the last 30 plus year I've been involved. I do have quite a few original springs of different types and the later hub springs as replica.

It's a resonance issue and I have seen the rear brake plate "explode" after the spring got caught up. A racer once finished the Manx with just the back plate centre boss and the cable trailing with the arm and cam attached. The shoes, springs and the rest of the back plate disappeared.

Regards Nigel

[Jordan]

Broken springs are quite a common issue on race bikes

Interesting, I didn't know that.
Because of higher revs?
Only Ducatis/Italian bikes, or is it the case for all racers?

[ranton_rambler]

brake plate.jpg

I thought this might be an example but both springs look intact. Not mine but this was a 450 Scrambler that was on the Giro SW last year and had a rear brake disintegrate suddenly. The other similar bike had an ignition failure so we swapped some bits around to make a runner. The other went in the van of shame.

[LaceyDucati]

The early back plates don't have any structural support webs in them. The back plates received more webs as the years went on, I guess Ducati had been aware of an issue! It's the reason racers tend to avoid the early unsupported back plates or fit different hubs. The issue with broken springs is more a Ducati thing, but I guess other bikes may suffer similar issues.

I will add, I think the use of some modern bearings can cause problems with the back plates. Some modern bearings have very thin inner side faces, which dig into the aluminium back plate boss, causing it to split. I am very selective which make bearings I use for this reason. Older bearings had side faces of maybe 2 to 3mm, whereas some modern bearings a little more than a 1 to 1.5mm. Currently I use NSK bearings as the faces are wider than most, It is one of those things surprisingly not in the specification of a bearing. I have also noticed that the axial movement varies dramatically from make to make for the same bearing, this is most noticeable when shimming gearboxes and is another reason why you shouldn't shim a gearbox on the tight side.

Regards Nigel