Author Topic: Rear brake making a knocking sound on plunger A10  (Read 136 times)

Offline owain

  • A's Best Friend
  • ***
  • Join Date: Mar 2017
  • Posts: 127
  • Karma: 2
At long last and with much thanks to this forum my A10 plunger is back on the road and the engine is sounding great. The only problem I seem to be having now however is an annoying 'knock' when I press down on the rear brake pedal. It feels like the brake doesn't work at all for the first few centimetres and then there is a noticable clunk/knock and a bit of kickback in the brake pedal when the brakes do engage. Does anyone have any ideas what might be occuring here?

Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online JulianS

  • 1962 A10
  • Resident Legend
  • *****
  • Join Date: Mar 2017
  • Posts: 892
  • Karma: 18
Re: Rear brake making a knocking sound on plunger A10
« Reply #1 on: 23.08. 2019 14:53 »
I think you need to strip the brake and check the whole setup to diagnose the problem.

Offline Swarfcut

  • Resident Legend
  • *****
  • Join Date: Oct 2018
  • Posts: 706
  • Karma: 9
Re: Rear brake making a knocking sound on plunger A10
« Reply #2 on: 23.08. 2019 15:19 »
Owain, Try this before you get the spanners out. With the bike on its stand, rear wheel off the ground, apply the brake and try to rotate the rear wheel back and forth. Any movement between the drum and hub is down to wear on the drive flange,which is bolted to the drum,and the hub splines. Worn splines or a loose drive flange will give a clunk on load and over run, and on braking. Anything that allows the shoes to move while in contact with the drum will also give a clunk. See if the brake backplate moves. The  backplate needs to be moved back to tension the chain and loosely tightened against the suspension lug with the big nut before finally  aligning the wheel in the frame and tightening. The spindle nut can then be tightened.. In other words the backplate is tightened against the lug  after final wheel and chain adjustment and does not float once all is assembled.

 The brake is straightforward to check, first establish that the nut securing the fixed shoe pivot is tight. Loose could be the clunk.The fixed shoe pivot sits in an elongated hole, so with  the retaining nut loose, the shoes can move slightly. Apply the brake to centre the shoes and retighten the nut with the brake held on. A few other things to note. Cam pivot wears, sometimes a custom bush will reclaim an otherwise good backplate. Cam lever position and splined pedal shaft will allow adjustment so the shoes just kiss the drum and neither lever passes the magic 90 degrees between lever and brake rod. A brake pedal that rises and falls on light braking  means an oval drum.

Swarfy.

Online Greybeard

  • Jack of all trades; master of none.
  • Wise & Enlightened
  • *
  • Join Date: Feb 2011
  • Posts: 5543
  • Karma: 29
Re: Rear brake making a knocking sound on plunger A10
« Reply #3 on: 23.08. 2019 22:58 »
I recently posted photos of my rear brake that had a nugget of brake material floating about in the drum. Check inside your brakes.

Offline owain

  • A's Best Friend
  • ***
  • Join Date: Mar 2017
  • Posts: 127
  • Karma: 2
Re: Rear brake making a knocking sound on plunger A10
« Reply #4 on: 25.08. 2019 19:22 »
Thanks for the responses. I took the rear wheel off and checked the splines on the QD drum and hub. Seemed fine. I then noticed a loose nut on the outer side of the drum and the drum rotating slightly when I braked. Tightened the nut up and the knocking stopped! Success. Finally got out and enjoyed a long ride on the A10 with no issues whatsoever...except for a few drips of oil from the chaincase...but I can live with that  *whistle* *smile*
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online Greybeard

  • Jack of all trades; master of none.
  • Wise & Enlightened
  • *
  • Join Date: Feb 2011
  • Posts: 5543
  • Karma: 29
Re: Rear brake making a knocking sound on plunger A10
« Reply #5 on: 25.08. 2019 20:00 »
Finally got out and enjoyed a long ride on the A10 with no issues whatsoever...except for a few drips of oil from the chaincase...but I can live with that  *whistle* *smile*
Sounds like perfection! *smile* *smile* *smile*