8" front brake suggestions please

[MikeN]

Hello All,
   I have just discovered this forum and it looks very interesting.Im hoping to receive some thoughts on a problem with my A10 rgs replica (yes another one).
  Ive had it on the road for a couple of years now and I really like it, it goes well and doesnt drop oil .Only done 5000 miles so far.
  However it has a  problem with the front brake.When I built the bike I must have been feeling particularly (unusually)wealthy because I splashed out on a Phil Pearson twin leading shoe front brake to fit the 8" half width hub.For the first 1000 miles it was fine but now I have to remember when I drive off in the morning and go down my road which is about 150 yards long to go at about 5-10mph and very gently squeeze the brake lever.When I do this the front wheel locks, the front end dives and the forks twist alarmingly.I have to repeat this 4-5 times before I get to the end of the road (bottom of a hill) and have to do it  for real. After this the brake performs normally for the rest of the journey and usually the rest of the day although sometimes it will do it again when i start off home from work in the evening. I am frankly terrified about what will happen on the day I forget to do this and it locks up going round a bend or at speed.
  The brake plate is a beautifully made piece of solid quality engineering and appears Accurately machined with polished stainless steel levers and a good finish generally.I had the wheel out again last night but can see nothing obviously wrong. Anyone got any ideas.
  I spoke to Mr. Pearson and apparently I am the only person who has had this problem. he could only suggest fitting stronger return springs.Which he doesnt have and nor do I.I dont think this is the problem as the existing springs are really strong.
  I dont think the drum is oval because when it is working correctly i get no juddering or movement at the H/bar  lever.the leading edges of the shoes came with chamfers although I have now filed them bigger.There was about .25mm play in the clevis pins on the adjustable turnbuckle/connecting link.I have reamed these out and fitted snug fitting oversize pins.the brake linings are a sort of charcoal black/grey colour which I believe are correct road linings for road use.The operating cams are not rotaing excessively and going "over-centre".But something is making it lock on and I am becoming more reluctant to use it.Also I keep snapping mudguard stays form the violent fork twisting .
What do you think. Mike

[BSA_54A10]

If the forks twist then the brace (?) under the mudguard is probably cracked. or the forks have turned a little on the legs or are loose in the bottom tripple tree or the top tripple clamp is not tight.

If the brakes lock up when cold and don't when hot then they are adjusted just a little too close to the drum or the attack angle is a little too steep

[MikeN]

Thanks for that.Can you explain what you mean by "angle of attack".
My shoes are adjusted to give minimum clearance so I think that is worth looking at.

The Brace certainly is cracked.its the viscious twisting that keeps busting them as the forks dive at 10mph in a straight line.All bolts a done up tight.
MN

[A10Boy]

Mike are you in the UK ? There is a great company called supreme motorcycles [no connection] in Leicestershire who will sort it out, they are Ferodo brake specialists and can fit your shoes with very good quality linings.

it sounds to me like there is some sort of contamination on your linings which is gassed off when you warm them up, but returns upto the surface overnight.

I once had a car that would nearly throw you through the windscreen in the wet when the brakes were damp and cold, but was fine when they had been warmed, I had them relined and they were great. the garage said they had oil contamination on them, maybe this is a similar problem.

BTW, those charcoal grey linings you can buy are not the best at all. I assume they are bonded, and you have checked they are secure, they have been known to come loose at the ends.

Here's their website good luck.

http://suprememotorcycles.co.uk/

[beezalex]

Two things I can suggest checking: 1.)Pad contamination with grease from a wheel bearing.  This will turn to goo and can make the pads stick.  2.)your brake stay.  Is it rally tight?  And solid? 

Just some thoughts.

[snowbeard]

not the typical complaint about a front drum brake, but sounds nearly as bad! 

my brake worked much better before I "fixed" it... i.e. cleaned all the grease off the pads and rust out of the drum.

best of luck tho, sorry I have no actual help.

[dpaddock]

I suspect oil or grease on the drum surface/shoe linings.
       David

[MikeN]

Thanks for all the replies,
   To A10 Boy,yes I am in the UK and I have had several brakes relined by Supreme over the years with what they call there "high friction" material with very good results.I will talk to them If I dont get anywhere in the next few days. Last night I put in some thinner shims under the pivots as suggested by BSA-54A10 .I will try it tonight after Ive made a new mudguard stay at work today.Its the short vertical one that attatches to the torque stay mounting lug that keeps fracturing.
  I definately have no grease contamination. I always use sealed bearings on my wheels.I have wiped the drum with cellulose thinners to degrease.All the nuts and bolts are tight.
  Strangely,I was talking to my neigbour who also has an A10 and we built ours at the same time.He has the more common Triumph/BSA type 8" TLS brake and he says he also has a similar brake locking trouble with his bike.but he never bothered to mention it to me until last night.Although I never told him about my problem either till then!
 Next instalment tomorrow.

[MikeN]

I think I have now cured my brake problem. After trying everything that was suggested to me and evrything I could think of I decided I would try getting the shoes relined with a different material.However i thought I would try one more thing before doing so.
  Looking at a valve seat cutter and observing how it had asymetrical cutting edges to stop chatter I decided to apply this principle to my shoes as a last resort.
  I have relieved about 50mm of material back from the leading edge of one of the shoes .So they now have different areas of material in contact with the drum.
  I can visualise why this should help ,but not what caused the problem in the first place.
  The shoe that I removed material from was what i call the "slave" shoe.The "master " being the one actuated  by the cam attatched to the operating cable.I dont know what the correct terminology is on a 2LS brake.
   I have ridden the m/c to work the last 2 days with no sign of brake locking or diving so hopefully it will be alright now.
  Braking retardation does not seem to be unduly affected if at all.
Mike

[RichardL]

Seems like a tip to give to Pearson.