The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: bsaalf on 18.05. 2009 23:45

Title: a10 brake judder
Post by: bsaalf on 18.05. 2009 23:45
hi all, everytime i apply the front brake on my a10 i get a judder through the handlebars its difficult to explain it properly a bit like when the abs on a modern car taps your foot in slippery conditions,i think it might be the fork bushes but aren't 100% sure and would appreciate any advise regards alf.
Title: Re: a10 brake judder
Post by: Brian on 19.05. 2009 01:11
This is one of those things that can be caused by lots of different things. I would start by checking the headstem bearings, if they have any play in them you will get shudder just as you have described. From there you could clean out the brake drum and shoes and check the forks for play while you have the wheel out. Its a process of elimination.
Title: Re: a10 brake judder
Post by: BSA_54A10 on 19.05. 2009 02:00
Start from the top, the steering bearings.
Next is the fork bushes
Next is the wheel bearings
then there a loose or worn backing plate
next worn brake cam ( check the hole in the backing plate )
End up with the drum , they can and do go oval
Title: Re: a10 brake judder
Post by: bsaalf on 19.05. 2009 07:52
ok thats very helpfull guys thanks for the advice much appreciated..
Title: Re: a10 brake judder
Post by: beezalex on 19.05. 2009 16:23
Don't forget: Wheel balance and runout.  I had imbalance cause this on one of my my race bikes.  You could feel a somewhat gentle once-per rev shudder that increased with speed, but once you put the brake on it got really bad.

Check for drum distortion.  Get the front wheel off the ground.  Gradually tighten the brake adjuster as you rotate the wheel.  They generally will have a gentle tight spot, but if can rotate it a ways and then can't rotate anymore, your drum is warped bad.  Get another one or get this one turned.

Cheers.
Title: Re: a10 brake judder
Post by: bsaalf on 20.05. 2009 00:34
thanks beezalex i will try that
cheers..
Title: Re: a10 brake judder
Post by: A10Boy on 20.05. 2009 18:14
Thats what I had, and worn fork bushes makes it worse.

The drum will need skimming as Alex said, and if its warped badly, you will need thicker linings machined to the same radius as the drum.

If you are in the Uk Supreme in Leicester do a good job
Title: Re: a10 brake judder
Post by: bsaalf on 20.05. 2009 21:25
thanks for the advice andy, tell me do i need to send them just the drum or the whole wheel as i don't fancy getting it stripped and then having to get it respoked again as i believe its a very specialist job to get it straight .
Title: Re: a10 brake judder
Post by: LJ. on 20.05. 2009 21:31
I believe that they would want to skim the drum as a whole wheel and not just the hub. If it was just the hub and then respoked there would be a further risk of distortion. And yes... I have also heard a few times that Supreme Motorcycles at Earl Shilton just outside of Leicester on the A47, they do a good job.
Title: Re: a10 brake judder
Post by: bsaalf on 20.05. 2009 21:35
thanks lj much appreciated great advice cheer's.
Title: Re: a10 brake judder
Post by: bsaalf on 20.05. 2009 21:49
one more thing just wondering would you also check anything else for possible cause first or just get the drum skimmed first and where is the best place to get new shoe's they are 8" twin leading type!
Title: Re: a10 brake judder
Post by: beezalex on 20.05. 2009 22:02
FIRST, check your wheel balance.  This is by far the easiest thing to correct.
Title: Re: a10 brake judder
Post by: bsaalf on 20.05. 2009 22:35
surely i could discount the wheel balance as a possible course as it only judder when the brake is applied not at any other time?
Title: Re: a10 brake judder
Post by: MikeN on 20.05. 2009 22:45
If you block up the front end of your bike so you can spin the front wheel.If you gently apply the f /brake you will start to hear the b/shoes start to rub .if they rub intermitently it is an indication that you may have a distorted drum .If you have had a MOT recently and stayed around to watch them put it on the brake testing rig you can observe the needle fluctuating on the dial which will also tell you if you have distortion (at least you can where i take my bike). Another indication is to ride along slowly and gently apply the brake lever.Distortion will  show up as the lever moves in and out and you will feel it in your right hand.
  When I have bored hubs for my bikes I set them up so that the hub revolves on the lathe on its own bearings, so ensuring concentricity (you need a big lathe if you have a complete wheel with tyre).So stress this if giving the job to someone not familiar with bikes.
  You shouldnt need new shoes.Supreme will re-line them with either standard or 0/size material.they use what they call their "high friction material".They will also machine the brake shoes  to match your drum .whatever diameter it may end up .
 Having said all that. Have you checked the adjustment of your steering head races yet?
  I bet thats your problem.
Mike
 
Title: Re: a10 brake judder
Post by: bsaalf on 21.05. 2009 00:46
thanks mike i will check that first cheer's.
Title: Re: a10 brake judder
Post by: beezalex on 21.05. 2009 19:55
surely i could discount the wheel balance as a possible course as it only judder when the brake is applied not at any other time?

Surprisingly enough, no.  See my above statement about my experience.  Some shudder was felt without the brake applied, but when I applied the brake, it was almost disastrously bad.  This ended up being cured by balancing the wheel.  It's about the easiest thing to check...so why not?
Title: Re: a10 brake judder
Post by: MikeN on 21.05. 2009 20:01
Thats good, Saved you a lot of work.
did you have to add much weight?
Title: Re: a10 brake judder
Post by: beezalex on 21.05. 2009 20:54
Thats good, Saved you a lot of work.
did you have to add much weight?

I don't recall exactly, but I think it was pretty far out.  Mind you, this was happening at about 90+ mph.  I'm guessing the pulsing in the wheel excited some resonance in the front end, but only when a lot of load was applied.
Title: Re: a10 brake judder
Post by: rocket man on 30.05. 2009 19:15
90 mph on an old bsa show it some respect
it over 40 years old