Author Topic: Pulsating front brake A7SS?  (Read 134 times)

Offline Peter Gee

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Pulsating front brake A7SS?
« on: 01.10. 2019 19:41 »
What would cause the front brake lever to gently but noticeably  pulsate when applied, as if one shoe was egg-shaped (which it is not!)?

Offline berger

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Re: Pulsating front brake A7SS?
« Reply #1 on: 01.10. 2019 20:01 »
distorted drum mine does it when I brake really hard which is often *eek* , by the way did you sort the mag problem out?

Offline RDfella

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Re: Pulsating front brake A7SS?
« Reply #2 on: 01.10. 2019 20:04 »
As berger says, distorted drum, usually caused by spoke tension, especially with modern rims that are more pear-shaped than round. Means spoke tension is all over the place, in the attempt to produce a round wheel.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Offline Peter Gee

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Re: Pulsating front brake A7SS?
« Reply #3 on: 01.10. 2019 20:17 »
Burger and RD.thanks .how interesting because this was not the case until I had the rim re-spoked and onlydrove it home after the International show........you have really put me onto something here tomorrow I shall be ringing the spokes and listening to the notes.

No I have not yet sorted the mag prob but am sure is down to a pattern part...makes sense.

Online morris

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Re: Pulsating front brake A7SS?
« Reply #4 on: 01.10. 2019 20:56 »
Distorted drum all right. Suffered those symptoms on the SA. Was going to re-rim and re-spoke the wheel anyway so thought a careful re-spoke would cure it, but no...
Then took the complete wheel to a machine shop for a drum skim and they did a perfect job. No more juddering brakes. Well worth the € 25 I paid for it.
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Online lawnmowerman

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Re: Pulsating front brake A7SS?
« Reply #5 on: 02.10. 2019 13:54 »
Had a similar problem on my SR which turned out to be a combination of four things:

I had rebuilt the forks and had the yokes out and after a while the head bearings had settled so needed to be nipped up.

The wheel has an Akront rim fitted by the PO which I think had pulled some ovality into the drum so I had it skimmed in a gap bed lathe.

The wheel had not been balanced so I fitted some weights.

There is a slight buckle in the rim which I have not fixed and still causes a slight tremor but I will live with that.

Jim
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Online Slymo

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Re: Pulsating front brake A7SS?
« Reply #6 on: 02.10. 2019 23:25 »
I think the BSA hubs with the straight pull spokes are particularly susceptible to distortion. I looked up Youtube vids of people truing hubs and the two that I found we both BSA hubs identical to my 58 Super Rocket. I tried to fix mine by re-positioning the Akront rim but even though it was a rim that required quite a lot of tension on the welded join to run true the shift is position made no difference. I ended up repairing it by stripping the rim off and setting the hub up in the four jaw chuck of a sufficiently beefy lathe. Took about 10 thou to get it clean and then I re laced it with stainless Dunlop/Jones pattern rims that were much truer rolling to start with. It's good now all the pulsing is gone and consequently the whole riding experience is improved. Funny how a small fault that really only manifested itself at low speeds really took the pleasure out of riding what is now a truly lovely machine.
NZ