Front brake grabbing

Front brake grabbing

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keithlawes
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Front brake grabbing

#1

Post by keithlawes » Mon Jun 04, 2018 8:57 pm

Hi Guys,

Have recently relined the front brake of my 43 WLA and re-assembled.
Brake much improved but problem is it suddenly grabs if you put too much pressure on, in particular at lower speeds. Very violent, locks the wheel.

Seems to be linked to the suspension movement somehow.

Anyone any experience of this? Is there an adjustment you can make to the suspension arm that holds the brake plate or somesuch?

Linings are OK and still fastened to the shoes but there are several very worn parts: brake cam profile in particular, and the cam shaft v loose in its bush. Guess I just need to go through it. But if anyone has any direct experience of fixing a similar prob would be grateful for a point in the right direction



Andygears
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Re: Front brake grabbing

#2

Post by Andygears » Mon Jun 04, 2018 10:02 pm

Not sure about your springer brake, but it sounds like an alignment/concentricity issue. Maybe the order in which the bolts to the hub or to the stay arm are tightened,.... With the brake held on? Someone here has the correct answer.

Andygears

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Re: Front brake grabbing

#3

Post by PanPal » Mon Jun 04, 2018 10:30 pm

When I open this thread to read it there is a thread below in the similar topics section "WLA front brakes. It also mentions advice about the stabilizer allowing the brake to rotate as the springer rockers move. worth a look!

RUBONE
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Re: Front brake grabbing

#4

Post by RUBONE » Mon Jun 04, 2018 11:55 pm

You may have an issue with too much clearance between the brake cam and the pads on the shoes. If the cam rotates too much it tries to go over center and will lock the brake, or even break the cam. If it occurs too violently it can even bend the fork. The easiest fix is to build up the pads on the shoes by either welding a piece on or building them up and grinding to proper clearance. The bushing in the backing plate needs to be good as well. Also check the backing plate for flatness as it can bend under too much braking force.
Robbie

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Re: Front brake grabbing

#5

Post by Panacea » Tue Jun 05, 2018 12:58 pm

That happened to me on my 49 pan, rear brake jackhammered itself and busted the camshaft off flush with the plate as well as tearing the loop off of the plate where it locks into the frame. I think the cam went over center. That was the only brake on that bike so it made for a spooky ride home, luckily it was very late so no other cars were on the road...

keithlawes
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Re: Front brake grabbing

#6

Post by keithlawes » Tue Jun 05, 2018 1:56 pm

Thanks for the input guys. Pretty sure the cam going too far over is central to it, it is very worn. Will try to source a new one or build the current one up and reshape it.

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Re: Front brake grabbing

#7

Post by kitabel » Tue Jun 05, 2018 2:07 pm

"Shop Dope" contains advice on beveling the edge of the leading shoe closest to the cam.
If the brake shoes do not touch the cam at rest something is wrong - the return springs should place them in contact every time the lever is relaxed.

keithlawes
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Re: Front brake grabbing

#8

Post by keithlawes » Fri Jun 15, 2018 2:11 pm

Hi guys,
After a short test ride appear to have sorted it (so far). Basically have as far as possible made everything tight and true. So far it has not tried to break the forks once.
Fair bit of fuffing about on the Myford lathe to replace the entire cam pivot bush assembly (the bit in the brake plate), which was very worn and also appear to have been bent over by the jack-hammering i.e. no longer perpendicular to the back plate. Also turned down the brake cam bearing surface (which was oval) and bushed to suit.
Also re-bushed the centre bearing of the brake plate which was incredibly loose. Think that's probably the root cause of the problem.
Also built up the edges of the cap with weld then turned and filed to get a reasonable profile. Not being aware of the jack hammering problem I had turned it down slightly (idiot!) to try to get more leverage, again could be a lot to do with it.
As for stopping performance it's not too bad. No stoppies possible but pretty much on par with any Brit bike of that age.

Incidentally think its the same brake as the big twin, with larger diameter cam bearing and the cable coming in from the top. In fact looking as if the bike rather than being based on a WLA is more likely a WLC. (see separate post).

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