1954 G80 Rear Brake Problem

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
alanengineer
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Re: 1954 G80 Rear Brake Problem

Post by alanengineer »

Another thought.
Have you tampered with the brake pivot pin and pulled it up too tight/missed a spacing washer(if their is one) so the shoes are being misaligned from that side. I had a quick look in the parts list,Very quick, didnt find anything obvious.

The shoes i replaced recently were very tight on the pivot area counterbore.
mrpjhancock_LAPSED
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Re: 1954 G80 Rear Brake Problem

Post by mrpjhancock_LAPSED »

I assume you mean the pin on the opposite end to the cam . . . . Its a solid piece . . . . no adjustment there ...
I'll have a look at the parts list too ...... maybe Iv got the wrong back plate?
alanengineer
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Re: 1954 G80 Rear Brake Problem

Post by alanengineer »

No
The pin can be taken out and replaced with/without washer altering how much it pinches the brake shoe counterbore. Its probably not designed to do that, but i think it is distorting the way the shoes sit
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ajscomboman
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Re: 1954 G80 Rear Brake Problem

Post by ajscomboman »

alanengineer wrote:No
The pin can be taken out and replaced with/without washer altering how much it pinches the brake shoe counterbore. Its probably not designed to do that, but i think it is distorting the way the shoes sit
I think he's referring to the solid pivot pin on the back plate. Personally I think the simplest fix would be to pack out the brake plate with a thin washer on the wheel spacer. Changing the brake plate will not solve the problem.
alanengineer
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Re: 1954 G80 Rear Brake Problem

Post by alanengineer »

I think im thinking of the ali backplate with removable pin. The backplate in the photo looks black and probably painted steel and the pin is probably welded into place.
Measure the thickness's around the counterbored areas and the depth of the pin, i recon the pin is holding the shoes out of square
Andy51
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Re: 1954 G80 Rear Brake Problem

Post by Andy51 »

The brake plate is positioned by the distance piece in your photo. Is this the correct length? I will be in the garage later today, will see if I have a spare to measure. Andy
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Re: 1954 G80 Rear Brake Problem

Post by Andy51 »

Hi, the spacer/distance piece on my '54 18S is 1.056 ins long. Andy
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ajscomboman
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Re: 1954 G80 Rear Brake Problem

Post by ajscomboman »

I'm still going for the shim out the brake plate option to allow a little more clearance as the easiest solution to the issue.
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clanger9
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Re: 1954 G80 Rear Brake Problem

Post by clanger9 »

I think your problem is at 'tother end i.e. the fixed pin. It's possibly leaning slightly outwards relative to the backplate, which causes the cam end of the shoes to lift up when you apply pressure to the brake.

If I was stuck, I'd clamp the pin in a vice and whack the backplate with a hide hammer just inside the pin to straighten it up...
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mrpjhancock_LAPSED
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Re: 1954 G80 Rear Brake Problem

Post by mrpjhancock_LAPSED »

Hi I have measured the spacer that you mentioned .. . . . I'm measuring at 1.575" . . . . I have attached pic of it . . . . Its certainly a different length/design to yours. Am i measuring the same thing?
I think Clanger9 may be correct with the idea about the fixed pin being out of square to the back plate. Although I'm loathed to bash anything! I'll take it to work and check the squareness
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