Rear brake bleeding - a solution - AJS 125

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Greybeard
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Posts: 456
Joined: Mon Jun 29, 2015 8:49 pm
Location: East Yorkshire

Rear brake bleeding - a solution - AJS 125

Post by Greybeard »

Or should that be bleeding rear brake?
Despite my vow never to work on a chinese 'AJS', this morning I answered a call for help from a clubmate who was finding it impossible to 'get a pedal'. I know theres a recall in the pipeline so to speak, but when he rang AJS they wouldn't tell him what the fault was or how to fix it..
Having stripped and measured the master cylinder it was apparent that the problem lay in poor manufacturing accuracy and quality control. It was apparent that the seal on the end of the piston was not uncovering the fluid inlet port (the tiny hole nearest to the output end) and needed the piston to move further back by about 1mm.
To get this extra travel I took 0.5mm off the back side of the domed end of the pushrod in the lathe as step one. That improved matters in that with a small amount of fluid in the inlet port it was actually making an effort to draw fluid in. I then took 0.25mm off the inside face of the washer that the rod bears against giving a total of 0.75mm extra space for the piston and it then sucked in fluid like a good un.
This has, he tells me, transformed the feel of the pedal and the system can be bled easily. He reckons the rear brake has never felt so good, with much reduced pedal travel.

It could be that the recall will involve replacing the shoddy original fitment - which should never have left the factory in the first place :roll:
In the spirit of 'Clubliness' I offer this as a potential solution for the widely reported issue of brake bleeding on these bikes, though I still hope not to work on another one ;)

Steve
39speedtwin
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Joined: Thu Jan 01, 1998 12:00 am
Location: ESSEX UK

Re: Rear brake bleeding - a solution - AJS 125

Post by 39speedtwin »

I had the same problem with my Tempest Scrambler at 200 km, phoned AJS, they said take it to a local dealer, who could not look at it for 3 days and then wanted to keep the motorcycle for a couple of days. When the pedal was operated there was pressure then none.
AJS then sent me a replacement master cylinder, which I replaced and bled both the rear and the single pot on the front calliper (operated by the rear) with a vacuum bleeding kit. It took all of half an hour.
Possibly the problem was that the front calliper was not bled properly at the factory.
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