I took my ‘72 Roadster out yesterday for the first time this year. After 5 miles I noticed that the front brake was binding and I had zero play on the brake lever (it had gradually been reducing). By the time I had found a safe (ish) place to pull over the front wheel was practically locked solid. With a piece of rag and a spanner I released the fluid pressure in the caliper which freed up the wheel and I was able to ride the short distance home.
This morning I was able to replicate the problem with the bike stationary at home by heating the brake caliper with a hot air gun. Removing the reservoir cap I can see the master cylinder piston moving back and forth through one of the ports in the base of the reservoir. I replaced the seals and brake pipe with new AN items last summer.
Any suggestions or ideas as to what the problem is would be gratefully received…
Regards to all
The m/cylinder piston seal…
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Master Cylinder Ports
As Peter says, this has to be the case. It only takes a tiny flake of rubber etc.
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brakes
I had the same symptoms, on a different bike, which turned out to be crystallized brake fluid blocking small passage(s) in the master cylinder. This was mainly because the bike had been unused for a couple of years, standing outside. This was only discovered by taking cylinder apart , and after careful cleaning, it worked to get me home from the TT.
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I’m must be going mad…
…I could swear I rebuilt the master cylinder on this particular bike last summer but obviously not! I dismantled the unit this morning to discover the innards are completely non standard. The PO seems to have fitted a brake upgrade which consists of a 1/2” sleeve for the cylinder bore, non standard piston assembly etc. The master cylinder boot was in tatters and almost non existent. I plan to order a complete set of 13mm parts from AN tomorrow and see if that cures matters.
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Photos of the M/C bits…
Photos of the M/C bits please, it will help identify who's sleeve kit it is. 13mm is bigger than 1/2"
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I found the original fitting instructions..
…for the sleeve kit in the bike’s history file. It was supplied by Don Plender (Triton Motorcycle Parts). I’ve attached photos of the innards and the sleeve in situ. According to the instructions it was locktited in place. It does feel securely fixed so I’m minded to ream it out to 13mm and then fit RGM internals.
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The m/cylinder piston seal is not uncovering the fluid release port (to allow the fluid to return to the reservoir) so when the system heats up in use the brakes get slowly applied. Looks like your seal replacement missed something or you got them installed wrong. What kind of M/C is fitted (std 5/8" bore) or smaller? Is the pipe from the M/C clear through to the caliper? Has your seal replacement somehow blocked the system? perished seal getting jammed in the pipe etc