Hydraulic Brake lines THREAD SIZE

[Arthur Farrow]

I'm having made up new brake lines (2) from my Silk using Spondon callipers and a new AP Racing CP 3125 master cylinder

Can anybody say what the thread on the callipers is 3/8 UNF maybe ?? There is a fair chance that what was fitted was crammed in the hole and is not right

Any help greatly appreciated

[hendred]

My Silk has  Lockheed calipers.  The thread is 3/8 UNF, 24 tpi.  This was a common size on British bike calipers of the era.  3/8 UNF is approx 9.5mm.  From another forum, a 10mm x1.0 thread banjo bolt  (which is close to 24 tpi) can be forced into the 3/8 UNF threaded hole but will wreck the thread.  Not a direct answer but may help you determine what has happened to your calipers.

[Arthur Farrow]

I confirm the SPONDON calliper (bulky one with the fins) seems to be 3/8 UNF and I bought some new Stainless bleed valves that seem to fit perfectly especially after gently running a tap down as the callipers seemed to have "grown" with corrosion.

I ordered some new HEL lines direct from them over the internet 86cm and 92am long (I have twin front discs on spoked original Spondon wheels) which is a relatively easy process with good options. I am using a double banjo at the top master cylinder end.

[hendred]

Be interesting to hear how you get on with the master cylinder with variable ratio.  The twin disc Lockheed set up used a CP2410 master cylinder with a 0.7" (17.7mm) bore and is very "wooden".  The single disk versions used a CP2215 master cylinder with 0.625" (15.9mm) bore.  I suspect the twin disc Lockheed set up would have better feel with the single disc master cylinder.

[Arthur Farrow]

My master Cylinder (a CP3179 marked underneath as .7 so presumably that the bore size HOWEVER Lockheed have it down as 5/8 bore) seems in good order (although as my bike has not run for probably 25 years I decided on the new unit) but my experience with a Norton commando Mk 3 made me go for the adjustable one  

On the Norton the piston diameter is reduced giving lots more feel, but increased travel , RGM do a sleeve for the standard M Cylinder , but Andover Norton do a complete new cylinder with reduced bore and I went for that so some experience.

The CP3125 adjustable cylinder achieves the adjustment by mechanical means---a screw pushes against an angled plate adjusting the effective throw up or down so should give the same effect. Clever....I got mine from Dennis Trollope racing in Bristol.

It will be some while before I can ride the bike , but restoration is going ahead strongly. Wiring and detail to finish. Its frame 3 engine 4 but has been a bit updated cosmetically.  I think.

I might try posting a picture.