G valve

[majcd213]

Hi all. Does anyone know whether its ppssible to test the G valve? Ive now rebuilt or replaced all of my brakes and the only thing not touched is this valce. I dont think its user srviceable... or if it is Ive never found a rebuild kit. Does anyone know where I could get a replacement? Also does anyone know how it works? Ive taken an old one apart but Im none the wiser!

Currently I do have brakes but a very spongy pedal. I know trapped air can be a problem after rebuilding the MC so Ill try that first but I still wonder about tje g valve. Maybe I can make a bypass hose and see if that firms it up?
Cheers
Mike

[AndyC]

Strange but I've never been tempted to take one apart, not until now. You've now cause my interest to spike but also concern that I would cause a problem by doing so.

Given it's height, I'd suggest bleeding it (G valve) by slackening off the output nut a fraction, while the pedal is depressed, check for air and if you get some then consider it success. It's easy to get air in the vertical pipes, and it can take ages to bled it out towards the calipers, so sometimes time is the best solution, just let the air back-track up to the MC over a day or two then re-bleed. Given the route of the brake pipes, it's sometimes best to use a bleeding system that can flush a large volume at speed so dislodge bubbles and air-locks. The Girling Ezi-bleed system with a tyre as air supply is OK, or just a one-way valve in a pipe on the caliper and pump the brake pedal like a nutter.

[v8 fou]

2 things. Clamp off all the flexis. Pedal should be rock hard. If not, then it's the m/cyl etc. If it is hard, undo the clamps one at a time and test the pedal each time. That should isolate any problems.
Get yourself a proper bleeder that sucks the fluid out via the bleed nipple. Do NOT bleed by pumping the pedal as you will be forcing the seals over an unused, possibly rusty area of the bore.

How do I know? Only 42 years in business this year.......

[majcd213]

Thanks for the tips. I have got both a vac bleeder and an ezibleed. The vac bleeder seems to suck in air around the bleed nipple threads so its always bubbly. The ezibleed showed it was bubble free though. I did loosen the g valve union to bleed any air there. Didnt see any, but rebled and got a firm pedal. My mc bore has just been honed so hopefully no rusty bits.
Cheers
Mike