+ chamber seems ok, but i pressurize the – take the pump off, refit pump and there is no air in the – registering. Are they ****?

how cold is it where you are?

I had similar odd negative pressure behaviour on my pikes the other week during a very cold night ride (sub zero). When I checked them again in milder weather they seem to be normal again – I was all ready to send them to TFT but I am going to just keep an eye on them for a bit

Tim

The -ve chamber is very small. It could be that the air is just filling your pump….

Set the pressures, and have a quick ride. Do they feel OK? If so they probably are
🙂

But even if they are leaking it’s nothing a service and new seals won’t fix.

Have you checked the -ve valve for air leaks?

The -ve chamber is very small, so when you connect the pump, the amount of air moving into the pump hose is large in relation to the chamber – will drop about 30psi when you connect.

If you check your pressures (+ve and -ve)in the house at +25c then go and ride in -2 or -3c the air volume will be greatly reduced – P=VT if memory serves.

Set your pressures correctly, re-attach the pump immediately and note what the pressure drops to. Pump back to correct pressure and leave for a day or two – check again. If the pressure drops back to the previous level you are OK

Any ideas as to what might cause sudden loss of positive air?

This happened the other night in blizzard conditions (however, we’ve ridden on colder nights this year, so I don’t think temp is that significant)

No idea what could cause a sudden loss of positive air, unless the fork seals got so cold they werent sealing. I’ve done plenty of rides in sub zero temperatures with no problem

The oil in there to help keep the air chamber airtight will have got thicker in the cold and may not have been sealing as well as a result.

Ahhh. That may explain it – although as I say we’ve ridden in lower temps the forks may not have been exercised enough to keep them warm.