I have a Cannondale Topstone lefty and took it to LBS last summer for the fork to get its first service, after about a year of trouble free light use. Since then it has been slowly losing air and been back in a few times. It is just back from a full rebuild with Cannondale, new seals throughout. I haven’t been able to ride it though as off bike post operation recovery for next 4 weeks, however I have just checked it and it’s dropped 4 pounds since Friday (taking into account the pressure drop by attaching and removing the pump).
I’m thinking it maybe needs ridden to bed in the seals etc before I can realistically assess whether it’s sorted or not ?
I have no issues with the shop, they are providing great service, just frustrating as I only put it in for a service for preventative maintenance and it’s been troublesome since.
How do you know how much pressure drop is due to attaching a pump? Has the temperature where you store the bike changed much?
Yeah, pump to 100 psi, when I reattach pump it’s at 86 normally. Today it was at 82. Stored in integral garage, temp probs 4 or 5 degrees down on when I pumped it up on Friday.
I don’t think riding the bike will help to seal the leak. If anything, it might make it worse. You should take the bike back to the shop and ask them to check the fork again. Maybe they missed something. It’s not your fault that the fork is faulty, so you shouldn’t have to pay for the repair.
You should take the bike back to the shop and ask them to check the fork again.
He's already taken it in a few times and it's been to Cannondale for a rebuild, if I'm reading the OP correctly?
Sounds like you're a trusted customer, might be worth asking for a replacement from Cannondale if they can't solve it?
Thanks, yes, just contacted shop to see what they suggest, I hope they may look at a replacement. It is now 2 yrs old, and first service was at 100 hours and 15 months old.
Dropping from 10 C to 5 C will lose 2 psi according to my calculator.
^^ yeah, my reckoning was about that too. Dropping it back to the shop this afternoon.
It's very rare for suspension to leak slowly in my experience. We're talking about small chambers and very high pressures. If it springs a leak, the air is gone.
Inconsistencies in shock pumps and gauges is much more common.
I have no experience of Lefty's so correct me if I'm wrong.
I've had slow leaks in suspension before.
Well it’s back at the shop now, will update once I have some answers
If I've understood correctly, then it sounds like your in the realms of error in the initial inflation & subsequent measurement.
How are you measuring the pressure? I wouldn't rely on the accuracy of the gauge on the pump.
You lose 14psi just connecting the pump? That's your 100psi down to 86psi normally mentioned above?
But it only measured 82psi, so a 4psi discrepancy? Temperature effect is potentially 2psi. So you are now down to a 2psi difference between what you expected & measured?
From your original inflation target of 100psi, that's only 2%, with lots of opportunity for slight variation to add up to at least 2psi.
I'm not saying there's no problem. But, I would be surprised if you can accurately measure a discrepancy of 2psi (once you've taken into account the temp variation).
Fair points, but it has been losing air consistently since serviced last summer. At one stage it sat unused for 3 months and had dropped 40 psi. I do know how to use a suspension pump, having being doing so for over 20 years. All valid points though.
I normally find air leaks by spraying with soapy water. I have had to fully submerge a rear shock to find a particularly small leak.
