Fox 38’s losing pressure

[N9VNS]

My bike is only 3 months old and my lbs who I bought it from has said drop it over and they’ll send the forks off but it’ll be a few weeks turn around so don’t really want to be without the bike for a few weeks.
I went for a ride a few weeks ago after not being out for 2 weeks and I noticed the front suspension didn’t feel right, and when pulling the front wheel up the suspension sounded horrible. So checked the pressure when I got home and it was at 20psi. Topped it back up to what I usually run it at, went out for a ride and all was well. Few days later and exactly the same thing happened and again on a night ride it done the same thing. Its losing pressure when sat in the garage and I’m assuming when riding too.

Anyone have any ideas what to check? Rather try and sort it myself rather than having to wait a few weeks and be without the bike.

 

[steve_sordy]

This happened to me after I had changed the number of tokens on the air side. I didn't fancy tightening the hex aluminium alloy top cap to the required torque, so I didn't. I just tightened it until it felt right. Unfortunately it wasn't tight enough to be airtight and the pressure slowly reduced. I removed the cap, greased the threads and replaced. I still didn't take it up to full torque because the tiny flats on that hex nut really concerned me. But it held and pressure was maintained.

I hope that your problem is as easy to solve. It is certainly worth a try as it will be quick to do and cost free unless you have to buy a socket to fit the hex. You can grind down a standard hex to remove the internal chamfer. This will increase the amount of nut-to-socket contact. Many newer forks now have dispensed with the hex drive and require the same tool used to remove your cassette.

 

[Superkoochy]

Do you keep it in a cold place?

 

[Mteam]

I guess if its not what steve mentions and the schraeder valve is not leaking, then It looks easy enough to rebuild the air spring side of the fork, but I couldnt find any seal kits when I quickly googled - maybe they're the same as used in the 36? - dunno

2021-2025 38mm FLOAT NA2 Air Spring Rebuild | Bike Tech Help Center | FOX

www.ridefox.com

 

[steve_sordy]

Top cap tightness and leaking valve. That is two simple and cheap things to take a look at before parting with your bike.
All hail the Forum!

 

[N9VNS]

This happened to me after I had changed the number of tokens on the air side. I didn't fancy tightening the hex aluminium alloy top cap to the required torque, so I didn't. I just tightened it until it felt right. Unfortunately it wasn't tight enough to be airtight and the pressure slowly reduced. I removed the cap, greased the threads and replaced. I still didn't take it up to full torque because the tiny flats on that hex nut really concerned me. But it held and pressure was maintained.

I hope that your problem is as easy to solve. It is certainly worth a try as it will be quick to do and cost free unless you have to buy a socket to fit the hex. You can grind down a standard hex to remove the internal chamfer. This will increase the amount of nut-to-socket contact. Many newer forks now have dispensed with the hex drive and require the same tool used to remove your cassette.

Thank you for the reply. I’ll check this today and report back, if I’ve got a socket to fit that is.

Do you keep it in a cold place?

Yeah I do, but my brother has kept his mtb’s in the same place for years without an issue.

 

[N9VNS]

Bit of an update on this. Forks were sent back under warranty and the paper work that came back with them just said that they’d had a full rebuild. Forks were great for about 5 rides. Last 2 rides though they’ve started doing the same thing again. They’re losing pressure just sat not being used and also when I’m riding. Getting really pissed off with it now as I’m having to check the pressure before, during and after every ride and having to take a shock pump wherever I go.

 

[steve_sordy]

That doesn't sound acceptable. It sounds like a fundamental problem somewhere. A full rebuild of a fork that was sent in for pressure loss would have had full attention paid to that aspect and so it should have been cured. Because it hasn't, then something else must be wrong with it that a full rebuild will never fix.

This may sound odd, but have you tried removing the fork and immersing in water? Probably best to pump up the fork first. You know it has a leak, you just don't know where from. It won't be a big leak, so don't expect to see a constant stream of bubbles rising to the top of the water. While the fork is under water, wipe over it with your hands to ensure any bubbles formed during immersion are removed. Leave it a while and bubbles should slowly form from the leak. Leave it overnight if you have to, then observe carefully. I'd use the bath and leave it in there. If your bathroom is anything like mine, there will be plenty of light to see small bubbles clinging to the source of the leak.

 

[Mikerb]

A couple of thoughts. First, a "full rebuild" by SRAM likely only involved a lower leg service in which case they probably did not touch the hex nut/shraeder valve at the top of the air spring stancion. They probably did check or change the seal at the bottom of the leg which seems to me to be the most likely leak area.
So I am wondering now whether your original leak is fixed but what you are experiencing now is the air spring not equalised. Try completely deflating the fork and then re inflating to your required pressure whilst cycling the fork a few times every 10 psi.

 

[Mikerb]

.........and do that with rebound/lsc/hsc all full open/fast. Then check your sag.............then set rebound...then lsc...then HSC if required.

 

[N9VNS]

That doesn't sound acceptable. It sounds like a fundamental problem somewhere. A full rebuild of a fork that was sent in for pressure loss would have had full attention paid to that aspect and so it should have been cured. Because it hasn't, then something else must be wrong with it that a full rebuild will never fix.

This may sound odd, but have you tried removing the fork and immersing in water? Probably best to pump up the fork first. You know it has a leak, you just don't know where from. It won't be a big leak, so don't expect to see a constant stream of bubbles rising to the top of the water. While the fork is under water, wipe over it with your hands to ensure any bubbles formed during immersion are removed. Leave it a while and bubbles should slowly form from the leak. Leave it overnight if you have to, then observe carefully. I'd use the bath and leave it in there. If your bathroom is anything like mine, there will be plenty of light to see small bubbles clinging to the source of the leak.

Exactly, its highly frustrating. I’ve checked the basics and all seem ok. I want to strip them down myself but I’m afraid to at the moment because it’ll void warranty. It’s just annoying that everytime the forks have to go back its a 2 week wait for them to return.
I haven’t tried placing them in a bath of water yet, I was a bit sceptical to do so but I think that shall be my next step. My bathroom is very well lit so it should be easy enough to spot any bubbles.

 

[N9VNS]

A couple of thoughts. First, a "full rebuild" by SRAM likely only involved a lower leg service in which case they probably did not touch the hex nut/shraeder valve at the top of the air spring stancion. They probably did check or change the seal at the bottom of the leg which seems to me to be the most likely leak area.
So I am wondering now whether your original leak is fixed but what you are experiencing now is the air spring not equalised. Try completely deflating the fork and then re inflating to your required pressure whilst cycling the fork a few times every 10 psi.

It was sent back to fox not sram, I’m pretty sure it went to silverfish in risca as they’re local to me and a big fox service centre.
You may be right there though thats a good call. I’ll try that tomorrow and report back. Thank you for the advice.

 

[Mikerb]

yep Fox not SRAM!!
I would also suggest riding the bike after you have done the re inflate.....just out on the road or close by and thoroughly compress the suspension by bouncing on the bike. Then return and re check your pressure. Maybe do this a couple of times. It makes sure the suspension is thoroughly equalised and it avoids having that process happen progressively on your first couple of proper rides.

 

[cozzy]

I was equally unimpressed with silverfish for warranty work. Maybe they are better if you are a paying customer. Won't be using them again that's for sure.

 

[N9VNS]

Still unable to find any leaks on the forks, tried all the advice above to no avail.
Went out for a ride yesterday and set the forks at 70psi which is what I usually run them at for my correct sag. Half way through the ride they seemed to have gained pressure, 10 minutes later I could barely compress them down. Put my shock pump on them and they’d dropped to 50psi but were rock solid to compress. Released all the pressure, cycled them a bit and set back to 70psi which sorted them for about 20 minutes and the same thing happened again.
Phoned silverfish today and spoke to a helpful guy and explained the issues I’ve been having. He’s told me to drop them down tomorrow and he’ll replace the air cartridge and seals. Should get them back in 2 days. Hopefully they’ll be sorted once and for all this time.
I’ll update once I’ve had them back and tried them. This thread may help someone else in future who has the same issue.

 

[N9VNS]

Took the forks to silverfish yesterday for them to have another look at them. They found the air cartridge was faulty so they have replaced that and all the seals again. Dropped them off yesterday at 9:30 and they were ringing me at 14:00 to say they were all complete so cannt fault their service. I asked them to remove a volume spacer for me while they were apart.
Been out today to try them and wow, what a difference. Forks held pressure the whole ride and felt so much better with a volume spacer removed.