Rail (750Wh) Faulty shock?

[ragnor]

Trek Rail 9.8. Shock is: RockShox Super Deluxe Select+ RT, 230 mm x 57.5 mm

When I attach the shock pump it reads zero. Start to pump and it shows pressure. If I pump up the pressure say to 100 it doesn't stay there but reduces. It doesn't reduce to NIL but below the pressure for a proper sag measurement. N.B. This is NOT the normal loss of a few lbs when you remove the pump.

The shock pump works normally on any other bike that I've tried so the pump is not the problem.

The shock still works & I haven't bottomed it out yet. Seems to have a fair amount of travel but I'd really like to properly set the sag.

 

[Stihldog]

I wonder if the air valve is faulty? Might be worth a try …those are cheap and having a few extras laying around might be a good idea.(I need to listen to my own advice )

 

[slomtbr]

If you don't have a Schrader valve core handy, at least remove, clean, and refit.

 

[arTNC]

Good points on questioning the schrader valve in the shock. It's such an easy and cheap deal to replace it and either find it as the problem or eliminate it as a cause. Since your shock does not appear to be losing pressure after you install air pressure, it doesn't really sound like the shock.

That interface between the schrader valve and the shock pump head is pretty critical. It sounds more like they are not playing well with each other, and since the pump works fine on other bikes, try a new schrader valve. Also your mention of a shock pump losing a few pounds of air in the shock on detachment isn't the way a quality shock pump is supposed to work. Surely there is some miniscule amount of air that escapes the shock, but not up into the "pounds" level. Shock pump heads have gotten really good at design to minimize this.

 

[ragnor]

Thanks. Not having delved into the mechanics of any shock on any bike that I've had I'd just like to pick your brains on how to go about replacing the valve. I assume firstly that I have to remove ALL the air from the shock before doing anything. Is that correct? Sorry if that's a simple stupid question. (I am aware that removing the valve will, of course, remove all air but I just like to get the steps correct.)

Second question. Is it the valve core that I'm replacing? Must get some as everything I've got is Schrader.

 

[ragnor]

Reading that again the brain clearly wasn’t connected to the fingers! What worries me always is what if I cock it up by doing something that screws up the situation!!
SO
Are there any specific steps or actions that I have to take BEFORE letting all the air out of the shock. If so what actions are required?
AND
Is it merely a case of removing the Schrader valve core by unknown means; sticking in a new one and pumping up the pressure.

There I think that’s what I really meant to say.

 

[Weeksy]

essentially yes. You can let the air out slowly with a few up/down squishing to equalise the pressure.

You'll need a valve core removal tool to remove/install.

 

[arTNC]

essentially yes. You can let the air out slowly with a few up/down squishing to equalise the pressure.

You'll need a valve core removal tool to remove/install.

Agree. Let the air out slowly first before unscrewing the valve core. I've never tried it, but I don't want to see what a 200-300 psi valve core might do if you just start unscrewing before depressurizing.

 

[irie]

Is it merely a case of removing the Schrader valve core by unknown means; sticking in a new one and pumping up the pressure.

Yes, but let the air out first. Schrader valve core removers are cheap as chips.

 

[steve_sordy]

I've had two shocks with a faulty Schrader valve, one Fox, one Rockshox. Simple fix to replace.

 

[John Beedham]

like others check/change the valve

 

[Stihldog]

There’s a few levels of bike repair we can delve into and with that involves some tools. Others in here may have certain ideas for the basic bike maintenance for a reasonable price or level of ability.

Most of us started off with nothing, or practically nothing, for bike maintenance. But there’s a few essential tools you’ll need to keep you rolling.
-full set of metric Allen wrenches (2mm-10mm) for bikes.
-Value Core removal tool.
-Small psi gauge.
…and the list can just get bigger .


…some spare parts.
-value core’s
-brake pads
-tires (maybe?)
…and the list gets even bigger .

I think I started off with a rock ,
…about the size of a potato

 

[RustyIron]

I tried the potato trick, but it didn't work. No one told me it goes in the front.

My advice regarding tools is to buy the set, not just the specific tool you need. Buy the set of allen wrenches. Buy the set of screwdrivers. Buy the set of combo wrenches (spanners). Buy the set of sockets.

Sure, you can save money by buying only the individual tools you need. Do that if you want to be the bike mechanic that can work on his 2023 Cube with Shimano drive train and Rockshox suspension, but can't work on anything else. Buy complete sets, and you'll be able to work on anything, whether it's your bike, your next bike, your vacuum cleaner, or your Ferrari Dino. Don't be the One Trick Pony.

 

[ragnor]

I wonder if the air valve is faulty? Might be worth a try …those are cheap and having a few extras laying around might be a good idea.(I need to listen to my own advice )

Spot on. After eventually getting a supply of Schrader valves & getting my sh1t together that's sorted. PHEW!

As an aside I've probably got all the tools that I need or can use. I did have a lot of tools from my long ago rallying days but what's left isn't an awful lot of use for bikes.

 

[steve_sordy]

I tried the potato trick, but it didn't work. No one told me it goes in the front.

I got the refence, but did anyone else?

 

[ragnor]

The potato sits on the saddle. Obvs!

 

[2WheelsNot4]

Cup of water, bit of fairy liquid in it, and a paintbrush.

Brush the soapy water around the shock after pumping it up. Bubbles indicate a leak

This is actually the standard way they find holes in things like high pressure air lines, and it will save you taking it off(at least initially)