Pressurizing Aftermarket Shock

[RossKean]

How many people check the pressure of their aftermarket (Penske, Olins etc.) shock between services? If you do, what do you use to have zero pressure loss? At 150 psi, there will be a significant loss of pressure in the shock just putting a regular gauge on and off the Schrader valve (because the gas volume of the shock is quite small). If you don't check, do you just assume that there is no pressure loss/change as long as there is no oil leaking?

How critical is the pressure? Will it even be noticed if the specified 150 psi drops to 125 or even 100 psi? I don't want to start the tire nitrogen vs. air debate but is there any real difference in using air vs nitrogen in a shock? The only thing I can think of is the possibility that the oxygen might hasten the degradation of the oil but that might be a bit far-fetched. Obviously, dry gas is preferable!

My Penske is in desperate need of a refresh and I have been doing a bit of reading on the subject. You can get a device for filling/checking the pressure for ~$75 or so. It has a dial gauge and clamps on the shock's valve stem. It connects to a nitrogen cylinder and after everything is hooked up, there is a thumbscrew that depresses the pin in the Schrader valve on the shock. Crank up to the desired pressure, close the Schrader valve and you're good to go.

https://www.kaztechnologies.com/wp-content/uploads/2014/03/How-to-Gas-Charge-Your-Shock.pdf

There is a local guy that will do a basic clean plus any needed O-rings and new oil for a very reasonable cost. I think, however, he just uses a regular chuck on a nitrogen cylinder (with regulator) and uses a standard pressure gauge to check. I doubt he is very close to the right pressure.

If you do this yourself, you still need a N2 cylinder and regulator unless you are OK with compressed air (in addition to the appropriate tool for zero-loss pressurization).

 

[bluesdog]

Nitrogen is reputedly less prone to leakage, so I'd stick with that. I also have a Penske, and last year I asked Lee at Traxxion about checking the pressure. He told me it wasn't critical to get exactly 150PSI.

I haven't checked mine yet this year, but plan to do so at a local shop equipped with the appropriate tools.

I wouldn't trust a standard pressure gauge.

 

[RossKean]

There is essentially no difference in leakage rate between N2 and air but the nitrogen is dry and (relatively) chemically inert (air is 78% N2). Even if you have a regular pressure gauge capable of reading 150 psi, the act of doing the measurement bleeds off enough gas to significantly change the internal pressure because of the low volume.

I was asking about the suggested frequency for doing the checks because I don't think there is anyone in town who does this service. If the consensus is that frequent checks are needed, I may go out and buy the tool. If using nitrogen instead of air, I would have to get the regulator, tank and associated plumbing - not cheap (unless one of the tire shops will let me hook up)!

 

[HotRodZilla]

Don't know about MC shocks, but the shocks on my Jamis Mountain Bike have air valves. It takes a special high pressure, low volume pump to bring them up. My rear shock maxes at 275 and right now it is right around 260. The difference between 260 and 230 is significant. I say 'around' because they get over filled by 10 lbs as some is lost when releasing the valve. The faster I am, the less is lost. 5-10 is normal.

I would take my MC shock to the MC shock guy and let him do it. My Jamis shocks are designed for user adjustment. MC shocks don't seem to be.

 

[escapefjrtist]

@Ross, I haven't bothered checking the N2 pressure in the Penske between changes, haven't seen the need if there's no indication of leakage.

I have purchased a no-loss chuck on Ebay for $50 ish and my local welding shop can set me up with N2 tank, regulator set, hose and chuck for $200. Next step is to buy a couple specialty shock tools and then rebuild my Penske's. All in, figure $350 and I'm money ahead after two rebuilds.

If you're so inclined, there are many N2 kits listed on Ebay for filling shocks. Search Nitrogen Shock Fill and have fun!

--G

 

[RossKean]

It would appear that most folks don't check N2 pressure between shock services. I have to wonder whether significant leak-down occurs over the year or three intervals and how that might affect performance.

 

[BkerChuck]

While not MC specific, I work for a shop that repairs hydraulic cylinders, mostly for the crane industry. We repair quite a few different cylinders that utilize nitrogen charges. My understanding from our hydraulic mechanics is that once the cylinders are charged and put into service there is no expectation of the end user to check it between rebuilds. That's part of why nitrogen is the gas of choice for this.

Just my .02 YMMV

 

[FJRRYDER]

The rear air shocks on my Vulcan Nomad required a tiny little pump with a zero-loss valve to get a pressure of about 25 lbs.

 

[RossKean]

The rear air shocks on my Vulcan Nomad required a tiny little pump with a zero-loss valve to get a pressure of about 25 lbs.

That is just a bladder that firms up the ride a bit. I had a Yamaha Venture with the same system. The Penske is pressurized to 150 psi with nitrogenbut I suppose air would work as well.

 

[bluesdog]

The rear air shocks on my Vulcan Nomad required a tiny little pump with a zero-loss valve to get a pressure of about 25 lbs.

That is just a bladder that firms up the ride a bit. I had a Yamaha Venture with the same system. The Penske is pressurized to 150 psi with nitrogenbut I suppose air would work as well.

I would not feel comfortable putting plain old air in my Penske. (Why does that sound slightly smutty?)

Anyway, I'm assured by the techs at Traxxion there is little if any pressure loss unless there's a catastrophic seal failure. Many larger motorcycle shops, and performance automotive shops have the nitrogen and equipment with which to check and pressurize nitro shocks, and will do so for a reasonably small fee.