KDXRIDER.NET

I was looking in my service manual and it said after putting new oil it says to first fill to 7 psi, check for leaks then fill to 147psi. Im asking this because my dad can fill it at work. Has anyone ever done this? And if so is it right?

It's right.... because if it leaks... the thing can explode!

One thing to add. As you follow the directions in adding the oil, pump thoroughly to get all of the air bubbles out and make sure that you COMPLETELY fill the reservoir with the oil. If you do it right, it'll be a bit of a messy job because you'll want to overfill it slightly. Reason: if you leave a bubble in there and it finds its way to the surface of the bladder, you can create a hot spot - during heavy use - where the bubble is and cause the bladder to rupture. That won't hurt you but it will seriously hurt your shock's performance.

Just a tip a local suspension guy gave me when I rebuilt my shock.

Concerning the pressure. A shop is typically within maybe +/- 5 psig from what you request. Bottom line don't sweat the 147 psig figure too much. I had our local shop charge the KDX shock to ~ 160 psig.

Thanks alot guys, I figured I ought to change before getting a new shock spring. Ill follow my manual and ask if I have any problems.

Don't recall if the manual says this...but the bladder should also be filled (some) during assembly. Kind'a like putting some air in a tire tube before you stuff it in..same reasoning.

canyncarvr wrote:Don't recall if the manual says this...but the bladder should also be filled (some) during assembly. Kind'a like putting some air in a tire tube before you stuff it in..same reasoning.

Pretty sure it didn't, thanks

Re: 'If you do it right, it'll be a bit of a messy job..'

Quite a good bit of a mess. That's part of the 'partial fill' thing. You re-place the bladder with the cannister plenty full enough to ensure there will be no trapped air. So, all that 'extra' oil you put in there comes out when you gently slip the slightly inflated bladder in the cannister.

Have fun makin' the mess!!

Since my regulator only handles about 140 lbs that's what I've used in all my bikes since the late 1980's...and the shocks all worked fine. Based on that, I don't think the exact pressure amount is all that critical, but getting all the air out is.

kawagumby wrote:Since my regulator only handles about 140 lbs that's what I've used in all my bikes since the late 1980's...and the shocks all worked fine. Based on that, I don't think the exact pressure amount is all that critical, but getting all the air out is.

I believe you are correct concerning the pressure. Less pressure will make your rebound a little slower which you compensate for by lighting the rebound setting. (A higher pressure does the opposite -) Within reseaon I believe you can use the pressure and shock oil viscosity as a tuning tool in help setting up shock action. (certainly there can be an argument made about cavitation issue within the shock at high velocities but I would suspect the cavitation issues would not be pressent until the pressure was dropped into the sub 50-75 psig range but someone like Wilkey or another suspension shop with a shock -dyno should be able to verify or quantify the lowest acceptable pressure)

Like you stated getting the air out is critcal to good performance and allowing the bladder to survive. (If you have ever blown a bladder it is likely that the shock still had some air in it and the bladder was overcompensating for the void - which stretch it beyond its limits. The air will go into the oil so it really is not an air pocket but more an oil emulsion issue.

When you install a bladder you also just want to ensure the bladder has (its form) - not that it is 'expanded' when it is inserted into the oil. Suspension tuners which I respect have basically stated that this (expanding the badder at insertion) leads to bladder wear though, since the bladder is basically held too tight to the resivoir walls and when as the bladder works and the heat builds it sometimes leads to localized failure of the bladder. (Likely the "hot spot" issue brought up in the earlier in this thread)

Disclaimer - No expert here concerning shocks - just stating my own experience/opinion and my understanding of shock issues.

When you install a bladder you also just want to ensure the bladder has (its form)..

That's what I meant by 'partial fill', but your explanation is much better. It didn't occur to me that anyone would even consider expanding the bladder for installation. That would be wonky.

Still, 'more correctly' stated is much 'more better'.

I don't understand the "emulsion" part - you mean from air? I know water would create an emulsion with oil due to immiscibility, but I'm not sure about air . . . I would think that the air would tend NOT to "go into" the oil but remain as bubble(s) - at that pressure - since the oil is largely uncompressible.

Jeb wrote:I don't understand the "emulsion" part - you mean from air? I know water would create an emulsion with oil due to immiscibility, but I'm not sure about air . . . I would think that the air would tend NOT to "go into" the oil but remain as bubble(s) - at that pressure - since the oil is largely uncompressible.

I believe it would be hard for the air to remain as a 'bubble'. My reasoning is - you may start with it as a 'bubble' at the high point in the shock - then as the oil transfers back and forth between the shock piston and shims and back into and out of the nitrogen resivoir can (area where the bladder is) the air is quickly broken down into molecular size bits. These molecular size bits of 'air' enter the oil and if you want to think of them as micro-pockets of air in the oil maybe that may be a better term than emulsion.

Point is - Ride a rough trail or a track for 10 or 15 minutes then stop and check how hot your shock body is. I know I'm old and slow but my shocks have been hot enough at times that I could not hold my bare hand on the shock for more than 2-3 seconds. i.e. conversion of energy into the shock oil by kinetic energy and friction. Let the shock sit for a while and you probably will have a pocket of air reform at the highest point in the shock at lest those air molecules not trapped under the shims and piston seal.

Maybe another way to look at it is similar to transmission oil - oil churned via the gears entrains air into it. Instead of gears though we are using small passages, shims, piston velocity to churn the oil. Probably clear as mud right?

I follow you now, IC. Emulsion made me think of something more permanent so I was scratching my head a little. I can certainly understand air breaking down through turbulence in shock movement - made even easier by the shock oil getting hotter - and creating a suspension of sorts.