There are very high pressures involved with servicing shocks. Only attempt at your own risk!
Fact 1: Shocks require regular servicing. Fact 2: Fox official tools are crazy expensive for the DIY mechanic! How do you go about servicing the damper in your DPS or DPX shock then? Fox provide comprehensive instructions on how to do this, so this DIY is only meant as a guide for how to do this without the official Fox tools.
Reasons to rebuild or service your damper
Fox recommend a full service and rebuild of the damper every 200 hours. I "slightly" exceeded this interval and at the time of the rebuild, the shock had seen 10 000km or about 600h or riding. A clear indication that a re-build is in order came at around 8000km, but due to time constraints and the lack of correct tools, I was not able to perform the service earlier.
In my case, and indication that the damper had cavitated, which means either air from the IFP chamber or heat build-up had cause air to mix with the damper oil, came as distinct lack of damping during the first 1/3 of the shock's stroke. This made the shock very bouncy, but still rideable in the open position, but completely unbareable in the pedal position. This could have obviously been avoided had a stuck to the Fox service intervals, so next time I will service the shock on time.
If your damper is leaking, you will need a full rebuild kit, but the basic oil change and usually even cavitated damper oil won't require the Fox seal kit. However, it's worth noting that if you shock is stuck down, or cannot be compressed, it's best to have the seal kit on hand.
WARNING! Pressure should always be released from both the air sleeve and the IFP chamber before completely opening the shock! The IFP chamber can be depressurized by carefully undoing the 4mm allen fill screw. Pressure will be slowly released through the puck as tension on the puck is eased by opening the screw. Use caution and only attempt this at your own risk!
DIY Tools
Fox use a special nitrogen adapter to fill the IFP, which stands for Internal Floating Piston. The IFP is used to separate the damper oil from the air or nitrogen in the damper. Pressure needs to be released and refilled to service the damper and change the oil, so the fill tool is necessary even for a basic damper oil change.
Fox shocks use a rubber puck that is piereced by the fill needled during filling, similar to a soccer ball, for example. The problem is the tools required and listed by Fox in their service instructions for the DPS and DPX shocks are either very hard to obtain, and/or crazy expensive. Enter the DIY solution!
The official tools are available from Fox, but at significant cost and they can be hard to obtain. This is why I built a tool set by myself, which consists of:
- 4mm allen key with a notch cut into it to allow the IFP fill needle to be inserted while the key is in the IFP fill screw
- IFP fill tool from ebay, which is meant to be used with a shock pump
- Shock pump capable of 500psi / 35bar or nitrogen fill station with Schrader valve adapter
- 7mm 90 Shore-A o-ring cord. This can be cut to 2-3mm thickness to replace the Fox fill puck, should you not have a new one available.
- Fox Float fluid for the air sleeve
- Fox 10W red or equivalent shock oil for the damper (I used Motul 10W motorcycle shock oil)
- 803-00-142 Kit: Rebuild, FLOAT Line Air Sleeve, Special Q-Ring (If you are re-building the air sleeve)
- 803-00-816 Seal Kit: CTD Boost Valve and Dish Shock Rebuild (Same for DPS shocks) (If you are rebuilding the damper)
- 398-00-638 Tooling: Custom Spanner Socket, 3 pin, Float DPS, Lockout Piston (This is the only special tool you will need to buy or manufacture, only needed for complete damper rebuild)
- 398-00-637 Tooling: Custom Socket, 5/8", 2016 Float DPS, Piston Bolt (Can be substituted with a suitable thin 16mm socket, or by cutting down the outer diameter of a standard socket, only needed for complete damper rebuild)
| The starting point |
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| At this point you can already tell the damper oil has cavitated |
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| No, the shock oil should not have a foam head! |
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| IFP fill with the needle tool |
what's the difference between filling with nitrogen or using 500 psi shock pump? will it have the same effect?
ReplyDeleteNitrogen is thermally stable where as air is not, so theoretically the IFP pressure will change slightly with air as the shock heats up. Will you notice it? Likely not.
DeleteThanks! ya I read that air is already 78% nitrogen so very small difference indeed.
DeleteI am using this article because I am replacement the bearing in my fox DPS shock so I will need to make the special tools but it looks very easy to do. I purchased the 10w red fluid, the fill tool, 600 psi rockshox pump and the replacement bearing. Do you think I will need anything else to do this job? I figured the fill puck is re-useable but now I do not know.. Also wondering when you are filling it to 500 psi does the needle tool have the tendency to want to shoot out of the puck from the preasure? or do you tighten the set screw to the point where it is hard to pull the needle out? Thanks for the great article!
DeleteSorry for the late reply! The fill puck is usable maybe twice, but no more. The needle stays in place quite well and you need to tighten the allen screw before pulling it out quickly. Finger tight, pull needle and tighten fully. There will be a hiss of air from the needle / hose on your pump.
Delete7mm o-ring cord in 90A seems impossible to buy in Canada. All 7mm o-ring cord comes in 70A, will that work or is 90A mandatory?
ReplyDeleteI’m sure it will work as well. You may need to tighten the allen screw a bit more for a good seal when removing the needle.
DeleteThanks again for this writeup! got the job done :)
ReplyDeleteThe oil was completely foamed up for me. I was actually changing the bearing assembly is the main reason I went through with this, but I got unlucky when removing the nut with the thin walled socket, for some reason the shaft loosened from the top hat instead of the nut coming loose... this was not supposed to happen because they are supposed to put red loctite on the part of the shaft that threads into the top hat but there was none. I put red loctite on it and let it sit for a day and lucky for me the nut came off next time around.
One of the hardest parts was filling the IFP to 500 psi, the only pump I found capable of this is the rockshox 600 psi shock pump. I consider myself a lot stronger then the average person and I had to use all my power to eventually get it to 500 psi, was a hell of a workout. I am curious what did you use when filling to 500 psi? Would you happen to know of a better pump for the job?
Good to hear it worked! I'm using a Rockshox 600psi pump as well and agree it's a bit of a chore.
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