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Old 05-24-2013, 03:41 PM
arnego2's Avatar
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Default WP pds rear shock oil change question


Hey all
How do I change oil on a WP PDS rear shock of a 2001 520 exc (I believe it to be) I converted the nitro charge allen entrance to a shredder valve, unfortunately for me the shaft did not raise so I think that oil has long lost it consistency or went south completely.

Any help, like filling amounts, how to are highly appreciated

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Old 05-25-2013, 05:14 AM
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Procedures for Servicing WP PDS Shock

1.Back out rebound adjustment all the way, then cycle shock through full movement 5 or 6 times.

2.Release gas pressure

3.Remove seal head cap.

4.Push down on seal head and remove seal head retaining snap ring.

5.Remove shaft assembly from body, if removal of shaft assembly due to excessive vacuum, remove servicing bolt next to compression adjuster.

6.Loosen set screw on the side on the compression adjuster knob. Be careful not to loose the small spring and detent ball.

7.Remove snap ring that secures the compression adjuster in place.

8.Disassemble compression adjuster to facilitate cleaning, just be sure and note order of components for re-assembly.

9.Place shock shaft clevis solidly in a vise, IMPORTANT, “rock” the large retaining nut back and forth with a wrench while noting if the shock shaft appears loose in the clevis. This is very important because there have been issue with some WP shaft coming loose in the clevis and breaking. All WP shocks need to be checked, although, primarily pre 2001 units are suspect.

10.Due a complete tear down of all shaft components.

11.On the 2001 and “some” earlier models the rebound adjuster needle can be removed through the bottom of the clevis. Remove the rebound adjuster with an adjustable spanner type wrench; remove the rubber plug on the bottom of the clevis.

12.Gently remove rebound adjuster needle with “smooth jaw” needle nose pliers.

13.Remove piston reservoir with the WP wrench, you might have to heat the threads to melt the loctite.

14.Remove piston from reservoir form cleaning.

15.Clean all parts.

1.Mount clevis in vise

2Install shock bumper, seal head cover, and seal head onto shock shaft. If you do not have a WP seal head seal bullet, the seal head MUST be disassembled and installed piece by piece on the shaft. If the seal head is attempted to be installed as one piece without the use of a seal bullet, oil seal will most likely be damaged. Make sure all components have a good film of grease during reassembly.

3.Install piston and shim stack assemblies

Make certain that the holes in the spacer in between the pistons is lined up with the holes in the shock shaft.

4.Reassemble compression adjuster.

5.Install compression adjuster into shock body ( with well greases orings), IMPORTANT, make absolutely sure that the oil port coming from the shaft side is perfectly lined up with port on the compression adjuster. Failure to do this will result in a restriction of fluid flow from the shock body through the compression adjuster.

6.Install snap ring.

7.Turn compression adjuster (without the knob being installed) full clockwise, grease the adjuster detents

8.Install the detent ball into the detent closest to the pin on the full hard side, put the small spring into the knob and ensure that the spring sits on top of detent ball, push all the down, then tighten the set screw. We are indexing the adjuster knob to the “full hard” setting.

9.Check to make sure that you have full range of adjustment on the compression adjuster.

10.Install o-ring and Teflon band onto nitrogen piston, put a good coating of grease on piston and on the inner surface of the cylinder.

11.Install piston all of the way into the cylinder, it will bottom out next to the servicing fitting.

12.Fill reservoir with fluid and then screw in the shock body. Make sure the reservoir is tightened all the way down and sealing with the o-ring. You can hand tighten it for now, we will use the WP wrench to tighten it later when the shock is installed in the vise.

13.Use a 4mm rod to push the against the reservoir piston from the servicing hole. Push the piston until fluid starts to flow from the shaft side of the body, once a solid stream is coming out, flip the shock body upside down while continuing to push on the piston. This procedure should eliminate any air trapped inside the reservoir and adjuster.

14.Mount the shock upside down in the vise; tighten the reservoir with the WP wrench.

15.Fill shock with fluid.

16.NOTE: This next step is only for the shaft assemblies where the rebound needle installs through the bottom of the clevis.

SLOWLY Install shock shaft assembly into the body. (note: at this time, the rebound adjuster needle is still out of the shaft). When fluid starts to flow from the rebound needle hole, insert rebound needle just until the o-ring on the rebound needle “takes a seat”. You don’t want to push the rebound needle all of the way in or it will close off the bypass circuit, making it difficult to move the shaft in the body during bleeding. Install rebound adjuster just enough to touch the rebound needle. Leave it loose.
This procedure will ensure all air removal of the cavity between the I.D. of the shock shaft and the rebound adjuster needle.

17.Once the shaft is installed, top off with fluid, move the shock shaft through its’ full range. Use a plastic hammer to tap on the clevis during the compression stroke, this will ensure the release of any air trapped between the two pistons. Make sure that you tap on the clevis hard enough to “unseat” the shim stack from the face of the piston; this is the only way that the trapped air will be removed.

18.Top off with fluid, and extend the shock shaft as far as possible while marinating the bypass hole on the shock shaft under fluid.

19.Push seal head into shock body and install retaining ring.

20.At this time, tighten rebound adjuster, and reinstall the rubber plug.

21.Pressurize the shock with shop air for bleeding.

22.Run the shock through its full travel about five or six times.

After we cycle the shock (step 22) put the shock upright in the vise. bleed ALL air pressure. After we pushed the seal head into the shock, it will be over serviced with oil. Remove the nitro servicing screw, and the bleed screw, (this is where we "tweak") push up on the shock shaft to reduce the amount of over fill and hopefully any air in the fluid. The bleed screw is on the shock piston side of the compression adjuster, which should enable you to bleed any air trapped above the shock piston.

There is a quick calculation method that should prevent you from removing too much fluid from the shock during this procedure.

Right after you remove the nitro servicing screw, measure how far the piston is in the gas chamber. 120mm is the recommended depth, now the gas piston is displaced a total of about 17mm from shock shaft extension to full compression travel (including mashing the bumper). Once you do the math, this will give you a good idea on how far the gas piston is traveling when you push the shock shaft into the body.

23.Mount shock in the vise with the bleed screw (next to the compression adjuster) at the highest point.

24.RELEASE air pressure.

25.Remove the nitrogen servicing screw completely.

26.Loosen the bleed screw next to the compression adjuster.

27.Use a 4mm rod (with a mark at 120mm) to push on the piston, back out the bolt on the servicing port just enough to let the excess fluid flow out, when the piston reaches a depth of 120mm , tighten the bleed screw.

28.Charge with 175 to 200 lbs. of nitrogen

29.Leak check, install seal head cap, and set clickers.
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Old 05-25-2013, 05:59 AM
arnego2's Avatar
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Thanks, great info,

I wonder what they were thinking when developing a shock needing a method using almost 30 steps just to change oil.
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Old 05-25-2013, 08:09 AM
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Default ???????

Well at least you don't have to just replace them like autos & trucks!

Paw Paw
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