rebuild rear Emulsion 2" Shocks

This thread, can be generic rebuild notes, comments.
Specific model I rebuilt were 10" travel, 2" diameter, Emulsion (ie no reservoir), Walker Evans brand shocks, onto stock mounting points.

Overall: I'm a 'backyard mechanic', comfortable around tools and the truck, and willing to tear things apart on the truck. I would rate this task as on the easy side of a moderate task, and can definitely see with practice this could be accomplished quickly. I would do it again. If you know of a better way to do something, feel free to comment; I am not an expert. Biggest headache was undoing the top mounting nut after a few years of road grime. Required patience to loosen nut until it got tight, re tighten, reclean threads with wire brush and plenty of WD-40, repeat until finally the nut came off the end of the threaded rod.

Parts required:

• Seal kit for your model shock, available from Manufacturer. Mine were US$20/shock.
• New Nylock nut for the top threaded stud. in my case a 1/2" x 13NC, went with 18-8 Stainless steel, no need for a Grade 8 Nut in this application I would think.
• Shock Oil, went with Manufacturer recommended 10 Weight, Lucas full synthetic. Redline is another brand out there, but is was special order and 3x the cost. Check with your shock manufacturer on weight, or more specifically viscosity index required. $5.00 for 500mL x 2.
• any replacement washers you choose to replace the potentially corroded/ distorted ones as part of the mounting.
• new valve core, in my case a simple Schraeder valve core to add Nitrogen pressure. I would order these from the Shock Manufacturer, as the valve cores on mine i noted had two Viton O rings on them versus the usual car tire valve core with just one Buna-N O ring.

Tools required:

• Instructions received were to bleed off the gas pressure first before shock disassembly, and after reassembly to add nitrogen pressure with the shock in upright position, and fully extended. ie before you mount it back on the truck.
• need to know the volume of oil to add, and a method to measure that. Graduated cylinder 500ml size, or in my case simply a cooking measuring cup that had a measurement line where I needed it.
• container to capture old oil.
• 17mm wrench, socket, ratchet for bottom bolt.
• in my case, a thin 3/4" open end wrench (grind one down) and a 3/4" ratcheting closed end wrench for the top end of the shock mounting to the truck.
• 1" wrench to unthread shock end cap.
• 11/16" wrench to remove nut allowing piston Valving assembly to come off of piston rod, and consequently the end cap to be removed.
• various dental picks to remove seals, and aid in putting seals back into machined grooves in end cap.
• toothbrush to clean grooves in end cap before adding new seals in.
  
• clean surface to layout parts on.
• wire brush to clean dirt out of threads at top end of shock mounting + WD 40, and patience.
• 1/2" die to chase threads of the same.
• anti-sieze optional for reassembly of bolts.
• hydraulic jack + a socket that is as narrow or narrower than rod end, used to compress shock push rod end into lower shock mount.
• punch or screwdriver to align rod hole with lower shock mount.
• optional hammer to tap lower bolt in / out, and tap rod end into alignment in lower shock mount.

 

Pictures I did not take any Before pics. Thought of making this thread part way through this job. Shock body looks like crap, as it was coated at one point by fresh road tar on one of my travels. Some corrosion on lower end of piston rod. Cleaned up a bit with a copper kitchen scrubby pad.

Thread sealant was for reinstalling schraeder valve. One of mine started spewing out oil under pressure as soon as I removed the valve cap. Ended up replacing just the core in the valve, but already had removed the valve from the shock body. Thread sealant easier to deal with than Teflon tape. Core removal tool, and spare valve cores shown. The cheap version of a valve core, so far is holding, though the original had viton O-rings (reddish color) versus just normal Buna nitrile (black typically)

 

• End cap view. After releasing all pressure out of shock body at Schrader valve, drape vise jaws with rag, & secure shock body in a vise. Unscrew end cap with 1" open end wrench.
• Once end cap is unscrewed from Shock tube / body, drain oil.
  
• Chasing threads of top mount with die, to clean out remaining gunk and corrosion.
• Piston and valving assembly at end of shaft. Removed the nut by securing nut in a vise and turning rod end with 1" wrench.

 

Piston + Valving assembly. Valving consists of 7 discs of varying diameter on each side of piston. The order of these discs matters. One side impacts compression stroke, the other rebound. When there is a pressure differential created as the shock piston moves, how quickly the piston moves generates a pressure differential. The amount of pressure will flex the discs allowing more oil to travel through the 3 sets of holes in the piston to the other side of the piston. I understand that a linear progression of large to smaller diameter discs outward from the piston creates a linear dampening response. You will note one side is linear (rebound) but the compression side varies the diameter of discs from large to small back to large again creating a digressive response I believe. Take care to keep the order of assembly correct, and note the piston is directional as well.

 

End cap seals. There are 3 stages, starting from the external side, a wiping seal made from Buna-N I believe, the next one internal has a wiping surface that faces the external, and the internal side has a groove or 'cup' inside. Fluid pressure within the groove pushes each edge of the seal outward, one side against the shaft, the other into the machined groove of the end cap. Finally the last (or first sealing surface if you prefer) is an O-ring made of Viton, I presume it's primary purpose is to center the rod within the seals.

1st pic - O-ring shown with pic tool, 2nd pic - the old cupped seal with wiping surface, 3rd pic - final wiping seal to keep dirt from getting inside.
4th pic - outside diameter O-Ring.

Patience and perseverance required to get the new seals to deform enough and be coerced into their respective grooved position.
Lastly an O-ring on the outside threads of the end cap is replaced. In my case, during reassembly I managed to roll this O-ring out of its groove and pinch it when retightening the end cap. After pressurizing the shock, and installing it the shock leaked. The clue was seeing some of the O-ring visible after tightening down the end cap. Have to redo that and replace that O-ring.

 

so end cap seals are replaced, it slides back onto the shock shaft, a carbon? spacer goes on, presumably a travel limiter, then the piston and valve is reassembled, nut added, and tightened. I don't know if there are seals at the top end of the shock body. Did not have any leaking there, suspect that part is an interference fit to the shock body, so I had no reason to attempt to take that end apart. Next is secure the shock body in an upright position and add oil, in my case 395mL. I measured out to just the bottom of the 400mL line of my measuring cup. Add the oil, then slowly, carefully align the piston rod, and screw down the end cap. You will note once the piston rod assembly is added in and the end cap secured there is very little volume left for the nitrogen gas.

 

I found a local shop that specializes in truck suspensions as part of their vehicle repair work to recharge my shocks with Nitrogen. Spec calls for 150 to 200psig. Recharged mine to 160psig. Looked up Torque specs for mounting bolts. Bottom mount is 74 ft.lbs, top nut is 15 ft.lbs. this is to allow the shock some movement as the shock needs to stay straight, but the leaf spring movement through articulation follows a radius curve, not linear, so the rubber isolators allow the degree of movement. Over tightening the top nut will not allow sufficient movement and any additional stress is transferred to the shock shaft.

 

Best to also charge the shock with little air and compress it by hand and see if it compresses and decompresses all the way. I do this to every shock I rebuild. Then recharge nitrogen after. I have done it several times where Internal floatin piston is not set right and the shock do not compress all the way and they then can hydrolock. I see that you didn't pull it out.

 

As long as the body/piston is wet with oil, could I test the fit prior to adding oil? I'm gathering the issue is if the piston is not exactly centered on the shaft?

 

No the Internal floating piston. It is another piece inside the shock that seperates the oil and the nitrogen. On a rebuild it must be taken out and have the oring replace and reset at a certain depth. If not you can overfill the shock and have it set at a wrong depth and have the shock bottom out on it self short of the bumpstop and possibly do great damage.

 

Here is a thread , and go down to number 12 it shows the picture of aluminum IFP with oring and white band.
https://www.tacomaworld.com/threads/icon-vehicle-dynamics-2-5-coilover-rebuild.515362/

 

I don't have that separation piston. What I do have is a free sliding spacer on the shaft.

 

It should be in there. It must seperate oil to nitrogen.

 

This is an emulsion shock,( vs IFP shock) by definition what I understand means no separation. Also note there are no Orings on the piston, so relies on the oil film between piston and wall, and must be part of the calculated transition of oil from one side of the piston to the other.