Giant NRS rear shock service/rebuild
So you've got a Giant NRS with a stock NRS shock, and for some reason such as its no longer holding air pressure you need to service it?   The bad news is that Giant unhelpfully say "take it to one of their dealers" and don't give any instructions at all for servicing it.  The good news is that they sell a rebuild kit for about £30 and the NRS shock is really easy to strip down.

This page shows how to rebuild a NRS rear shock.  I'm not claiming its totally correct as there's no manual available, however, I stripped the shock down, replaced all the seals, rebuilt it and it works.  That's good enough for me.

The exact model is a Giant 2005 NRS with a Giant branded shock.
 

Tools
You will need:

A bench vice to hold stuff

22 mm spanner

(external) circlip pliers

An old 5mm allen key (hex wrench) and a grinder or file

 

Preparation
Firstly, unless you've got a 5mm pentahedral male socket then you've got to make a tool up.  There is what looks like a 5mm hex head socket in the bottom of the shaft, however on close inspection its only got 5 sides so none of your allen keys will fit.  The way I got round this was to get an old 5 mm allen key (a freebie that came with some self assembly furniture), a bench grinder and convert the allen key into a 5 sided tool.  It doesn't need to be perfect as the screw isn't that tight. 

 

Parts
Buy a NRS rear shock rebuild kit from any Giant dealer.  This contains all the seals that you need.  If the shock is leaking air then you NEED new seals, just cleaning the old ones up won't work.
 

Disassembly
1.  IMPORTANT.  BEFORE YOU DO ANYTHING, DEPRESSURISE THE SHOCK.
2.  Remove the top and bottom bushes.  These are aluminium and are push fitted.  You may need to apply violence to remove them.  Don't worry about wrecking them as the rebuild kit contains nice new ones.
3.  Remove the travel indicator and the plug in the shaft.  This is what you made that pentahedral tool up for. The metal plug just unscrews and below it is a rubber push fit plug seal.  This plug seal is removed by using the point of a scribe or something similar.
 
4. Now disassemble the air can (this can be done before step 3).  The shock body is a hand tight screw fit.  Hold the top casting of the shock in a vice and simply unscrew the air can body.  Tools should not be necessary, it should only be hand tight, however, a squirt of penetrating oil the day before is a good idea.  If you can't get the can apart then find someone with a stronger grip.  Careful application of heat might help or careful use of an oil filter wrench might also help so try them at your own risk if needed, however, I never used either, I just unscrewed it by hand (and it had been on the bike for two years).
 
5.  The air can should now pull straight off the shaft.  Clamp the lower end of the shaft in a vice, pull up the damper assembly as far as it will go and undo the nut on the top with a 22mm spanner.  The damper and negative coil spring assembly will pull out.
 
6.  Almost there.  The last thing to do is to use circlip pliers to remove the circlip on the centre of the shaft allowing the central seal and PTFE scraper rings to be removed.
 

Rebuild
1.  Clean up all the parts with a cloth and methodically go through and replace all the seals.  The rebuild kit has every seal in it so make sure you find them all and replace them all.  A bit of grease or petroleum jelly or dab of oil should be used on all the new seals.  Take care not to pinch any new seals, especially when you start reassembling the shock.
 
2.  Reassemble the main central seal and PTFE scraper assembly.  Refit to shaft.
 
3.  A tricky bit.  I don't know how much or what type of oil goes in the shock as there's no manual.  This is what I did and it works.  Firstly I used SAE 20 oil.  Shop around for this, you don't need much, only about 50cc or so, mine came from a motorbike shop (for front forks).  Inside the damper tube you'll see a white seal, using a hex wrench or other flat implement, push this down to the bottom of the shaft (if you haven't removed that little screw at the bottom - step 3 - you won't be able to do this as there will be air pressure behind it).  Fill the shaft with oil.  Now put the plunger (top of the shock) back in and push down, then remove the plunger. If you don't remove the plunger, you'll have too much oil in there and will create a hydraulic lock.  You'll notice that the white seal will have pulled up about half way as you removed the plunger.  Don't push this seal down any more now, top up the oil if necessary - to the bottom of the threads - replace the plunger and screw the top assembly back on. I don't know if this is the correct procedure, but it worked for me.

[It is a good idea to change the damping oil as all oils degrade with use and lose their viscosity.]
 
3.  The rest is simply a reversal of the disassembly process.  Take care not to pinch seals, make sure everything's, clean.  It should all go back together easily.
 
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