Shock Absorbers- damper overhaul (also Quickly TT)

I've already covered removing the shock absorbers from the front wheel and noted that they had little if any damping action. They are clearly going to need attention. In fact replacements are available for the front at 66Euro a pair which I thought was quite good- but sadly no such luck for the rears- these will have to be overhauled. I decided to investigate how to do this using the fronts which are effectively disposable since I have ordered replacements. The first few pictures just recap how to disassemble the shocks to release the dampers but this is described under front end strip.

Lock the two nuts up against each other and gripping the top one only in a vice unscrew the damper shroud (CLOCKWISE)

Grip the end of the damper rod with a small screw driver as it becomes inaccessible in the shroud and keep screwing the shroud right off.

Invert the shock in the vice and tap the end cap off using a screwdriver

Rest the shock horizontally (dont grip it) and push the grey lower shroud upwards  to slip the black sleeving off

Remove the sleeve

remove the black sleeve and also the stepped ring that sits inside the grey lower shroud

Then looking inside the grey lower shroud-locate the snap ring in its groove about halfway down the damper and spring it out with a fine screwdriver.

The grey shrouds then slide off the assembly below shows all these components except the grey shrouds.

Snap ring removed from damper groove shown after the grey plastic shrouds have been removed.

Looking at the top of the damper you can see an internal snap ring that holds the damper end cover in place. 

Remove this snap ring- its quite difficult but best option is to use a very fine screwdriver or a sharp pointed  probe to get behind it and ease it out of the groove. You may need two such implements- one to lever and one to slip behind the ring to stop it popping back home. In extremis you can cut a very SHALLOW groove in the end of the damper just down to snap ring height so you can lever it through the slot again using a fine screwdriver but be careful  to cut no lower than the snap ring groove

Whoppeee- its out

The damper end cap isnt held tightly and just lifted off with a magnetic probe.

This revealed the radial seal beneath which acts as the barrier to keep damper fluid in. Its a tight fit and I was unable to find any non-destructive means of removing it. Obviously this seal has to mate smoothly with both the damper rod and the inside of the damper tube so levering is not a good idea- scratch either surface and you can expect oil leaks. Luckily new seals are available from Krippl at 10 euros a piece. 

The seal actually incorporates a metal washer for rigidity- I exposed this in my attempts to remove the seal.  This was an old component and there was no flexibility in the rubber at all- it just cracked off. As you can see the rubber actually surrounds the damper rod and its possible to very carefully insert a fine screwdriver...

... and lever the seal upwards. If doing this again I think I would just drill a hole through the seal and insert a probe to lever from there

The old seal then slips off up the damper rod exposing the discs beneath. These are held in with a circlip- but in fact I'm hoping that this is as far as I need to go and that just cleaning and refilling with fresh oil will restore function. 

I cleaned out all rubber debris above the brass discs and then was confronted with this upper circlip.

Using circlip pliers compress the internal clip whilst pulling upwards on the damper rod. The upper brass bush will slip out...

... fallowed by the rest of the rod assembly and lower rubber seal and base bushes.

When I emptied the damper the oil that came out was black. Since the unit is completely sealed the only source for this dirt has to be wear on the rubber bush- certainly it had a dull, worn-looking appearance. I'd like to change the lower rubber. This looks feasible after removing the E clip at the base of the rod. However new rubbers for this position are currently unavailable, so Im pinning my hopes on a clean and refill.

The complete rod assembly is shown above. It consists of 3 brass bushes  a rubber bush and at least 2 telescopic tubes. I couldn't work out how it works but it obviously pushes oil around.

I cleaned all components including inside the damper tube and then started the  reassembly. The capacity of the damper is around 45ml so I measured 25ml of straight 10W fork oil and poured that into the tube before carefully lowering the damper rod assembly into place.

I found that by gently moving the rod up and down I expelled air and the oil level fell- top up again and repeat etc etc. Eventually I got to the point where both the rod and most of the oil fitted inside. I could slip the upper brass bush down whilst compressing the circlip. Note that there are several locating grooves inside the damper tube- so make sure the brass is down at the right level and has room above it for the seal.

I then fitted the new top seal- you need to remove the oil above the bass disc so that the seal can fit. This meant pulling out another 5ml so the dampers were probably filled with 35-40 ml in total 

Finally I refitted the seal cap and its circlip. The rest of these pics show the reassembly of the shock and are here mainly for my reference. I have to say that the improvement was only marginal and in the absence of any new rubbers for the base of the damper I think it might be useful to move to thicker oil so if I rebuild the second damper Ill try straight 20W to see if it helps (obviously Ill replace the oil in the first if it does).

The only points of note in the rebuild are firstly that if you are using new dampers from Krippl, note that these come with 2 circlip grooves- perhaps so they can be used on different bikes? Compare with the old to determine which groove should be used. I found it was the upper.

The second point is that the parts diagram shows the spring base fitted upside down. The spring seat has a flat and a stepped side. The step is a perfect fit for inside the lower shrouds- it doesnt fit inside the spring and so cant act to locate it as shown in the parts book. Mine were fitted with the flat side up when I stripped them so Im rebuilding them this way.