Clutch Cylinder - Strip Down and Overhaul

Time to rebuild the clutch cylinder.

Up until some point in 1971, clutch operated Ds (i.e. not the Borg-warner gearbox ones) and with carbs, had the 'long' clutch cylinder (my description - not Citroens) with an 18.5mm diameter piston. After that they swapped to a different design which, from the outside, is shorter and squatter and has a 24mm piston.

As a 1968 car, mine has the earlier version - which seems to be a much simpler design. Just one seal to change. Instructions for the rebuild are omitted from the later Manual 814, but is covered in Operation 314-3 in Manual 518.

The rubber cover was perished and I would be replacing that - but would need to re-use the overflow pipe.

I carefully pulled out the overflow pipe from the rubber cover and then removed it.

Pushrod in the piston

I removed the circlip and unscrewed the top collar.

Rusty locking collar removed

 The cylinder sits at the bottom of the bore and is a hollow cup to take the push rod.

The piston cup lip is the shiny circle at the bottom of the shaft

I was able to get the piston out just by tapping the cylinder on the workbench top. This told me that the rubber seal was not gripping and sealing the piston as it should and confirmed that it needed changing. The other way to get the piston out is to put a squirt of compressed air down the aperture where the hydraulic pipe fits - but be prepared to catch the piston!

The piston just came out with a tap

The rubber seal that I wanted to replace is quite near the bottom of the cylinder shaft and sits in a recess in the inner face. It was tricky to winkle out - especially as it had hardened with age. I took my time as I didn't want to rush it and end up scratching the bore.

Winkling out the old seal

Winkled.....

I also winkled out the rubber pipe seal on the LHM pipe - and all the little shards that end up trapped in the threads.

Chewed up rubber pipe seal

I ran the cylinder and collar over my wire wheel to clean it up, and had to use a little wire wool to clean up the threads where the collar fits. I flushed it through with Jizer to remove any gritty bits inside and, after a rinse, used some compressed air to dry it quickly. De-greased,  I then gave the outer surface (not the bore) a thin coating of phosphoric acid to kill any rust.

All cleaned

Fitting the new seal is tricky: as the ridge is not at the bottom of the bore, it's very easy to push it down too far. Below is the diagram from the Citroen Manual. Basically, tool MR.630-31/11 sits at the bottom of the cylinder to form a platform against which the new seal can be pushed into its's slot. Once it's fitted, the tool has a 6mm thread down the centre so that you can run a bolt into it to pull it out.

The tool sits below the groove of the 'O' ring

I found that one of my 12mm sockets was just under 18mm diameter and so slid into the cylinder easily. It was not so loose that the seal could slip past it when being fitted, but equally not so tight that it would not slide out past the seal once it was in place. It was also JUST the right height to sit just below the seal groove.

I used a socket as a substitute tool

With a liberal coat of LHM on both, the seal popped in to the groove on the cylinder very easily - with just my fingers. No need to use the piston. The socket slid out afterwards.....

.......leaving the seal behind.

The new seal is the glinty bit right near the bottom.......

In his "Godess" book, Chas Vyse uses a similar trick using a piece of dowel - which he then withdraws with a screw.

I refitted the piston: I coated the piston in LHM and used a 13mm socket and rubber hammer on top to help encourage it past the new seal. The collar needs to be flush to the surface of the clutch cylinder or no more than 0.5mm below the edge. 

The collar screws in the top

I fitted my collar so that it was flush to the cylinder edge. It has four different holes for the split pin around its circumference so there was plenty of choice:

Collar was set flush to the cylinder end

I then replaced the split pin. 

Split fitted to hold collar in place

Then it was painted........

.......the dust cover and push rod were added..........

......and it was fitted. Job done.

I can't adjust it just yet though.