replacing rear wheel cylinders

[hayesey]

what are people's theories on these?  Some people I know say these have to be replaced as a matched pair, i.e. if one side is leaking then you still need to replace both sides.

I've never done that, I've always only replaced the side that's leaking.  It's obvious to me that things like pads, discs, drums & shoes have to be done as pairs but doing wheel cylinders doesn't seem to make much sense, unless it's that the other one will still be slightly worn and not have the same effort as a new one?   

[PeteG40]

as long as both are free. wont make much difference.  I suppose the same is true for front calipers, if one seizes then you could just replace that if the other is free.

However there is always the arguement if one is 10 years old the other is about the same age and prone to failure.

[Alexiskayak_7]

As long as one cylinder is leaking it's a mater of time the other cylinder begins to leak.. The brake fluid destroyes the drum pads..Drum shoes are replaced as a set... So it's pity to throw a set of pad shoes for a cylinder...
Also cylinders are prone to fail and the pots don't expand fully...

[scotsjohn]

For reasons unknown, I always seemed to be renewing the nearside. Washed brakeshoes in carbon-tet. if soiled. Never changed as a pair though they aren't axactly costly.

[SuperMario]

i had to change one of mine due to seizer, figured the other side isnt going to be great nick so done both, there cheap so not to bad.

[cheys03]

For the price and effort I'd change them in pairs.
If you've got a leaky cylinder there's a good chance you'll need to change the shoes on that drum also. Shoes are changed in pairs so you'll have to open up the other drum anyway. Providing the bleed nipples, brake pipe and back plate bolts are in reasonable condition it should be a easy swap for an additional wheel cylinder. Should only take around £15, 20mins extra and you'll have the piece of mind that neither cylinder should leak in the near future and cost you another set of shoes.