Clutch slave issues

In common with all the Aprilia 1,000cc V twins, the Futura can suffer problems with the clutch operation. Usually, but not always, these can be traced to a leaking clutch slave cylinder. Other clutch problems, while not unheard of, are rare.

Symptoms

  • Difficulty finding neutral;
  • Difficulty changing down;
  • As the situation progresses the clutch lever shows excessive free play and becomes grabby, with the bike creeping forward in gear with the clutch pulled in, worsening until clutch function is lost altogether – i.e. pulling in the lever has no effect at all.

This usually (but not always) happens slowly.

The cause

clutch slave

Original clutch slave, with the piston (minus seal) on the left, and the cylinder on the right. The seal fits in the groove in the piston.

In most cases the cause is fluid leaking from the clutch slave cylinder, which sits in front of the front sprocket on the left hand side of the engine. Occasionally it can be the brake line itself, in the bend above the bleed nipple.

It’s common for the clutch fluid to turn black in use and this may be part of the problem – it’s been suggested that the black is actually tiny bits of seal dissolved in clutch fluid.

Whatever the cause, fluid seeps past the slave seal, into the clutch push rod chamber and out of a small weep hole.

This in turn drains the clutch reservoir at the handlebar until there’s no fluid left – especially since the reservoir only holds a tiny amount of fluid (about 8ccs), thanks to the diaphragm that sits in there.

The cure

In some cases the leak is so slow that it’s easy to keep on top of by topping up the fluid periodically and maybe bleeding the system.

But this won’t stop it happening and the leak will only get worse as time goes on. There is a school of thought that failure is in part caused by friction between the seal and the inside of the cylinder as the piston moves up and down with each clutch application.

Most failures are accompanied by black marks inside the cylinder.

In practice, if it’s the slave, you can either re-condition the slave cylinder, replacing the seal, or buy an aftermarket slave cylinder.

Repair or replace?

The first issue is cost. A replacement slave cylinder seal costs (at February 2010) about £13. An aftermarket slave cylinder costs upwards of £100.

There is some evidence that since 2001 Aprilia changed the design of the seal to make it less prone to failure. Also the friction problem can be eliminated by applying O ring grease (also called silicon grease), available for about £4 from diving shops and on e-bay.

Owners who have done this report no further problems.

Most aftermarket clutch slave cylinders give reduced lever effort by using a design assembled by a machine – i.e. usually by the manufacturer. Therefore if it fails, you’re stuck. The Aprilia seal can easily be repaired with a readily-available and cheap part with a minimum of tools. I have also seen some DIY repairs done on leaky aftermarket seals.

There is no evidence to suggest an aftermarket slave is any more reliable than a stock one assembled with O ring grease.

See Ken’s Falco site for a guide to how to replace your clutch slave seal. It’s a straightforward job.

Conclusion

Some owners see this as more a maintenance issue than a reliability one and the evidence is that replacing the seal and lubricating it with O ring grease cures the problem.

If you do decide to replace rather than repair, be aware that the slave sits on a mounting that you’ll need for the new slave. Carefully prise it apart because it’ll be stuck.

More information is available on the Apriliaforum, where this problem has been discussed at length. The link below details the problem and the fix well: