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What are the differences between a mechanical clutch and a hydraulic clutch?

  • Applications
  • Performance/driving
  • Reliability
  • Maintenance/Repair
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I'm assuming that you mean mechanical and hydraulic clutch actuation. If you mean "wet versus dry" clutches, or a torque converter (as used in automatic transmissions) and a "dry" disc clutch (as used on manual transmissions), please update your question. – Sean Reifschneider Aug 30 '11 at 21:34
+1 I'm quite interested in the answer; can't figure out what's supposed to be better about hydraulics here. I have one of the first Civic models where they switched to hydraulic clutch and I've mildly considered putting in a plain old cable if/when the hydraulics go bad... – R.. Aug 30 '11 at 23:40
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The nice thing about hydraulics is that they automatically adjust, rather than a cable which you have to adjust as the clutch wears. – Sean Reifschneider Sep 4 '11 at 8:45

3 Answers

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Mechanical clutches have a cable for actuation, and typically need adjusting throughout the life of the clutch. Hydraulically actuated clutches tend to be self-adjusting, as long as there is enough fluid in the reservoir. However, this does mean that hydraulic clutches can be susceptible to air bubbles in the lines, and water in the system which can lead to premature rusting. Consider silicone fluids for clutch applications to reduce water problems.

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Can you elaborate on perfromance? Does a cable driven clutch engage/disengage any faster than a hydraulic clutch? Are there issues with hydraulic being sluggish or having delays in disengaging? – DustinDavis Aug 30 '11 at 21:58
I can't speak with authority on the performance, but in my experience the performance in terms of delays is similar to a cabled clutch. It uses the same technology as your brakes, so any lags would be similar to what you see when you apply your brakes. I'd guess that if there were any lags, it might be caused by air in the lines, which shouldn't normally be a problem. – Sean Reifschneider Sep 4 '11 at 8:42
I was thinking the same thing (about the brakes). – DustinDavis Sep 5 '11 at 5:45
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@DustinDavis, from the physics standpoint, the liquid, for the purposes of this application, is considered as “incompressible”. Therefore, as soon as the pressure applied on one end of the pipe, liquid instantaneously transfers that force over to another end. It is like pushing a stick, except that stick is wet, and can follow elaborate route. – theUg Mar 6 at 19:12
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A cable clutch is pulled in and out by a cable from the pedal to the lever which operates it. A hydraulic clutch has a cylinder at the pedal like the brakes and feeds fluid to another cylinder which pushed the lever to move the clutch in and out.

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I don think this adds anything to discussion. It repeats same things that had been said in other answers or comments. – theUg Mar 6 at 19:14
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Having owned cars with both, I can't say I've noticed any significant performance difference between the two. I can't see any reason why a hydraulic one would be slower or more sluggish than a cable one - bear in mind they both work on the same principle, just that a hydraulic system pushes an incompressible inner medium (the fluid) through a flexible outer pipe, wheras a bowden cable typically pulls a non-stretchable steel cable through a similar flexible pipe.

I have found hydraulically operated clutches to be more reliable in the shorter term (i.e. they don't need to be constantly adjusted), but more expensive to fix when they do eventually go wrong (Typically the seals on one or other of the cylinders perishing after a decade or so) - but then it is typically easier to get at the cylinders than it is to get at the cable runs on some cars I've dealt with. I have found that cables tend to sieze or break through rust at similar intervals.

Hydraulics are better for cars where the clutch and pedal are far apart, such as rear engined cars, as a long cable would otherwise be needed. They can also go round much tighter corners than a bowden cable. A cable however is much cheaper to make in the first place, and requires less space as it doesn't need cylinders and reservoirs.

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