difference between mechanical and hydraulic clutches

Question

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

• Applications
• Performance/driving
• Reliability
• Maintenance/Repair

Answer 1

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.

Answer 2

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.

Answer 3

Any lag when the foot is lifted is likely to cause wear on the facings. It is possible that with a cable that doesn't slide easily in the outer, this would happen. With a hydraulic system that has not been maintained ie old fluid with water in it & worn cups or rusty worn cylinder bores lag could also happen. Subaru first series 1600 had a cable & 2 litre hydraulic. I'm thinking the 2 litre clutch is likely to be heavier & a hydraulic system would be easier to engineer than altering the pedal leverage. I had a car with a hydraulic system that had no maintenance & the clutch facings were worn out at a fairly low mileage.

Answer 4

I know this is an old post but as it comes up on search engines I would like to add... It seems as though clutches last longer with mechanical linkage . Additionally, when replacing clutches on hydraulic systems- if you have the flywheel turned(resurfaced) then you need a spacer, whereas with the old mechanical linkage it would simply require adjusting prior to the first drive after reassembly of the clutch setup.

Answer 5

I would also like to mention z bar linked clutches, my old old trucks from the 70's did not use a cable it was a mechanical bar from the clutch pedal to a bracket that went back to the clutch fork on the old 4 speed. That is now 43 years old and has not been replaced. I like the feel of the direct mechanical clutch best. I do not like cables, or hydraulics.

Answer 6

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.

Answer 7

To answer each area:

Applications - On anything that uses a clutch actuator.

Performance/driving - Lighter than cable-operated actuator.

Reliability - Should be more reliable than cable.

Maintenance/Repair - Regular fluid top up.