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  1. #1
    Platinum Member
    Join Date
    Apr 2002
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    864
    Location
    Raleigh, NC USA
    Tractor
    Massey-Ferguson MF 1220

    Default What is a "wet-type" clutch?

    I gather a "dry" clutch is the same type you'd find in a manual automobile, two metal friction plates. What is a "wet" clutch? Is this anything like the fluid-based "torque converter" found on autos with an automatic? Or something similar? I've seen notes about "wet clutches never wear/have to be replaced", so I'm wondering how they work...please post if you know!

    Thx,
    Dave

  2. #2
    New Member
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    Sep 2005
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    Default Re: What is a "wet-type" clutch?

    Wet clutches run in an oil bath and usually have multiple plates. Many, if not most motorcycles use them. I believe the primary reason for using them is to allow a common sump for engine and transmission. There may be other advantages that I am not aware of.

    I don't think there is any such thing as a clutch that doesn't wear, although some types may be more durable than others.

    I didn't know wet clutches were used in tractors.

    SnowRidge

  3. #3
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    Sep 2005
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    Default Re: What is a "wet-type" clutch?

    It is in most cases multi plates clutch. It has 5-10 metal disks connected to "bell" (engine side) by splines on the outer side, and similar number of friction material covered metal disks connected to "outgoing shaft" (by splines in centre of disks). They are mounted in enclosed housing, filled with ATF oil, and rotate with engine. From "shaft" side is mounted hydraulic cylinder, which press plates together when clutch drive. It rotates together with clutch bell, and has oil pressure feeding through shaft. It is simple explanation of its construction.

    Metal plates rotate together with engine, when plates connected to shaft stop together with it. When you want to carry power through it, you activate valve (usually via solenoid) to start gradually feed pressure to cylinder. Hydraulic power is generated from pump, driven from engine. That means - clutch is open when engine stops.

    Why it is maintenance free?
    -First, it has bigger contact area than single plate dry clutch, even with significally smaller diameter than dry clutch (2-3 times).
    -Second, it is lubricated when slipping during engaging clutch.
    -Third, it is well cooled during slipping, so contact temperature is few times lower, compare to dry plate, and avoid burning friction material.
    -Fourth, pressure between plates is bigger, thanks to hydraulic pressure. Dry disk clutch has spring-generated pressure, which is limited, because disengaging force will be too big on clutch pedal and on axial bearing on engine crankshaft. Wet, multi plates clutch not generate any axial pressure force to crankshaft. During time dry clutch plate gets thinner, and spring pressure force decreasing causing first occasional slipping during transferring peak torque and later normal torque.
    -Fifth, it is harder to reduce pressure if you are riding your leg on clutch pedal. Pedal is soft, and when you occasionally press it, clutch disengages.

    Why it, sometimes, lasts short?
    - Not enough oil level.
    - Wrong oil type.
    - Worn rings on pressure transfer path, and not enough contact pressure - especially visible/feelable on low engine RPM.
    -Worn hydraulic pump, clogged filters etc.

    Conclusion
    Power reversers on any type tractors and backhoes use this system, but with 2 clutches (one for each direction). Geared ones, not hydrostatic ones, of course.

    Comfort clutch for use, excellent in performances, more complicated than dry plate clutch, and EXPENSIVE to repair.
    Anyway, I regret I haven't it on my tractor(s).

    Disadvantages
    It is almost impossible to start engine by towing with this type of clutch.
    Not possible to leave tractor in gear when engine stops. Need very reliable parking brake, and retirement blocks under wheels.

    Some tractors use multi plates disk clutches for engaging MFWD. On them usually pressure force is generated by load spring, and hydraulic pressure is use to disengage. This system is always used on tractors with front axle braking by engaging FWD (on 25 MPH tractors in Europe, don't know for US). Similar system is used for on load differential locks.

    The best example where this clutch type is used are New Holland TND series. System is called Dual command. In Europe (don't know for US), TND even have two stage powershift for FWD direction.


    Hope this helps. [img]/forums/images/graemlins/wink.gif[/img]

  4. #4
    Gold Member
    Join Date
    Jun 2000
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    499
    Location
    Syracuse, New York
    Tractor
    1952 Case DC-4, 2001 JD4300 MFWD, HST

    Default Re: What is a "wet-type" clutch?

    ZJ_Hrs description is correct for certain types of wet clutches. In a more general sense, however, a wet clutch is simply a clutch that runs in some type of oil. The clutch on my old Case is a wet clutch which in most respects is the same as any generic single disk automotive style dry clutch. A wet clutch will generally last longer and engage smoother than a dry clutch. The downside of a wet clutch is that as the clutch wears the particles from the disk end up in the oil. In the case of my Case, this is the engine oil, so changing the oil on schedule becomes more important.

  5. #5
    Veteran Member
    Join Date
    Jul 2000
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    1,344
    Location
    West Virginia (Eastern Panhandle)
    Tractor
    '78 Kubota B6100DT

    Default Re: What is a "wet-type" clutch?

    I've also read the term "wet brakes". Are these descriptions the same for wet brakes?

  6. #6
    Gold Member
    Join Date
    Jun 2000
    Posts
    499
    Location
    Syracuse, New York
    Tractor
    1952 Case DC-4, 2001 JD4300 MFWD, HST

    Default Re: What is a "wet-type" clutch?

    Yup. Same deal for wet brakes.

  7. #7
    New Member
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    Sep 2005
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    Default Re: What is a "wet-type" clutch?

    Michael,
    I tried to describe newer, today type of wet disk clutches.
    When I was describing it, I have in mind power reverser on JCB 3CX backhoe.
    Anyway, thanks.

    A word about wet disk brakes: similar to wet clutch; one or more plates, but, fortunately, no rotary oil pressure feed (if they are hydraulic actuated). Just curiousity for you:
    my Same has wet disk brakes in front axle too [img]/forums/images/graemlins/grin.gif[/img]

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