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Technical Hydraulic Throw-Out Bearing Questions ?????

Discussion in 'The Hokey Ass Message Board' started by ace high, Mar 27, 2018.

  1. ace high
    Joined: Dec 15, 2007
    Posts: 210

    ace high

    Anybody familiar with Hydraulic Throw-Out Bearings. I have a McLoed Racing throw out bearing in my rod. Early Hemi backed up by Muncie 4spd. Trying to find out if the problem I'm having is something others have run into. The Throw-Out bearing was originally set up with approximately 1/8 inch clearance between the T/O bearing and the pressure plate clutch fingers. (it's a diaphragm type pressure plate.) Well as time went on, the clearance gap closed up and the bearing is constantly against the fingers and is under slight pressure. The problem is that this constant pressure is pushing the crankshaft forward and wearing out the thrust surface on the crankshaft main bearings.

    I've been told that as the clutch "disc" wears, the pressure plate fingers extend backward closing up the clearance gap to the T/O bearing. This doesn't make sense to me. ANY THOUGHTS ?
  2. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,502


    Hydraulic t/o bearings keep constant pressure on the pp. This is why they never need adjusting. Short of putting mechanical linkage on it, I am not sure how to help the bearing wear.

    Sent from my Moto G Play using The H.A.M.B. mobile app
  3. no55mad
    Joined: Dec 15, 2006
    Posts: 1,857


    That's correct, as the disc wears, the clearance goes away. The pressure plate fingers are hinged between the to bearing contact area and the disc. As the disc wears, the fingers move in in that area, and move out at the to bearing which takes up the clearance. Another reason to avoid this set up because you have to pull the tranny for adjustments. My hyd bearing started to leak, common problem. Replaced it with a slave cyl and a fork. If it leaks or needs adjusting, it is much easier to fix!
  4. Happydaze
    Joined: Aug 21, 2009
    Posts: 962


    I've had good experience with a couple of hydraulic bearings, but there's plenty of adverse opinions.

    I suspect your (OP) problem is that you have a 'race' bearing, which I suspect means in it's design / application it will be routinely dismantled and refitted (race meeting / race season?) and as such will not require much in the way of automatic adjustment provision, unlike a fit and forget for 70k miles street application.

    The fingers do indeed move away from the flywheel as the clutch plate wears, but that's been already explained.

    From my experience of a RAM bearing my take on it is this:

    1. the bearing only has so much travel available in it. I don't know whether a 'street' bearing has more travel than a 'race' bearing but I suspect that to be the case. Hopefully someone has both to hand and can confirm?
    2. That available travel has to achieve 2 things - to operate the clutch properly and, over time, to compensate for the clutch plate wear
    3. Both street and race setups will (presumably) need identical travel to operate the (same) clutch, the remaining travel is used later in the wear compensation, experienced as the fingers move away from the flywheel.
    4. if the race version indeed does have less travel when used in longer term application it will soon give the kind of problems the OP has experienced
    5. Similarly, if either is set up incorrectly but the clutch still operates ok there will be an excess of travel available (and unused) in the operation of the clutch and a corresponding reduction in the wear adjustment capacity, so the problem arrives sooner
    6. From what I have seen installation instructions don't expressly mention this, it's all explained in measurements which doesn't really explain what's going on, and, more importantly, why. Maybe it's obvious to some?

    Edit - the 1/8" clearance between the bearing and the fingers is effectively lost, but i am beginning to think that maybe there isn't any / much wear clearance / travel available at all (or that the 1/8" is it)!!
    Last edited: Mar 28, 2018

  5. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,915

    jimmy six

    We use a Ram on a Ram clutch. It's set bu measuring the fingers to the flat of the bellhousing where the trans mounts. We measure out from the trans snout with the bearing on with .100" clearance and never have had a problem.
    I can't believe you have a McCleod that doesn't leak.
  6. I run a Tilton Hydraulic in my 32 with a Ford Top Loader.
    It does NOT keep constant pressure on the diaphragm.
    As per Tilton's instructions, I set it up with approximately .200" Clearance between the bearing and the Pressure Plate - this allows for wear of the disc over time.

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