Well this is a very good time for this thread. About 2 weeks ago my B
started having some vibration when ever the clutch was pushed in. Deciding
it was time to get it home I took off and the next gear change the clutch
went to the floor, major grinding sounds, and smoke coming out from under
the car. I was able to place the car in 1st to get going w/out using the
clutch and then high speed shifted it to 3rd and ran in 3rd o/d to get it
home (no slippage in the clutch when I accelerated. Engine was running
fine). I will be pulling the engine in about 2 weeks after I move into my
new house to see what happened. This is a Roller T.O. Bearing that was
replaced in 1995. If this was the cause then looks like it will be back to
the stock T.O. bearing. Hard to say but it has only been 4 years and under
15K miles.
Has anyone had this same thing happen?
Don Collins
70B
70BGT
-----Original Message-----
From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net]On
Behalf Of James H. Nazarian
Sent: Wednesday, October 20, 1999 5:26 PM
To: Max Heim
Cc: MG Listserver
Subject: Re: Roller Throwout Bearing
Maybe that explains why the roller bearings sometimes work (concentric) and
sometimes don't (eccentric). Good 'splanation Max!
Jim
Max Heim wrote:
> I think someone said the issue was concentricity; i.e. the MGB clutch arm
> is not designed in such a way as to perfectly center the throwout bearing
> on the axis of rotation, every time. For the "friction" type of bearing,
> this doesn't really make any difference, which explains the
> "shortcomings" of the original design in this context. But the roller
> bearing assumes concentricity of rotation.
>
> Think about it. If the axis of rotation of the roller bearing, when
> applied, doesn't precisely match the center of rotation of the clutch
> disc, you get an effect like a tiny bicycle crank. This would cause
> vibration, and enormous side stresses on the bearing, which it might not
> be designed to support for long.
>
> Of course, if your clutch arm components and bushings were all new, you
> might have something close to concentricity, and thus enjoy reasonably
> long roller bearing life (as many have reported). But if your clutch arm
> was anything like mine (when I last replaced my clutch), with worn-out
> bushings and pins and ovaled-out holes, no two clutch pedal applications
> would result in the same alignment, and you'd probably experience
> catastrophic or premature failure (as has also been reported).
>
> Anyway, I think that is a plausible explanation of both sides of this
> situation...
>
> James H. Nazarian had this to say:
>
> >Chris,
> >
> >I quote British Automotive:
> >
> > "Before you consider installing aftermarket ball/race type throw out
> >bearings,
> > be sure to read the following information. If you have already
installed
> >this type
> > of bearing, it is doomed to failure. Presently there are two styles
of
> >ball/race
> > type bearings available:
> >
> > 1.- A black plastic housing type
> > 2.- A steel housing type
> >
> > Both of these types of bearings suffer from premature "run-dry"
> >conditions
> >and
> > their failure is directly related to being in continual contact with
the
> >clutch cover
> > thrust pad. No.1 will self destruct in a very short time; No.2 will
> >survive much
> > longer and failure will not be as catastrophic."
> >
> >Why would a sealed, permanently lubricated roller bearing designed for
> >continuous operation with load applied along the axis of rotation, run
dry?
> >Could it be defective? Or damaged during installation? If so, was it
returned
> >to and examined by the manufacturer? If so, might we see their analysis
or
> >reply? If Doug's right, I've been driving several time bombs for the past
15
> >years. Maybe Doug will share some of his exhaustive test data and methods
> >with
> >us.
> >
> >Before I ask Mr. Moss to fly out to Ohio to help me change all these
heavy
> >duty
> >roller bearings back to the original graphite type, I think I need to see
> >some
> >proof. Thanks in advance for enlightening us.
> >
> >Senior Doubting Thomas
> >
> >AKA Jim
> >1960 MGA
> >1974 MGB-GT
> >and a pool of other octagonal delights
> >
> >Chris Attias wrote:
> >
> >> Peter C. wrote:
> >> "A few quick thoughts. Roller bearing or carbon.... don't "ride" the
> >> clutch. The only time that a clutch can become worn is when your foot
is on
> >> the pedal. If you don't touch the pedal, the clutch wont wear."
> >>
> >> This seems to disagree with what I understood about the design of the
> >> MGB Borg & Beck clutch assembly. See Doug Jackson's write-up on
> >> clutch bearings @ www site:
> >> http://www.mgbmga.com/tech/index.html
> >>
> >> While I realize Doug has some commercial interest in his development
> >> of a fix for the problem he finds with roller bearings, he does
> >> exhaustive research and shares his experimentation and research
> >> freely...(No commercial interest disclaimer...)
> >> Chris Attias
> >> '64 MGB
> >> '84 Alfa Romeo GTV-6
> >
> >
>
> --
>
> Max Heim
> '66 MGB GHN3L76149
> If you're near Mountain View, CA,
> it's the red one with the silver bootlid.
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