[Spridgets] 1275 pressure plate question

[David Riker]

You would be right on most cars.  But the throw out bearing on a stock 
A-series car doesn't have a true "throw out bearing".  It has a self 
sacrificing carbon disc. More like a throw out bushing.  It does not spin. 
Each of the parts of the MG clutch system were carefully minimized by bean 
counters to last no longer than 30,000 miles and to be completely worn out 
at almost the exact same time.  I also said constant contact, not constant 
pressure.  The system is self adjusting.  If a spring is added to pull the 
carbon disc away from the mating surface on the pressure plate diaphram, it 
ceases to be self adjusting. A return spring would always pull the throw out 
bearing away from the pressure plate the maximum amount, requiring an 
adjustable push rod be substituted for the non adjustable one, and you would 
have to gradually lengthen the rod as the carbon bushing and friction 
surfaces wear out.
David R.

----- Original Message ----- 
From: "Dave Grandeffo" <davegran at tds.net>
To: <spridgets at autox.team.net>
Sent: Wednesday, May 06, 2009 1:22 PM
Subject: Re: [Spridgets] 1275 pressure plate question


> David Riker wrote:
>> The TO bearing is supposed to be in constant contact with the pressure
>> plate.  Like the pads on disc brakes, there is no spring to pull the
>> throw out bearing away.  It is the diaphram spring itself returning to
>> rest that pushes back on the TO bearing....
>>
>> David R.
> Not to start an argument, but every clutch I've worked on is supposed to
> be set up with a measurable amount of "Free Pedal". This means that the
> first small increment of clutch pedal travel (typically 1/2" -1" or
> thereabouts - check your manual) doesn't move the pressure plate. In
> other words, there should be no tension/pressure on the throwout
> bearing. A lack of free pedal means that the throwout bearing is being
> held against the pressure plate, is spinning constantly, and will have a
> greatly reduced life span. This is the same reason you shouldn't come up
> to a stop sign and stay in gear with the clutch disengaged, no matter
> what they say in driver's ed....
>
> I've never had to replace a throwout bearing on one of my own cars and I
> usually keep 'em for over 200,000 miles before they succumb to the tin
> worm. A throwout bearing is not designed to spin constantly.
>
> -- 
> Dave Grandeffo
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