I had a roller throwout bearing in my '70 B back in the 1980's -
1990's. Put in new clutch parts when I rebuilt the engine. That B was
my daily driver for 5 yrs or so until I sold it; had no problems with it
during that time. My current '69 B has the stock clutch parts including
the graphite throwout bearing (bushing). All that went in in 1999 when
I rebuilt the engine and installed an OD tranny.  Around 25K miles on
the car since then, no problems with the drive train.  The worst
beating the clutch components had to take was when I and the B got
volunteered into a small-town parade. (Ah, the irony; a British car in
an Independence Day parade.)Â I thought I'd stick her in first gear and
idle along. Not! It was like being in stop and go traffic for an
hour. I figure I took several years off the release bearing in that hour.
CR
On 8/20/2019 2:49 AM, PaulHunt73 via Mgs wrote:
> It's a bit of a minefield with many variables.
>
> A graphite release bearing _should_ last the life of the clutch
> friction plate, apart from my roadster described below I've never had
> one fail, the clutch has started slipping from friction plate wear
> before that. But if the main driver rides the clutch and sits at
> traffic lights with the pedal down then its life will be reduced.
>
> A few years ago someone started making them with the graphite ring
> pinned into the casting instead of being glued and they tended to
> explode in a short time. Hopefully they will be out of circulation now.
>
> Suppliers want you to buy roller bearing release bearings at extra
> expense (clutch kits normally come with the graphite type) but they
> have their own problems. John Twist describes how they aren't the
> complete answer by demonstrating how they move in an arc as the pedal
> is operated and released, so sliding across the face of the release
> ring on the cover plate, which causes excessive wear. Graphite
> bearings are designed to cope with that, roller bearings aren't.Â
> Whilst what he says is true the arc they actually move in use is very
> limited, the real problem is there is nothing to centralise the
> bearing to the cover plate in the first place. Depending on how far
> your release arm is off-centre - and I found mine a good 3/16" - as
> well as sliding back an fore all the time the load will be on one side
> significantly more than the other, something else they are not
> designed for http://www.mgb-stuff.org.uk/clutchr3a.htm#5Â ; I've been
> told by someone who has worked on these cars for decades that "They
> are all like that". Proponents say all modern cars have roller
> bearings so they must be good, so does the MGB GT V8 and the Midget
> 1500, and they don't fail. But that is because they have a guide tube
> over the first-motion shaft to keep the bearing centralised to the
> cover plate.
>
> On the roadster I've had a graphite bearing break up because the
> casting wore through on one side, and a roller bearing get destroyed
> when the friction plate was barely half worn. At that point I noticed
> how off-centre the release arm was, so brought it back into line. The
> most immediate effect is the biting point is now much higher than it
> has ever been - almost too high. It was always lower than my other
> cars before and extending the 'throw' of the hydraulics made little
> difference. I'm sure that is because before it was pushing one side
> of the pressure plate down less than the other side because of the
> offset. There is a graphite bearing in now, time will tell.
>
> As for the gunge, that is normal as the flex hose ages. That will
> have no effect on release bearing wear.
>
> PaulH.
>
> ----- Original Message ----- I have a 71 MGB and Iâ??m wondering how
> many miles people are getting from the carbon release bearing.
>
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