443
Replacement
clutch master cylinder on an MGBGTV8
David
Brown, with a rubber bumpered V8 Roadster Conversion carried
out by David Franklin using a late 1980 MGB with a five speed
gearbox, posted a query on fitting a replacement clutch master
cylinder. (Mar 12)
David Brown said"having replaced the clutch slave
cylinder, I set about replacing the clutch master cylinder too
with part number GMC 1011 (plastic reservoir type). But I've
found the plastic cap can't be undone as the cap fits under
the pedal box recess on the bulkhead with insufficient clearance.
I have stripped out that replacement unit and put back the old
master cylinder. What do I need to do to make the replacement
and what part number do I need? The clutch pedal was pretty
heavy compared to the Factory MGBGTV8 we have but this has always
been the case with this car.
Bleeding the clutch proved an issue too; what's the best way
to bleed the clutch hydraulics and are there any good devices
to help - my old Eezibleed must have had it as it was by no
means easy! The system on my car has a braided hose between
master and slave cylinders. Any advice will be gratefully received
as three hours were spent getting nowhere this afternoon other
than flushing all the muck from the master cylinder. It feels
like a wasted afternoon and management feels my time should
have been deployed on the garden!
Geoff King, with a V8 Roadster built on a Heritage shell,
responded saying "you are not the first to discover that
GMC 1011 with the plastic reservoir doesn't fit but it can be
made to fit by removing the reservoir from the master cylinder
and refitting it the other way round.
Bleeding the clutch system should be easy with the Eezibleed,
just connect it to the bleed nipple and bleed from the bottom
up. Obviously stop the flow when the master cylinder reservoir
is almost full." In
a subsequent posting Geoff King highlighted the Leacy Classics
at Perry Bar Birmingham have a GMC 1011 (metal reservoir type)
on their website: www.leacyclassics.com/gmc1011.html
GMC 1011 V8 clutch master cylinder for an MGBGTV8 (1973-76)
is shown on offer from Leacy Classics Clive
Wheatley noted "the hard clutch pedal problem could be
the wrong clutch flexi pipe which could have the wrong internal
diameter - like brake flexi. We have the correct flexi pipe
in stock priced at £24.71 plus VAT. Also make sure your
clutch slave cylinder is the correct way up with the bleed nipple
at the top."
Mike
Howlett added "I have fitted the plastic reservoir
clutch master cylinder by turning around the reservoir. It isn't
too difficult but does need a little ingenuity to make it work.
I have a couple of photos I can email to illustrate the change."
The photos Mike provided are included in this note. Mike then
added "I bought GMC 1011 from a well-known supplier and
when I found it didn't fit, I contacted them and they were completely
unhelpful saying they had never come across this before. There
seemed to be no alternative but to swap the reservoir round,
so that's what I did. I have had three year's use so far with
no problem."
We contacted
Ron Gammons at Brown & Gammons to see if they had
come across this problem with the new plastic replacement V8
clutch master cylinders and he replied "there is a slight
problem in that the GMC 1011unit is currently on back order
here so I cannot |
Back
to homepage
Diagram of the MGB pedal box and clutch master cylinder (MGB
Workshop Manual, page E6 AKD3259)
inspect a unit and check it for the difficulty David
has experienced. That V8 unit has a bore of 0.7" whereas
the MGB one (part number GMC 1007) has a bore of 0.75"
The GMC 1007 is still available with a metal case at present.
The smaller bore of the V8 unit is to reduce the pedal load
of the heavier V8 clutch. When we get in new stock I will inspect
the GMC 1011 and advise. In the meantime if you want to use
the image by all means go ahead. As for the adjustment described
to get the unit to fit, we believe that the GMC 1011 replacement
units we have had previously have had smaller plastic caps,
because we have not experienced the problem. It's possibly a
result of standardisation. If members want we can arrange for
the original clutch master cylinder to be sleeved and re-rubbered
which would help preserve the originality. I suppose that we
could sleeve the new 1007 as well but that would be rather expensive!"
Mike Howlett later highlighted what may well be an explanation
for the difficulty experienced by David Brown by saying "from
memory, and from looking at my photo of my pedal box (see below)
I think it was more than the cap size that prevented me from
using the replacement clutch master cylinder without modification.
I really wonder if it is only a problem with the very late MGB
pedal box which I used and I believe David is also using. The
Factory MGBGTV8s used single line brakes with remote servo didn't
they? If so, the pedal box is quite different (see the diagram
below reproduced from the workshop manual) to the later one
designed for the in-line brake servo and dual circuit master
cylinder. Have a look at my photo and see what you think."
Barrie Jones mentioned his way of bleeding the system
- "I find it best to remove the two bolts holding the clutch
slave cylinder to the bellhousing, pull the pushrod out of the
gaiter, and allow the cylinder to dangle downwards on its flexible
hose. Then I use a blunt Philips screwdriver to push the piston
of the slave cylinder upwards two or three times. This forces
the fluid up the pipe (including any bubbles of air). The bubbles
exit the system via the master cylinder, so it may need topping
up afterwards. No special tools, no bleeding, job done."
Footnote: GMC 1011 replacement V8 clutch master cylinders
- B&G
website
See our illustrated note online. More |
