Subject: Re: [Mgs] [MG-MGB] Clutch problems with thermal component

From: David Councill via Mgs <[email-masked]>
Date: Tue, 8 Nov 2016 08:26:19 -0800

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Paul,

It is a bizarre problem. I was hoping someone might have had similar
problems. Since my last email, I have made two 15 mile drives with the same
very predictable issue. The master remains the primary suspect because the
issue happened after replacing the master cylinder. The slave cylinder was
an aftermarket replacement I put in about 4-5 years ago but the only thing I
have done with it is to drain the brake fluid.

A recap of this morning's typical drive - solid pedal through several gear
shifts through town, started highway drive. During this highway part, I
slightly pressed on the clutch pedal several times on the drive until
resistance was felt to see what was happening After a couple of miles and
coolant temp up to 160F, some slackness and as soon as I got to the next
town where I work, I had almost full travel to the floor. But the one press
of the pedal and it was back to almost normal, next time I shifted, the
pedal was solid again and a routine drive to work through town. It should
now be fine until I start the next highway drive.

(if I was only doing city driving, I wouldn't be having any issues)

The symptoms appear more to be like a seal issue as one to two presses of
the pedal resolves the issue (until next time). However, I have seen
hydraulic leaks before which are slight enough to allow air in/out but not
leak fluid. The seal on the banjo is still the place of primary suspicion so
I'll probably drain the master and then completely redo the connection to
see if I can get a better seal. There is a slight wetness at that connection
but not enough to make for even a minuscule drop of fluid. Also relevant, I
installed a new Lockheed master cylinder as I mentioned. This is part
LM13105, "fits all years 1962-1980". However, sources like Moss list
separate clutch master cylinders for 62-67 and 68-80. From what I can tell,
they are identical with one small difference in how the master cylinder
mounts to the pedal box (how the bolts line up) such that this new master
cylinder does not sit up straight but has a slight tilt clockwise (5-10
degrees). That could be enough that the flare fitting might be damaged or
slightly off on the banjo connection - or at least that is my primary theory
at present. The only problem with that theory is that somehow air would be
getting pulled in under no pressure or vacuum other than that generated by
metal expansion. Hopefully, it is not the master cylinder and its seals at
fault because that involves a lot more work.

Still, I thought about asking the group about master cylinders before I
started - re-sleeve versus new. The costs were about the same so I went with
new. Maybe I should have tried one of those new plastic reservoir
after-market units since this is my almost daily driver. For now, I will
work with the banjo fitting but I may end up trying another master cylinder
if that fails, perhaps take the one out of my 67 BGT which is slated for an
engine overhaul due to worn rings and excessive oil consumption. Either way,
I'll get this figured out sometime in the not too distant future and then
I'll report back.

David Councill

64 MGB

67 MGBGT

72 MGB

From: Mgs [mailto:[email-masked]] On Behalf Of PaulHunt73 via
Mgs
Sent: Tuesday, November 08, 2016 12:52 AM
To: [email-masked]; [email-masked]
Cc: [email-masked]
Subject: Re: [Mgs] [MG-MGB] Clutch problems wuth thermal component

"pedal goes almost to the floor with no resistance but enough to still work"

Expand?  If the biting point is very low when this happens, then either the
pressure seal is not sealing when it should be, or there is air in the
system.  If the biting point remains 'normal' then it's a purely mechanical
issue, possibly pivots binding with heat expansion.

If the banjo union at the master is wet then that does imply a leak, which
may or may not let in air, and further tightening may not seal it.  Also if
it's wet it implies fluid loss, which should eventually become visible from
the level in the master.  But that may take some time, and it will be
affected by fluid expansion and contraction with heat/cool cycles.

If there is air getting in, then I can see that this becomes apparent on
flooring the pedal, which will tend to push the air down while compressing
it.  But it will float to the top of the pipe while the pedal is down, then
when the pedal is released it will be flushed out of the system into the
reservoir.  That is one of the many techniques that may be needed to get
full travel of the clutch slave after working on the hydraulics.  The
effects of incomplete bleeding i.e. air remaining in the system would
normally be apparent on every pedal operation.

However that begs the question of how the air is getting in in the first
place.  The fluid is either under no pressure at all (pedal released), or
under pressure (anywhere beyond where the master piston seal closes off the
bypass hole to the reservoir).  If air was getting with the pedal released
then it would be apparent on the first operation no matter what the
temperature was, and more than once on each drive.  And the pressure while
the pedal was anywhere in its disengagement portion should stop air getting
in, even on the upwards stroke, as it is the cover plate that is pushing
back on the slave piston and hence the fluid, which is the main factor in
returning the master piston and hence the pedal.

The other possibility is that something is causing the slave piston to be
pushed back into the cylinder while you are driving, pushing fluid that
should normally be in the system back into the reservoir, and creating
lost-motion at the release arm.  This has to be taken up before you can
start to disengage the clutch, so reducing pedal back-pressure and lowering
the biting point.

But I can't really see how that could suddenly start happening with the new
master, so the new master (subject to getting a proper seal on the banjo)
has to be the prime suspect.

PaulH.

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class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>Paul,<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>It is a bizarre problem. I was hoping someone might have had similar =
problems. Since my last email, I have made two 15 mile drives with the =
same very predictable issue. The master remains the primary suspect =
because the issue happened after replacing the master cylinder. The =
slave cylinder was an aftermarket replacement I put in about 4-5 years =
ago but the only thing I have done with it is to drain the brake =
fluid.<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>A recap of this morning&#8217;s typical drive &#8211; solid pedal =
through several gear shifts through town, started highway drive. During =
this highway part, I slightly pressed on the clutch pedal several times =
on the drive until resistance was felt to see what was happening After a =
couple of miles and coolant temp up to 160F, some slackness and as soon =
as I got to the next town where I work, I had almost full travel to the =
floor. But the one press of the pedal and it was back to almost normal, =
next time I shifted, the pedal was solid again and a routine drive to =
work through town. It should now be fine until I start the next highway =
drive.<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'> (if I was only doing city driving, I wouldn&#8217;t be having any =
issues)<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>The symptoms appear more to be like a seal issue as one to two =
presses of the pedal resolves the issue (until next time). However, I =
have seen hydraulic leaks before which are slight enough to allow air =
in/out but not leak fluid. The seal on the banjo is still the place of =
primary suspicion so I&#8217;ll probably drain the master and then =
completely redo the connection to see if I can get a better seal. There =
is a slight wetness at that connection but not enough to make for even a =
minuscule drop of fluid. Also relevant, I installed a new Lockheed =
master cylinder as I mentioned. This is part LM13105, &#8220;fits all =
years 1962-1980&#8221;. However, sources like Moss list separate clutch =
master cylinders for 62-67 and 68-80. From what I can tell, they are =
identical with one small difference in how the master cylinder mounts to =
the pedal box (how the bolts line up) such that this new master cylinder =
does not sit up straight but has a slight tilt clockwise (5-10 degrees). =
That could be enough that the flare fitting might be damaged or slightly =
off on the banjo connection &#8211; or at least that is my primary =
theory at present. The only problem with that theory is that somehow air =
would be getting pulled in under no pressure or vacuum other than that =
generated by metal expansion. Hopefully, it is not the master cylinder =
and its seals at fault because that involves a lot more =
work.<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>Still, I thought about asking the group about master cylinders before =
I started &#8211; re-sleeve versus new. The costs were about the same so =
I went with new. Maybe I should have tried one of those new plastic =
reservoir after-market units since this is my almost daily driver. For =
now, I will work with the banjo fitting but I may end up trying another =
master cylinder if that fails, perhaps take the one out of my 67 BGT =
which is slated for an engine overhaul due to worn rings and excessive =
oil consumption. Either way, I&#8217;ll get this figured out sometime in =
the not too distant future and then I&#8217;ll report =
back.<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>David Councill<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>64 MGB<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>67 MGBGT<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>72 MGB<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p>&nbsp;</o:p></span></p><div><div =
style=3D'border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in =
0in 0in'><p class=3DMsoNormal><b><span =
style=3D'font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span>=
</b><span style=3D'font-size:10.0pt;font-family:"Tahoma","sans-serif"'> =
Mgs [mailto:[email-masked]] <b>On Behalf Of </b>PaulHunt73 =
via Mgs<br><b>Sent:</b> Tuesday, November 08, 2016 12:52 =
AM<br><b>To:</b> [email-masked]; =
[email-masked]<br><b>Cc:</b> =
[email-masked]<br><b>Subject:</b> Re: [Mgs] [MG-MGB] Clutch =
problems wuth thermal component<o:p></o:p></span></p></div></div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p><div><p class=3DMsoNormal><span =
style=3D'font-size:10.0pt'>&quot;</span>pedal goes almost to the floor =
with no resistance but enough to still =
work&quot;<o:p></o:p></p></div><div><p =
class=3DMsoNormal>&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><span style=3D'font-size:10.0pt'>Expand?&nbsp; If the =
biting point&nbsp;is very low when this happens, then either the =
pressure seal is not sealing when it should be, or there is air in the =
system.&nbsp; If the biting point remains 'normal' then it's a purely =
mechanical issue, possibly pivots binding with heat =
expansion.</span><o:p></o:p></p></div><div><p =
class=3DMsoNormal>&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><span style=3D'font-size:10.0pt'>If the banjo union at =
the master is wet then that does imply a leak, which may or may not let =
in air, and further tightening may not seal it.&nbsp; Also if it's wet =
it implies fluid loss, which should eventually become visible from the =
level in the master.&nbsp; But that may take&nbsp;some time, and it will =
be affected by fluid expansion and contraction with heat/cool =
cycles.</span><o:p></o:p></p></div><div><p =
class=3DMsoNormal>&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><span style=3D'font-size:10.0pt'>If there is air =
getting in, then I can see that this becomes apparent on flooring the =
pedal, which will tend to push the air down while compressing it.&nbsp; =
But it will float to the top of the pipe while the pedal is down, then =
when the pedal is released it will be flushed out of the system into the =
reservoir.&nbsp; That is one of the many techniques that may be needed =
to get full travel of the clutch slave after working on the =
hydraulics.&nbsp;&nbsp;The effects&nbsp;of incomplete bleeding i.e. air =
remaining in the system would normally be apparent on every pedal =
operation.</span><o:p></o:p></p></div><div><p =
class=3DMsoNormal>&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><span style=3D'font-size:10.0pt'>However that begs the =
question of how the air is getting in in the first place.&nbsp; The =
fluid is either under no pressure at all (pedal released), or under =
pressure (anywhere beyond where the master piston seal closes off the =
bypass hole to the reservoir).&nbsp; If air was getting with the pedal =
released then it would be apparent on the first operation no matter what =
the temperature was, and more than once on each drive.&nbsp; And the =
pressure while the pedal was anywhere in its disengagement portion =
should stop air getting in, even on the upwards stroke, as it is the =
cover plate that is pushing back on the slave piston and hence the =
fluid, which is the main factor in returning the master piston and hence =
the pedal.</span><o:p></o:p></p></div><div><p =
class=3DMsoNormal>&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><span style=3D'font-size:10.0pt'>The other possibility =
is that something is causing the slave piston to be pushed back into the =
cylinder while you are driving, pushing fluid that should normally be in =
the system back into the reservoir, and creating lost-motion at the =
release arm.&nbsp; This has to be taken up before you can start to =
disengage the clutch, so reducing pedal back-pressure and lowering the =
biting point.</span><o:p></o:p></p></div><div><p =
class=3DMsoNormal>&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><span style=3D'font-size:10.0pt'>But I can't really =
see how that could suddenly start happening with the new master, so the =
new master (subject to getting a proper seal on the banjo) has to be the =
prime suspect.</span><o:p></o:p></p></div><div><p =
class=3DMsoNormal>&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><span =
style=3D'font-size:10.0pt'>PaulH.</span><o:p></o:p></p></div><div><p =
class=3DMsoNormal><span =
style=3D'color:#1F497D'><o:p>&nbsp;</o:p></span></p></div><blockquote =
style=3D'border:none;border-left:solid black 1.5pt;padding:0in 0in 0in =
4.0pt;margin-left:3.75pt;margin-top:5.0pt;margin-right:0in;margin-bottom:=
5.0pt'><div><p class=3DMsoNormal style=3D'background:#E4E4E4'><span =
style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p>&nbsp;</=
o:p></span></p></div></blockquote></div></body></html>
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