Morris Minor Owners Club

I am finally getting my modified mog back on the road after a long time in mothballs and have a problem with the front disc brakes dragging. I read somewhere that a minor with marina front discs should have a modification done to the master cylinder. I am guessing this was not done when the discs were fitted. Does anyone know what this mod entails?

dismantle the master cylinder assembly. At the rear of the spring is a dark metal cup and within this a rubber lining. Remove the rubber lining ONLY, then reassemble.

The part to remove looks like a little rubber cup, that you have to fish out of the metal cup. (like Peetee says).

You might want to replace the master cylinder as a matter or course, while you have gone to the trouble to dissassemble everything, it's only £50 ish and it saves doing it all again later.

The rubber part refered to maintains a very low pressure on the brake system. This is only required with drums.

So in theory having discs on the front it is not required, but what about the rear drum brakes?

We have never removed the seal when we have fitted disc brakes and have had no problems.


John

So in theory having discs on the front it is not required, but what about the rear drum brakes?

Ideally, a one-way valve type arrangement as fitted to cars with front discs and rear drums (mini etc), but doing without one does not seem to cause any problems.

having the little rubber cup present does cause a slight binding effect on the discs which is why all Moggy centres that sell the conversions tell you to remove the part, which removes the problem!

Logically, John, if you have never removed the seal, then you must have slight pressure present. Either you have not noticed it or the seal was duff to start with.

or the seal was duff to start with

The last MS I took apart had a duff seal - the cup seal was OK but the washer it sits against was rolled so it was bypassing. That explianed why, with a spongy braking system (due to another fault), pumping the brakes did not help.
The faulty assembly looked like the original factory item :-S

The valve is a major assistance on a car where the shoes need to be adjusted or there is air in the brakes as you can pump the system up. I would not see the need for it on a disk braked car if it is well serviced (especially with a remote reservoir so you can check fluid levels regularly).

Still - if you remove it you may find out it was just sticky calipers in the first place :-S

Ok,lets chew this over. I have fitted a Servo to DRUM
brakes. I did not remove the 'residual pressure valve'
as I reasoned that,as I still have drums, the pressure
was still 'as designed'. This seems logical to me UNLESS
a Servo unit also applies some sort of pressure,in the
unoperated condition, to the
shoes when fitted???? However, my brakes will not
release unless I undo a bleed nipple to ease the pressure.
Obviously I will check the Master Cylinder for a blocked
return hole etc but do you think I should remove the
'cup' while I am at it? I have no intention of fitting disc
brakes.

If I was you, Willie, I would leave the cup in place, as it would seem necessary for the correct functioning of the drum braking system.

It does sound like you may have a fault in the system if your brakes are not releasing properly.......

We agree on that Cam. I thought i would follow my own
advice and 'think simple' so found that the rears do not
stick on only the fronts!! I then removed the Servo vacuum
pipe....no difference though,of course,the fluid is still passing
through the Servo. The two return holes in the Master are
clear(checked in situ with a long needle) so I reckon the
problem must be in the only section of pipe which would
prevent BOTH front brake assemblies from easing off...
i.e. the pipe from the Master Cylinder to the Servo. I intend
to fit the original pipe from the Master to the 3way(brake
switch)junction and see what happens.

Willie I assume that you have checked that the front flexible pipes have not deteriorated and have suffered from a partial internal collapse

Kevin, Yes, I have tried unscrewing brake unions all along the
pipe lines and all of them allow the stuck open wheel cylinders
to relax(proving an uninterrupted fluid flow exists) right back to
the front pipe take off from the Master cylinder! Since I have
re-fitted the original factory piping (thus eliminating the Servo) and
the rear brakes operate but do NOT stick,where the fronts DO
stick I can only deduce that there is a blockage in the banjo union
on the Master which allows fluid to pump out but restricts the rate
of return to the reservoir?? OR there is a problem with the front
wheel cylinders themselves(since,even with brake unions undone
the wheel cylinders STILL do not return to rest completely unless
I push the brake shoes back). This would suggest that the flexies
could be the problem except that even if I undo the bleed nipples at the front hubs the cylinders do not return completely without
help!! I cannot prise out the slave rubbers until the new ones
arrive so I am awaiting the new parts before I dive in.

Well Willie as you say until you take the front cylinders apart you cannot rule them out, it might be a partial rubber collapse although I would have thought that both sides at the same time would be unusual, also if the internal ones have gone home the outers will not look too good either and I think you would have already spotted that.

Willie
I have found this problem with faulty front cylinders before. Hope that helps at all
Regards
Ben

Thanks Ben, I will post the reason for this fault when I have
found it to help others in the future

reference the front brakes sticking 'on' while the rears were
ok. The problem was with the front slave cylinder rubbers,
all four of them!!! swollen enough to prevent complete
return to rest. I didn't believe that all four could give
trouble at the same time but replacement has cured the
problem. In retrospect the clue was that I had a very
hard brake pedal(because the shoes were in contact
with the drum at all times),and,undoing the bleed nipple
on the backplate allowed the pistons to relax but NOT
completely without a push.

If all the cylinders/rubbers were renewed at the same time in the past I suppose it's quite possible that they'd all fail at the same time. Assuming deterioration at a similar rate. What brake fluid do you use Willie?
I've heard varying reports about silicone fluid attacking the system but used it without problems in both my Minors.

How long had they been in the car Willie, this is similar to what can happen to when a Moggie is not used for some time ( I know this does not apply as you use yours regularly ) and the brakes jam on, I just wondered if the cause is the same ?

I use Halfords DOT 4 fluid, the front wheel cylinders were all
fitted new at the same time and,I am ashamed to say,after
checking my records,that they wwere installed NINE YEARS
AGO!! Doesn't time fly when you are enjoying yourself!!
Learn from my mistake.

Ah well they've done quite well then. What about the rears?
Other than dismantling components i.e. wheel cylinders for inspection, which I suppose shouldn't really be recommended when everything is working, there's no way of predicting a problem until something doesn't quite work properly. Can't remember if component inspection is specified at any service interval, don't recall seeing anything. Which may of course, if allowed to continue, prove disastrous.

Willie that`s not bad then nine years old and only needed new rubbers