Morris Minor Owners Club

Hi

I've got marina calipers that will eventially go on my mog - the discs and hub are on after much messing about.

I've read that you need to modify the master cylinder.

I can't really see why (which is why I'm asking!!) there needs to be a mod as the old wheel cylinders move back by the springs, calipers are pushed back by play in the discs and the master cylinder pushes fluid to the wheels and the fluid is pushed back from the wheels through the valve in the master cylinder. Please correct me if I'm wrong.

Can someone explain why? first why any mod at all and why the mog master cylinder works different to any other, eg, MGB! (oh and what the mod is).

cheers

Keith

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Our Mog restoration
http://www.1000fluffyclouds.co.uk/OurPr ... logger.php

I've no idea why the Minor master cylinder is designed as it is - the idea is that it retains a small pressure (~8psi I believe) which holds the cylinders and shoes up near the drums - so you have a nice short pedal without need for regular adjustments. If you don't modify the master cylinder you will find the discs dragging all the time - slowing the car and wearing out the pads! It involves removing the master cylinder, stripping out the seals and throwing away the little 'top hat' seal - then re-install the master cylinder. Of course - it would seem wise to fit a complete new set of seals in the master when doing the job - but, it's generally considered unwise to fit new seals to an old master - because the unused portion of the bore tends to rust - and fitting new seals involves dragging the seals over the rusted section, and destroying them. So really - a new master cylinder is the better answer - and take the 'top hat' seal out of that before installation!
Of course - you will probably find the discs far too heavy on the road and then you will want a servo - which involves re-piping to the rear brakes because they are normally fed directly from the back of the master cylinder. Oh and of course with discs - you should really fit a remote fluid reservoir because the pads as they wear take quite a lot of fluid away from the master cylinder - and under the floor it's not too obvious.

It's no surprise some us fit a much simpler and very possibly better braking system to the front of our Minors. It's certainly much much easier to install and much less expensive to buy.

is there anything to add?? i think youve got it covered fully there bmcecosse

I could go on about what a dreadful job it is to remove the master cylinder etc but I would only get pelted with bricks (again)!

Thanks for the info.

Sounds really odd for the master cylinder to retain some presure as the brake shoes sit on their little adjuster cam. I guess they sit back after a short time when the pressure leaks past the master cylinder.

I have a new master cylinder - the top hat seal is the one on the end of the spring isn't it? rather than removing it has anyone just made a hole in it - I am wondering if it plays any part in stopping the spring and the odd shapped washer touching the bores.

Thanks for the help - I probably wouldn't have fitted these it was just that I had the bits already. I've retained all the original bits as I never had any complaints with the brakes - they lock up quite easily - although I do remember once going down some very long hill somewhere in the west country and the brakes fading into insignificance - I had to repeatedly do 5 or so seconds off the brakes then slam my foot down - scary stuff.

I'm now going to try and get seal sealer off my hands - very messy stuff but at least I know it stays put !!

cheers

Keith

I suppose a hole should do it - but i'm no expert at that job - someone else will be along in a minute I'm sure!

A 1/16 hole is all that is required, but its not the easiest thing to do sucessfully. Removing the seal totally was deemed to make bleeding more difficult, but I have yet to experience any issues.

mine bleed prefectly, no issues at all. whats the point in having a 1/16 hole in it, the master cylinder will push and fluid through anyway meaning that the cup was useless. simplier just to remove it alltogether

Well, a technical question was asked and given. Apparently a 1/16 hole is required, but as I said in my post simply removing the seal is a more common approach, but some have had bleeding issues. I'm not going to argue the point, just giving info.

Thanks for the info.

My point of enquiring for making a hole rather than removing it was that maybe the seal is also providing location for the end of the spring thus stopping it from touching the cylinder bore. When I take it apart I should be able to see but its reassuring that someone else has thought the same.

Cheers

Keith

Hi,

Sorry if I'm going over old ground, but can I check exactly which seal is the "top hat" one?
I'm looking at the diagram of the brake master cylinder on page 122 of the Haynes manual. Are we talking about the "valve cup" which is normally fitted inside the "valve body"? Is it this valve cup which needs to be removed?

Thanks,
Ed.

Sorry - no idea. This is not a conversion I recommend at all - must be difficult to explain to your insurance co that you removed a seal from your brake master cylinder...........

bmcecosse wrote:Sorry - no idea. This is not a conversion I recommend at all - must be difficult to explain to your insurance co that you removed a seal from your brake master cylinder...........

Watch out for those flying bricks

[quote="bmcecosse

It's no surprise some us fit a much simpler and very possibly better braking system to the front of our Minors. It's certainly much much easier to install and much less expensive to buy.[/quote]

What could he possibly be referring to? I am going to have a little walk outside in the countryside and see if I can, by quiet reflection and pondering, fathom the meaning of this.

Thick freezing fog up here matey - advise quiet pondering by the fireside - with a glass of something warming in your hand!

cormorant wrote:[quote="bmcecosse

What could he possibly be referring to? I am going to have a little walk outside in the countryside and see if I can, by quiet reflection and pondering, fathom the meaning of this.

if you are going for a walk in this weather I think a "woolseley" jumper might help you

It's not a seal that is removed, it is a 'residual pressure valve'. It was fitted to retain a low pressure to 'keep the cups of the wheel cylinders expanded' (Ref BMC Minor Workshop Manual). The pressure is not enough to move the cylinders against the brake shoe return springs.

Since the front wheel cylinders are to be replaced, which is where the cups are fiited, removing the valve is not detrimental to the operation at all.

With disc brakes, it is quite the opposite, there are no return springs, the piston is retracted by the seal itself which distorts slightly as the piston moves out. When the pressure is released the seal regains its shape, and drags the piston back into the caliper. The movement is very small, and will not necessarily be the same amount on 'return' as it was on 'pressure', which is how they are self-adjusting and give a 'good pedal'.

Leaving the valve in place is very likely to maintain the pads against the disc and create heat and wear - just ask our local tyre fitter a few months after I had completed the restoration and had forgotten to remove the valve from the new master cylinder. I wanted the front wheels balanced, so he removed the first wheel nut with the windy gun, and promptly burnt his fingers when removing it from the socket - oops!!

No such problem after removing the valve.

It does however keep a 'short' pedal if/when the brakes are needing adjusted. First push of the morning can be very long - as the cylinders travel outwards - and the subsequent pushes are much less as the cylinders are held out slightly and the shoes are close to the drums. It's a warning sign to adjust up the brakes! Can also see it in action if you squeeze the brake pedal with a drum off. The cylinders move out, and retract only slightly when pedal is released - but retract further if a bleed nipple is then opened allowing a small 'squirt' of fluid - and the residual pressure releases. It's how the 'gravity bleeding' gets started! And yes - the valve has to be removed if using disc brakes. I guess the rear cylinders just get on ok without the residual pressure!

ET_in_black wrote:Hi,

Sorry if I'm going over old ground, but can I check exactly which seal is the "top hat" one?
I'm looking at the diagram of the brake master cylinder on page 122 of the Haynes manual. Are we talking about the "valve cup" which is normally fitted inside the "valve body"? Is it this valve cup which needs to be removed?

Thanks,
Ed.

to get back on track yes it is the valve cup that needs removing