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help needed with brake master cylinder assembly
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Author:  richarde [ Sat Aug 05, 2006 8:07 pm ]
Post subject:  help needed with brake master cylinder assembly
I pulled the brake master cylinder out of my clubby today to overhaul it and found that one of the seals in the overhaul kit is different to the one in the master cylinder. The brake master cylinder bore is 0.7" and i bought the kit for this size master cylinder. It is a single circuit master cylinder with a plastic reservoir. The car is a '76 and apparently they had 0.75" bore master cylinders, so it must have been swapped at some point.

Does anyone have an exploded diagram of the master cylinder, or photos? i have a manual but it doesn't include this diagram. I have a couple of other master cylinders lying around but they will take a while to get apart because they badly rusted. :x

There also appears to be a one-way valve in the master cylinder, at the top, where the brake hose comes out. Does anyone know why this is there? I can't see any reason to have a one-way valve in here and if it is a one-way valve then it would mean that the brakes would not come off after braking.
Author:  feralsprint [ Sat Aug 05, 2006 8:26 pm ]
Post subject: 
The one way valve is fitted to cars with drum brakes as they use mechanical springs to retract the shoes when the pedal is released, without the one way valve the springs will pull the shoes so far back you would have to pump the peddle before you had any pedal next application, if your car has disc brakes the valve must be removed or the brakes will bind on

Jon
Author:  richarde [ Sat Aug 05, 2006 8:32 pm ]
Post subject: 
my mini has brake drums all round. If you have drum brakes adjusted correctly then this shouldn't be an issue should it? Doesn't the adjuster on drum brakes change the stopping point of the shoes so that they stay closer to the drums? Then you can apply the brakes and won't have to pump them to get them to work.
Author:  TheMiniMan [ Sat Aug 05, 2006 8:51 pm ]
Post subject: 
WHoOAaaa there!!!!!!!!!!!!!

Please,,,,, what ever you do,,,,whenever you are "Re-Kitting" brake master cyls in minis,,,please make sure that you """DO""" re-fit a "Slow return valve" (what has just been called a "One Way Valve")

whether you have front discs or drums!!!!!!!!!!!!!

It`s needed to be there & for good reason,""" DON~T leave it out"""

A "Clutch" master cyl doesn`t need it & is also very bad if you do fit it into a clutch master cyl

If you have the wrong kit for the cyl then get the right one

When fitting---> from top to bottom---> Valve first, then spring, then a little plastic seat for the spring , then cup type seal, then thin brass washer, then piston with the other seal fitted widest end of seal upwards just like the cup type seal.

ok?
Author:  richarde [ Sat Aug 05, 2006 9:04 pm ]
Post subject: 
I was considering putting it back together without the "slow return valve" because i thought it was a one way valve. decided i better check first and i was going to see if i could get one of the rusted master cylinders apart first and check if they had the valve. What happens if you put it back together without the valve?

I understand the fitting procedure/order (kept the parts in order when i took it apart :) ) , but i found that there was another rubber seal jammed in the very top of the my master cylinder. This seal has gone all hard and it deformed, so it is no good any more, but is there meant to be a seal in here? Are there meant to be any seals up near the top end of the spring and valve? I have three seals from the overhaul kit, and can't work out where the third one goes. Unless it is just a red herring :)
Author:  TheMiniMan [ Sat Aug 05, 2006 9:50 pm ]
Post subject: 
Ok,,,some "slow return valves" come as (what looks like) a black seal type thingy

others come as a white-ish colour plastic thing with 3 legs (sort of thing)

If---Maybe--- someone left an old type rubber return valve in the cyl when they last (tried to) overhaul it, then maybe that`s all it is

& you may have bought a repair kit with a new one of these (old type) valves in it

Maybe,,, by the sounds of it all,,, hard to know for sure unless i actually see what you have there,,, but i`m hopin gthat i`ve guessed it pretty right :-)

& if you don`t fit the valve then ypou won`t ever be able to pump up a pedal,,,that would mean that """IF""" you left your brakes wear quite a bit & didn`t bother to adjust them for ages, making it go to the floor for the first pump type of thing---> then you won`t be able to pump it up to get that pedal to actually stop you anymore

& there`s other reasons, but that`s a dam good one to start with hey?

:-)
Author:  richarde [ Sat Aug 05, 2006 10:17 pm ]
Post subject: 
Thanks for the help. I can see why i need the "slow return valve" now :)

In my Mini manual (Haynes, covers Minis from '69 - '01) it shows an exploded diagram for the tim can master cylinder type (not the same as mine) and this doesn't have a "slow return valve".

The damaged seal that i got out of the top end of the cylinder can't be a "slow return valve" because it has a hole through the centre - it is almost the same as the seal that fits over the piston.

The spare seal i have has a small hole through the centre of it and doesn't seal against the bore of the master cylinder because it has gaps to allow fluid through. it also fits into the end of the spring where the "slow return valve" is/was. Maybe this seal is supposed to be fitted in the place of the "slow return vlave" if the car has disc brakes?

the "slow return valve" that i have is a small metal cup that fits inside the end of the spring and has eight small holes through the bottom. in the inside of the cup there is a small piece of rubber, kind of like and o-ring which sits over the holes, to make it hard for fluid to flow back through the holes.

I have a feeling that there is meant to be a seal near the top of the cylinder because if there isn't then the fluid does not have to flow through the valve - unless there is supposed to be some leakage around the valve and this is how the fluid gets back into the master cylinder?

I can post some photos if that will help, but I will have to work out how first :) [/img]
Author:  drmini in aust [ Sat Aug 05, 2006 11:21 pm ]
Post subject: 
There are 2 types of tin can cylinder. :wink:
The ones with a ring marked on the body (below the can) use that top seal with the hole in, not the cup type one yours has.
The seal fits ON the piston, not above it.
Author:  richarde [ Sat Aug 05, 2006 11:35 pm ]
Post subject: 
mine isn't a tin-can type though, it has a plastic reservoir (details in first post).
Author:  richarde [ Sun Aug 06, 2006 1:05 am ]
Post subject: 
Here are some pics.

Master cylinder and parts:

Image

The old seal that i got out of the top of the brake cylinder is circled in red and the "slow return valve" is circled in blue.

Seal kit:

Image

The seals are, from left to right:

diaphram for inside reservoir, dust cover/boot, cylinder to reservoir seal, piston seal, thin washer, cup seal and the spare seal that i don't know what to do with.

I can post closer pics of various parts if that will help

Thanks
Author:  drmini in aust [ Sun Aug 06, 2006 7:36 am ]
Post subject: 
The seal kit for that type cylinder is the same as the tin can one with the plain bucket main seal (without hole).

That plastic thing is not a seal, it just sits in the bottom of the spring- inside the cup seal. In the Leyland black book it's called a spring retainer. :wink:
Author:  richarde [ Sun Aug 06, 2006 10:57 am ]
Post subject: 
The part that i circled in orange is the one i am unsure of - i didn't get a spare seal like this and this one has gone hard and is damaged so i can't reuse it. It makes sense to have a seal near the top of the master cylinder though because it would make sure that all fluid flow went through the valve instead of leaking around it.

Can i put it back together without the seal that i have circled in orange, or do i need it? - is this seal supposed to be there?

I guess the seal that is on the far right in the photo of the parts from the seal kit is not necessary then?
Author:  TheMiniMan [ Sun Aug 06, 2006 6:07 pm ]
Post subject: 
Ok,,,the old "thing" that you have circled in red is part of the old "Slow return Valve"

disgard it & the metal thing under it circled in blue ring (they are both parts of what used to be a one piece slow return valve, now split apart & rooted.)

ok?

The new kit shows the "slow return valve" on the far right,,,fit that "into" ontop of the spring before fitting the rest of the kit

OK?
Author:  richarde [ Sun Aug 06, 2006 11:07 pm ]
Post subject: 
Ok, it all makes sense now :)

Thanks heaps for the help!

I am cleaning it up at the moment and will put it back in the car tomorrow. I'll let you know if i have any more troubles.

Thanks again for your help,

Richard
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