Brake master cylinder

[biomed32uk]

As part of my maintenance this year I have taken the opportunity to remove the brake master cylinder, mainly to sort out one of the gearbox cross member nuts underneath it, that has been replaced with an ordinary nut and left floating.

The MC has been fine, but stripped it for an inspect and clean, the bore is perfect so a rebuild kit will be fine. I can't see how to get the secondary cup off of the piston and I don't want to do any damage. Is someone able to confirm as to how to remove it please.

[Nickol]

nothing extraordinary - you prise it off. It sits in a sort of groove. You might well damage the Cup when taking it off but you want to fit a new one anyway. See here

http://mmoc.org.uk/Messageboard/viewtop ... 9&start=80

Scroll to the bottom of the page to see

[biomed32uk]

Excellent thanks very much, I thought that would be the way but wanted to make sure. That's quite a stretch needed there but a new one is probably a bit more pliable, plus I will do it inside in the warm.

I am pretty certain the valve cup is missing as well from the cylinder but I think they come in the kit, no discs on this car so the MC may have come from somewhere else.

[DAVIDMCCULLOUGH]

Dip the seal in some brake fluid as you assemble, makes it easier to slide over into the groove.

[rayofleamington]

I've had to split one of the seals to remove as it was pretty stiff.

Brake fluid for lubricating on assembly - yes OR brake seal grease (it's not common stuff)
Just as a warning NEVER use normal grease / copper grease etc.. on brake seals..

Most greases are mineral based (as per standard engine oil) and will ruin brake fluid seals.

(Also worth noting that some cars have mineral based hydraulics e.g. French suspension - although I don't know of British ones)

[philthehill]

The Mineral based brake grease is BLUE and should not be used on brake hydraulic components (rubber seals) that use a non mineral brake fluid.
Mineral brake fluid according to the information on the Girling tube of mineral brake grease I have states that mineral based hydraulic fluid is mainly used on agricultural equipment.
It also states that hydraulic systems using mineral hydraulic oil are identified by BLUE banding/paint.

The majority of rubber greases which can be used on hydraulic systems using non mineral hydraulic oil are RED but the instructions on the tube/tin must be read and understood before use.

If I remember correctly the Riley 1.5 was fitted with Girling brakes which used a mineral based brake fluid.
When I fitted the Riley 1.5 - 9" dia front brakes to my Minor there was some concern raised as to whether the Lockheed brake fluid would be compatible with the Girling wheel cylinder seals. Thankfully all turned out well and the Riley 1.5 front brakes were used over many miles.

[biomed32uk]

I got the seal off without doing any damage to the piston, and everything is indeed present in the cylinder. Had a good inspect of the bore last night and it is again perfect.

All parts washed in meths and cleaned up.

Just some lubrication with clean brake fluid and a wipe of red rubber grease will be all it gets on reassembly.

And now to sort out the main reason for pulling the cylinder out.

[biomed32uk]

Well it didn't work, car is all rebuilt after its front suspension overhaul and thats all good.

After bleeding the brakes through the pedal just did not feel quite right, although the pedal is good and when weighed down the car pulls up nice and sharp.

However if I sit with my foot on the brake I can feel the pedal move, if I wiggle my foot up and down quickly on the pedal I can get it to sink to the carpet. No fluid coming out anywhere else so the MC is just not holding.

So joy of joys out it has to come again, should have just put a new one in and been done with it. At least the bolts are in so I can get them out without wrestling with the torsion bar, other than the really fiddly rear union it's not too bad.

[mogbob]

Oh happy days !! The joys of Classic car ownership. Still , braking simply has to be right.
Having " been there " I sympathise with you. At least you know how it all comes apart and goes back together again.
Keep up your high personal standards and congratulations on all the stuff that did go right.
Bob

[biomed32uk]

Indeed, its all part of the fun, the most awkward part is the rear union, especially getting it back in and started.

As you say brakes have to be right, and I would much rather find this problem in the garage and not when buried in the back of another car. No room for less than perfect with single circuit, or any brakes for that matter.

I make a regular point of keeping sustained pressure on the brake pedal, normally everytime I take her out, just to make sure as best I can everything is good.

[biomed32uk]

New master cylinder fitted yesterday evening.

Took the boot off and a good whack of red rubber grease in there and over the end of the cylinder, and coated the bottom of the cylinder in cavity wax before fitting.

The rear union was fiddly, but if done before bolting the cylinder in at least you have the best chance of lining the threads up easily, plus I have fairly small fingers, can just about get middle and index fingers onto it.

Bolted in, brakes bled and all feels good now. Just the cover plate and carpet to put back.

Now I want rid of the awful under felt that's just shedding hair everywhere, like having a 100 dogs under the carpet !, dreadful mess.