71 replies to this topic

[miniGTS]

Glad you found the leak without it ruining any paint.

You should be able to get a full pedal with Metho in the system, though, I never bother, I just get enough of a pedal to be able to get some pressure in the system to check for leaks under pressure. Just don't drive with it in there and be sure to drain the system as much as you can and flush through with brake fluid to get it all out. I lower the level in the reservoir but don't let it run dry, then add the brake fluid.

I didn't use too much care when I used the methylated spirits, it was more of a flush and pressure check for leaks. I will flush with brake fluid before the final bleed.

Getting close to dropping the engine in now...

[miniGTS]

Some voice in my head said 'test again' so I did.... Missed a leak on the dual master cylinder where the plastic switch turns in. I assume that's a bad thing.

I had this master cylinder resleeved with stainless steel and changed all the seals. Including the ones in that chamber behind the the master cylinder. This leak could mean that I got those seals incorrect or does this mean I should get a new master cylinder?

[Spider]

I just read your other thread and replied there before reading this one.

As you've had your Master re-sleeved, including the PDWA Valve that's part of it, I'd check this first. With the leak you are seeing, it'll be one of the O rings that's not sealing for what ever reason. If you undo the Hex Plug of top of the Cylinder, you can remove the O Rings and the Piston they are fitted to through there.

 

There was a change in design of the Piston Assy in the PDWA Valve and they used different O Rings between them. Both are usually included in the kits.

 

[miniGTS]

I just read your other thread and replied there before reading this one.

As you've had your Master re-sleeved, including the PDWA Valve that's part of it, I'd check this first. With the leak you are seeing, it'll be one of the O rings that's not sealing for what ever reason. If you undo the Hex Plug of top of the Cylinder, you can remove the O Rings and the Piston they are fitted to through there.

There was a change in design of the Piston Assy in the PDWA Valve and they used different O Rings between them. Both are usually included in the kits.

Thanks. I'll check the O rings in that chamber. Would be good if it's just that.

I don't have a PDWA valve. I went from the diagonal split system and originally never had any kind of valve. Change that to front rear split with a pressure regulator valve on the rear subframe

[miniGTS]

Looking at this again, mine does have that with the plastic on the end.

I didn't realise that was also called a PDWA. I thought the PDWA valve is the external valve on the bulkhead just below the master cylinder

Edited by miniGTS, 22 June 2024 - 07:53 PM.

[Spider]

Looking at this again, mine does have that with the plastic on the end.

I didn't realise that was also called a PDWA. I thought the PDWA valve is the external valve on the bulkhead just below the master cylinder

 

On most Brake System (not Mini specific), if they have a PDWA Valve, it usually is external, however, these particular Master Cylinders are a bit unique in that it's in built - something else to go wrong and give grief !

[miniGTS]

I checked the pressure failure piston and it seems the 2 smaller O rings are missing. I'm fairly sure I put at least one on when I fitted it. So all I was able to remove is the pistons with the larger of O ring and the plastic spacer. No small O rings.

What I have left in the kit is a larger O ring and a smaller O ring. The smaller O ring is too big for the slot at end of the piston. Do you perhaps know the dimensions of the O rings?

[Lplus]

I checked the pressure failure piston and it seems the 2 smaller O rings are missing. I'm fairly sure I put at least one on when I fitted it. So all I was able to remove is the pistons with the larger of O ring and the plastic spacer. No small O rings.

What I have left in the kit is a larger O ring and a smaller O ring. The smaller O ring is too big for the slot at end of the piston. Do you perhaps know the dimensions of the O rings?

For the new design, the O rings are the same, with an overal external diameter of 8 mm and a rubber diameter of very slightly over 1 mm.  That is for used rings which I just took off the PDWA valve of an old  master cylinder I recently replaced (with a yellow tag M/C) and disassembled for interests sake.  It was a later type because it has the plastic spacer.

 

I think the drawing above is slightly misleading as it implies the o ring next to the spring on the new design is a larger o ring - whereas both o rings on the new design are the small ones.

Edited by Lplus, 23 June 2024 - 09:38 AM.

[miniGTS]

This is what came out of my master cylinder

 pressure failure piston.jpg   21.98K   4 downloads

[Lplus]

This is what came out of my master cylinder

pressure failure piston.jpg

The o ring next to the spring looks too big and there should be another small o ring on the small end.  The o rings are only just larger than the steel piston.

Edited by Lplus, 23 June 2024 - 10:08 AM.

[miniGTS]

I found a picture of what came out originally and I'm fairly sur
e I put it back the same but when I took it out today, the seal by the plastic spacer didn't come out.

This is what came out.
 IMG_20240405_123907_edit_561467364253388.jpg   19.04K   3 downloads

[Lplus]

I found a picture of what came out originally and I'm fairly sur
e I put it back the same but when I took it out today, the seal by the plastic spacer didn't come out.

This is what came out.
IMG_20240405_123907_edit_561467364253388.jpg

That looks more like mine, though even then the ring near the spring looks a little larger than mine.  Note how small the rubber ring is by the plastic spacer, both mine are the same size.

[miniGTS]

Thanks. This helps...i checked inside the chamber and can see the one O ring is still in there.

The kit came with 2 big and 2 small O rings.

What came out looked like 1 big and 1 small and that's what I did when I replaced it but the small somehow seems to have come off.

So to confirm it's just the two O rings and the spacer on the end?

[Spider]

This is what came out of my master cylinder

pressure failure piston.jpg

 

It's missing the small O Ring. That'll make it leak in a big way.

[miniGTS]

So just one smaller O ring like in the picture I posted of what came out?