Porous brake master cylinder

I fitted a new 13mm AN master cylinder to my 74 mk2a 850 a couple of weeks ago and haven’t ridden it much since doing my recommissioning of the machine.

while I was doing a bit of self-isolating yesterday, in the garage, I noticed a damp mark in the outside of the cylinder body midway up the reservoir. I wiped it away and can see several pinholes in the reservoir casting.

I believe that the unit is weeping through the body of the cylinder and have been in touch with AN about it, and I’m waiting for an answer.

has anyone else experienced the same situation?

Is there also another leak, near the handlebars just under the cable tie in your picture?

Cheers,

cliffa.

Strange. Guess it could be corroded through. Be sure to check you've got a seal/spacer/gasket thing under the cap to contact against the rubber accordian moisture seal. My cap would not thread down enough to snug against the accordian and that lead to fluid leaks (thogu your image doesn't show that as likely cause). The pre-MKIII MC's with alloy caps should have an extra spacer seal up inside the alloy cap, I think I recall someone stating it was originally a cardboard type of material. I made one out of some 0.5mm high density plastic sheet. cured the MC weep. Careful to leave the vent hole in the cap clear.

I would say you have a flawed casting . If it is new it should be replaced by AN .

absolutely , you need a replacement .... almost looks as if flaw was noticed and botched repair is visible , my eyes and brain are both fogged from passage of time , so others may see differently .... I like my CNW M/C fit and forget , "just sayin" , realize the CNW unit looks different than original and I'm okay with that ....

@cliffa - it’s a trick of the light only

@Tornado - no, it’s nowt to do with the cap, it’s slap bang in the middle of the body of the reservoir

to all, yes, I will be getting a new cylinder under warranty (whenever conditions allow one to be sent to me) I was just wondering if it is something others have experienced to then be able to judge if I made the right decision to keep the bike looking stock.

@Craig - no the discolouration you’re see is where I’d wiped it with a finger. Once cleaned off with a cloth it looks exactly like the rest of the paint.

Landspeedracer said:

@cliffa - it’s a trick of the light only

@Tornado - no, it’s nowt to do with the cap, it’s slap bang in the middle of the body of the reservoir

to all, yes, I will be getting a new cylinder under warranty (whenever conditions allow one to be sent to me) I was just wondering if it is something others have experienced to then be able to judge if I made the right decision to keep the bike looking stock.

@Craig - no the discolouration you’re see is where I’d wiped it with a finger. Once cleaned off with a cloth it looks exactly like the rest of the paint.

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Good to know it's only porous around the reservoir. I had no doubt AN would replace it.

Cheers,

cliffa.

I fitted my AN master cylinder 18 months ago. Absolutely no problem, and works great.

Yes, same here.

One bad egg in every dozen , eh?

I put one of the AN complete units in this week to replace an Old Britts - Miles Brake resleeved cylinder. No evidence of rework in that area on mine. No leaks so far but only been 2 days. Seems like the casting flaw would be something that could be detected by pressure testing or maybe dye testing at the manufacturer. Oh, you want quality? That'll cost you extra.

I have been in touch with AN, and have removed the cylinder and have returned it to them for replacement. The paint in that exact area was lifted by the escaping fluid, and then it was apparent that the exterior of the whole unit has a pock-marked appearance rather than a smooth finish. On discussion with AN I was advised that the casting procedure isn’t done with a melted alloy, more like heated to almost molten and this can then cause the appearance. I think I understood what I was told and have explained it here.

if it wasn’t for my desire to maintain an illusion of total originality, and had I realised that this could have occurred, I would have simply replaced it with a modern unit and a suitable adaptor to allow the use of the stock switchgear.

if the bike had been less well presented to me I would consider doing a total rewire and use modern switchgear as well. Then I’d also consider looking at a hydraulic clutch conversion that I have seen on some pictures.

The Brembo master cylinder assemblies sold by people like cNw are in a different league, dog leg levers, adjustable span, these things make a big difference.

And the switchgear... A) it wasn’t exactly top drawer when new and B) it’s now well past it’s intended life expectancy!

I just fitted Brembo brake and clutch master cylinders, along with a hydraulic clutch conversion and modern switchgear on my T140. It makes a huge difference to rideability.

candyapplered said:

Yes, same here.

Click to expand...

yes same, no problem here