Lotus Elan

Clutch MC seal gets stuck

PostPost by: nigelrbfurness » Sat Nov 09, 2019 5:55 pm

Don't forget to anneal your copper washers before tightening up the banjos. They are unlikely to seal easily if you don't.
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PostPost by: englishmaninwales » Sat Nov 09, 2019 8:38 pm

That explains why I’ve had problems in the past with new copper washers and banjos leaking...Thank you,
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PostPost by: MarkDa » Sat Nov 09, 2019 11:55 pm

If you really get stuck trying to get a seal on banjos try Dowty washers with a "rubber" seal on the inside.
Pretty common on motorbike brake banjos - you pull up solid on the metal and the rubber does the sealing. Capable of containing very high pressures - the seal gets better as pressure rises.
I used them on my carb fuel pipes which I just couldn't get to seal with copper washers never mind how much annealing and facing I did. Without the silly torque you sometimes end up with on carbs.
A really quick easy solution.

sealing-washer.jpg
Dowty sealing washer
sealing-washer.jpg (19.94 KiB) Viewed 249 times
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PostPost by: The Veg » Sun Nov 17, 2019 4:48 pm

The plot sickens.

I'll admit that I didn't know that annealing was recommended for copper washers. Melted the first one I did (learned something!), but did a few more without a hitch. That solved the leak at the MC but not at the SC.

I ordered a bag of the Dowty washers. I'd seen them at some point in the past but never knew they were called that (learned another thing!). They didn't help either.

So then I dressed the mating surfaces on the SC with 400 grit, then 1000, then 3000, then 6000, wrapped around a very stiff piece of flat stock and used very carefully, ensuring flat, even contact. Made the surface look almost like surgical stainless by the time I was done. Dressed the mating surfaces on the banjo itself too. Made sure the rubber in the washers was getting well-squished.

And it still pissed fluid at the banjo connection, just as eagerly as ever.

Nothing looks amiss with either the banjo or the SC, but I'm wondering if there's some defect with either that isn't obvious.
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PostPost by: MarkDa » Sun Nov 17, 2019 6:25 pm

There's not an awful lot of pressure in the clutch system so with some rubber to help out a seal ought to be fairly easy.
At the risk of appearing rude (again!) However flat the slave surface is, if it isn't square to the bolt you won't get a seal.
Is it new?
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PostPost by: The Veg » Mon Nov 18, 2019 2:49 am

MarkDa wrote:At the risk of appearing rude (again!) However flat the slave surface is, if it isn't square to the bolt you won't get a seal.


This thought occurred to me too. It looks OK, even when I made the connection outside the car and on the bench to give it a good look, but something could of course still be off.

Is it new?


Pretty much. It was new-in-box and included with the car when I bought the car four years ago. I installed it and a braided MC/SC line at the time, but the car has been off the road as a project all that time and the SC hasn't had any further attention until now.

It's one of the 'PT' branded cylinders, which costs a little less than the Girling units. I wonder if it's a case of getting what you pay for.
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PostPost by: 2cams70 » Mon Nov 18, 2019 4:37 am

Don's use Dowty washers for that application. They just aren't suited for anything high pressure. Only copper washers or a flare connection are acceptable.
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PostPost by: MarkDa » Mon Nov 18, 2019 10:08 am

It is my understanding that they are widely used to replace copper washers in modern motorbike brakes.
I attach a spec sheet which would suggest a burst pressure in excess of 1000 bar at the size we'd use.
Ought to be enough for a clutch line!

Dowty seal data.
https://www.google.com/url?sa=t&source= ... 4070284462
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PostPost by: 2cams70 » Mon Nov 18, 2019 10:23 am

I don't understand why you would want to seal with a piece of rubber when a much more reliable seal is with metal (soft copper or aluminium) unless there was some limitation on the torque the fitting was capable of handling.
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PostPost by: MarkDa » Mon Nov 18, 2019 12:02 pm

Speed, convenience, reliability and tolerance of surface imperfection.
Certainly were a godsend on my carburettor unions where I just couldn't get copper to work - that of course was somewhere I didn't want to apply high torque.
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PostPost by: MarkDa » Mon Nov 18, 2019 12:10 pm

@The Veg
Turning to the slave cylinder union.
You said you could see the rubber compressing - was this top and bottom as the SC tappings do have a bit of a taper?
You may have to revert to copper washers?
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PostPost by: 2cams70 » Mon Nov 18, 2019 12:54 pm

MarkDa wrote:Certainly were a godsend on my carburettor unions where I just couldn't get copper to work


Jeez......I'd never entertain the thought of using them on something as critical as a fuel union! If they sealed with metal originally it should still seal with metal. Either your metal washers aren't soft enough or you aren't using enough torque tightening them.
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PostPost by: MarkDa » Mon Nov 18, 2019 1:53 pm

Probably both :D
But i did try pretty hard with annealing, finishing and torquing before I gave up and used something that worked instantly and hasn't given any bother for 3 years.

A few psi from the old school mechanical pump shouldn't be too tough an assignment and you still have full metal contact to deal with vibration and prevent loosening.

I know that they are a bit different but you don't find a lot of copper washers in 3000 bar common rail diesel injection systems :D
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PostPost by: 2cams70 » Mon Nov 18, 2019 3:12 pm

MarkDa wrote:A few psi from the old school mechanical pump shouldn't be too tough an assignment and you still have full metal contact to deal with vibration and prevent loosening.


It's more the elastomers in the seal I'd be worried about. Unless formulated for petrol specifically I would not trust them to have a long life.
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PostPost by: MarkDa » Mon Nov 18, 2019 3:51 pm

I take your point - they are made in a wide range of materials to cover different temperatures.
Most readily available seem to be nitrile and pitched at mineral oils and petrol.
So that covers most automotive applications.
The original Dowty company was big in aircraft landing gear (used to have a factory near me as it happens) so hydraulic oil was probably the target liquid.

I'll pull mine out over the winter and see what they look like after three years in petrol.
Last edited by MarkDa on Mon Nov 18, 2019 3:59 pm, edited 1 time in total.
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