Clutch slave cylinder

[BenMcCarthy]

My plus 2 has got a new standard clutch, new standard slave cylinder and new standard master cylinder.

And yet for the fourth time in two years the new Lucas/Girling slave cylinder fitted just a few months ago seems to have packed up and consequently dumps clutch fluid on the floor at an alarming rate such that I won't be driving it to work today.

Does anybody have any ideas? Could there be something I'm missing?

[types26/36]

A couple of things came to mind after reading your post, I presume you are using a decent brake/clutch fluid, are you using silicone fluid (not that I am saying its at fault)
The exhaust is not to near the slave cylinder creating a heat problem,
and last, I have never tried to prove it but I suspect if carbs drip petrol (most do) petrol could end up getting into the master cyl. via the breather holes in the caps. I keep a plastic sandwich bag over both my brake and clutch master cyls.
Brian.

[BenMcCarthy]

Thank you for your reply -

I'm using a standard Castrol Dot 4 clutch fluid. The car isn't used for racing although I do a fair amount of stop/ start town driving.

The exhaust/ manifold is standard (although Stainless Steel) and in the standard location - I can't see how its especially close to the slave cylinder.

I will try your idea re sandwich bag although the carbs don't appear to leak much (if at all)

[carrierdave]

Hi there,
I seem to remember reading a post where someone comented that synthetic brake fluid has a tendency to attach the rubber in the piston of the slave cylinder - I have changed mine back to mineral oil and will replace the seals. The other problem I had was the brake fluid became discoloured; I put this down to either the rubber being taken into solution or heat from the exhaust.

I would pump through some mineral oil and give it a whirl.

Dave

[Hamish Coutts]

Dave,

I have the same problem in that the fluid (synthetic) becomes cloudy after a couple of weeks. Looks awful in the master cylinder. I flushed the system (both brake & clutch) and put in new Castrol dot4 synthetic fluid and the same thing has happened again.
Most annoying. I hope it is not the seals disolving in the fluid.

Do you think it is worth changing to mineral fluid. If so do I need to change the seals?

Hamish.

[carrierdave]

Hi Hamish,
It?s difficult to say. I am sure that Keith (Type26) mentioned something in a recent post about the synthetic fluid making the rubber seal go all "mushy".
I have changed back to mineral fluid however I have not changed the seals yet. I also didn't run the car long enough to see if I had the same discolouration in the mineral fluid; my other concern was the location of the braided hose to the exhaust ? would this burn/boil the fluid if too close.
I have the engine and gearbox out at the moment so I will take the slave cylinder apart to see if the rubber has started to deteriorate and let you know.

Keith ? If you pick up on this ? what has been your experience?

Thanks

David

[types26/36]

I will try your idea re sandwich bag although the carbs don't appear to leak much (if at all)

Just relised its a plus 2 so the bags over the cyls wont help from memory the cyls are not below the carbs like the Elan are they?
Brian

[BenMcCarthy]

Thanks for the advice. Correct on the positioning of the brake/ master cylinders they are behind the carbs so bit of a jump required.

I will check the hoses again and try using mineral brake fluid - it would be a useful experiment. First job is finding where to get some...

[BenMcCarthy]

Just checked with the garage who put the slave cylinder on last time. They used mineral clutch fluid - then I topped it up with synthetic when the level started going down. hmmmm......

[carrierdave]

Hi all,
Just taken the clutch slave cylinder apart and found no wear and no softening to the rubber seal!! So why did the synthetic oil discolour?

(From memory I think I may have used a master cylinder seal rather than the slave one)

Does anyone have any experience with mineral oils and heat from the exhaust?

Thanks

Dave

[type26owner]

It's federal law here in the USA all brake related elastomers are required to be EPDM. EPDM is impervious to all the brake fluids. The seal in the slave cylinder is not a brake component so is not bound by that law. Some penny pincher decided a silicone seal would do okay there. Well that's correct except for silicone oil happens to be a solvent for silicone elastomers. Given a bit of time it will turn it into goo much like the consistency of chewing gum. A slip of paper in the box warning not to use silicone brake fliud would have eliminated the problem. As the consumers we should be irate over this crap!

The normal wear process of the components will discolor any of the brake fluids in a short amount of time. This is not a problem just an optical effect.

[patrics]

Hi Ben,
When you say it dumps fluid over the floor what has actually failed on the slave cylinder ? is the seal swollen or the bore worn / scored?
Traditional brake fluid is vegetable based not mineral, its fatal to let anything mineral based come in to contact with you brake / clutch system . So under no circumstance use mineral type grease on the out put rod from the slave.
Mineral fluid was used in the previous generation Roll Royce cars and old power system Citroens.
Currently there are two types of rubber used in brake systems - EPDM and SBR. The fluid you are using is fine for both types.
Regards
Steve

[BenMcCarthy]

Not sure whether it was the bore or the seals. The slave cylinder got chucked away again.

As I understand, he only grease in contact with the output rod is that pre-packed by Lucas/Girling in the cylinder.

I'm just wondering if it could have been a bad batch of slave cylinders is in the best traditions of British parts quality control

[phatmendus]

Just a point that may have been made (I havent read every post) But If the seals are made of a Nitrile or neoprene (which I am pretty sure they are) Then under no circumstances should you use a synthetic brake/clutch fluid. These disolve oil based rubbers like nothing else. You should stick to a standard fluid or equivilent as the manual specifies.

That is just my experience as people seem to think the silicone based fluids are better... not the case for standard road driving (in my experience) and certainly not the case for seals made from standard materials.

Simon