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MG Midget and Sprite Technical - Concentric clutch slaves

Can any one tell me why I'm only getting 4 or 5 years out of my Saab type concentric clutch slaves, the last one looked terrible when removed. The current one has turned the fluid black as if the seals have emulsified, and it's now losing fluid.
I've not removed it to inspect yet as I need to psych myself up for an engine out job.
The car's in pretty constant use but surely they should last longer than that?
Paul MkIMkIV

Paul are you sure it is the slave that is causing the black fluid?

What DOT number are you using?

Mine "seems" OK on DOT4 so far and is operating so much better since I installed the later type pedal box and master.

If the fluid in the reservoir is black I would assume that the seals in the master are causing the trouble, because there is no flow return in the pipe that I can see.

Of course if it is black when you bleed it out but doesn't look black in the reservoir I'd concur with blaming the slave.

(Further question, what slave are you using? SAAB's own or an aftermarket German one? Mine is the £76 German unit)

Mine seems OK still, using a Ford slave. Touch wood!

I've got a saab concentric that's been in about 10 years and I haven't bled it through since installing it.

There is only one o ring in there from my memory.

I know this sounds like a daft question, but have you got the right type of o ring for hydraulic fuid?
Lawrence Slater

It's an aftermarket Saab 900 slave from the place Bill recommended in 2008 when the last one did the same thing, master cylinder was replaced for new at the same time because I thought that was the problem, using dot 4 fluid, it bleeds out of the cylinder black, it's filthy black in the reservoir too.
I seem to have the same erratic fluid loss as last time, fine for a while then dumps half the fluid into the bell housing, maybe worse when very cold.
Perhaps it's just bad luck, I've ordered a Saab original this time.
Paul MkIMkIV

I can't remember how long my aftermarket Sayab one's been in, over five years I reckon.

You say you are using DOT4, I suppose the next theory to have bears upon the make of fluid...

I use the often maligned Halfords company's own brand DOT4, what do you use Paul?

My thinking is that I read somewhere (maybe in here, I don't buy magazines these days) that some fluids are less "component friendly" than others.

Bill, I suspect you're right and it's related to the fluid eating the alloy or seals, last time this happened the slave was full of debris and pitting, I wondered then if I'd been sold a used cylinder but maybe not. I wasn't using a big name fluid, I'll check.
Slightly irritating as I didn't have pulling an engine/engine & box out on my agenda, I was Frog fixing.
Paul MkIMkIV

Well, it's out and for a four year old cylinder it looks horrible, I was using Comma dot 4 fluid, will have to try something different and change it yearly perhaps.
Still it gives me the opportunity to try my spare gearbox because the current one is rubbish, synchro's gone, horrible when cold and for some reason won't go into first if it's in a bad mood.
Paul (MkI

I posted some stuff here recently about the various DOT types. Here's another explanation.

There are two main types of brake fluids:
* DOT 3, DOT 4, Super DOT4* and DOT 5.1 which are based on poly glycol compounds.

* DOT 5, which are based on Silicone.

Note the two types of fluid are not compatible and must not be mixed in a braking system.

SILICONE BRAKE FLUID (DOT 5). Silicone based DOT 5 was originally introduced to give higher temperature performance over glycol DOT 4. Silicone fluid also has other advantages, it does not damage paintwork and itdoes not absorb water. However, silicone fluid is a poor lubricant and does not lubricate ABS pumps as well as PAGfluids (Polyalkylene Glycol ). It is also more compressible than PAG fluids, which can result in a sluggish or spongy pedal. It therefore requires special design considerations in braking systems. Further, because it does not absorb water, any water remains as globules, which can pool in low spots in the system and cause corrosion. This water can vaporise when heated under heavy braking giving a disastrous effect on braking efficiency.
Lawrence Slater

Lawrence, thanks that's useful, I have a bottle of dot 5, but it says it's silicone free, also says it's synthetic.
From what you're saying I should use dot 4 with lubricant properties and probably change more often since it can absorb water and corrode the cylinders.
Paul MkIMkIV

Paul, If it's silicone free, it should be DOT 5.1 not DOT5.

Or maybe it's marked incorrectly. Have you been using that in your brake system?

Just in case you have any doubt. I found this on the AA website.

DOT 5 is silicone brake fluid, purple in colour and not compatible with any glycol based fluid – it doesn’t absorb water, it doesn’t damage paintwork and has a higher boiling point. However, the fact that water isn’t absorbed by the fluid doesn’t mean it isn’t getting into the system, so rather than the water being held in the fluid, it sits outside it. The danger here is that the water falls to the bottom of the system – usually the caliper – where operating temperatures are very high. Silicone brake fluids contain inhibitors which help prevent the corrosion caused by the water, but there is more chance of it boiling under relatively light braking. DOT 5 is more compressible and can make the brake pedal feel spongy. Very importantly DOT 5 aerates very easily and is not suitable for any car fitted with antilock brakes.
Lawrence Slater

great link

of special note to those that don't see the need for regular servicing (changing the brake fluid) -

'This water absorption occurs whether the car is driven for 30 000 miles or sits in the garage. Fluid contamination is a function of time and humidity rather than mileage.'
Nigel Atkins

Funny really, I've never been a member of the AA (well not this one anyway lol), but I've had loads of free information from them. :).
Lawrence Slater

Yeah but can you trust what they put,

‘Wet figures indicate the drop in performance when the fluid has a certain water content (less than 3%).’

‘After only a year DOT 3 fluid may contain as much as two per cent water and after several years service without being changed the fluid is likely to have soaked up around seven or eight per cent water.’

‘Most manufacturers recommend changing the fluid every two years.’

I mean this last bit is dangerously close to what’s in the Driver’s Handbook :)

of course you’ll have to take my word for this as I have a copy and have read it and you have neither benefit :)
Nigel Atkins

Thanks, now I understand!
I've checked, it is 5.1, but that bottle goes in the mountain bike brakes (I hope it wasn't supposed to be dot 5 though having read the above).
I've had dot 4 in everything car related.
Needless to say I'll be changing it more frequently in future.
Paul MkIMkIV

interestingly although there is a recommended change period for brake fluid in the braking system there's no mention of the same for the clutch fluid

of course the braking system is of much greater importance than the clutch but surprising there’s no mention
Nigel Atkins

Like you said Nigel, if the clutch fails, you can still stop the car.

Still, it seems unlikely the slave cylinder is rotting due to the age of the fluid. Whilst I DO bleed through my brake fluid (that may surprise some on here), I've never bothered to do more than top up my Clutch fluid, and as it doesn't leak, it's been sitting in there for over 10 years :(.

This could of course mean that I am in for a nasty surprise when I next get a chance to see my Saab concentric cylinder too. It works ok, and the reservoir fluid is clear, but who knows. Maybe I'll bleed it through soon just to take a look see.

Here's another note worth keeping in mind.

"Never keep Brake fluid stored in the plastic container it came in for longer than it's use by date. Plastic containers absorb water. Metal ones are better and the fluid will last far longer -- if unopened --- ."

"Poly-based plastics are slightly water permeable, so even brake fluid packaged in plastic bottles is subject to water absorption. Metal cans are superior, Ford Heavy Duty DOT 3 ("Preferred by Racers Everywhere...") is packaged in metal, as is Castrol SRF. If you're buying fluid in plastic, try to find a date code on the bottle, get the most recent batch if you can decode the numerical mess. "

I've read that 2 years is the shelf life of Brake fluids, but I don't have a can of it to take a look.
Lawrence Slater

Interesting about plastic against metal bottles and use by dates

A tip I give is to mark up a container when you open it and with the other date information on the packaging you can decide when it will or has gone by its useable period – I never have to do it as our place is far too small to stock and store stuff

I remember some didn’t agree with this be necessary for engine oil

I known people with garages full of completely unmarked containers so that they don’t even known what’s inside let alone how old it is – remember my mate using an unmarked container to fill up his cooling system to discover after it was all in that it was a cleaning product
Nigel Atkins

Without googling it, I think unused engine oil is good for about 5 years if stored in moderate temperatures. But I've used older 20/50 and not seen any difference. Don't know about the modern blends though.

With the cost of the stuff though, you ought to be able to lay down for a vintage. lol.
Lawrence Slater

don't worry Lawrence there was a long debate on that subject you've obviuosly forgotten

what I got from it was look for filling date of can, use ASAP, shake if standing for more than 2 years but I could be remebering wrong
Nigel Atkins

Well, I found a 5 litre Castrol GTX 15/50 that I've had sitting about, that I'd completely forgotten about. Nothing marked on the plastic container about use by date or the like. So I rang Castrol technical.

Generally, -- shelf life is 3 years, because the various additives tend to seperate out, and can drop to the bottom as sediments. But, it's a judgement call. As long as it hasn't been subject to extemes of temp change, i.e. freezing and roasting, it could well still be ok.

Advice is, turn it upside down and leave for a while. Then pour it out into a transparent container, and have a look at it.

If it's cloudy, it's got water in it. Dump it.

If it's clear and there's no sediment in the bottom, use it.

Also I was told 20/50 motorbike oil is good, because it's designed to take the punishment of the integral g/box. Castrol ActEvo 4T 20w-50.
Lawrence Slater

that's good info

can't remember that being in the other thread

I'm waiting to see some fully synthetic on special offer as I think my engine's probably well run in by now

notified my mate about Castol

I sure I'll be told it'll leak through the seals and not be good for the engine despite my experience of fully synthetic for many tens of thousands of miles with my previous MGs

when the time rolls around I'm also going to put fully synthetic in the gearbox and back axle so that they can all fall apart at the same time
Nigel Atkins

I used Mobil 1 back in the '80s in my Sprite and Triumph Bonneville. It was pretty expensive back then, but I reckon the engines ran better and lasted longer. My then Sprite engine (now my unused spare awaiting a rebuild), did way way way over 100K miles. I wish I'd kept an accurate record.

Now oil in general is expensive, and with synthetics giving a longer oil change interval, there's probabably not much in the price difference between a decent mineral oil and a synthetic these days.

I just looked at the Mobil website and they reckon use Mobil 1 Extended Life 10w-60 for older engines. So I've emailed them to get more information.

What synthetic oil are you going to use Nigel?
Lawrence Slater

Well, to return briefly to the original subject it's all back together now.
OEM Saab concentrics are a slightly different size to the aftermarket version, so my hydraulics didn't seat and seal, I only discovered this after refitting the engine the first time.
Having installed my spare Type 9 while doing this job I may have to take back all the negative things I've said previously, this one has a nice light change and working synchro. There was an anxious five minutes when I thought first didn't work but it just seems to be at a different angle in the gate than the last, I'm not sure why this is. Does the plastic saddle the lever sits on make much difference?

Guy, do I remember you saying you had some rebuild information for Type 9 gearboxes? I'm thinking of rebuilding the old one.
Paul MkIMkIV


Do you have the specs for the oem Saab o ring used for the seal?
Lawrence Slater

I have scanned copies of the relevant Haynes Sierra manual for the T9. And a German version Manual which seems to have more accurate detail. I am not sure if this is what you want, but can e-mail them if you like.

May I ask for a copy of that too Guy?
Lawrence Slater

Guy, that would be very handy if you don't mind, it's worth planning ahead and having a working spare gearbox on the shelf, thanks, simpsonpaul ATT mac DOTT com

Lawrence, sorry no I don't have the specs for the O ring. It's in the car now and I'm hoping I don't see it again for a long time.
Paul (MkI

ha ha, no worries Paul, yes I quite understand. :)
Lawrence Slater

Paul; Lawrence. You have mail. Big files though, so let me know if they don't come through

Thanks for those Guy.
Lawrence Slater

Guy, Excellent, thanks, all came through nicely.
Paul (MkI

Kind of a similar problem? I have converted my Type 9 to a concentric clutch and I have noticed that the fluid in the clutch master cylinder has started to get dirty/black??

It is the same style as the one Burton Power sell but not from them.

The master cylinder is the std 1275 master with one of the plastic reservoirs is about 4/5 years old and was used with the std midget slave cylinder before I converted to a concentric cylinder.

I flush the fluid annually anyway but with std Midget slave the fluid only darkened (dark yellow colour) a bit as it became old/ absorbed water.

But since fitting the concentric slave 6 months ago the fluid has gone this dirty/ black colour. I have flushed out the entire clutch system with clean new fluid but the fluid has returned to this dirty/ black colour in about 2 weeks.

Clutch still works as it on day 1 and no leaks.

Could it be the seals in the slave are being "eaten" by the clutch fluid? (Just std dot 4)
M Slater

Hi Guy,
any chance of a look at that too please nigel atkins (one word) at bt internet (one word) dot com
Nigel Atkins

M Slater

The hydraulic clutch system is not a circulating one so any blackness in the reservoir is extremely unlikely to have come out of the concentric, my usual diagnosis would be that the seals in the master cylinder are rotted and fluid is recirculating from the reservoir through the master then back into the reservoir.

And I'd think any likely fault inside the concentric would have pressure failing rather than piping dirty stuff back up the pipe.

Brakes are not "circulating systems" either. Fluid goes to and fro, and fro brings back black death.

Despite brake fluids "meeting standards" they are noticeably different, the key words being "or exceeds".

I have flushed "other fluids" - really nasty stuff - out and replaced with Castrol GTLMA and had clean systems ever after on many cars, including my American and Japanese ones. Never use anything else. DOT 4 was developed as a new standard for GTLMA originally, as it is so much better than DOT 3. The "LMA" means "Low Moisture Activity", so water is not nearly as much of an issue, but change it anyway. I'm sure some other DOT 4 might be as good, but I don't KNOW that, or the brand(s).

FR Millmore

Cheers guys.

I know the clutch system isn't recirculating but I did wander about the fluid getting "mixed" as the pedal is released/ clutch cover pushes the slave cylinder back.

As an easy/ quick check I'm going to remove the master cylinder and give it a good clean out/ inspect the seals & flush the whole system with new fluid and see what happens.

Hopefully that sorts it as if it's the concentric slave it's an engine out job plus the company that I bought it from no longer seem to be in business :-(

Although it looks very similar to the one Burton Power sell.

M Slater

If the flushed clean fluid discoloured again in so short a time as two weeks, I would agree with Bill - it is unlikely to be discolouration working its way back up from the slave that quickly. Though this might depend on how many 1000's of gear changes you managed to do in 14 days!

Master cylinder seals I would imagine. There used to be an issue with changing over between mineral and synthetic fluid and its effect on seals. And I am surprised that Nigel hasn't been along to discourse on the problems he has had with rubber products that he has recently bought.
Guy W

>>And I am surprised that Nigel hasn't been along to discourse on the problems he has had with rubber products that he has recently bought.<<
I'm too busy still sorting out the mess Moss left me in by denying they made a mistake and not offering me the product I ordered
Nigel Atkins

I'm pretty sure the black in mine had come from the slave because I initially changed the master cylinder for a new one, flushed it all out with new fluid which then went black as well.

A week or so later the concentric's seals failed completely and on engine removal the inside of the slave was a horrible corroded mess. It hadn't taken long to get that way, I may be more diligent about replacing the fluid in future.

The replacement genuine Saab concentric was ever so slightly different to the original non OEM Saab unit, necessitating a second engine removal at the time. That was a bad week.
Paul MkIMkIV

I removed my clutch master cylinder last night, cleaned it, striped it and inspected the seals- which were all fine???

The seals themselves looked perfect and didn't feel overly soft i.e. didn't feel or look like they were being eaten by some reaction with the fluid.

Bore of cylinder was also perfect no marks or scores.

The "old" fluid (about 3/4 weeks old) looked like it had been mixed with some sort of grey/black grease???

I power flushed the system with new fluid out of a sealed bottle and it took about 1/2 ltr before it ran clear of the black/ grey stuff.

I know the system isn't recirculating but I think that whoever manufactured the concentric slave has used some sort of black grease to assemble or the seals in it are starting to breakdown??
M Slater

I decided the black stuff in mine was related to corrosion of the concentric slave's aluminium rather than from the seals, but presumed the corrosion had led to seal failure. There's no black grease or anything in a new Saab cylinder. The black had definitely not come from the master cylinder, I have the same master cylinder now with a new slave and the fluid is clear.
Paul (MkI

This thread was discussed between 15/01/2012 and 05/09/2012

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