very dark hydraulic clutch fluid

[k80rum]

...is, I suspect, not a Good Thing.

 

I've got the 'external slave cylinder' type hydraulic clutch arrangement fitted to my K.

 

It's worked beautifully for just over 360 miles but yesterday started giving problems. The pedal felt different, with more travel before anything happened - it put the biting point closer to the floor and on a couple of occasions, I was unable to select a gear.

 

I dived in to a Toyota forecourt and hid around the back to pull the bonnet off. Working along the system - pedal conenction was fine, master cylinder was not moving, there were no leaks anywhere, slave cylinder was not moving, ram connection to clutch release arm was fine. (Clutch and CRB have covered the same mileage and feel fine) The ram arm has always been completely covered by a rubber boot.

 

Given all that, I'm fairly dubious that the cause could be the seals; everything has done under 400 miles and moving parts have been protected. It does feel as though the hydraulic fluid isn't doing its job though, I suppose it's tired/damaged enough to get past seals/not compress properly or it may be aerated.

 

After my half hour stop it seemed okay driving back although I still think the pedal has a bit more travel than it did before. The amount of clutch movement I got during the whole thing was not consistent.

 

The fluid is a very dark, almost black colour. I'm sure this is the problem and I'm going to drain and refill to see if this cures things. Question is, what's happened to it? is this a symptom of it getting too hot, too aerated or something else?

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

[Peter Carmichael]

If there is no leak then the only fault will be at the M/c

[DaveK]

Darren

 

What fluid are you using, i had a similar problem with the integral bellhousing cylinder and we sussed out that the fluid dot 5.1 was too aggressive / dry and it allowed the seals to pick up and leak.

 

Supplier reccommended using cheaper dot 4 fluid .

 

Dave

[I.Mupferit]

That's interesting, mine went black in the clutch MC reservoir as well which happened pretty soon after building the car and I couldn't work out the reason why at all. I changed the fluid but I probably put the 5.1 back in so I must check.

 

I am assuming/hoping the same won't be true of the brakes!

 

Brent

(aka Arfur Nayo)

 

2.3 DURATEC SV Reassuringly Expensive

R 417.39 😬

[k80rum]

Thanks Peter, Dave and Brent.

 

I'll be pretty gutted if it's the m/c seals, considering how few miles they've got on them. I couldn't remember what I had in the system so I've just been out to the garage to check - it's definitely DOT4, so it doesn't look as though that's going to be the culprit.

 

I was reading on a Ducati Monster forum, that owners seem to suffer from black clutch fluid (a case of TADTS apparently) although from what they're saying, the discolouration doesn't affect operation.

 

It's annoying that this isn't consistent, which leads me to think it may in part be heat-related. I'm going to try bleeding and renewing the fluid before I go to the effort and expense of renewing the m/c seals.

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

[Foxy Smith]

Yup, it's a bizarre one this. I get the same with my hydraulic clutch set up. I'd always assumed it was aluminium/aluminium oxide from the slave (concentric bellhousing type) colouring the fluid. But giving it some thought just how much circulation of fluid is there between the save and the M/C reservoir?? the fluid only shunts back and forth in a narrow tube. Implication is then that the colour is coming from the master cylinder, Ok so why does the brake M/C which looks to be of identical materials not suffer the same problem??

[k80rum]

It's a bit intrigiung isn't it ? The closest thing I could find is this, which backs up PC's comment about the m/c.

 

Perhaps discolouration is increased in the clutch circuit because of the continuous heat-soak it receives from the engine through what compared to the braking circuit, is a very small system with much less fluid.

 

I still can't understand how 400 miles on completely new components and DOT4 could cause the seals to start failing. The main culprit must be air in the system that needs to be bled out, despite there being no visible fluid leaks.

 

I could accept the discolouration is an indicator of *some* seal wear which for whatever reason is more noticeable in a short system continually exposed to heat, but I'd still expect that wear to be gradual enough not to be significant for some period of time - as evidenced by people with discoloured fluid and no clutch problem.

 

Time to get out the turkey-baster and bleeding-spanner

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

 

Edited by - k80rum on 12 Feb 2008 09:25:46

[captain chaos]

Interesting...I've got excatly the same scenario...doesn't effect operation though, so I've never worried about it too much.

[Peter Carmichael]

A clutch circuit moves a significant volume of fluid up and down the hydraulic lines. Brake circuits don't. Brake circuits are based on pressure. Clutch circuits are based on movement. I reckon the slave cylinder is the source of aluminium oxide particles ending up in suspension in the fluid and then migrating to the m/c. I reckon an m/c failure is unconnected with the clutch fluid colour.

 

An m/c failure is likely to have been caused by the seal closing off the relief hole. The seal lip passing over a hole may have torn.

 

The only other likely mode of failure is that the clutch pedal is just not returning to fully released, where the reservoir joins up with the hydraulic circuit to allow for thermal expansion and wear etc. Check the pedal box for free movement of the pedal resulting in the m/c piston being fully extended.

[Mick Day]

I had a Triumph Spitfire in the 70's & I was forever replacing leaky clutch master cylinders.

[susser]

A couple of clues make me think that the pedal is not returning to it's rest position and uncovering that "to allow for thermal expansion and wear etc.". If that were the case, then leaving the pedal unused, such as when you were firtling about for half an hour, would allow the piston to pass fluid through the seal and refill the system enough to be ok for a bit.

Get someone to operate the pedal while you look into the reservoir; you should see the small squirt as the piston moves forward to the hole. No seeing it might be a clue that the pedal is stopping too low.

 

Or something.

[k80rum]

Thanks susser

 

I've whipped the hydraulic setup off the car now and replaced it with the cable temporarily while I take a look at it.

 

When I compress the m/c, I can briefly hear a hissing from the slave before the slave ram moves, as if there is air in it being compressed (or possibly, fluid getting around the seals I s'pose). This fits with what I was getting in the car - more inital take-up before the clutch moved. I'll keep looking at it, to see where the problem is, but will try the pedal-return and bubbles check when it's re-installed.

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

[Mickrick]

As PC says, probably MC seals. Usualy get full movement by pumping the pedal if it is.

The clutch fluid will get darker than the brake fluid because it operates more than the brakes, and there is a much longer range of travel on the clutch slave cylinder than the brakes, so more wear/contamination in the fluid.

You should be changing it every two years anyway, irispective of milage.

 

If all around you say it can't be done, all the more reason to do it!