How much fluid would clutch master cylinder leak?
 

New to me S60, 2005 MY.

The cruise control will not engage. Previous owner advised me this is due to a minor leak from the clutch master cylinder, dripping onto the sensor, and that previous mechanics have advised it does not need immediate attention (as did a garage I called to discuss this and other issues prior to the purchase) if I can live without CC (which I definitely can!).

The brakes have felt a bit soft since I've had the car but they're strong enough once pressed. I was driving Wednesday night and got "BRAKE FLUID LOW - URGENT SERVICE" in the DIM. Brakes still felt fine, maybe a little softer but it may well have been my imagination after seeing that message.

Got her home and checked her yesterday - parked on a slight hill but the brake fluid level is just above the MIN mark in the reservoir.

Car was serviced in early March (previous owner) and although I'm not 100% sure, I cannot believe it would have gone in and come out again with brake fluid sitting barely above the MIN mark - so I presume it must have been done then (and the notes I do have show it has been changed fairly regularly.)

So I'm led to hypothesise that the brake fluid is draining at a rate of about a reservoir full per every 2-3 months. I will be checking the level again later to make sure this has not accelerated.

Other points of note:

- I could dismiss the DIM warning (to my surprise as it was a red alert)
- The DIM warning didn't reappear through the remainder of the drive, and didn't come up yesterday after starting the car twice (I believe it would show on startup if it really was low? - although the car is on an uphill gradient currently)
- There's an oily patch below the car, although I am 95% certain it's not my car! (Parked on the road so it could have come from anything. I noticed it incidental with the other symptoms so it added to my concern. However the "patch" doesn't seem to be growing, and in any case if it was mine draining brake fluid out underneath, I'd expect the reservoir to be empty now... so at this point I've basically discarded this evidence.)

So my question to the forum is - can this amount of fluid loss be explained by what I was told was a minor clutch master cylinder issue?

Car's currently grounded while I wait for some more DOT 4 to arrive and then I intend to take it into my local Volvo independent specialist next week for this and other issues. I'm really wanting to know whether to ask them just to check/replace the CMC or whether this might be something else. I don't know for sure that it had brake fluid in March but even if it was a couple of years ago it shouldn't have disappeared!

Thanks
ilmiont


(edit - I know the thread title is a bit vague and obviously a huge spectrum depending on the problem... I'm more just wanting to know based on my description above, what your instinct would be about whether this is purely the issue I'd already been advised of, or whether it's also likely to be leaking from elsewhere.)

Brake and clutch should have separate compartments in the reservoir. If you lose all the clutch fluid it should not affect the level as far as the braking system is concerned.
The famous clutch leak on to the pedal position sensor is more of a mist. I would not expect there to be serious loss there.
If the reservoir is low I would suspect leakage somewhere on the braking system.

There’s been talk of wrapping the sensor in a plastic bag so weeping fluid doesn’t affect it.
It’s always possible that your brake pads are almost worn out, the fluid gradually goes down as the pads wear as it fills the caliper as the pistons move out. Shouldn’t be enough to put the warning on though.

I’d be tempted to put some clean cardboard under the car overnight and check it for drips in the morning. Be aware of the aircon dripping under there as it’s supposed to.

Thanks, sounds like this may not just be the CMC then.

I had read about the plastic bag technique and might try it but to be honest I'm not sure yet where that sensor is or whether it can be easily accessed myself. Might ask the garage about it next week...

Haven't checked the car today but will tonight or tomorrow and see if the level seems to have changed or not. I know that worn pads would cause loss of fluid but it seems to me like it's lost rather more than it should have done.

Got some ATE TYP200 on the way so will put some in once it arrives.

I checked the footwell yesterday and there's possibly a little bit of damp - particularly on the post/cylinder between the clutch and brake pedals (not too sure what it is, learning as I go and still waiting on my Haynes manual to arrive). But there's definitely not a reservoir's worth of fluid sitting in my footwell...

Sensor is actually quite easy to reach, if you don’t mind your head in the footwell. Finding it is the hard bit - it’s next to the throttle pedal, can’t remember which side, but it’s obviously connected by brackets to the clutch pedal when you see it.

The panel with the foot well lamp will need to come off. The sensor is a pale greenish thing like a miniature bicycle pump. It's closer to the brake pedal and linked across to the clutch pedal. the ends are just pop on off and there will be a two wire plug to disconnect.

Hi, nice looking car.

I would strongly suspect a failed clutch slave cylinder which unfortunately means a gearbox out job.

The Brake reservoir is a shared unit with the clutch fluid although the two are not connected so even if the clutch pedal goes to the floor the brakes will be unaffected.

Take the undertray off and look to see if there is any hydraulic fluid dripping/;leaking from the gearbox area.

I had this on my 2006 S60 and although the part is only about £90 it's the labour that makes it an expensive job.

I hope that I am wrong but...……………………...
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@S60D5-185 Hi thanks for your post, responding in this thread to keep it altogether.

I've read about the clutch slave cylinder issues but to be honest I can't find anything wrong with the clutch - or is it possible the slave cylinder could fail without compromising the pedal?

The pedal depresses smoothly, bites cleanly, quite low, and always raises straight back up, at least as far as I've seen so far.

Any other symptoms I should look for that may indicate the slave cylinder's at fault?

At this point, with the consensus being that this is more than the known issue of the CMC dripping onto the CPS, and what with me already planning to take her in as soon as next week, I think I'm just going to wait for my brake fluid to arrive, top it up, take her in (all of 2.5 miles) and ask them to inspect. I haven't observed any leaks, although as said there is something on the ground under the car, but I'm pretty sure it's not actually from it!

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@BrendanW Re. the CPS - is my CPS likely to need replacement given I believe it's had this issue for a year at least? Or would it work OK with just the brake fluid cleaned off?

Some have had success cleaning the track with contact cleaner. One of mine, the track had gone to complete mush. I suppose it depends on how far it's gone. My first replacement lasted barely eighteen months. I fitted a bag on the second and that was the end of problems down there.

Hi, yes the clutch pedal will feel entirely normal and operate correctly so long as the fluid level is kept up.

When I spotted fluid on the drive coming from my S60 D5 I took the tray off and spotted the tell tale leak.

I couldn't get the car booked in for about 10 days and just kept topping the fluid up every day to ensure that it never created a complete fail.

My car had 56k on the clock when it failed.😢