Where's my brake fluid gone?

[Electric_Andy]

I'm a bit baffled by this one and wondered if anyone could enlighten me?

About 10 months ago my partner's car (Renault Captur) flashed up a warning message when she braked hard. It went away before she could read it but she said it was to do with brakes. I checked the brake fluid and it was very low, and took 3/4 bottle of fluid to fill it to the maximum line. I checked again about a month ago and again it was low, and took another 3/4 bottle to fill to maximum. So we took it to our trusted garage and they said they have fixed it; it had an air lock butt here were no leaks. They flushed the system and tested it and now it's fine. But they still couldn't answer my question which was "if there's no leak, where has all the fluid gone?".

Anyone have any ideas? I trust the garage but I don't like it when they fix something but can't tell me the exact cause of what was going on!

 

[BigSid]

Could it be the pads wearing so there's more fluid in the brake cylinders?

 

[Electric_Andy]

Could it be the pads wearing so there's more fluid in the brake cylinders?

that's what I thought but I can't imagine it taking up 700ml? Or maybe it does, I know bikes but not so much cars

 

[Drago]

If its not leaking then the only other alternative is as Sid describes.

Is it a manual,does it have a hydraulic clutch?

 

[I like Skol]

Wow! If it took 3/4 of a litre then another 3/4 of a litre later in the year then there has to be a leak somewhere. Even if you started with full thickness, brand new brake pads and wore them out to almost nothing left I still wouldn't expect to put in that much fluid. Has the car covered much mileage between the top-ups?

If I were you and wasn't going to investigate it myself I would definitely get it into a good garage to be rechecked. This is safety critical! Is the car due an MOT? Mention it to the MOT inspector, they are usually really good at spotting things like this and unlike a general garage, the MOT tester will know which makes/models have issues and where the typical failure points are.

 

[postman]

It might be my mate.he drinks the stuff.I have told him it is very dangerous.don't worry he said I can stop anytime.

 

[I like Skol]

Just a thought, and probably a stupid question but....

You are pouring it into the right hole aren't you?

 

[Electric_Andy]

Just a thought, and probably a stupid question but....

You are pouring it into the right hole aren't you?

You've got me worried now, but I'm pretty sure it said DOT4 only on the cap

 

[fossyant]

That's way too much fluid to lose. I've never put more than a tiny drop in my car over the 22 years (other than fluid changes).

 

[CXRAndy]

If it's not visible leaking from any wheel area, then most likely is it's leaking into the brake servo from the back of the master cylinder.

Loosen the bolts that mount the brake master to the servo and check for wetness at the back. If it's wet replace master cylinder and the servo unit. Careful when removing, you have servo full of brake fluid

Check out south main auto, he has had this and simple way to check if fluid is in the servo


View: https://youtu.be/QatUPW94WIo?si=h5gzHNRBH5ys2hWp

 

[rogerzilla]

To check for leaks is pretty simple, and is what anyone should do immediately after working on the brakes: with the engine stopped, hold the pedal down hard for a minute or two (pump it a few times first to get rid of the servo vacuum). If the pedal creeps towards the floor, you have a leak.

 

[Electric_Andy]

To check for leaks is pretty simple, and is what anyone should do immediately after working on the brakes: with the engine stopped, hold the pedal down hard for a minute or two (pump it a few times first to get rid of the servo vacuum). If the pedal creeps towards the floor, you have a leak.

The garage have checked it and said no leaks. The brakes have been functioning fine. All I can think of is, when it last had it's full service, perhaps the brake fluid was refreshed but not bled properly (garage said it had an air lock in it). Meaning there was a big air gap in there somewhere. Perhaps me putting more fluid in was filling that gap but not fully. Even though I expect that air would have bled itself out by this point, you never know. And I've heard ABS systems are more of a pain than conventional systems that I've done on bikes

 

[gbb]

Master cylinder was my initial thought. I remember Fuzz and Tim having a similar problem, it was an internal seal that fails and he fluid leaks into the vacuum chamber (something like that) that's why you don't see any leaking fluid..

 

[Drago]

Aye, fluid can sometimes leak into the servo. Rare though.

Or if it had a hydraulic clutch it can leak from the slave cylinder and, dependent on where that is mounted, may not show immediately.

You'd have known if there was a "big air gap" anywhere, besause the brakes wouldn't have worked well, possibly losing one circuit entirely. It just doesn't work like that.

 

[rogerzilla]

The total fluid capacity of most brake systems is less than 1 litre, so I don't think it was just air. Even an internal leak in the ABS unit wouldn't lose 3/4 litre, so I'd also be looking at the servo. There's a lot of room in there.