Breaking fluid in brakes

This is the place for posts that don't fit into any other category.

Moderator: RichardW

vborovic
Locked user account
Posts: 1753
Joined: 31 Oct 2013, 18:07
x 16

Breaking fluid in brakes

Post by vborovic »

May I have your attention please ... :) ... I'd like to have some usable inputs and thoughts on a fairly simple matter, and that is the low level of braking fluid in the car's system ... why does it usually occur, and is it a "normal" remedy to just top it off with extra fluid and just keep on driving? Not my car of course, but today I had a heated argument battle, and gave up because the other side was so fixated on a "specialist's" conclusion (some individual who had years of experience working as a mechanic in BMW). The "specialist" fixes this on a daily basis, saying that's just how it is and that they normally "repair" this situation by adding extra fluid to the required level.

My way of thinking is that breaking fluid can't just disappear, if not leaking somewhere (lower levels -> lower pressure -> lower braking capacity). And leaking is definitely not desired in any car's system. Can the braking fluid just be "spent", and then be brushed off by regular services that it just happens, and that it is normal to just top up the fluid? The car in question is less than 2 years old, with less than 40,000 km ...

Anyone?

User avatar
Stickyfinger
Donor 2016
Posts: 10005
Joined: 28 Mar 2013, 22:05
x 734

Re: Breaking fluid in brakes

Post by Stickyfinger »

Are all your pads low ? With my car low pads give a low fluid -to- L the mark.
The "tank" is not very large.

vborovic
Locked user account
Posts: 1753
Joined: 31 Oct 2013, 18:07
x 16

Re: Breaking fluid in brakes

Post by vborovic »

Once again, not my car ... :D ... the pads and everything else is in top condition, the regular service was done just a few months ago with replacing everything (pads and discs), and the driver noticed that the brake pedal isn't as responsive, or that it goes lower than it should ... the car went to another mechanic (BMW guy), who supposedly checked everything, found nothing wrong (no leaks), and said that everything is in order, but that he topped up the breaking fluid, and that's seen normally on a daily basis in his garage and that's how they "solve" the problem ...

User avatar
bobins
Donor 2020
Posts: 3312
Joined: 05 Jul 2012, 18:07
x 935

Re: Breaking fluid in brakes

Post by bobins »

What normally happens is the brake fluid in the reservoir drops, it's then topped up, then you realise it was low because the brake pads are worn and due for replacemnt, so you replace the pads and in doing so wind the pistons back into the calipers - thus squeezing the fluid from the pistons back into the pipework, which causes the brake fluid reservoir to overtop in you're not careful ! :-D

vborovic
Locked user account
Posts: 1753
Joined: 31 Oct 2013, 18:07
x 16

Re: Breaking fluid in brakes

Post by vborovic »

That I understand, but why would the level of the break fluid drop if the pads are new, and everything else is in top shape, if not for a leak somewhere (which couldn't be found)?

Online
Hell Razor5543
NOT Alistair or Simon
Posts: 10607
Joined: 01 Apr 2012, 09:47
x 1021

Re: Breaking fluid in brakes

Post by Hell Razor5543 »

Unless they checked the fluid BEFORE replacing the discs and pads, then bled the brakes, and finally forgot to check the fluid again. I once forgot to check the level on my Xantia after bleeding the brakes, but all was well; Gracie told me herself when I then did a Citrobics session, and on full height the STOP light came on.

vborovic
Locked user account
Posts: 1753
Joined: 31 Oct 2013, 18:07
x 16

Re: Breaking fluid in brakes

Post by vborovic »

But would that really take 2 months after regular maintenance to first be felt by the break pedal? And, if the break fluid would be topped up in that case, wouldn't it be necessary to release the air from the system?

User avatar
Stickyfinger
Donor 2016
Posts: 10005
Joined: 28 Mar 2013, 22:05
x 734

Re: Breaking fluid in brakes

Post by Stickyfinger »

There must be a small amount of loss on the piston walls, but its tiny.....large loss must be a leak or a mistake about the level.

I had to remove a small amount today after the pad change, about the same amount as I topped it up about 4/5 months ago

Online
User avatar
CitroJim
A very naughty boy
Posts: 41886
Joined: 30 Apr 2005, 23:33
x 1169

Re: Breaking fluid in brakes

Post by CitroJim »

I had this many years ago on a Volvo 340. It was leaking into the brake servo due to a duff master cylinder. No sign of external loss but when the servo was removed it was almost full of fluid!!!

elma
Posts: 3745
Joined: 13 May 2007, 02:17
x 212

Re: Breaking fluid in brakes

Post by elma »

I agree completely. A healthy brake system with new pads and discs should be bled and the fluid left on Max. The fluid level will decrease with wear but reset to Max with new friction material. If it does not then the brakes weren't bled correctly or there is a leak. If the brakes felt right but became spongy it must be a leak.

vborovic
Locked user account
Posts: 1753
Joined: 31 Oct 2013, 18:07
x 16

Re: Breaking fluid in brakes

Post by vborovic »

That's just what I was thinking, if everything seems fine, and the breaking parts are new and in order (MOT passed as well in the meantime) ... somewhere a leak occurred where some of the breaking fluid got lost (hence the drop in pressure which resulted in dropping of the break pedal, and the BMW guy just adding breaking fluid - I didn't get the info about how much was added, that's to technical for the other person) ... or, in other words, if the leak (if it exists) isn't fixed, it would be safe to assume that in due time it will once again be necessary to top up the breaking fluid, and doing so indefinitely, unless someone reasonable actually goes and fix the leak issue, right?

User avatar
Stickyfinger
Donor 2016
Posts: 10005
Joined: 28 Mar 2013, 22:05
x 734

Re: Breaking fluid in brakes

Post by Stickyfinger »

CitroJim wrote:I had this many years ago on a Volvo 340. It was leaking into the brake servo due to a duff master cylinder. No sign of external loss but when the servo was removed it was almost full of fluid!!!

It is possible for the leak to be into the brake servo as well, the fluid then gets "used" in the engine, again no evidence until you pull the vac hose

Online
User avatar
CitroJim
A very naughty boy
Posts: 41886
Joined: 30 Apr 2005, 23:33
x 1169

Re: Breaking fluid in brakes

Post by CitroJim »

Stickyfinger wrote: It is possible for the leak to be into the brake servo as well, the fluid then gets "used" in the engine, again no evidence until you pull the vac hose
Sometimes a clue this is the problem can be seen from a puff of quite distinctively smelling white smoke from the exhaust...

User avatar
Zelandeth
Donor 2016
Posts: 3612
Joined: 17 Nov 2014, 00:36
x 352

Re: Breaking fluid in brakes

Post by Zelandeth »

Would probably expect fluid getting into the inlet manifold to throw up an engine management light these days as it would mess with the emissions too...not certain but seems likely.

Certainly sounds like there's a fault somewhere there though. Actual fluid use in a healthy system is essentially nothing - it will drop a bit as the pads wear, but when new ones are fitted should return to the same or very nearly the same level it started from.

If there are no external leaks visible, have they carefully checked inside the car? A leaky master cylinder can dump quite an alarming amount of fluid into the carpet and sound deadening before it's really noticeable - until you pull the carpet up anyway!

Other thought which springs to mind is does the car have discs all around? If there are drums on the back you can have a leaky wheel cylinder drop quite a bit of fluid into the drum before it becomes visible to the outside world.

I'd certainly never be returning to a garage where the "fix" for a loss of brake fluid was simply to top it up and send the customer on their way. Especially as the customer has mentioned that the feel of the brakes has changed, something clearly isn't right. Time for a thorough inspection at another garage I reckon. Preferably an independent with knowledge of the car in question.

User avatar
xantia_v6
Forum Admin Team
Posts: 7433
Joined: 09 Nov 2005, 23:03
x 415

Re: Breaking fluid in brakes

Post by xantia_v6 »

A bit of topic drift here...

I recently borrowed a 1995 Landrover Disco 3 TD V6 from an old friend, and when I borrowed it, he mentioned that he thought the brake pads might need changing, as it didn't seem to stop as well as it should. Well I was going down a steep-ish hill with a heavy-ish trailer on the back, approaching a hairpin bend, and found that I was standing on the brake pedal as hard as I could, but not really slowing down (I was not going very fast anyway).

After getting around the bend, I tested the brakes again, and they were fine, and were fine for the rest of the day, but the next day, the pedal went hard again for the first sharp application of brakes downhill.

I thought that it might be an issue where the ABS was kicking in at the wrong time, so I did some googling, and found that the 1996 model year and later with the same engine had been recalled to fix an issue with engine oil being sucked back into the servo from the vacuum pump, eventually causing the vacuum valve in the servo to stick.

I checked the UK and Australian recall notices, and the VIN number was definitely outside the recalled range, being a couple of months before the affected vehicles. I opened the vacuum line at the connector before the servo and there were definite signs of engine oil in the pipe. So I returned the vehicle to its owner and advised him to take it to the dealer and be prepared for a long conversation.

The dealers looked up there records and decided that the vehicle should have been recalled and are fitting a new servo, vacuum pump and check valve at no cost to the owner. It is a puzzle as to how they had not recalled the vehicle previously, as the same dealer had sold the car new, to its current owner, and had done most of the servicing during its life. It is also puzzling that the official UK recall did not include the first years worth of vehicles with the fault.