Odd braking problem - almost total brake failure

[MikeBamber]

Hi, I've just joined the forum but have tried to read through as many related posts to the problem I have.

I have a 2013 UK Leaf Tekna.

It developed a problem where I would experience a total loss of braking at low speeds (and any other speed!) - and would have to use to footbrake to stop.

I have bled the brake system and quite a lot of air came through the lines especially the rear. Bingo, I thought.
The brakes worked perfectly for a few miles then all of a sudden failed again. Which makes me think that the master cylinder is OK as it worked temporarily. But I don't have much experience with master cylinders.

I have a brand new 12v battery.
No errors on LeafSpy or warning lights on the dash.
If I bleed the lines again, it all works for a few miles then fails again.

So I think air is coming into the system but have no idea currently where.

Could anyone shed some light on this? It doesn't seem to be a problem that I've seen on here before!

Many thanks

Mike

 

[sungkang]

Did you carefully inspect all brake calipers and hoses for signs of leaks, damage, or wear?

 

[MikeinPA]

A more complete description of the symptoms will be helpful. Does the pedal go to the floor, or does it stop in the normal place with no braking? Is there any resistance change between braking and no braking in terms of pedal feel?

Does pumping the brakes help? In the old days is was common for brakes to have some air in there (after amateur maintenance), and we just got used to giving the brakes a pump or two to get pressure up. --This would be your main clue that there is air in there.
Modern brakes need to be bled according to the manual, did you follow the procedure on page 517 of this? https://www.nicoclub.com/service-manual?fsm=Leaf/2013/BR.pdf ?

Are you seeing regen bubbles when brakes are working? When they are not?

There is a recalibration procedure for brakes, but your issue does not sound like it needs this, but anyway here

Needless to say, don't drive it on public roads until you have tracked this down.

If you are getting situations where the pedal just goes to the floor with little resistance, and there is little or no braking, probably in the master cylinder somewhere.

 

[Drew21]

All the air you bled out got in somehow. The fact that the brakes worked for a short time and then went bad again suggests that the air can get into the system relatively quickly/easily.

I don't know about road conditions (e.g., use of winter salt) in your location, but your car is old enough that you could have rusted (i.e., leaky) hard lines in the brake system. Similarly, at that age you could have leakage in the rubber brake lines from the hard lines to the calipers. On top of that, the master cylinder itself can begin to fail over time.

Have you noticed the brake fluid level in the reservoir dropping? Any sign of brake fluid anywhere on the vehicle?

If you can't spot an obvious leakage point it's probably time to consult a professional.

 

[MikeBamber]

Did you carefully inspect all brake calipers and hoses for signs of leaks, damage, or wear?

Hi - yes I did

 

[MikeBamber]

All the air you bled out got in somehow. The fact that the brakes worked for a short time and then went bad again suggests that the air can get into the system relatively quickly/easily.

I don't know about road conditions (e.g., use of winter salt) in your location, but your car is old enough that you could have rusted (i.e., leaky) hard lines in the brake system. Similarly, at that age you could have leakage in the rubber brake lines from the hard lines to the calipers. On top of that, the master cylinder itself can begin to fail over time.

Have you noticed the brake fluid level in the reservoir dropping? Any sign of brake fluid anywhere on the vehicle?

If you can't spot an obvious leakage point it's probably time to consult a professional.

Hi - I can't find a leak - and no fluid is missing from the reservoir. It's quite baffling.

 

[MikeBamber]

A more complete description of the symptoms will be helpful. Does the pedal go to the floor, or does it stop in the normal place with no braking? Is there any resistance change between braking and no braking in terms of pedal feel?

Does pumping the brakes help? In the old days is was common for brakes to have some air in there (after amateur maintenance), and we just got used to giving the brakes a pump or two to get pressure up. --This would be your main clue that there is air in there.
Modern brakes need to be bled according to the manual, did you follow the procedure on page 517 of this? https://www.nicoclub.com/service-manual?fsm=Leaf/2013/BR.pdf ?

Are you seeing regen bubbles when brakes are working? When they are not?

There is a recalibration procedure for brakes, but your issue does not sound like it needs this, but anyway here

Needless to say, don't drive it on public roads until you have tracked this down.

If you are getting situations where the pedal just goes to the floor with little resistance, and there is little or no braking, probably in the master cylinder somewhere.

Hi - Initially works like a brand new car. Then, will get progressively 'slacker' for a few miles then total loss of braking. Pedal easily to the floor with absolutely no effect.

Pumping does not help.

I've bled them fully three times, once with a power bleeder, twice following the service manual order.

Yes regen works perfectly and there are no warning lights.

I can understand master cylinder internal seals going wrong, but don't understand where the air is coming from.

 

[MikeinPA]

Hi - Initially works like a brand new car. Then, will get progressively 'slacker' for a few miles then total loss of braking. Pedal easily to the floor with absolutely no effect.

Pumping does not help.

I've bled them fully three times, once with a power bleeder, twice following the service manual order.

Yes regen works perfectly and there are no warning lights.

I can understand master cylinder internal seals going wrong, but don't understand where the air is coming from.

Baffling. How much air is coming out?

 

[MikeBamber]

Baffling. How much air is coming out?

Not quite sure how to measure that, but I'd say from the total line maybe 1/5th is air.

It takes a little while for the air to come through which makes me think that the issue originates from the 'engine bay' although I have deep cleaned and blow dried any braking hardware and cannot detect any leaks.

 

[nlspace]

Do you think air is leaking in at the master? Does the reservoir level remain steady or drop? Is there any wetness around the bottom of the booster?

 

[MikeinPA]

In the picture above, and at 9:34 of this video one can see there is a lot of internal volume in the booster. I wonder if this is where the lost fluid is going? If one of those seals was sucking air and leaking fluid, until one of those chambers is mostly air--would this do it?

 

[nlspace]

Why some people should not be allowed to buy tools, wish i could get my 15 minutes back

 

[MikeBamber]

Do you think air is leaking in at the master? Does the reservoir level remain steady or drop? Is there any wetness around the bottom of the booster?

the fluid level stays the same, an absolutely no wetness anywhere, I even totally cleaned and dried the 'engine' bay then rebled so I could find leaks!

 

[Drew21]

Doing DIY work can be fulfilling and save you lots of money at the cost of your time (and sweat and sometimes blood). Your significant other might even give you a high five and slap you on the butt for a job well-done.

It can also be extremely frustrating and mind-boggling.

Eventually every DIYer reaches a point where some diagnosis or repair defeats them and can only be done by a more experienced mechanic/technician, especially when they're dealing with a critical safety component like the brakes. If I were you I would be at that point now.

 

[nlspace]

Here's a test: Turn on the car to READY mode, then have someone press the brake pedal while you hold your hand on the master e-brake assembly to feel if you can the motor spinning in, and out when pedal is released. Open the reservoir lid and put a paper towel over the opening while doing the pedal test. There should be some "fountain" of fluid rising up in the reservoir that you can observe (just don't get sprayed in your eyes).

If the motor is extending and retracting, then maybe the o-rings between the reservoir and the piston assembly are leaking air into the system. One port is an inlet feed side and the other is a return and over-pressure relief side.

If the motor is not retracting, then it is stuck in the forward position and that would explain why your foot goes to the floor to compress the master cylinder. That is the fail-safe backup mode for braking in the case that the motor actuator fails.

If air leaks into the master piston area, then the motor drives forward but has no effect on braking, hence the need to press further to manually compress the brakes. There is also a wiper seal between the motor "piston" and the master piston, but doubt that is serviceable.

 

[MikeBamber]

Update -

I serviced all 4 brake calipers with new pistons and seals along with new bleed screws. Problem still occurring.

I have obtained a new brake booster/master cylinder unit and decided to just remove the master cylinder to assess state of play. Carefully undid the bolts while using a piece of wood to push the unit - I was aware it is spring loaded.

Master cylinder came off quite easily and lo and behold there is fluid behind it... so must be the seals.

I'm now going to seperate my donor unit and attempt to fit the replacement master unit.

 

[nlspace]

Thanks for the update and the pictures.

How much fluid was down in there?

 

[denwood]

Just curious if the brake fluid was flushed every 2-3 years? Good catch on the fix…I was thinking master cylinder from your first post…

 

[MikeBamber]

Thanks for the update and the pictures.

How much fluid was down in there?

not a great deal.

 

[MikeBamber]

Another few pictures of the donor unit.

Have successfully transplanted into car. It's not a difficult job but you need to apply quite a lot of pressure to the unit to compress the springs enough to get the bolts done up. A piece or 2x2 wood pushed with my hips while I leant over did the trick!!

Not driven it yet but hope to later on.

Either way, it is clearly possible to transplant master cylinders on a Leaf without having to replace the whole EBU.