Leaking master brake cylinder, 2011 Nissan LEAF

If there are no symptoms, then why not just top up the master cylinder reservoir periodically?

alozzy said:

If there are no symptoms, then why not just top up the master cylinder reservoir periodically?

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Sure, I suppose I could try that. I don't really know the severity of this issue, but the mechanics at the dealership seemed to think it was a pretty serious issue.

It depends on what he means by "leaking master cylinder"...

Within the master cylinder is a pair of pistons, which seal against the bore within the master cylinder block via rubber seals. Those seals wear out over time, particularly if the brake fluid is dirty.



So, if brake fluid is bypassing the pistons due to seal wear, you'll notice that the brake pedal doesn't feel like it has the same resistance as normal. In other words, when you press on the pedal, instead of a solid pressure the pedal continues to slowly sink towards the floor. However, that same sinking feeling can be caused by a leak in the brake lines, at the wheel cylinders, or where the brake line connects to the caliper. So I would check for leaks in those areas too. Usually, you'll get a brake warning light on the dash though, which it sounds like you aren't seeing.

Unfortunately, there's no master cylinder repair kit available for the LEAF, which typically includes new seals, springs, etc to rebuild the parts that typically wear out the fastest.

If the brake fluid leak is external, then it could be something as simple as a leaky cap on the master cylinder fluid reservoir. If that's the case, you'll likely find that if you top up the brake fluid then the fluid level will go down very slowly over a few months time. A replacement cap is less than $20, if that's what's leaking.

I would take your Leaf to an independent mechanic, explaining that Nissan says that the master cylinder needs to be replaced and that you want to confirm that's true.

Well, for your master cylinder to need replacement, then there has to be some "symptom".... A visible Leak in the firewall where the master cylinder is mounted, a computer error code, or abnormal consumption of brake fluid over a short time.

I don't know why there is so much cost and labor for a master cylinder repair.. It is just a reservoir/pump that is attached to the car with 2-3 bolts...

If you cannot confirm one of those symptoms, then just have the brake fluid replaced, and keep on driving....

Agreed, with a lack of symptoms it seems like the dealership is trying to scam him. An independent garage might not want to work on a repair, but they should at least be able to verify that the master cylinder needs to be replaced.

alozzy said:

Agreed, with a lack of symptoms it seems like the dealership is trying to scam him. An independent garage might not want to work on a repair, but they should at least be able to verify that the master cylinder needs to be replaced.

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Agreed, but something like a master cylinder is not an EV special repair. Maybe, after installed, Nissan has to reset the computer, but that cannot be a big expense.

I see NEW master cylinders on Ebay for about $500. Change it yourself with any mechanic you want, and then take it to Nissan for the computer update. Most of the car is made of common ICE-like parts anyway..

Thanks for the Info folks! I'll take it to another mechanic and see what they have to say about the severity.

powersurge said:

I don't know why there is so much cost and labor for a master cylinder repair.. It is just a reservoir/pump that is attached to the car with 2-3 bolts...

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Iirc, the master cylinder , control module and the electronic brake booster are all one assembly -- the "Intelligent Brake Unit". :roll:

Hello, folks. This is my first post to the great forum. I have regret that I should've known this place earlier.

alozzy said:

If there are no symptoms, then why not just top up the master cylinder reservoir periodically?

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Hi, I come up with this idea as well, right after getting a quote of $ 5K for cylinder replacement. And the repair fee is equal or even a little higher than my car's value. Let me cry for a while
As to my brake, I have never felt it sinks or fluid stains, or anything wrong when to brake the car so far. Only have to refill the reservoir every 200+miles in the past few months, that's the reason brought me to the dealer. The Nissan dealer says it is because of the internal leaking of a cylinder.
So I am wondering is it still safe to drive with this issue if I do the routine check with what you said "periodically refill" (never let it down to the min line) ? I am wondering, in theory, Is the cylinder supposed to be deteriorated slowly or just fail suddenly at an unknown moment?
Is it a scam of Nissan to give me a crazy quote in order to persuade a customer to sell the car to them with a junk price? He warned me not to drive it back home even, either repair or sell to them. :roll:
Thanks a lot for any suggestions.

They want to buy it because they know it can be repaired for little cost.

Take it to a brake shop, an auto repair that specializes in brakes. They should put it on a lift and inspect the calipers at each wheel along with the master cylinder to find the source of the leak. The fluid has to be going somewhere and it should be visible.

nlspace said:

They want to buy it because they know it can be repaired for little cost.

Take it to a brake shop, an auto repair that specializes in brakes. They should put it on a lift and inspect the calipers at each wheel along with the master cylinder to find the source of the leak. The fluid has to be going somewhere and it should be visible.

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Thank you so much for your prompt reply. I did what you suggested, yet...

First I drove it to a local chain car shop (which provides free brake check) to check. They said everything seem fine except the cylinder or booster could be the suspicious reason since it leaks, and suggested me to a dealer to find the reason. I guess it is because the Nissan Intelligent Brake Unit is a combination and quite complicated.

After reading these posts here, I figured out there was a cheaper way to buy parts online and find a reliable mechanic to install and reprogram the code with Nissan. But it is way over my capacity to handle this work.

Can I keep driving with refilling the reservoir until the leaking speed is too quick then junk it? It is 9 bar with 50miles range. I guess it's worth no more than 4K. I hope I can hang on 6~12 months then trade in it with a reasonably priced car. Currently, we have a shortage supply on every type of car. Some 2016~2019 used cars' prices are even close to the same brand new MSRP ones.

i would just keep on driving it and add fluid as needed.

You could get a paper towel and pat it along the bottom of the master cylinder to see if it gets wet spots. That would indicate the issue was with the reservoir or seals of the master. If it is dry, then the leak is probably at a piston seal on one of the calipers.

The thing is, who uses brakes on an EV anyway? i just lift the throttle and let the regen slow the car down. If you are looking far ahead you can time the stoplights too and never hit the brake pedal.

The master cylinder on a Leaf is an expensive and complicated part. The wheel cylinders are generic and cheap. Hopefully it's just a wheel cylinder that is leaking.

goldbrick said:

The master cylinder on a Leaf is an expensive and complicated part. The wheel cylinders are generic and cheap. Hopefully it's just a wheel cylinder that is leaking.

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Although on average Master cylinder lasts 60,000 ~200000miles, it could fail anytime. If Nissan leaders' quote is as high as $5K for a replacement, while it is hard to get common body shops to do so with reasonable charges, why would customers bother considering buying a used Leaf?
I even thought about upgrading to a Leaf later than 2018~2019 before.

nlspace said:

i would just keep on driving it and add fluid as needed.

You could get a paper towel and pat it along the bottom of the master cylinder to see if it gets wet spots. That would indicate the issue was with the reservoir or seals of the master. If it is dry, then the leak is probably at a piston seal on one of the calipers.

The thing is, who uses brakes on an EV anyway? I just lift the throttle and let the regen slow the car down. If you are looking far ahead you can time the stoplights too and never hit the brake pedal.

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Appreciate your tips.
But, whattttttttt? ? ? :shock: :shock: :shock: :shock:
We don't need to use brakes on an EV? Sorry, I didn't get it.
Did you just mean that any EV car slows down so quicker than gas cars after lifting the throttle? So basically, you are saying that you press the brake so few on daily driving, only when you encounter an emergency brake for avoiding pedestrians or parking?
Even you are looking far ahead, won't a driver behind you get road-angry at you?
To me, it sounds unrealistic. I drive a lot of local roads with so many changing speed limits, all-way stops, and yield signs. If I didn't give it a full stop, a $136 fine ticket comes soon or later.