Leaking master brake cylinder, 2011 Nissan LEAF

[alozzy]

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

[jmr2413]

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

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.

[alozzy]

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.

[powersurge]

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....

[alozzy]

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.

[powersurge]

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.

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..

[jmr2413]

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

[Nubo]

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...

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