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Can a brake flush cause master cylinder and clutch issues?

In May I asked my dealer to change my tires and check my fluids.

They recommended a brake fluid flush. I agreed. they said I had room left on my brake pads, etc.

Had the car for 2 weeks and then completely lost my brakes on major road. Pedal to floor. No response. After 4 pumps it came back. I went to dealership and they said it was the master cylinder. Needed replacing. Along with brake lines. I agreed.

Noticed on leaving the dealership that the clutch felt a little different, hint of vibration, but thought it was just the new hardware. It still engaged. After 4 weeks my brake light on dash started coming on, and would not go off. I went back to dealership. They say I need a new clutch.

I had zero brake or clutch issues prior to the initial brake flush. I have only 68K km and a new clutch on average is 100K. I’ve driven a standard 20+ years and never replaced a clutch. My last vehicle ran for 19 years. I get reg maintenance. But I’m not a DIY person.

Is this triple hit a coincidence? Or can those services - brake flush, master cylinder replacement have toasted my previously trouble-free clutch? I know the brake and clutch have a shared reservoir.

They say the brake fluid is pooling in the clutch due to a clutch leak.

Any help/thoughts on this that help me navigate the discussion is appreciated.


The master cylinder may have failed, hard to speculate, you didn’t note the fluid level at the time of failure.

If the clutch slave cylinder is leaking the transmission must be removed to replace it. It is reasonable to replace the clutch assembly during the repair, unless you are confident that you can get much more life out of it. If the clutch disc becomes worn out a year from now you will fault the shop for not replacing it during the hydraulic repair.

You need to discuss this with the shop, what is leaking and why is a clutch replacement suggested.

A brake system flush is not the cause of the master cylinder failure but there could be some affect the hurried along the failure. If they used a pressure bleeder they could have used a bit too much pressure and driven debris into the seals. The debris shouldn’t be there if you’d had the brake system flushed regularly but things happen. Same for the clutch cylinder. Impossible to prove, however, just speculation.

As @Nevada_545 points out, if fluid has gotten on the clutch disk, it can’t be cleaned and if the slave cylinder needs the transmission out to be replaced, there is no point in risking a “cleaned” clutch. Many newer cars use a co-axial slave cylinder that wraps around the input shaft to depress the clutch spring. If it leaks, brake fluid goes all over the clutch disk.

Thanks for this info.

At the first visit there were no leaks under my car - I park on a light colored park pad and didn’t have any drips/spots. I don’t recall them saying any levels were low.

They just said that it was recommended to have the brakes “serviced and flushed” at this time. They also recommended a “Transmission oil change”. I normally do any recommended service so I said yes.

At the time of my full brake failure the paperwork notes the brakes were tested and confirm failure. And brake master cylinder was leaking. They then replaced master cylinder and brake lines from master to hecu, bled system and tested brakes.

I guess that’s what I was wondering - if the 7 yr old clutch & master cylinder were likely impacted by the brake flush.

I think I am mostly concerned about fully loosing my brakes on a busy fast roadway just after taking action to improve my brake safety/performance - and I am wondering if I should take this to another dealership if this sequence of failures seemed too coincidental.

You and @Nevada_545 indicate this is within the realm of normal.

I really appreciate your thoughts.

Maybe the lesson here is, “If it ain’t broke don’t fix it”. I have owned vehicles, new and used, for over 60 years. I have never changed brake fluid, never changed transmission fluid, never changed differential fluid, never changed power steering fluid – and never experienced any, none, zero, brake down of aforementioned systems. I once knew a lady where I worked who said she was advised to “change the air in her tires”.

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I don’t think we should be in the business of giving bad advice on this forum. Changing fluids is important. Personal anecdotes about how you got away with failing to maintain your car represent a statistical sample size of one and are therefore irrelevant.

At any rate, OP, it depends on how they exchanged the brake fluid. If they had someone pumping on the brake to bleed it, and they didn’t put a block under the pedal, then they might have sunk the pedal to the floor. If that happens the master cylinder piston, which seals to the cylinder wall using rubber, picks up all the gunk that’s been accumulating at the end of the piston travel since you bought the car. That gunk gets between the rubber and the cylinder wall and prevents it from sealing, which allows fluid to leak past.

It doesn’t leak out. It stays inside the cylinder, just on the wrong side of the piston, which means it also doesn’t press against the brake caliper, so your pedal sinks to the floor and you don’t stop.

It is also possible that the dealership knocked some crap from the cap or the outside of the reservoir into the reservoir when they opened it up to change the fluid. If that happened, it could travel into both the brake and clutch cylinders and lines and cause problems, although unless they also bled the clutch lines it’s less likely that such debris would make it all the way down to the slave cylinder.

Unfortunately it’s pretty hard to prove one way or the other whether debris got in there because of something they did, or something else. Unless they bled the clutch lines, it’s probably more likely that the seals in the hydraulic system are just old, and need to be replaced.

If they did bleed the clutch system as well as the brakes, then I’d be looking at the introduced-debris-theory.

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I assume these two aren’t related; i.e., you were low on brake fluid (possibly air working its way out after the brake work) but in addition now they say you need a new clutch. Sounds fishy. Can you check your clutch fluid reservoir? I’d drive it and keep an eye on the clutch fluid level.

I’m with patgurr. The chances of unchanged brake fluid causing you trouble are far less than those of mechanics screwing up. I also have driven for a half-century never changing any fluid besides oil, without a single issue.

A shop should have no trouble to replace the brake fluid as routine maintenance and not cause other problems. A diy’er might cause problems if they used the “pump the brake pedal” method to get the old fluid out. That can damage the seals. But shops don’t do it that way, they use a pressure bleeder instead. So if the brake and clutch hydraulics got damaged from what they did, it would be more likely they had a batch of contaminated brake fluid. If there was an oil in it for example, that could cause this symptom, along with a host of others. Still that seems very unlikely. If they did use contaminated brake fluid, you’ll know sooner or later, b/c all the calipers and rubber hoses will also have to be replaced b/c the seals and rubber components will swell. So if the fixes they propose work for the long term, I think it is just a coincidence, and once fixed, you are good to go…

Truth is I don’t know enough about cars to know what is essential and what is not. So I usually do what is recommended while under warranty and then what is recommended with rationale after warranty.

I’ll be keeping a close watch on the vehicle now as that complete loss of brakes freaked me out quite a bit! Thanks!

They told me the Sante Fe brake and clutch have a shared reservoir - so the brake like came on because the brake fluid level dipped due to the leak in the clutch. At least that was my understanding.

I now understand as well that the brake part of the shared reservoir has a safety separator (?) that prevents clutch from completely bleeding dry the brakes. And vice versa

I’ve decided to move ahead with the clutch work at this dealer - they are absorbing 1/3 the cost and have provided a loaner till he work is completed. It seems to be required work - there is a vibration in the clutch that I now assume is the result of the leak affecting the clutch.

I figure even if I go elsewhere they aren’t going to absorb 1/3. And from most people weighing in here and offline, it seems its possible that the brake flush just accelerated a problem that might have been coming anyway.

Thanks for your input everyone!

Best of luck there OP. Sounds like a good decision. I’d probably ask them to take a sample of the fluid checking if it separates into layers, which would indicate contamination.

Good to know.

Brake fluid is contained in a sealed system. Over many, many years a minuscule of moisture may develop within the system. Moisture can cause corrosion. But I doubt there would be damage in the life of the car.