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Please Help - I just did someting REALLY stupid - Transmission Fulid in the Brakes!

Help! I just did something really stupid! I got up early this morning to top off the brake fluid in the car, before my roommate drove off to work. It was only a little low on fluid, less than a 1/4 of a cup.

But after she left I realize that I had just topped of the braks with transmission fluid!! So do I need to send the police to get her off the road belfore she loses her brakes??? (No cell phone…)

The brake hydraulic system needs to be flushed immediately.

Even if this is done right away, it is still possible that rubber parts in the brake system have started to soften and deteriorate, but the faster that you can get this stuff out of the brake hydraulic system, the better your chances of not having to replace calipers, seals, master cylinder, and ABS components.

The worst-case scenario could wind up costing a whole heap of money, so the faster you get that trans fluid out of the brake system, the better your chances of avoiding major repair costs. And, in the future, perhaps you should consider leaving maintenance to the professionals.

She drives about 45 miles to work - Is she (or other drivers) at immediate risk from my mistake??

She’s not likely to be at immediate risk, but the more the car is driven the higher the likelihood of brake system damage and potential failure.

I’d give serious consideration to having the car towed, from wherever it is now, to a mechanic for a brake system flush. I would not drive it.

Cross your fingers and hope the transmission fluid stays in the reservoir and is not drawn into the brake system.

Is there a way to tell if that has happened? We have Triple A, so I can have the card towed to the mechanics from when she works (he is just up the street).

Drive it. The small amount of fluid you used is probably all still up in the reservoir and is doing no harm. Have the system flushed and refilled and you should be A-OK from now on.

While the shop is flushing the brake lines have them check to see why you were 1/4 a cup low, that is a lot of fluid

They are both hydraulic fluids and both automatic transmission and brake master cylinder/caliper etc use pistons and rubber seals for hydraulic integrity. It wont hurt your brake system. The only thing I would worry about is the brake systems run hotter than automatic transmissions and ATF breaks down faster the hotter it gets. You DO need to flush it out but dont worry about the ATF damaging anything.


You have nothing to worry about. Transmission fluid is oil based. Brake fluid is glycol based. When you add oil to glycol the oil floats on top of the glycol.

Suck the brake fluid out of the master cylinder reservior and add fresh brake fluid and you’ll be good to go.