Wrong fluid - help!

Aug 26, 2007 7 Replies

I just topped off my brake fluid with transmission fluid. Bad idea, I was not paying attention.



I suctioned out what I could and then filled it with brake fluid - DOT3. Then I realized it should be DOT4. Suctioned that out too.



I haven't started the car so figure there has been no circulation yet. How much damage did I do? Should I have the car taken in for some work before I run it?



It's a 98 Saab 93, my daugher's car.



Gary



I bet she's really pleased about your 'help'.

Graham

If you have not stepped on the brake, you are probably OK as the fluid would sit in the reservoir. However, since tranny fluid is heavier than brake fluid (at least that's my intuitive guess), it may have settled. If you can suck all that fluid from the reservoir, then replace it, it's probably OK...but I'd have the system flushed completely.

A good shop will have a power system whereby they open the bleeders, put the power system on the master, and push the fluid out, refilling as they go. I'd want a good flushing done. Brake fluid contamination is not a good thing.

Best bet is to completely flush out the brake system by doing a full bleed of the brake lines using the correct type of brake fluid. If you end up sacrificing some DOT-4 fluid to get all of the DOT-3 that's remaining out of the lines that's certainly worth it since brakes are the #1 most important system on a car. Doesn't matter how fast a car can go, but it does matter whether or not it can stop effectively.

Craig.

AS others have said, it is unlikely the ATF has migrated into the system, but best to flush the brake lines.

By the way, there is minimal dfference between DOT3 and DOT4 brake fluid. They are both glycol based fluids and can be mixed in a pinch. The only real contamination would be having the ATF fluid in there.

DOT5 is where the fluid changes completely to a silicon base and is not compatable with the earlier spec fluids. And no, you do not want to use DOT5 fluid.

But 5.1 is OK and mixes! Pity they couldn't find a better designation for it.

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