I accidently put power steering fluid in my master cylinder thinking it was break fluid. (Don't judge it was dark and no light). Anyway brakes are not working so good! Can I just bleed system and put new fluid in? Or will I need to replace master cylinder as well?

 

How long has the oil been in the system? If it's recent then a good flush of the entire system would likely take care of it. If it's been weeks then better plan on changing at least the master if not hoses and calipers too. I had a girlfriend that did that, and she had the brakes fail while in a drive thru. Thankfully it was then and not at any kind of speed. Nothing scarier than hitting the brakes and nothing happens.

 

How empty was the system? If you just topped it off, you SHOULD just be able to replace the master cylinder....get it off there NOW before more stuff is damaged.

If you have a leak and fluid has made it past the master cylinder it could be anywhere in the system by now. The thing about the brake system is that unless there are leaks, the fluid never really moves....and what does move goes right back once the pedal is released. As the brakes wear the fluid does slowly migrate to the calipers but there's no mass exodus of fluid from the reservoir down the
the line.

Why did you have to add fluid in the first place? A functional, properly working system holds enough fluid to maintain a level in the reservoir even when all of the pads are worn out. All adding fluid does is **** off the guy doing brakes when the caliper pistons are forced back in for the new pads.

Worst case scenario is that you get to do the master cylinder, ABS module, all rubber lines and all four calipers. You can't flush it and fix it once petroleum products hit the rubber parts in the system. They swell up like botox in Bruce Jenner's lips. The hard lines will be fine.....it's going to be expensive to fix! You won't do that again.

 

What Cleatus said. Brake fluid is water soluble and not even close when it comes to chemical structure between brake fluid and petroleum based power steering fluid. Your only hope, IMO is that the PS fluid floated on top of the brake fluid like oil does on water and it will be a simple matter of removing the master cylinder and giving it a good cleaning. Otherwise it can get expensive.

 

And just for the record, brake fluid is hygroscopic, meaning it can soak up water into itself right out of the atmosphere. Which requires that every two years a good service interval is a complete brake fluid flush to maintain a good brake system. Regardless of how many miles the vehicle is driven.

 

He mentioned his brakes don't work so good now. The master cylinder is already junk.

 

I am not sure on the solubility of one with the other. I would think power steering fluid is heavier and would sink to the bottom of the reservoir, increasing the risk of system contamination. In other words, I hope you are removing it as I type.

 

I can tell you that whenever I replaced a master cylinder on a customer's vehicle, the best way to clean out all the old sludge from the reservoir was simple dish detergent and water. Brake clean wasn't anywhere near as good. Then a good long blast with an air nozzle from every direction to remove every water molecule from the inside to dry it out.

 

Can't beat Dawn Platinum for grease and grime. The doctor that sewed my finger back on asked how I got the oilfield crud off my hands everyday. Suspected I used gasoline or solvent, I told him "oh no Dawn dish soap". I wish they'd had some in the OR because when I unwrapped my hand it still had most of the gunk that was on it when the finger tried to come off.

 

I keep Dawn at the garage sink instead of GoJo.

 

If it's good enough for the little otters and ducklings then it's good enough for me.

GoJo's a joke, in the field I keep Joe's Waterless hand cleaner in the truck. It's not as good as Dawn, but it cuts the grime and doesn't require water. It actually works better when you don't use water.

 

Ok, to answer the question of why? I was getting "low" and pulsing pedal on the brakes, so I thought I needed a little brake fluid as I could tell through dirty reservoir that the fluid wasn't up to the fill line. Went behind the seat and grabbed what I thought was the brake fluid and topped it off. Drove for about a month no problem till there was a problem "NO BRAKES"! Ended up my initial problem was the Hydro boost. So now I have new master brake cylinder, new hydro boost, all new brake lines, and a rebuilt driver side front brake caliper. As mentioned above it was a costly mistake and now carry a pocket size flashlight without fail now.