Power steering fluid into brake system

Hey everybody, I had a line blow on my steering rack, and I was taking it to the garage well I decided to add some power steering fluid but instead I added it to my brake system , (yes I know it was bonehead move on my part when I do know the difference). Any ways I drove my 2008 jeep liberty about 5 miles to the garage, they are changing my rack and pinion because the initial problem, but my question is do I bite the bullet and change the master cylinder, brake lines and calipers??? I do a lot of driving on highways , and I am been getting mixed answers yes change it all and no just flush it out. ???

Here is an excellent discussion of your problem:


"Severe damage results from even the smallest amount of petroleum-based fluid added to the brake system. Oil-based fluid causes the rubber in the braking system to swell and very rapidly deteriorate.

“Brake fluid is heavier than petroleum-based fluids and does not automatically mix with them. If we discover the error before we apply the brakes, we could syphon the contaminant from the master cylinder immediately. We then purge the system in reverse, forcing all fluid to flow back to the master cylinder. Replacing the contaminated master cylinder and bleeding the brakes could repair the system.”

Such a repair is rarely possible as most often people apply the brakes before they discover the error. Hydraulic pressure has more than enough force to push the contaminant deep into the system and thoroughly mix it.”

“Proper repair can be quite expensive, especially on a modern vehicle with Anti-lock braking. Because of the costs, it may be tempting to replace only the master cylinder and perhaps the brake calipers. This results in repeat contamination as the petroleum soaked into other parts again enters the system with use. Failure to remove every contaminated component causes repeat failure.”

Thanks for the info do you think the ABS module will need to be replaced? It didn’t mention it, I don’t want to change all these components only to have the abs module contaminate the system again, can it even do it?

Yes, the ABS module can indeed spread contaminated fluid to the rest of the system. Fluid flows through the ABS unit to get to the brakes from the master cylinder. It also has EPDM rubber seals that can be damaged by petroleum oil in the brake fluid. Sorry, that was a very expensive mistake.

If only driven 5 miles I would suggest replacing the master cylinder and then totally flushing the system. And when flushing it would be worthwhile to disconnect the lines at the ABS unit from the master cylinder and pumping fresh fluid out, then reconnecting those lines to bleed/flush each wheel’s brakes.

To get an idea of how well and how quickly brake fluid and power steering fluid mix, pour a little of both in a clear glass jar, brake fluid first…See how the two fluids behave in the jar.

Then I would flush the entire system thoroughly, after removing the contaminated fluid from the master, working the brake pedal full stroke during the process… I would repeat this in a week time…Hope for the best…

Just for fun, I might buy a couple of brake cylinder cups and drop them in a jar (the one from the mix test above) and see how long it takes for any deterioration to take place, just to keep all the experts honest…

Ince you get the mix out of the master, by suction or what ever way you can. I’d then remove all the lines from the master and refill it and let the fluid flow into a drain pan.

Then I’d remove all the lines from the ABS module and suck those dry.
Then suck dry all the lines to each wheel.

The more you can remove from the system, the less the chance that further damage will be done.
This is what I use and I’m sure you could rig something to feed in fresh fluid while at the other end you evacuate with this.

It will cost you but maybe you can flush all the PS fluid out.

If you know your mechanic real well and you have a compressor you could remove all the lines, ready some feeder bottle with brake fluid and borrow his unit for a Sunday.


Any oil contaminating brake fluid results in a Bubonic Plague scenario to all rubber in the system… I will stand by my recommendation but will add that ‘better safe than sorry’ is fitting.

I remember some years back rebuilding a clutch master cylinder on a SAAB. It worked fine; for a few minutes. It then gave up completely and I tore it back apart wondering WTH?

Once disassembled I found the new seals in the cylinder swollen up by about 25% and were foam rubber spongey. Eventually putting 2 and 2 together I remembered that my hands had been in mineral spirits right before putting that cylinder together. The residue from the spirits had caused the seals to swell and soften quickly which quickly led to hydraulic failure.

After thoroughly washing my hands with soap and water I installed a second kit and all was well after that. Point being that the residue in this case was very slight but still caused a major problem.

I’m just thinking that today, with todays chemistry, they have developed synthetic rubber compounds that will resist attack from ANYTHING…Bunna M comes to mind, a material used in industrial pump seals that is almost indestructible…Pumps with Bunna M seals will pump almost anything…Another type of synthetic rubber used in brake systems EPDM, resists almost everything EXCEPT Mineral Oil…Sooooooo Putting mineral oil in a brake system was a big, big, mistake…