6.7l forum,

I bought my first 2015 F250 diesel super duty with high mileage (200k miles), in July of 2020 the brake power booster failed so I replaced it as well as the master cylinder with OEM parts from Rockauto. When I took the battery holder/coolant reservoir off I removed the vacuum lines from the degassing reservoir and saw black sooty oil draining out, I did my best to remove it all, reassembled and the brakes work until recently. I could feel a hard spot when braking and noticed the truck wouldn't stop as fast when I pressed hard on the brake pedal. Similar to the first time the brake booster failed, pedal got very hard to press with no assist and no brakes.

I've removed the power booster and saw the diaphragm was broken and there is oil inside the power booster, again when I took off the battery holder/coolant reservoir there is oil draining from the degassing reservoir. All makes me think the oil in the booster is weakening the diaphragm. I've done some reading and know the vacuum pump bolts tend to loosen, also read a failed pump can pump oil into the vaccum lines. I've got good vacuum at 25". I'm new to diesel motors so don't know the problems oil can cause in the vacuum system. I'm planning to replace the vacuum pump, clean up the vacuum lines and battery holder coolant reservoir draining all the oil.

Would really appreciate if anyone has fixed a similar problem and can help me out with a solution

Shenner#17

 

Hey folks,

A quick refresh on this request hoping someone can help with oil in the vacuum system.

Shenner#17

 

Usually, the only way oil can get into the brake booster is through a leaky master cylinder. As the vacuum pump (diesel) sucks on the booster, it is not like a bad vacuum pump could migrate oil into the booster, instead it would leak out of the vacuum pump discharge. Have you noticed low brake fluid level at any point?

 

Thanks Sailor#10, thé brake fluid did drop some when booster failed, would that mean it’s brake fluid that has collected inside the booster? I’ll check in the morning. Curious what caused the booster to fail inside a year.

would that also mean the oil in the vacuum system and collecting in the degassing reservoir is a separate issue?

 

If brake fluid is leaking from the master cylinder into the booster, it will also find its way into the vacuum system. The vacuum system pulls from the master cylinder side of the booster and relies on the seals in the master cylinder to keep fluid where it belongs. Brake fluid has a distinctive smell. Familiarize yourself with the smell and then check the "oil" that's in your vacuum system. If it is brake fluid, then failure of the master cylinder seals is your problem.

 

Took me a little while to get back to this but thought I’d share what I learned. Thank Sailor#10 for the vacuum pointers, it makes sense that it would be brake fluid that is draw but from the master cylinder. When I removed the old power booster there was an o ring that look a little kinked which could have allowed brake fluid through. It was quite black in color that made me think it might have been oil.

Another observation was that the battery holder serves three purposes and has to come out to get at the power booster, it holds the battery, is the filler and reservoir for the primary coolant and has a degassing reservoir with two vacuum lines hooked to it. I drained about a quart of the same black oil (brake fluid ?) from the reservoir. It took awhile but I did manage to get it all out. I cleaned up all the vacuum lines back to the vacuum pump.

When I got at the vacuum pump I noted there was no oil leak and the bolts were tight so left it alone. I reassembled everything clean the air box and filter answer, filled the coolant and master cylinder and bleed the brakes. Happy to report the brakes work great. I’m going to drive it for a couple of weeks and then check the power booster for any signs of brake fluid.

Thanks for your help.

Shenner#17