Hello, all!

The F-150 in my signature has started to leak between the brake master cylinder and the brake booster. I guess this is what Ford placed the recall on these trucks for. From what I understand, the brake fluid leaks down and drips onto the cruise control wiring harness and shorts it out.

Anyway, I just despise leaks, so I want to fix it. Do I need to replace the brake master cylinder or the brake booster? How difficult is it to replace either of the two, or both?

Thanks for any insight!

Nightrain

 

While this isn't the leakage related to the recall, if it's leaking, I would replace the master cylinder only. This of course if the booster isn't leaking vacuum or hissing while you hold the pedal. The master cylinder is pretty easy to replace. There are two brake lines, possibly the pressure switch (I'd get a new one of those just to be safe) and two bolts holding it to the booster. Be sure to bench bleed the master cylinder before installing it in the truck; it will make bleeding the lines on the truck much easier. The recall is for the pressure switch on the front of the master cylinder.

 

Thanks for the tip. I was thinking that the recall was due to the leakage that I described, but I see that it's now due to the pressure switch.

Now, about that hissing you were talking about... Will you hear that CONSTANTLY when the engine is running while holding the brake pedal? If so, what do I replace, then? Both the master cylinder and the booster?

Thanks!

Nightrain

 

Yes, if it hisses with the engine running while you are holding the pedal steady, it will probably be corrected by a new booster. It will hiss some when the truck is off, but that's normal. The booster replacement is a little more involved, but still not very hard. I'd get a Haynes manual if you don't have one already so you can have some detailed instructions. The booster is held on by four bolts that also hold the pedal frame to the firewall. These bolts are removed from the inside of the truck. You have to take off the brake light switch to get the pushrod off of the brake pedal and then the booster comes out. NAPA sells a master cylinder-booster kit, which is what I used in my truck. The only bad part about doing it that way is that the new master cylinder doesn't come with a new fluid reservoir. So if you go that route, I recommend getting a new fluid reservoir from the dealer (~50 bucks). Or, you could get a new master cylinder with the reservoir from NAPA and buy the booster seperately. I thought about re-using the reservoir I had on the old parts, but it was very dirty and I didn't want to run the risk of instantly ruining the new master cylinder.

 

Make sure that the leakage isnt coming from the brake proportioning valve--that two inch long cylinder that is between the master brake cylinder and the rear brake line.

I had leakage that ran down the outside of the brake booster housing and I thought the master cylinder needed to be replaced--but only the proportioning valve needed replacement. I suspect that there is a lot of master cylinder being replaced unnecessarily.

The Ford Parts guy didnt know that it was there on F150s--I had to show him on his parts diagram. It is much less expensive than a master cylinder.

Place your finger under the proportioning valve--after taking a rag and removing temporarily all of the leakage and after then driving the truck for several miles-if the bottom of the proportioning valve is again wet --only it needs to be replaced-- if there nothing else is wet and if there are no other problems with your brakes.

The recalled pressure switch fails internally--is my understanding--the brake
fluid leaks into the switch contacts internally and causes heat and then the plastic switch melts and then the fire occurs . And the CC pressure switch is bolt upright in the extreme front part of the master cylinder--it wouldnt get wet even if there is leakage from the master cylinder.

 

Thanks again for these responses!

I'm going to check all of this out here in the next couple of days. I only noticed the leakage the other night while changing my oil and transmission fluid. The brake fluid checked as full.

Nightrain