Master Cylinder or BrakeBooster? Or both?

Hi,

There is a seal around the stem that is connected to the high pressure piston and brake pedal. That seems to be leaking fluid back into the cab.

You found the right part to replace. Clear fluid is brake fluid, especially if it trys to eat all the paint and any skin it gets on, or starts to disolve the carpet. Red fluid is normally power steering fluid, and indicates the power brake booster system is leaking hydralic fluid, a $1,000 fix.

Be lucky it is only clear brake fluid, a $100 - $200 fix.

Buy a quart of the highest quality brake fluid and pump out all the old stuff. Once over 6 years old, it can absorb enough moisture to cause air bubbles in the front brake calipers while hot, and lose braking on steep mountains. By bleading out the old fluid, you can tell it changes from a yellow color to clear fluid once the new stuff has filled all the lines.

Ford sells a very high quality brake fluid recommended for it's 26,000 GVWR motorhome chassis, it has the highest "Wet" boiling point, and is only about $20 a quart. Even if you take it someplace, it is better to bring your own fluid than to get it from a open container that has been absorbing air (and thus moisture) for a couple of days or longer.

All brake fluid must meet the minimum Federal Standard, and once it is saturated with moisture must not boil below about 375F. However brake calipers can reach over 800F while going down a steep mountain (especially if the owner did not take it out of overdrive or shift to 2 gear to assist in slowing the vehicle). Some of the brake fluid will always be near the caliper and brake shoe, thus it is important to have something rated more than 400F, and change that brake fluid with dry stuff about every 6-8 years.

Fred.

When my '89 Jamboree was only 2 years 0ld I found out the value of flushing brake fluid. I had an E350 and when I pushed on the brake pedal I went through a red light at the bottom of a hill. After they cooled off everything was OK. Mine was a dragging brake that caused the fluid to heat up. Moisture in brake fluid will boil and become vapor. A gas can be compressed while a fluid can not be compressed. That is the advantage of a MH. Clean underwear are only a step away.

Whatever you find please do REPLACE the front brake lines at the same time. Small price for safety. You may have to order them as only OEM are available depending on your chassis.

The brake lines are known to collapse ON THE INSIDE. You won't see anything from the outside.

I damn near died coming of a ramp last year because of that. Everyone checked and checked my brakes before I headed out on my big trip. Yup they look fine. Well duh yea these lines look great on the outside.

I white knuckled pulled into the first truck repair and they knew right away it was the inside of the brake lines collapsing. It does have a symptom of just bad calipers when they start deteriorating. Boy let me tell you when they do collapse have a change a clothes handy! :C

If the insides of the booster got soaked, it could be rusting inside and the vacuum bladder could be damaged.

Based on what you added, now I would recommend you change out both the master and the booster to play it safe. You will already have it apart and at that point, the booster really isn't much more parts expense.
Jose

There's no leakage under the hood, only inside the cab. The brakes work well UNTILL the pedal goes to the floor, then I have very little braking. No doubt that the MC is bad. I guess my concern is that since the fluid is actually getting all the way through the booster to the inside of the cab, then the booster is likely also bad, right?

Sounds like a failing Master Cylinder.
I've heard of the MC leaking and the Booster "absorb" the fluid up. Would fill up enough to reach the level of the vacuum hose, then the engine would "drink" it.
When we had the '83 E350, I replaced both with a lifetime warranted set from AutoZone.
Caution: Be sure if you're replacing MC or Booster, that the Booster's actuating rod mates properly with the back of the MC's piston. If some rebuilder used a piston with too deep a recess for the rod, then the booster can's actuate it. Even with a new "set" like I bought, it wouldn't hurt to separate the pieces and be sure the little threaded tip on the rod is adjusted correctly. There should be just a touch of clearance.

Sounds like the seals on the piston in the master cylinder are leaking and the fluid is squirting up the center of the MC and spraying against the firewall.

If the brakes apply strong, then the booster might be ok and it's just the MC leaking down. Have someone apply brakes while you look under the hood. Unless the booster looks really bad, I would just replace the master.

Jose