The first thing to do is invest in the service manual. Visit the dealer to order the factory manual. It's available on DVD which every mechanic hates because you can't write notes, bookmark a page, or carry it over to the car. We will save paper, apparently by printing off pages, using them, throwing them away, then printing them again the next time. (If you can get a paper manual, get that).
I've included a drawing of the caliper from a '99 F250-350. Number 1 shows the location of the two mounting bolts. Ford has had a real lot of trouble for decades with their caliper designs. This pin system is what Chrysler and GM have used for a long time and it works well, but you must be sure the bolts are straight and free of rust pits. Replace them if the chrome plating has lifted due to rust. Coat them lightly with high-temperature brake grease when you reinstall them. Scrape any rust off the backs of the pad backing plates, then coat the contact points with brake grease where they touch the calipers. They are going to vibrate. That grease lets them vibrate freely without transmitting the vibration to the calipers where it would be amplified into an audible squeal. The brake glues that used to be available don't do a good job of that. They try to hold the pads from vibrating but that never works. The products you want contain molybdenum disulfide. One trade name I'm familiar with is "Rusty Lube" but there are many others. These are high-temperature greases that don't travel like axle grease.
Be very careful to not get any grease on the rotors or brake pad linings. That includes fingerprint grease. If you do, wash it off with a spray can of brake parts cleaner before they get hot. When they get hot, grease will soak into the linings and cause a squeal.
The hose is bolted on with a hollow "banjo" bolt that has two copper washers on it. One is under the head between the bolt head and the hose. The other one is between the hose and caliper. You can reuse them but pop them off and use new ones if they come with the calipers. The soft copper will crush and bite into the ridges on the hose to form a better seal. You can also turn each washer over so they will form new ridges.
Don't let the master cylinder run dry while the hose is disconnected. Fluid will be dripping slowly from it. Bleeding the air out becomes a bigger job if the master cylinder runs dry. A simple trick to prevent loss of fluid, if it's going to take you more than a half hour or so is to use a stick from the seat to the brake pedal to hold the pedal down about two inches. Gravity won't be strong enough to draw the fluid out of the reservoir past the lip seals.
When you remove the stick from the seat to the brake pedal, gravity will cause fluid to run to the calipers. That "gravity-bleeding" is the only method I use. When only fluid, and no bubbles come out of the bleeder screw, snug the screw just enough to stop the flow. When both calipers are bled, irritate the brake pedal a few times by pressing it down a few inches. That will wash the few remaining bubbles into them. Open each bleeder screw once more to get those few bubbles out, then tighten the screws.
Some people prefer to use the "pedal-bleeding" method with a helper. The biggest thing to watch out for is to NEVER never ever push the brake pedal all the way to the floor. Some misguided people will tell you to do that. Even some text books tell you that too. Under normal operation, the pedal only goes half way to the floor. Crud and corrosion build up in the bottom halves of the two bores where the pistons don't normally travel. When you press the pedal all the way to the floor, you run the lip seals over that junk and they get ripped. Then you have a sinking brake pedal. That will require a new master cylinder.
Also, these calipers each have two pistons so you're going to have to move a lot of brake fluid to push them out to where the pads contact the rotors. Until that happens you'll be able to push the pedal to the floor. You must be careful to not let that happen. Just stroke it repeatedly no more than half way until the pedal becomes firm.
There are three switches that turn on the red brake warning light on the dash. One is for the parking brake, one is the low fluid level switch, and one is the pressure-differential switch in the combination valve below the master cylinder. He trips when there's a leak in one of the two hydraulic systems. When the pistons haven't been pushed out yet in the new calipers, no pressure will build up in that front system, but it will in the rear system if you push the brake pedal far enough. (It looks like the front system has a leak). That pressure-differential valve is spring-loaded in every car and truck in the world, ... Except in Fords. Normally you can reset that switch by just pressing the brake pedal once the pressure imbalance is fixed, but on Fords you have to know which system caused it to trip, (the front in your case), then do something to the rear system so it can't build up pressure. Now a helper must push the brake pedal very slowly until the light goes out, then he has to hold it there until you tighten the bleeder screw, hose, or steel line; whatever you disconnected or opened. That can be real frustrating because it's easy to miss seeing when the light goes off. That valve typically sticks until enough pressure builds up on one side, then it pops the other way so fast it's easy to miss. You may not know if it is moving back and forth or is stuck in one position. I've seen students use an entire 4-hour class period trying to reset one of those valves on a Ford. All of that grief can be avoided by just never pushing the pedal to the floor.
Keep your container of new brake fluid sealed except when you're pouring some out. Also keep the caps on the reservoir except when you're adding fluid or want the fluid to drain down during bleeding. Brake fluid sucks moisture out of the air. That moisture promotes corrosion of metal parts and it lowers the boiling point of the fluid. Brake fluid boils at well over 400 degrees. Water boils at 212 degrees and when it vaporizes in the hydraulic system it will cause a spongy brake pedal and one type of brake fade.
Caradiodoc
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Sunday, February 6th, 2011 AT 7:51 PM
