2001 Ford econoline 350 - I have fluid leaking past the seal onto the emergency brake pads on my rear wheel. How do I replace that seal?

You should check again because either a caliper seal or a line is letting fluid escape and yes it also could be leaking into the booster from seals in the master cylinder un bolt it and push it forward to check for fluid leaking past the seals on the master cylinder also make sure the top is tight on the reservoir also check all the way down the left side from the master cylinder to the rear wheels especially at the proportional valve and and the line block fittings for each wheel there has to be a wet spot on something fill up the fluid and pump the brakes without moving then inspect everything and also make sure you have thick linings on the pads

The only things I can think of at the moment, is either brake fluid or rear end fluid.

There are a number of steps for each style of rear brakes. For one thing, if brake fluid leaked onto a disc pad or brake shoe for a drum type brake, the material should be replaced.

Each style of brake has a different Emergency brake unit. The disc Caliper may have 2 braking systems inside 1 wheel.

Really the best advice to give is only do this with someone who has done this before. Or take it to a brake shop. Brakes are a Key area and a mistake can be serious.

Providing you take off the leaking parts, remove the soaked braking pads or shoe, you still have to reassemble and bleed the brakes to restore the function.

I hope my solution is helpful.

Bleed your brakes, starting with Right rear, left rear, right front and ending with left front. You have air in the lines or a bad master cylinder. Bleeding is the cheaper of two options.

Rear To Remove:

1. Remove the brake master cylinder filler cap and remove fluid until the reservoir is half full.
2. Raise and safely support the vehicle.
3. Remove the rear wheel and tire assembly. CAUTION
   Never allow the brake caliper to hang from the brake hose.
   
4. Remove the two disc brake caliper pin bolts.
5. Lift the disc brake caliper from the anchor plate and position the caliper out of the way. Do not disconnect the fluid line.
6. Inspect the disc brake caliper for leaks and replace the caliper if necessary.
7. Remove the pads and retraction clips.

To Install:
CAUTION
Do not allow grease, oil, brake fluid or other contaminants to contact the pad lining material.

1. Install retraction clips.
2. Install the brake pads.
3. Slowly compress the caliper pistons with a large C-clamp. CAUTION
   Use care not to damage the bleeder screw or front disc brake rotor shield.
   
4. Install the disc brake caliper.
5. Install the disc brake caliper pin bolts. Tighten the pin bolts to 26 ft. lbs. (35 Nm) (F-250, F-350 SRW). Tighten the pin bolts to 56 ft. lbs. (76 Nm) (F-350 DRW). Tighten the pin bolts to 46 ft. lbs. (62 Nm) (F-450 F-550).
6. Install the wheel and tire assembly.
7. Lower the vehicle.
8. Fill the brake master cylinder reservoir with DOT 3 motor vehicle brake fluid.
9. Inspect for correct brake operation.

That sounds like the culprit. the seal inside the caliper cylinder goes bad and leaks past the piston.

this could be either the brakes adjusted to tight or wheel cylinder is leaking and making the shoes sticky or the brakes went metal to metal and has seized up in the drums if it has disc brakes the hardware on the calipers are badand need replaced or the calpers are locked up and needs to be replaced i hope this helps

The emergency brake light is also the low brake fluid warning light. Check the level in the reservoir. As the brake pads wear the fluid will drop, so if the brake fluid is low, check the pads to make sure the lining material is thick enough. If you have drums in the rear, check the wheel cylinders to make sure they aren't leaking. If everything checks out ok just add a little fluid to the reservoir and that should take care of the light.

As the brake pads/shoes wear. Fluid level will decrease in the master cylinder resovoir. If the master cylinder ran empty you will need to refill with appropriate brake fluid (should say DOT 3 on cap) and bleed air from the system.

It appears the rear axle shaft seal is leaking. You will need to pull the axle and replace the seal. Then check the rear end for adequate gear oil. The iron filings I am not to sure about. It sounds as if something came loose from the brakes or brake hardware and got chewed up in the drum. You will need to replace the brake shoes and maybe the brake hardware kit. Always change the shoes or pads on both sides when working on brakes, rear or front. If the inside of the drum is not perfectly smooth it will need to be turned or replaced. If this were brake fluid leaking from the wheel cylinder the master cylinder would be low on fluid and your brake pedal would go down much further than normal.