Please note: This information is from Bill Sherlock and is regard to bleeding the brakes on our Aerotrek taildraggers (older and newer versions) and on our A240 tricycle-gear aircraft.

A220 taildraggers with Berringer dual piston type brakes (red master cylinders):

To bleed the brakes you need a bleed nipple and a large syringe (at least 250ml) full of DOT 4 brake fluid with a transparent 3/16" ID tube attached. Autozone sells an ideal syringe advertised for topping up gear oil.

I have made several bleed nipples in the field by drilling a 3/32" hole through the center of a 5mm bolt with the head cut off. But a more elegant bleed nipple may be available. (note: check with Aerotrek Aircraft for availability and cost)

First, disconnect the master cylinder (for the brake side being bled) from the (rudder pedal - do not detach the brake lines) for the left seat only, and lay the master cylinder down with the in and out brake line compression fittings vertically up. Make sure the parking brake lever is in the off position. Before proceeding further have the bleed nipple and full syringe handy with all the air purged out of it to the very end of the attached tube.

Ideally, the brake caliper pistons should be pushed fully into the cylinder. I do this by removing the caliper and allowing it to hang on the hydraulic fluid hose, then push the pistons fully into the caliper and jam in place with an appropriate shaped piece of wood. If the brake pads are at all worn, then the brakes will not bleed properly without doing this. If the brake pads are new, you may get away with leaving the caliper assembled on the wheel.

Use rubber/latex gloves. Remove the Allen head set screw from the caliper, and the steel ball should then fall out starting a weep of fluid. Put finger over the hole to stop fluid leak as soon as the set screw and ball are removed. If the ball stays in place, just a minutest touch of the brake pedal will dislodge it, so have a catch tray handy. I've lost count of the telephone conversations starting with "what steel ball?", "mine didn't have one" -- they ALL have one!

Remove finger and screw the the bleed nipple in place, followed by finger over the bleed nipple. Check there is no air in the syringe or the attached tube (just like a nurse does in ER). Remove finger from bleed nipple and attach syringe with tube.

During the above procedure some fluid will be lost, but provided the brake fluid reservoir (in the cockpit, on the firewall, just slightly higher than the Beringer brake cylinders) still has some fluid, no more air will have been introduced, gravity makes sure of this. In practice, I can get to this stage with barely any loss at all, and therefore, the next step is to empty the reservoir from the top with a separate syringe.

Get a helper to hold a second 3/32" ID tube firmly pressed into the bottom of the brake fluid reservoir with the other end into a sizable catch receptacle.

Steadily apply pressure to the syringe allowing the fluid to flow fairly fast upwards through the system. At the same time, get the helper to move the appropriate loose master cylinder around, tapping it and generally trying to orientate the output tube, to tease the air upward out of the loose cylinder. The air moving through the translucent tubes will clearly be seen. The more "teasing" the helper does with the loose cylinder, the quicker the operation. Sometimes it takes a couple of syringe fills. Between syringe changes, apply finger to nipple and ensure the syringe is purged of air.

Before the end of the final syringe stroke, get the helper to release the catch tube enough to fill the reservoir to at least half full. This will ensure no air is introduced while the syringe and bleed nipple is removed and the ball and set screw are refitted.

I find this method of bleeding the A220 brakes to be foolproof. It should be noted that Aeropro use a different method to initially charge the brakes with fluid. They remove the reservoir and connect a temporary pressure bleeder and tube to the reservoir, remove and lay down the master cylinders from both sides. They thus charge the brakes with fluid from top to bottom. When bleeding the brakes I have tried both methods. I have not had much success with Aeropro's procedure.



A220/Eurofox taildraggers with pre-2009 single piston brakes (silver master cylinders):

To bleed the brakes you need a bleed nipple and a syringe (at least 100ml) full of DOT 4 brake fluid with a transparent 3/16" ID tube attached.

I have made several bleed nipples in the field by drilling a 3/32" hole through the center of a 5mm bolt with the head cut off. But a more elegant bleed nipple may be available. (note: check with Aerotrek Aircraft for availability and cost)

Make sure the parking brake lever is in the off position. Before proceeding further have the bleed nipple and full syringe handy with all the air purged out of it to the very end of the attached tube.

The master cylinders on the right seat pedals have built in reservoirs with a serrated edge screw top. It is not necessary to remove the screw top. Working with the master cylinder in the side being bled, In the screw top is an Allen head set screw, remove it. Wrap plenty of shop towel paper or rag tightly around the master cylinder to catch fluid being pushed through the system.

Ideally, the brake caliper pistons should be pushed fully into the cylinder. I do this by removing the caliper and allowing it to hang on the hydraulic fluid hose, then push the piston fully into the caliper and jam in place with an appropriate shaped piece of wood. If the brake pads are at all worn, then the brakes will not bleed properly without doing this. If the brake pads are new, you may get away with leaving the caliper assembled on the wheel.

Use rubber/latex gloves. Remove the Allen head set screw from the caliper, and the steel ball should then fall out starting a weep of fluid. Put finger over the hole to stop fluid leak as soon as the set screw and ball are removed. If the ball stays in place, just a minutest touch of the brake pedal will dislodge it, so have a catch tray handy. I've lost count of the telephone conversations starting with "what steel ball?", "mine didn't have one" -- they ALL have one!

Remove finger and screw the the bleed nipple in place, followed by finger over the bleed nipple. Check there is no air in the syringe or the attached tube (just like a nurse does in ER). Remove finger from bleed nipple and attach syringe with tube.

During the above procedure some fluid will be lost, but provided the reservoir still has some fluid, no more air will have been introduced, gravity makes sure of this. In practice, I can get to this stage with barely any loss at all.

Steadily apply pressure to the syringe allowing the fluid to flow upwards through the system. At the same time, get a helper to watch the master cylinder for leaking fluid from the removed set screw hole soaking and overwhelming the rags or paper towels. Sometimes it takes a couple of syringe fills. Between syringe changes, apply finger to nipple and ensure the syringe is purged of air.

With this type of brake cylinders, a couple of 100ml syringe full's should be enough to remove all the air. remove the bleed nipple and refit the ball and set screw. Refit the Allen head set screw into the top of the master cylinder, then with a rag or paper towel over the top of the cylinder to catch excess fluid, pump the brake pedal. Excess fluid will squirt from the tiny breather hole also in the screw cap.



A240 / Eurofox tricycle-gear single piston brakes:

To bleed the brakes you need a bleed nipple and a syringe (at least 100ml) full of DOT 4 brake fluid with a transparent 3/16" ID tube attached.

I have made several bleed nipples in the field by drilling a 3/32" hole through the center of a 5mm bolt with the head cut off. But a more elegant bleed nipple may be available. (note: check with Aerotrek Aircraft for availability and cost)

Remove and hang the instrument panel to gain access to the Magura master cylinder reservoir. Remove the screws from the lid of the master cylinder and remove the lid and rubber cap seal. Make sure the brake lever is in the off position. Before proceeding further have the bleed nipple and full syringe handy with all the air purged out of it to the very end of the attached tube.

Wrap plenty of shop towel paper or rag tightly around and under the master cylinder to catch fluid being pushed through the system. Or, a helper can remove fluid from the reservoir with a second syringe as the bleeding process progresses.

Ideally, the brake caliper pistons should be pushed fully into the cylinder. I do this by removing the caliper and allowing it to hang on the hydraulic fluid hose, then push the piston fully into the caliper and jam in place with an appropriate shaped piece of wood. If the brake pads are at all worn, then the brakes will not bleed properly without doing this. If the brake pads are new, you may get away with leaving the caliper assembled on the wheel.

Work on one wheel brake at a time. Use rubber/latex gloves. Remove the Allen head set screw from the caliper, and the steel ball should then fall out starting a weep of fluid. Put finger over the hole to stop fluid leak as soon as the set screw and ball are removed. If the ball stays in place, just a minutest touch of the brake pedal will dislodge it, so have a catch tray handy. I've lost count of the telephone conversations starting with "what steel ball?", "mine didn't have one" -- they ALL have one!

Remove finger and screw the the bleed nipple in place, followed by finger over the bleed nipple. Check there is no air in the syringe or the attached tube (just like a nurse does in ER). Remove finger from bleed nipple and attach syringe with tube.

During the above procedure some fluid will be lost, but provided the reservoir still has some fluid, no more air will have been introduced, gravity makes sure of this. In practice, I can get to this stage with barely any loss at all.

Steadily apply pressure to the syringe allowing the fluid to flow upwards through the system. At the same time, get a helper to watch the master cylinder for over flow and soaking and overwhelming the rags or paper towels, or remove excess fluid with a syringe. Sometimes it takes a couple of syringe fills. Between syringe changes, apply finger to nipple and ensure the syringe is purged of air.

With this type of brake cylinders, a couple of 100ml syringe full's per side should be enough to remove all the air. Remove the bleed nipple and refit the ball and set screw.

Move to the other wheel and repeat the process.

Then ensure that the master cylinder reservoir is filled to the level hole and refit the seal and cap.


      --- Bill Sherlock
      Aerotrek western-USA sales/service rep