Brake Fluid

The manual & brake reservoir call for DOT3 fluid. It is unclear why this is specified, however it is thought to be to ensure that no silicone (5.0) brake fluid is used which would eventually destroy the braking/ABS-braking system through corrosion.

Choose a main brand of fluid and ensure the container is clean & unopened. Never use brake fluid which has been partly opened or left on the shelf for a time. Brake fluid is hygroscopic, absorbs moisture from the air, and so the boiling point progresses over time from the "dry" boiling point to the "wet" boiling point. Additionally, water separates out from brake fluid under compression and temperature of over 100oC - easily encountered within brake systems.

Favoured brake fluids are Super ATE Blue (DOT4) and Motul 5.1. Ford USA list a special HD Brake Fluid originally intended for a design of truck with brake lines too close to the exhaust (Ford don't build aeroplanes). The Ford HD brake fluid offers a very high boiling point matching the top Castrol fluid at a considerably lower price, part # C6AZ-19542A. The fluid is extremely popular amongst NSX & 911 drivers when it can be found.

Preparing

1. There are three basic methods of accessing the calliper bleed screws: with a pair of wheels off and the car on jack-stands/hydraulic-jack; with one wheel off and the car on it's own jack; with no wheels off & reaching through the spokes or around the wheel. Bleeding should start at the wheel furthest from the brake master cylinder - for RHD this is the left rear, for LHD this is the right rear (as viewed from behind the vehicle).

2. Ensure the handbrake is applied, the car is in gear or Park, and the ground is level. Jack the car up at the correct lifting point, and place it on jack stands. The front wheels must be chocked if the rear wheels are off the ground.

3. Place newspaper around & under the brake Master Cylinder reservoir and over the fender/wheel-arch. Brake fluid is extremely corrosive and attacks steel & paint by permeating through the paint. Spilt brake fluid must be wiped & flushed off any surface including wheels by liberal use of water.

4. Wipe the Brake Master Cylinder area completely clean of all dirt, particularly the reservoir lid.

5. Open the Brake Master Cylinder and ensure the fluid level is at Full.

At no point during brake bleeding must the brake fluid reservoir fall below half full. If the brake fluid reservoir does fall below half full then air will enter the system requiring bleeding to be commenced again and risks damage to master cylinder seals (exposed to previously uncontacted bore areas that could be corroded/dirty).

At no point should the brake pedal be fully floored, bleed only by repeatedly pressing it half-way. Some people prefer to remove the strainer in the Master Cylinder and syphon out half of the fluid and replace with fresh fluid to avoid pumping old fluid through.

Bleeding the Brakes

6. Starting at the caliper furthest from the Master Cylinder, remove the rubber cap from the bleed screw and attach a one-man-bleeder to it. A one-man bleeder consists of a government official or a short piece of flexible hose with one-way valve attached - the latter is required. Place the end of the hose in a jug which is weighted down with stones for stability. Under the jug place a few pieces of newspaper to catch any drips.

6. Despite the name "one-man bleeder" a second person is essential to bleed the brakes effectively. Once the brake pedal has stopped descending there is no positive pressure to prevent air seeping back into the brake system by the bleed screw threads.

7. The second person presses the brake pedal half-way down only on command, during which time the bleed-screw at the caliper is opened to allow fluid and air-bubbles to be ejected from the braking system. Once the brake reservoir is half empty it must be refilled. This process is repated until only clean fluid emerges at the caliper end and no air bubbles are seen, so ensuring only air-less fluid exists between that caliper & master cylinder.

8. Whilst the brake pedal is descending for the final time, with no bubbles coming through, tighten the bleed screw to ensure air is not drawn back into the system. Bleeder screw tightening torque is 6.9-9.8Nm.

9. Verify the pedal will not sink and there are no fluid leaks when pressed. Verify the brake lines are not damaged, bulging, deteriorated or loose.

10. Wash any spilt brake fluid off wheels, pathway & car body immediately.

11. Repeat this procedure at the other three wheels, doing the other rear wheel first and then the front wheels.

12. Finally verify there are no fluid leaks and the brake master cylinder reservoir is full. Start the engine and test the brakes at just rolling speed. The brake pedal should not sink to the floor, the pedal should be firm and the brakes should engage with little pedal travel and a considerable distance from the stop or bottom of edal travel.
Dealers are best used to bleed brakes, but many do not change the fluid which should be done every 2 years - water corrodes ABS systems & caliper piston bores.

Notes

1. Many owners find one brake bleeding is not enough. If they bleed the brakes again on a 2nd day (flushing plenty of fluid through) and ensure they cinch the bleeder screw finally off before the pedal has stopped descending then the pedal will achieve the brick-like feeling and maintain it for some time. Tapping a spanner on a caliper during bleeding can help to free up air bubbles caught on the inside surfaces.

2. Stainless Steel braided brake lines are available in DOT-approved form (Goodridge). Despite ensuring DOT approval, it is advisable to get a supplier to put heatshrink tube over the braiding before putting fittings on. This prevents dirt getting underneath the braiding & acting as a hidden abrasive.

Even with DOT-approved (essential) brake lines must be checked annually and ideally replaced every 4 years. Regarding cost, a set of 4 brake lines from Goodridge is around £60.00, the US price around 70$US. Probe lines will fit the 626 with a little modification to the brake line strut bracket.

Goodridge can also make up front clutch line sets for the gearbox to clutch slave cylinder flex line. RHD owners should bleed their brakes more frequently considering the location of the master cylinder and reservoir over the rear-bank exhaust downpipe.

3. The cheapest supplier of replacement brake master cylinders is Trussville Mazda, MTX-equipped cars with ABS costs 120$US/£75.

Last Upload: 31st January, 2002. V1.50a
URL: http://homepage.ntlworld.com/dorothy.bradbury/probemx/p_m12.htm