Replacing A Master Cylinder And Servo Unit

How To Replace A Master Cylinder At Home?

Its important to replace a master cylinder if it has started bleeding. The cylinder is often installed on the wall that separates the engine from the vehicle’s inside. It might be equipped with just a vacuum servo unit.

A pushrod connects the master cylinder towards the braking system in most cases. However, it may well be located on the driver’s side of the engine bay and attached to the pedals by a crossed rod in some automobiles, notably those initially built for left-hand drive.

A damaged or leaky servo unit must also be changed. If the brake pedal is difficult to depress and all other brake issues have been addressed, it may be defective.

Monitor the air filter’s performance before actually changing it since it may be influencing slow performance. It should also be replaced every three years, or 36,000 miles or 60,000 kilometers.

Draw a drawing of where all the brake systems or electrical connections, such as those to the stop-lamp button or fluid-level indicator light, is before disconnecting them.

This is critical if the vehicle has dual brake lines. Outline the cylinder body and label them accordingly.

Take special note of the locations of the screws, shrubs, and pedal returning springs. Examine how the pushrod is attached to the brake pedal; there could be many holes in the pedal rod.

If you empty the brake fluid from the master cylinder, you should not reuse it.

Getting ready to replace the master cylinder

Start by removing the reservoir first from the master cylinder if that can be disconnected. If it hasn’t been emptied yet, use your fingertips to close the bottom ports to collect any spills.

The braking fluid in the reservoir can be emptied or kept in and closed. In actuality, it is preferable to open the entire system.

Open the offside front-wheel bleeding valve to empty the cylinder. If the vehicle has a splitting arrangement, release the offside rear-wheel valve. If in confusion, open every bleed nipple in the tum first, then the other. You can check out this guide if your brake fluid is not coming out while bleeding.

Pump the brake pedal until the cylinder is empty and place a jar under each nipple. Because brake fluid is corrosive, avoid splashing it on your car’s paintwork. If something is mistakenly spilled, clean it up immediately.

If you end up leaving the master cylinder filled, use sticky tape to close the breathing gap in the breather lid. Alternatively, put the top onto a thin piece of plastic.

A tiny quantity of fluid would still leak, so place several cloths beneath the cylinder and brake pipes.

On some vehicles, the reservoir is an independent device that may be disconnected from the cylinder and replaced.

If it’s filled, close the breather hole and rapidly cover up the bottom ports with your fingertips as you extract the reservoir to collect spills.

Unplugging a pushrod

Align the splitting pin and draw it out with pliers to disengage the pushrod. Next, extend the hose clamp pin horizontally.

Some automobiles have a clevis pin that connects the pushrod to the rear brake arm and is kept in line by a splitting pin or clamp.

The connection may be located so far up the lever arm that you must detach a boot shelf or trim panel to access it.

Align the split pin with pliers and draw it out. Next, extend the clevis pin outward. When reattaching, use a new setup pin and ensure the rod is connected to the right hole.

If the connector is difficult to reach, consider inserting the pin through a piece of sticky tape and wrapping the tape around your fingers to keep it in place while you look for the opening.

Taking out the master cylinder

Try checking and renewing the brake cables before separating the brake lines from the master cylinder; either cover the lines to avoid leakage or empty the fluid into a bottle.

Remove all electrical connections to the fluid-level caution indicator and the stop-lamp switches.

Other elements in the path, including the choke or throttle cords, may also need to be disconnected.

The master cylinder is held in place by twin nuts and bolts or nuts and screws in most cases. There may also be a clip anchoring it to the flap’s interior. Also check this guide on removing the broken bolts from an engine.

The master cylinder on certain cars is located within the front baggage carrier and is unbolted from within the front tire arch. To access the nuts, unscrew the wheel.

Start by removing the cylinder’s nuts and pulling them off, careful not to lose any nuts.

After installing the new master cylinder, secure line and CV joints by fingers first, then a wrench; they are conveniently cross-threaded.

Changing out a servo unit

When replacing the servo unit separately, removing the master cylinder without detaching the brake lines may be feasible – these may well be sufficient to enable the master cylinder to be relocated to another end.

If this is the case, there is no need to empty the master cylinder. If that isn’t the case, detach the pushrod and replace the master cylinder as stated.

Look at the sealant quality between both the servo and the master cylinder and replace it if needed.

Unscrew and remove the servo unit from its wall mounting. If there is indeed a gasket in between the servo and the bulkhead, inspect it for wear and replace it if required.

After assembling, bleed the system if the master cylinder has been detached somehow.

Unplug the servo again from the master cylinder. Examine the situation of any seals between the servo and the cylinder, and replace them if required.

Please take note of how and why the vacuum hose is attached to the servo, then detach it by loosening the hose clamp.

Please note how the servo unit is connected to the braking system and then unplug it. Next, remove the servo from its support frame.

Remove the servo unit. Unless there is a gasket between the servo and its attachment, inspect its situation and replace it if it is damaged.

Changing out a servo air filter

On many of the newer vehicles, a felt air filter is installed on the back of the servo unit, surrounding the pushrod.

To refill the filter, removing the servo is not typically required. You should really be able to access it from within the vehicle or between the back of the module and the bulkhead.

A quilted rubber vest protects the filter. Move the gaiter down the pushrod to reveal the filter, then pry it off. Cut the new filter along its radius with a paring blade.

Slide the filter from over the pushrod, place it in its casing, and squeeze the filter’s two sides tight. Reinstall the rubber gaiter that was covering the filter.


What should a master cylinder replacement cost?

If you hire a competent technician to repair your brake master cylinder, the overall cost should be between $250 and $550.

A new brake master cylinder as well as any associated parts (such as fresh brake fluid) will range between $100 and $300. In addition, labor will cost between $150 and $250.

Is it difficult to change the master cylinder?

With most cars, changing a brake master cylinder is a simple procedure that can be completed in your own yard.

You may need to shift certain parts, hoses, or cables to make room for others. Keep note of where they will go and their corresponding attachments so you don’t lose them.

Bottom Line

The brake master cylinder is an important part of a vehicle’s braking mechanism. If this failure happens, the braking capacity of your car will be diminished or eliminated.

Changing the brake master cylinder is essential to prevent this safety danger.

To prevent chasing or to move little packages of air throughout the system, a manufacturer may prescribe an alternative technique. As an alternative, follow bleeding the brakes system measures outlined here.