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Brake Master Cylinder Replacement
 
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Pelican Technical Article:

Brake Master Cylinder Replacement

Time:

2 hours2 hrs

Tab:

$150 to $250

Talent:

**

Tools:

Socket set, flare nut wrenches, power bleeder

Applicable Models:

R50 MINI Cooper Hatchback (2002-06)
R52 MINI Cooper Convertible (2005-08)
R52 MINI Cooper S Convertible (2005-08)
R53 MINI Cooper S Hatchback (2002-06)

Parts Required:

new master cylinder

Hot Tip:

use paper towels and plastic bags to contain any fluid leaks

Performance Gain:

better braking

Complementary Modification:

replace brake booster
How to Maintain and Modify your new MINI

This article is one in a series that have been released in conjunction with Pelican Parts' new book, How to Maintain and Modify your new MINI The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 500+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any MINI owner's collection. The book is due to be released in late 2015. See The Official Book Website for more details.

Without a doubt, your brakes are one of the most important systems on the car. The heart of the brake system is the master cylinder, which controls the hydraulic pressure of the entire system. Unfortunately, over many years, the master cylinder has a tendency to wear out and leak. The leakage can occur internally or externally, resulting in a weakened braking system. If you have any problems with your brakes, and you think that it's related to the master cylinder, you should probably replace it.

Replacing the master cylinder on the R50/R52/R53 is not very difficult and should take no more than two hours. The first step is to disconnect the negative terminal going to the battery in the rear trunk. This is a safety precaution against any possible electrical problems.

You'll want to try to get as much brake fluid as you can out of the fluid reservoir on top of the master cylinder. Open the cap on the reservoir and remove the strainer. Using a fluid pump or turkey baster, get as much of the old fluid out as you can. This helps prevent excessive spilling of brake fluid inside the engine compartment. It's also helpful to stuff a bunch of old rags or paper towels under the master cylinder to absorb any spills.

On both Cooper and Cooper S vehicles, the front plastic firewall splash shield will need to be removed in order to access some of the mounting hardware for the master cylinder. On the Cooper models, you will need to remove the airbox, battery box and move the fuse box in order to access the splash shield. On the Cooper S, you will need to remove the airbox and move the fuse box. Please see our articles on airbox removal and transmission mount replacement for more info. Once removed, you will have better access to the master cylinder mounting nuts and also the brake lines attached to the side of the cylinder.

Disconnect the electrical connectors going to both the brake fluid level sensor on the top of the reservoir and the DSC pressure switch at the bottom of the cylinder (if so equipped). Now locate the two hydraulic lines going to the master cylinder on the right side of the car. Both lines use an 11mm fitting. You'll need to loosen these fittings to remove the brake lines from the old master cylinder. The best way to do this is to use a flare-nut wrench. These special wrenches are designed to wrap around hydraulic fittings and prevent rounding off the nut. It's very easy to round off brake line fittings, especially if there is any corrosion present around the master cylinder. Break the fittings loose and un-thread those until you can pull each brake line out of the master cylinder. Make sure you have plenty of paper towels under each brake line to catch any fluid that spills out. Once free, place the ends of the brake lines inside some plastic bags to catch any brake fluid that spills out of the lines.

On the left side of the master cylinder, you will see a long T25 Torx bolt that holds the fluid reservoir in place. Loosen and remove the bolt. Now locate and remove the two 13mm nuts holding the master cylinder to the brake booster on either side. You'll probably need an extension to reach both nuts. Once both nuts are removed, carefully move the brake lines out of the way and pull the master cylinder out of the brake booster. You may hear a slight hissing when you do this. Don't worry. What you're hearing is the brake booster depressurizing. Unhook the vacuum line going to the brake booster from the brake fluid reservoir. Carefully pull the fluid reservoir out from the top of the old cylinder and set it to the side. You'll want to leave the feed hose going from the reservoir to the clutch master cylinder connected. Keep in mind that you'll probably also have fluid spill out from the reservoir. Keep the paper towels underneath.

Once the old master cylinder is removed, you'll want to remove the DSC pressure switch from the bottom and transfer it to the new master cylinder.

Now take the new master cylinder and lightly lubricate the insides of the grommets on top with brake fluid. Remove the plastic protective plugs from the new master cylinder and pop the reservoir in until it seats fully. Re-fit the T25 Torx bolt back into the master cylinder. Now position the new master cylinder in place on top of the brake booster and bolt in down. Torque the two 13mm nuts to 21Nm (15ft-lbs.)

Next, carefully position both of the brake lines into the new cylinder and thread in the brake line fittings. Be very careful when doing this as these are very easy to strip out. Go slowly and make sure they thread in easily by hand. Torque the fittings to 14Nm (10ft-lbs.). Now reinstall the throttle control module.

Now fill the master cylinder with new brake fluid and pump the pedal a few times to build up pressure. Do not pump the pedal without fluid in it. You could score and damage the inside of the cylinder bore, rendering it inoperable. The last step is to bleed the braking system of air. You'll have to bleed all of the brake lines at each wheel to get all of the air out of the system.

Shown here is a new master cylinder for your MINI.
Figure 1

Shown here is a new master cylinder for your MINI.

Here is the master cylinder mounted to the brake booster after the air intake box/battery box and fuse box have been removed.
Figure 2

Here is the master cylinder mounted to the brake booster after the air intake box/battery box and fuse box have been removed. The remaining plastic panel on the firewall must be removed for better access to the hydraulic lines, electrical connections and mounting nuts. Remove the plastic nut (green arrow) to remove the plastic panel.

Disconnect the electrical plug (green arrow) going to the DSC pressure switch at the bottom of the master cylinder (if your car is equipped with DSC).
Figure 3

Disconnect the electrical plug (green arrow) going to the DSC pressure switch at the bottom of the master cylinder (if your car is equipped with DSC).

Disconnect the electrical plug going to the brake fluid level sensor at the top of the brake fluid reservoir (green arrow).
Figure 4

Disconnect the electrical plug going to the brake fluid level sensor at the top of the brake fluid reservoir (green arrow).

Take off the brake fluid reservoir cap and carefully pry out the strainer screen inside (green arrow).
Figure 5

Take off the brake fluid reservoir cap and carefully pry out the strainer screen inside (green arrow). Once removed, use a fluid pump or turkey baster to suck all of the old brake fluid out of the reservoir.

Remove the long T25 Torx bolt (green arrow) holding the brake fluid reservoir to the top of the master cylinder.
Figure 6

Remove the long T25 Torx bolt (green arrow) holding the brake fluid reservoir to the top of the master cylinder.

Use a 11mm flare-nut wrench to loosen and remove the two hydraulic fittings on the right side of the master cylinder.
Figure 7

Use a 11mm flare-nut wrench to loosen and remove the two hydraulic fittings on the right side of the master cylinder. Make sure to place a rag or some paper towels below the hydraulic connections before you finally remove them to catch any fluid that may leak out.

ThisPicture shows one of the two hydraulic fittings removed from the master cylinder.
Figure 8

This picture shows one of the two hydraulic fittings removed from the master cylinder. Carefully pull the line ends out of the bores on the master cylinder.

Remove the two 13mm nuts that hold the master cylinder to the brake booster (green arrows).
Figure 9

Remove the two 13mm nuts that hold the master cylinder to the brake booster (green arrows).

Now carefully pull the master cylinder off the brake booster.
Figure 10

Now carefully pull the master cylinder off the brake booster. You may hear a slight hissing as you separate the master cylinder form the brake booster. This is normal as the brake booster is depressurizing. Now pull the brake fluid reservoir off the top of the master cylinder and set it to the side with the clutch hose still attached.

Remove the DSC pressure switch from the old master cylinder and fit it to the new master cylinder.
Figure 11

Remove the DSC pressure switch from the old master cylinder and fit it to the new master cylinder. Also place the included O-ring around the new master cylinder.

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Comments and Suggestions:
Turbo Comments: Think I need a new reservoir... I pressurized the reservoir with brake bleeder pump, it reached about 10 psi and fluid was everywhere. I can't tell where it coming from but I'm guessing around the seams on the back side. What part are needed to complete this job other than reservoir? How do I disconnect the clutch line and reattach? Thanks!
November 24, 2016
  Followup from the Pelican Staff: The reservoir may be available. Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
sparkyj Comments: What is the easiest and best way to remove only the top plastic reservoir without disrupting the master? And can this carefully be done without introducing air into the system lines?
August 26, 2016
  Followup from the Pelican Staff: Remove the fluid using a pump. Then pop it off then on. As long as you don't open a line once removed, no air should enter the system. Install the new reservoir, then allow it to vent as fluid is added, the air should escape. - Nick at Pelican Parts  
SC Comments: Good points...and I tend to agree – Although following that line of thought, we probably shouldn't be fitting BBKs onto the 1st Gen anyway..!

It was just that I've seen it often mentioned in forums as a likely solution to the deeper pedal issue when the JCW/Brembo 4 pots are installed on the R53, more balancing the ratio of the calipers to the master cylinder....However, I guess it's just theory and 'forum talk' as I've never read about anyone actually 'doing' it....

Perhaps even a new R53 OEM cylinder will help, as I'm sure mine will be the original, so may be a bit tired....I just don't know if that will 'stiffen' things up any...??

Anyway, thanks again to Nick and all at Pelican.
December 6, 2013
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it. - Nick at Pelican Parts  
SC Comments: As with all of your articles, great write up and advice...I use this site a lot for my R53 Will you ever release the planned book ?!

Does anyone know if the R56 Master Cylinder can 'easily' be fitted to the R53..??

I've just fitted the JCW/Brembo BBK to my R53, and while the brakes probably haven't fully bedded in yet, there is a noticeable deeper pedal travel, which I'm not sure I like, would like the pedal to be much further towards the top as it bites....

From reading around, I understand some of the reasons why there may be more pedal travel with a BBK fitted, but some have mentioned that fitting the slightly larger sized R56 Cylinder will help with a stiffer pedal etc....

Question is, I can't seem to get any confirmation or experiences of anybody actually fitting it...?

Appreciate any thoughts....
December 3, 2013
  Followup from the Pelican Staff: It's risky to recommend brake system modifications. Highly trained and paid factory engineers do the best the can with that--it's hard to beat that in a little experimental shop. - Nick at Pelican Parts  

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