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Brake Master Cylinder Overhaul

This is a surprisingly easy job to do on the Capri and all you need is a clean area to work on, and a bit of care when you are working on the innards of the cylinder.  To overhaul the master cylinder involves stripping the unit and replacing all the rubber components with new ones supplied in the 'overhaul kit'.

Before you start you will need to ascertain which master cylinder is fitted to your car.  It is either Girling or ATE.  Mine was the former which can be identified by looking at the plastic reservoir which should have the Girling logo embossed in the plastic.  It's a G shape with the tail of the G in the shape of a hand.  You need to obtain a brake master cylinder overhaul kit of the correct sort.  I got mine from a Capri spares company for about £16 but you can probably still order them from any big motor factors.

The kit comprises several rubber seals and washers and all will become more obvious once the master cylinder is in bits.

First stuff an old towel around the bottom of the master cylinder to catch the brake fluid.  You need to undo and remove the three brake pipes by undoing the unions with an 11m open ended spanner.  These should come undone nice and easily.  With these undone all you need to do now is to unbolt the master cylinder from the front of the servo by undoing the two large 15mm nuts.  The master cylinder will simply lift straight out of the car.  Note that there is a rubber seal here that needs to be rescued.

Tip the cylinder upside down and let the fluid in the plastic reservoir drain out.  Now give the plastic reservoir a good hard tug and it will pop out of its place.  Remove the two rubber seals that hold it in place - these are included in the kit.  The next job is to remove the plastic circlip from the servo end of the cylinder.  It is easy to remove with a pair of long nose pliers.  Take care not to lose it as it is not in the kit.  With the circlip removed the next job is to remove the retaining pin.  This is located in the top most recess where the reservoir was located.  It is a small round pin which you can just get a pair of pliers onto.  To remove it do the following: take a screwdriver and clamp it vertically in your workbench.  Then place the exposed part of the piston onto the screwdriver and push down gently.  This will push the piston (it's spring loaded) up the cylinder a bit allowing you to remove the retaining pin.  The pin should come out really easily this way.

With this pin and circlip removed you will be able to extract the piston completely.  It may need a gentle tap to get it out and take care not to bend anything or scratch the cylinder wall.  The piston is in two separate halves and the top half will need a few taps to encourage it to come out.  Eventually you will have both halves out and you can place them on the bench and give them a good clean with a cloth.

You will see which bits are to be replaced by comparing what you have in the kit with what you see.  To do the top most part you need to unclip the spring at the end which allows you to get to the washer and seal assembly.  They are easy to change over but make sure that the seals are the correct way round!

The lower part of the piston is a bit more tricky as this has a much stronger spring on it.  To remove this you need a 2mm Allen key and if you look down the spring you will see where to put it.  I found this required a good hard twist to undo.  Note that you need to undo it whilst the spring is compressed down to take the pressure of the screw.  With the screw undone the spring retainer will come away together with the spring.  This allows you access to the other two sets of seals which can now be replaced.  Note that the seals are all identical but are fitted as mirror pairs (i.e. with their flanges pointing away from each other).

With the seals replaced you need to refit the strong spring and refit the retainer using the Allen screw.  Again you need to compress the spring by hand before the screw will locate.  With both halves of the piston finished it is time to refit them in the cylinder.  Wipe down the inside of the cylinder as best as you can and pour in some new brake fluid; just enough to line the cylinder walls.  Soak the piston assembly in new brake fluid and insert slowly into the cylinder.  With the second part of the piston in place you can pop the plastic circlip back in place with your fingers.  To refit the retaining pin you need to press the piston down the cylinder as before and insert the pin by hand.  When you release the piston it will lock back on the pin and the whole thing is secure.

Fit two new seals into the recesses (wipe over in brake fluid to lubricate) for the reservoir and fit the reservoir by pushing it down firmly until it pops back into place.

The master cylinder is fitted back on the car by following the  procedure for removal in reverse.  However you should recharge the cylinder first by filling up the reservoir and allowing the fluid to drain down until it pours out of the three holes.  Then refit the three brake pipes taking care not to go crazy and over tighten them.  Always hold the spanner down at the union end to make sure you don't use too much force.

All the remains is to re-charge the system with new brake fluid (DOT 4 spec or DOT 5).  However this can be a bit tricky when there is so much air in the system.  I actually found that the best way to get things started was to completely remove the front nipples from both sides and allow gravity to let the fluid work down into the brake calipers (keep topping up the reservoir!).  Eventually it will start to seep out and you can refit the nipples (now fit your bleed kit).  Clean up any fluid that went on the caliper.  You can start to pump the brake peddle to try and get the fluid moving.  This may take a long time so be patient.  If you are getting nowhere fast then undo the nipples again and leave it for half an hour to drain down.  As a last desperate measure you could try removing the unions at the master cylinder and pumping the brakes to try and free the air trapped in the cylinder.  Make sure you have a towel handy as the fluid will squirt out when you press the peddle.  You will get all the air out eventually, trust me!

For details of how to bleed the brakes to completion check out the other pages in the service guide.


 

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