Master Cylinder Removal
MASTER CYLINDER REMOVAL
by MMOC Technical Advisor, Rob Thomasson
The Minor brake master cylinder is unusual as it is situated in the chassis rail under the drivers left heel. This was apparently done to keep the engine bay clear for the flat four engine that never made it into production.
This makes it difficult to remove but not as difficult as some would make out. The problem is the two bolts that come through the chassis leg from the side where the torsion bar is found. The bolts have special thin heads to clear the torsion bar. This makes extraction difficult as the torsion bar is in the way. The Morris Minor workshop manual advises removal of the front suspension and this is what some garages will bill you for! However this is how you do it yourself. Remember brake fluid is more inflammable than petrol so no smoking!
Raise the car on axle stands or ramps to improve access later. Remove the carpets and the little plate on the right of the transmission cover. You can either remove the transmission tunnel cover as well, or go underneath the car to undo the unions on the master cylinder.
Pump out the brake fluid by simply undoing one bleed nipple on a wheel and pumping the brakes. Catch the fluid with a piece of tubing and a jar. Dispose of the old fluid as it cannot be used again.
Use a brake spanner to remove the two unions. If you look carefully down the chassis rail you will see a brass T piece. One end points down the chassis rail and one pipe is screwed into this. It requires patience to undo this union as access is poor. I use a 7/16 open ended spanner and a lot of care.
Now go under the car and undo the second union on the T piece. This one is a doddle in comparison. Next come the two nuts which hold the master cylinder in place. You may need to hold the bolt heads to stop them turning. Now push the bolts slightly out so the heads are proud of the chassis. Take a BIG screwdriver and place the tip under the first bolt head. Lever down so the torsion bar bends sufficiently to allow the other bolt to pull out. Release the screwdriver and place the tip in the hole left by the first bolt. A posidrive type often goes in the hole better. Again lever the rod down and remove the second bolt.
When you put things back, put the bolts in from the other side. There is always enough clearance for the nuts. Morris was overcautious when they designed things. They wanted to be sure the bolts would not touch the torsion bars, as any scratch will cause them to crack at a later date.
Master cylinder stripping and re-assembly
Having removed the unit give it a good clean with paraffin. Don't forget to do inside the reservoir. Now wash your hands to keep everything clean.
Remove the large circlip from the end. It is possible to use a pair of point nosed pliers to do this but it is much easier with the proper circlip pliers. Unless the unit is seriously corroded it will pop apart very easily.
Use a piece of rag on a stick to clean the inside of the bore. Examine the inside carefully. If there is any corrosion the cylinder must be replaced. This is due to the rough nature of the rust which will rip up the new seals very quickly. The old seals can be eased off with a small screwdriver . It is possible to just cut them but the former way gives you practice for fitting the new ones.
Don't forget to remove the old valve washer which sulks at the end of the bore. Be careful to fit the bits correctly as in the diagram. NOTE THAT THERE ARE TWO SIZES OF MASTER CYLINDER: 7/8" AND 13 /16". The size is written on the side of the casting. Make sure you get the right size seals. You may decide to replace the seals in the slave cylinders at the same time.
Replacing the master cylinder is easy, but removing the air from the system can be difficult (while the master cylinder is out you may decide to remove all the rubbish in the chassis leg and put some anti rust agent down there).
Getting the union back in the end is a fiddle. It may be easier to drop the cylinder into the chassis fit the pipe and then fit the cylinder in properly.
To get the push rod from the pedal in place, the master cylinder pushes slightly down the chassis and then pulls forward. Another technique is to remove the pipe that goes down the chassis leg from the far end, as this allows you to fit the master cylinder end more easily. You can then fit the pipe to the master cylinder before you fit the master cylinder into the chassis. Do take care not to kink the pipe when you put it back if you use this method.
When you put the master cylinder back put the bolts in from the other side. There is a one in thousand chance that the bolts will foul the torsion bar. If so there will be a clunk as you go over bumps and you will have to put the bolts in the right way round (or grind a bit off the end).
Taken from the new MMOC Technical Manual, available excusively to MMOC members.
Advice is given by the MMOC in good faith. The Club and its officials can in no way be held responsible for advice given.