Morris Minor - brake repairs

Symptoms of problem : Poor footbrake - handbrake not working at all.

Vehicle : 1957 Morris Minor 1000 Pick-up (LCV) - a CKD MM built in Petone, New Zealand. (part Series II, part Minor 1000 I think!)

Time : 2-6 hours depending on which repair or replacement is needed     Difficulty : 4-5/10   

Parts required :  New brake cylinders  Cost : approx. 16 each (2005 prices)

Parts required :  New master cylinder + 2 new copper washers for banjo bolt (note there are 2 different washers needed)  Cost : approx. 55 (2005 prices) 

Tools required :  Set of AF spanners, brake-bleeding kit, jam-jar, brake fluid, hammer, screwdrivers, etc..

With any brake problems, don't cut corners or try to save money - replace EVERYTHING that is not 100% OK or you may regret it later. I would recommend replacing the entire existing braking system of your Morris Minor before investing in a Servo unit or Disc-brake conversion. The original braking system works reasonably well if it is all working correctly and is kept in good condition. Always use new brake fluid (Dot 4).  I purchased a 'one man' brake bleeding kit, which was quite cheap and works well - saves a lot of shouting 'up - middle - down - middle - up' and arguing with whoever has 'volunteered' to help you bleed the brakes ! 

1    Brake Master cylinder

The brake master cylinder is mounted under a cover plate held down by 8 brass set-screws on the driver's side floorpan - just behind the brake pedal which drives the main piston directly through a mechanical linkage + plunger/pin. There is a hole in the cover plate to allow topping-up of the brake fluid.  Access to the brake master cylinder is by removing this cover plate. The master cylinder is held in place by 2 bolts which run through the chassis member which runs fore/aft on the vehicle - i.e. these 2 bolts run from L to R across the vehicle if you are sitting in the driver's seat. When originally installed in the factory, the heads of the bolts are to the right - under the RH torsion bar, which made them very difficult to remove - in my MM the heads of the bolts are to the left and the nuts are to the right - a sure sign that the Master cylinder has been removed at some stage in the past. Once the bolts are this way around, removal of the Master cylinder is much easier. Refer to other websites or renovation manuals for details of the technique which involves levering the torsion bar just far enough out of the way to remove the original factory-fitted bolts - I'm a bit unsure about this technique because the force needed to move the torsion bar far enough out of the way is considerable.

The Haynes manual has a long-winded method for removing the master cylinder, which involves a lot of un-necessary dismantling and time-wasting. It is a lot easier and quicker than they suggest to remove and replace the master cylinder.

Step 1 - Removal of the master cylinder - remove the 2 mounting bolts as described above. At the rear of the master cylinder is a 'banjo' bolt (see photo below - the banjo bolt is just visible below the drain plug) - this screws into the body of the master cylinder and has 2 brake pipes screwed into it - it acts as a T-piece - the brake pipe feeding the rear brakes heads back along inside the chassis member (for about 6 inches then it exits through a hole with a rubber grommet) and the other brake pipe feeding the front brakes exits sideways through a hole in the chassis member directly beside the banjo bolt. These 2 brake unions need to be undone, but the banjo bolt should be left on the master cylinder until after it is removed from the vehicle. Using a 7/16ths AF spanner, undo each of the 2 unions in turn - the one at the rear has limited access, so it is a slow job - one eighth of a turn at a time! The side union is easily undone from underneath the vehicle. Carefully push the rear union and pipe back along inside the chassis member until it clears the threaded hole in the master cylinder - if you unhook this brake pipe from the 2 clips on the outside of the chassis member which hold it further back towards the rear wheels, this makes the whole length of pipe move more easily backwards - be careful not to damage the end of the brake pipe.

With both brake unions disconnected and out of the way, the master cylinder can now be easily removed - it may still be a tight fit in the chassis leg, depending on how much rust is there, but can now be levered upwards at the rear end. The 'drive' from the brake pedal is simply a pin which fits into a hole under the rubber boot at the front of the master cylinder - you do not need to disconnect anything at the front of the master cylinder luckily. Lever the rear end of the master cylinder gently upwards until the master cylinder can be pulled firmly backwards off the pin and lifted out completely.

mastercyl1.jpg (1081186 bytes)

Step 2 - Installing the new master cylinder.  Clean out the dirt from inside the chassis member - you may want to paint inside it with Hammerite or some other anti-rust compound while you have the chance. Check that no dirt goes into the open ends of the brake pipe unions. Smear the brake pedal pivot and spring with copper or graphite grease - check that the small clevis pin and R-clip or any other parts do not need replaced.  Installation is the reverse of removal.

Pressing the brake pedal fully down allows you to lift the pin fully up and engage it in the hole under the rubber boot - then you can slowly slide the master cylinder down into position - keeping the pin fully engaged as you do so. It may need some 'gentle persuasion' with a few taps from a hammer as it is quite a tight fit. Go under the vehicle, use a screwdriver to lever the mounting holes into line, then install the 2 mounting bolts, with their heads on the inside (i.e. to the left) of the chassis member.

Reconnecting the brake pipe unions is probably the most time-consuming part of the job now - a lot of patience is required to work in the restricted space inside the chassis member and get the rear brake pipe fitting into the threaded hole, then tightened up 1/8th of a turn at a time. I find that if you have the brake pipe itself fully seated in the hole, this helps the thread of the union to 'catch' properly. Never force a brake fitting because they can cross-thread and damage the fittings.

Finally, bleed the brakes, then look closely for any brake fluid leaks around the banjo bolt or brake unions. Check that there is about 18mm of free travel on the brake pedal before you feel the resistance of the brake master cylinder piston - if there is too little or too much free travel you will need to adjust the nut on the brake pedal plunger/pin at the front of the master cylinder - use a 16mm AF open-ended spanner. (There may or may not be a locknut here as well)

2    Front brakes

Most of the stopping power of an MM (which is not considerable by 2005 standards) comes from the front brakes. There are 2 brake cylinders on each side, each driving a brake shoe. A flexible pipe connects the front brake cylinder on each side to a chassis-mounted bracket which connects to the incoming fixed pipe, and a short length of metal pipe connects across the backplate to the rear brake cylinder. The bleed nipple (10mm AF) fills the upper hole on this rear brake cylinder.   Note : in the handbooks the 2 brake cylinders in each front wheel-drum are both described as 'leading brake cylinders' (which is technically correct) - however to reduce confusion I've called these 2 front brake cylinders   front   and   rear   i.e. there is one front and one rear brake cylinder on each side of the vehicle ..... hope this makes sense   ;-)

front brake 1   Front-brake horror picture ! 

Leaking rear brake cylinder and grease bypassing the worn stub-axle oilseal - repairs needed ! The brake shoes look new simply because there has been hardly any braking happening here recently !

Replacing a front brake cylinder - for example, the left-hand front brake cylinder

Replacing a brake cylinder is reasonably straightforward, but can take a hour or two, depending on what problems are encountered. On both sides of the vehicle, the front brake cylinder is easier to replace than the rear one. 

CAUTION : Make sure you buy the correct brake cylinder for whichever one of the four you are replacing. The 2 brake cylinders on the RH front wheel are identical to each other and the 2 brake cylinders on the LH front wheel are identical to each other, but mirror-images of the RH ones.. Different manufacturers use different part numbers, but these are the numbers of the cylinders I used :  Left rear cylinder and left front cylinder : 35001 - 4266 (P4845)   Right rear cylinder and right front cylinder : 35000 

Jack up the vehicle, remove the road-wheel and use car-ramps, axle-stands or large wooden blocks in addition to the trolley-jack for safety.  Remove the 2 Philips head screws holding the brake drum on (the heads are often mangled so you may need an impact screwdriver - when replacing them, make sure you tighten them just a little). There is a hole in the brake drum to allow you to see the two brake adjusters (one for each brake cylinder/shoe - you can see one in the photo above), you should 'release' the brake shoes by turning each adjuster fully anti-clockwise - you will see the heads of the adjuster screws (on the front left brake drum) at about '2 o-clock' and '8-o-clock' approximately. Remove the brake drum, if necessary tapping it outwards with a 2lb hammer - if the drums are worn there is often a 'lip' of rust which can catch on the brake shoes as you try to slide the drum off and a bit of levering force and patience may be needed.

CAUTION : Note carefully which hole in the brake shoes that the springs go into, and the position of the springs behind the brake shoes.

The springs holding the brake shoes are strong, but it is easy to remove and replace the shoes - they can be levered up, or down, then out onto the wheel nut studs, then the springs are easy to remove or replace. Lift the brake shoes and springs off and lay them somewhere in the same position as they were installed in the brake drum.  Soak the flexible pipe union and the inlet pipe union in WD40 or Plus-gas (Diesel is also a good penetrating/releasing agent) and have a cup of coffee.

Carefully undo the union (7/16ths AF) of the short fixed pipe. Bend the fixed pipe GENTLY a few mm to clear the threaded hole in the old brake cylinder. Each of the 4 front-wheel brake cylinders is held in place by a 1/2 inch AF bolt and at the side by a smaller bolt - I found that a 9mm socket was the closest fit for this side bolt, but none of my AF sizes was correct, which is surprising for an old British car. These 2 bolts must be removed to release the brake cylinder from the back-plate.

front brake 2   flexible pipe

                  Left front cylinder removed from backplate                                Cloth over open end of pipe. Inner flexible pipe chassis bracket

CAUTION : Don't let dirt get into the open end of the brake-pipe and watch where the drips of brake fluid go.

On the front brake cylinder there is the complication that the flexible pipe has to be removed first because the outer end covers the upper brake cylinder securing bolt head. This involves undoing the union at the lower end of the chassis-mounted bracket, then the large nut with lock-washer which holds that inner end of the flexible pipe onto the bracket. The flexible pipe is now free to turn completely as you unscrew it from the brake-cylinder - there should be a copper washer at this cylinder end of the flexible pipe. Make sure no dirt gets into the open ends of the fixed brake pipe. When replacing this leading brake cylinder, removing the short fixed pipe completely (see photo below) makes life easier, but this short pipe can be difficult to reconnect - it needs to be in EXACTLY the correct position at each end before the union threads will 'catch' the threaded holes in the brake cylinders - don't force anything or you will damage the threads.

backplate pipe    new brake cylinder

                     Short fixed pipe which crosses the back-plate                                                   New left-side leading brake cylinder

Installing the new brake cylinder is the reverse of removal - don't over-tighten any of the unions (which may be brass). Smear the bottom of the brake adjuster mechanism and the metal ends of the brake shoes with copper or graphite grease. Check that the brake shoes are correctly seated - one end in the slot in the end of the opposite brake cylinder and one end onto the brake adjuster, which in turn slides on the thin metal cover of the brake cylinder piston. Check that all 4 ends of the 2 springs are correctly seated in their holes in the brake-shoes (remember, the springs should be behind the brake-shoes)  Tap both brake-shoes to centralise them, which makes putting the brake drum back on easier.

Replace the brake drum, gently tighten the 2 retaining screws. One at a time, adjust the brake adjusters by turning them clockwise until the brake shoes completely 'lock' the wheel, then backing them off one or two 'clicks' only - just enough for the brake drum to turn freely, although it may scrape slightly part way around - don't worry about this, as long as it is not rubbing too much - the shoes will soon bed in.

Bleed the brakes, taking care to keep the Master cylinder topped up with brake fluid at all times. Test drive the vehicle, then check for any leaks in the braking system. Re-bleed the brakes after a week or two and recheck the setting of the brake adjusters.

3    Rear brakes and Handbrake

The MM rear drum brakes have 2 shoes, but only 1 cylinder. This brake cylinder is an unusual design - there are 2 pistons - the inner piston has a rubber cup behind it and is moved by the hydraulic pressure of the brake fluid in the brake pipes. Immediately above it is a lever which is moved by the pulling of the handbrake cable or by the movement of the inner piston. Above this lever is a second piston which presses against a thin metal yoke, which in turn presses against the end of the lower brake shoe. The whole brake cylinder can move up and down about 12mm in a slot, which allows it to exert a force on both brake-shoes. The outer piston moves about 5-6mm in total when driven by either the footbrake hydraulic pressure or the force of the handbrake cable.

These rear brake cylinders are prone to internal rusting and seizing up and if the outer piston also seizes up, the handbrake will not work either.

I am intending to replace the rear brake cylinders in the next few months - more info and photos then ....

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