Lee’s Mini Prep – Brakes

Brakes

 

Having a decent set of stoppers on the trip is rather important!

 

We find that people often struggle with getting good brakes on their minis. There is the assumption that mini brakes are “just not very good” leading to the expectation that poor brakes are normal. This is not so. Well setup and maintained mini brakes should be very effective.

 

There are three main types of mini brake setup. Very early cars had single leading shoe drum brakes with only one wheel cylinder each side at the front. To be fair these were pretty poor and are very rare to find these days so I’ll skip onto the next type ….. twin leading shoe. These are similar to the early type but have two pistons each side on the front and are more effective that the earlier type. The bulk of NZ minis still on the road have these brakes fitted. Lastly there are disc brakes, which are the best of the bunch. These were fitted to the front only and came in three different sizes depending on the year and model of mini. All models share the same rear setup of drums with a single cylinder either side.

 

Regardless of which brake type is fitted to your mini they all need periodical manual adjustment to compensate for wear in the friction linings. Good brakes should provide a firm pedal, which requires minimal pedal travel in order to function.

 

A long pedal or the need to double pump the brake pedal in order stop is an indication that adjustment or maintenance is required.

 

So, lets assume you are keen to do a thorough check and go through what to look for. Jack the car up, put on axel stands and remove the wheels.

 

The drums are secured by two ¼ UNF phillip head screws so remove these. If the brake drums are in good condition they will now just slide off. If they have wear there will be a small ridge on the inside edge that will catch on the shoe stopping the drum from coming off. To get around this the adjusters will need backing off. On the front there are two adjusters either side and the rear have one either side. The adjusters are ¼” square pegs protruding through the back plate. If these are stiff spray with CRC first and work them back and forth until free. Make sure to have the correct size brake adjusting spanner. Adjusters can round off if you use a poorly fitting spanner and then you’ll be in a pickle.

 

Once the drums are off next thing to inspect is the brake cylinders. Peel the rubber boots back and check for leaks. Under the boot should be dry with no signs of corrosion. Any sign of fluid means the seals are shot and the cylinder needs replacing. In some cases there will be lots of fluid leaking out onto the shoes etc. In this instance the shoes will also be toast. Don’t try and clean them for reuse as they will not work properly and give unstable braking. Also do not waste time trying to re-kit wheel cylinders as they are inexpensive and readily available new.

 

If you do find leaking cylinders it’s probably a good idea to consider changing them all. Reason being that they are all more than likely of a similar vintage, so equally prone to failure. We have found from experience in our workshop that if we just change one leaky cylinder the car will back within a few months for a leaking cylinder on the other side, so lesson learnt.

 

Assuming cylinders are all good or if not you have replaced any that are leaking the next thing to do is look at the shoes and springs. Shoes should have plenty of friction lining and need to be fitted with the “leading edge” in the correct direction. The illustration below shoes a L/H front assembly. Note how the brake shoe has more friction material at one end as shown in red. Ensure you have shoes set like this. The brake springs fit behind the shoes. A bit fiddly to do but that’s how they are designed. Front twin leading edge brake shoes are 1 ½” wide. Make sure you don’t have narrower 1 ¼” wide rear shoes fitted by mistake!

 

 

Rear brakes are pretty much the same deal so follow the same procedure. Rear shoes are 1 ¼” wide, again make sure this is what you have. Front shoes will fit but don’t sit square against the back plate meaning only one edge of the shoe will be in contact with the drum if fitted by mistake. Illustration above is for R/H rear and shows leading edge direction in red.

 

Brake bleeding is pretty straight forward. There are several bleed sequences depending on the braking system you have fitted. The general rule of thumb with most systems is to start at the corner farthest from the master cylinder and work your way forward. L/H rear, R/H rear, L/H front, R/H front. The bulk of minis have a compensator valve on the rear subframe. This prevents the rear brakes from locking during emergency stops. The valve will lock when bleeding the brakes if the pedal is pushed too quickly so, slow and steady is the way to go. Bleed each corner until the fluid runs clear with no bubbles. Sometimes it is necessary to go around the car a few times to get this spot on.

 

If there are any issues getting fluid out of any particular corner it could be that the brake flexi hoses have collapsed. This can also show as a brake that locks but does not release as soon as the pedal is lifted. Happens more often on cars that have been parked up for extended periods but we do come across this fairly often.

 

Adjustment – this is the part that most folks get totally wrong. Usually followed by swapping master cylinders, pipes, wheel cylinders etc because they mistakenly think air is trapped in the system.

 

Front – as mentioned there are two adjusters either side on drum brake cars. All front adjusters are on a cam that lifts the shoe out towards the brake drum. These adjusters need to be rotated in the direction of wheel travel, in other words towards the front of the car on both sides. Turn the adjuster until the wheel locks then carefully back off until the wheel just starts to rotate freely. It’s a very fine adjustment on the front to get things spot on so take your time.

 

Rear – one adjuster either side. These differ from the front as they adjust inwards on both sides. So, turn to the right to tighten. The adjuster has a fur sided cam so as the brake shoes start to make contact you will feel the adjuster go stiff then loosen off as the cam rolls around.

 

The trick here is to turn the adjuster until the wheel locks completely, then back off one quarter of a turn. Job done.

 

Disc brakes – there is no adjustment required at the front, but you will need to keep an eye on the pads as they wear. Rear brake adjustment on these cars is still required as above otherwise there will be excessive pedal travel.

 

On all systems the brakes will need adjusting every 3000 miles or so.

 

Failure to get the adjustment correct will lead to a spongy pedal and brakes that do not function until the pedal is almost on the floor or worse still needs pumping to get a firm pedal.

 

If you find your mini still has a spongy pedal after doing all the above and you are confident there is no air in the system then probable causes will be shoes that have too much wear, brake drums that are worn or have been machined out too far or incorrectly radiused shoes.

 

If it’s worn shoes or drums replacement is the only option. If it’s poorly radiused new shoes this will show if you remove the drum and check for high spots on the shoes. You will see wear marks on the shoe where they make contact and areas that show no wear due to the friction lining not contacting the drum fully. The only way to remedy this is to sand down the high spots on the shoes, reassemble, readjust and road test. Once the shoe is in full contact with the drum the pedal will be firm and at the top of it’s travel.

 

Good luck and give us a shout if you need parts or advice with any of this.