Rear Brake Disks

Rear Brakes	Rear Calipers

Now that 20,000 miles had passed, I began to notice that the brakes, while still very powerful, were becoming difficult to 'feather' to a stop. I had changed the front disks to cure a judder under medium braking and I had noticed then that the rear brakes disks were corroded. I had another look in January 2000.

Rear disks are heavily corroded. Although the pads are relatively new they have never been able to get through the crud to the meat of the disk. They should have been changed before I bought the car! As usual, the current owner pays for the mistake of the previous one.

Looking at the pads it was obvious that they were relatively unworn, but they had been replaced onto disks which are heavily corroded and the pads could not get through the rust and crud to give their share of the braking effort. With the tremendous pressure on the pads during braking the friction surface of the disk should be clean and bright. Another hint - while cleaning the wheels I noticed that there was almost no brake dust on the rear wheels. While it is true that the front brakes make most of the braking effort, there should still be some dust on the rear wheels if the disks are working properly. Having noticed this absence of dust before on one of my old Granadas I decided to change the disks.

I ordered the disks from Ford at £68 each plus VAT. They are 270mm diameter ventilated (no, I don't know the new money either, it is 10.75 inches diameter). The first two were corroded, so I had to refuse them and wait for another set which arrived the next day. Ford wanted £40 for a set of new brake pads, plus VAT, so needless to say I went to Halfords for them where a Halfords set of pads were £16 inclusive of VAT! The guy there said that Halfords pads are made by Mintex, so they aren't rubbish.

On a Sunday it was wheels off and get started. The brake caliper is fixed onto the hub by two 13mm allen bolts through the rear at 11 and 1 o'clock each protected by a rubber boot, and with a brake caliper allen key suitable for Fords, (it will fit most Sierras and Granadas as well as the Scorpio), these are off quite quickly and the caliper is lifted away from the disk. The brake pads float on a shelf in the caliper on each side of the disk and pressing them towards each other one at a time will drop them free. The disk is secured by a little star washer on one of the wheel studs. This is prised off and the disk pulled off the hub without pursuasion.

On the left, the brake caliper allen key. This has seen hard use on both my Sierras and my four Granadas – and now my Scorpio!

On the right, the rear brake piston retractor. Although it seems a bit of a luxury, it makes the sometimes difficult job of retracting the piston very easy. The little pins on the silver disk engage in quadrants on the face of the piston. The large black disk fits inside the caliper and is held, while the large hexagonal nut is turned, which forces the piston back into its cylinder.

If you work on your own brakes – get one!

Because the self-adjusting mechanism winds the piston face further and further towards the disk to compensate for the worn pads, the single rear piston on the caliper needs to be wound back into the caliper in order to free enough space for the new disk and pads,. This can be tricky, but I have a Sykes Pykevant tool (see above) for the job. This both winds the piston and presses on it, and pushing the piston back into the caliper was a doddle. A careful check to make sure the piston boot is dry ensures that there is not a leak through the piston seal. The new disk is cleaned with spirit to clean off any preservative and then placed on the hub, and the caliper slid over it. The two 13mm bolts are tightened and the protective rubber boots are replaced. (Missing them will allow corrosion to start and it may be impossible to remove the allen bolts the next time, so don’t forget to put them back!!)

Even though the brake pads were nearly new they had to be discarded and the new Halfords pads fitted. Any new disk must have new pads to bed into. For the torque settings for this job see Torque Settings

New disk and pad in place. The wheel stud threads have been cleaned by wire brush and a light coating of copper-grease applied.

For the Torque settings, see Torque Settings

In less than two hours the job was complete, and I took the car for a test run. The brake pedal has to be pumped at first to bring the new pads up to the disk and there is still a slight sponginess which will last while the new pads are bedding in; but the sharpness has gone now and progressive braking is much easier. They recommend using the brakes carefully for the first 200 miles to allow them to bed in.

The new disk shines through the Ultima alloy wheel shod with the new Michelin MXM.

By June 2001 and after running the car for three years, all four brake disks and pads and all four tyres have been replaced. The brakes are smooth and powerful without a hint of judder. The tyres are quiet and after sixteen months wear is quite satisfactory.

It has occurred to me in the past that since they removed asbestos from brake pad material the wear on brake disks is much greater than it used to be. My old Cortina Mk I (MNK 459C) as far as I know ran on the original front brake disks and still had them when it eventually gave up the ghost after about 15 years (Yes, the front suspension turrets gave way and the MacPherson struts came through the bonnet!). It was usual to replace brake pads after only about a year to eighteen months, but the brake disks had virtually no wear.

Today it seems, the brake disk is far more sacrificial than it used to be. The brake pads now last four times as long – but they are cutting through brake disk material instead! It is probably the longer service intervals as well as the change in pad material which has prompted this. Manufacturers cannot risk pads wearing through during a twelve-month service interval and made the friction material much harder.