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Brake disc wear and advice. 10 years 8 months ago #44254

No mgs where hurt during this process :broon:
mad about cars and bikes :)
if it aint broke dont fix it :)
The following user(s) said Thank You: David Aiketgate, Leigh Ping

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Last edit: Post by Leigh Ping.

Re: brake discs and what to look for 10 years 8 months ago #44260

After seeing some worn brake discs on another MG forum inncluding our own blue mgf. I thought I'd put something together on what to look for as brakes are important.

Below are some mgf rear discs. As you can see the shiney area is different on each disc but the front of the discs look perfect.

As you can see one has a lot more braking surface than the other.
The one with the less shiney braking area was caused by a faulty handbrake on the caliper. Basically the handbrake worked to a point but the piston was not close enough to the disc so a larger gap was there, thus the pads were not rubbed the disc so the dreaded rust got to work eating the discs away.

Now this disc has worn really badly on the inside. This was due to the outer pad being siezed on the carrier so the inner pad did all the work. It also shows some cracks in the face.

This is the same disc. The outside face has worn again but the disc edge has had the dreaded rust on it.

Now this disc has had the face deterioriate to the point that parts of it have come off.
This disc was on a car that sat through winter without moving. Most discs will rust up and some will clean up with emery paper and a good run will bring the disc back to a nice shiney face. But if left too long the disc face will fail.

All of the above discs are mot failures. So when you change the pads check the operation of the handbrake etc.
If a caliper ever sticks and you smell burning, stop the car and let it cool down and slowly make it to a garage, home or call the breakdown people.
If you don't then the disc can get too hot and will fail. Or the pads will overheat and harden to the point there is no braking effect.

So a couple of pointers when replacing pads -
1. Ensure the pad moves freely in the carrier.
2. Make sure the carrier moves freely.
3. Ensure the hand brake works correctly.

If you need to replace a caliper here is a basic way of doing so without draining all the fluid in the system.
Remove the cap on the master cylinder and place a cling film bag etc over the top seal with an elastic band like this -

Go to the caliper (obviously have the car supported and the wheel off the car).
Loosen the 2 carrier bolts then loosen the banjo bolt for the brake line as shown here (the red cap is where the banjo bolt fits).

Now get the brake line put a piece of rubber over each side of the hole and clamp. This will stop any brake fluid leaking out and makes it easier later.
here is a banjo ( i use to make my own lines up thats why i have this to do the photo )

this photo is to give you and idea of how to seal the end :broon:

Remove the caliper and repair, paint etc (ensure piston is fully inserted).

now put the caliper back on the car when placing the brake hose back on new banjo washers must be used.
Tighten to the correct torque.

now remove the cover off the master cylinder.

Open the bleed nipple and place the pipe on to allow the brake fluid to drain into a suitable container.
To speed things up I use a large syringe to draw the fluid through. Once no air is present close the bleed screw and bleed the brakes as normal.

Ok, most of the main jobs have been done. So a little more info to make life easier next time -

Try to replace the carrier flat spring fittings each time (rear brakes)

On the hub, if the disc is removed, always clean the face and outer edge, paint if you have time (outer edge only).
apply copper slip

here is a hub in need of a clean

Place the new disc on the hub use 2 new locating counter sunk screws and check to make sure the disc runs true. I use a 'DTI' (dial test indicator) but you can use a straight edge and rotate the disc and see what the 'run out' is.

If the run out is out of tolerance check to see if the hub face is clean etc.

I hope the above helps. :)
mad about cars and bikes :)
if it aint broke dont fix it :)
The following user(s) said Thank You: west470

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Last edit: Post by MGF MARK.

Re: Brake disc wear and advice. 10 years 8 months ago #44285

Added to the A to Z under 'Brake wear'. Thanks.

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