Binding brakes
Hoping you can give me some help on why the rear brakes on my 2006 MINI Cooper may be binding. I have had the car for about a month now and noticed a bill to the previous owner for stripping and cleaning the rear brakes and a replacement nearside handbrake cable. When I jacked up the car and spun the rear wheels, they seemed a bit tight and only turned a couple of times before stopping.
My local garage said the calipers were seized and the pads had worn a bit oddly, so I let them replace them all, but the problem is still there. They also get hot quite quickly – after around four miles, mainly in traffic, you can’t touch them and they are much hotter than the fronts.
I seem to remember on CM’S MINI project a couple of years ago that you replaced the handbrake cables as the ones on the car were aftermarket and didn’t fit properly. I discovered that there are two different-length handbrake cables and I wondered if the garage that replaced the cable for the previous owner fitted one that was too short, which was causing the brakes to hang on when the handbrake is released. However, my garage has confirmed that the resistance on the wheels is still the same with the cable disconnected, so the problem can only be the hydraulics holding pressure or the pads being too tight in the carrier.
What could cause the hydraulics to lock only on the rear and on both sides? I’m hoping it’s not an ABS fault, although no warning lights are on. The tyre pressure warning light did illuminate, but I put this down to a difference in circumference as the rear tyres need replacing and the fronts are still good. Matthew Smith
As you have confirmed that the handbrake cables are not the cause of the problem, then you need to establish if the friction is being created due to sticking pads or unwanted pressure in the system causing the brakes to apply.
The first point I will make is that the split-braking system on your MINI works diagonally, so any pressure applied from the master cylinder may also be acting on the opposite front brake. This means if hydraulic pressure is acting on the offside rear, it may also be applied to the nearside front. This is worth bearing in mind when testing the system and it may be worth jacking up the front up to ensure there is no binding of the front brakes.
Testing the brakes to see if the problem is due to hydraulic pressure is easily done by jacking up and supporting the vehicle, then spinning the wheel to confirm the resistance present. Next, open the bleed screw on the caliper and, if pressure is being exerted through the hydraulic system, fluid will escape from the bleed screw and the pressure will be released, allowing the wheel to spin freely. If there is no change, then the problem is because either the brake pads or calipers are sticking. This may be due to the slider pins or the pad edges, although I would have hoped that when the garage replaced the calipers they checked the fit of the brake pads and the free movement of the slide pins.
If the problem is due to the hydraulic pressure, the test after securing the bleed screw and bleeding out if necessary, is to unbolt the master cylinder to see if this releases the pressure. If it does then the problem is very likely a faulty servo, which is applying unwanted pressure to the system. If it doesn’t release the pressure, the problem may be in the ABS unit and I would find a garage capable of bleeding the brake system using diagnostic equipment to open the valves in the ABS unit while bleeding. This may then bring to light or resolve any problem in the unit. If there is a problem with the ABS unit, ecutesting.com can inspect and rebuild the it for you.
Autodata informs me that there is a common problem with the rear brakes binding on your model of MINI, but this is due to the routing of the handbrake cables. As your brakes still bind with the cables disconnected, this is not relevant.