Practical Automotive Maintenance: Brake Calipers

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Brake Calipers

06.01

00:00	The brake calipers are responsible for converting hydraulic pressure into mechanical force, clamping the brake pads against the disc to give us the friction that we need.
00:09	Looking at a section view of a simple caliper, it looks a little bit like the reverse of a master cylinder.
00:15	There's a connection between the brake hose and the caliper that supplies the hydraulic pressure.
00:19	The pressure inside the body of the caliper acts on the pistons in the caliper.
00:23	There are many different layouts of brake calipers, but the fundamentals remain the same, regardless of the details.
00:30	The amount of clamping force applied to the brake pads is a function of the fluid pressure and the total surface area of all the pistons in the caliper.
00:38	Let's have a look at a couple of types now, starting with what we're most likely to find on basic OE cars, the sliding caliper.
00:45	In this type, the piston or pistons will only sit on one side of the caliper.
00:50	The caliper body can slide on its mount, meaning that we get equal clamping force applied to both pads, despite the pistons only being on one side.
00:58	The other style that we'll find in high performance OE cars and motorsport style calipers is where the caliper is fixed rigidly to the upright and there are opposing pistons on each side.
01:09	The number of pistons can vary wildly from as few as two to as many as 12 in extreme cases.
01:15	In the majority of performance applications, four and six piston calipers are by far the most common.
01:20	This is where it will have two or three pistons per side of the caliper respectively.
01:25	Single piston sliding type calipers suffer from significant compliance compared to fixed multi -piston calipers.
01:31	This is usually very obvious to see with the wheel off and if we watch the caliper while someone else firmly applies the brakes.
01:38	From a performance perspective, this compliance results in a longer pedal travel in order to achieve the required braking force.
01:45	This also makes it more difficult to accurately modulate the brakes in a race application.
01:50	Fixed calipers are usually made from aluminium and maybe either cast or billet parts and in general terms, caliper designs fall into two categories.
02:00	Multi-piece or monoblock.
02:01	Multi-piece calipers generally consist of two pieces bolted together.
02:06	This helps reduce the cost and manufacturing complexity.
02:09	Monoblock calipers on the other hand are made from a single piece of material which makes them more expensive and challenging to manufacture.
02:16	An advantage of monoblock calipers is that they tend to have higher stiffness for a given weight.
02:22	This is simply down to having fewer bolted joints as part of the main structure.
02:26	The stiffness of the caliper reduces the compliance in comparison to the sliding caliper we already discussed.
02:32	Before finishing up, let's discuss some of the common things that can go wrong with a caliper that will require maintenance.
02:38	The most common issue with sliding caliper is sticking or even seizing entirely.
02:43	This happens when the pins or the slides become corroded, dirty or lack lubrication, preventing the caliper from moving freely.
02:50	This results in brake pads that might not retract properly or one pad may drag constantly against the rotor.
02:57	Over time this causes uneven wear, heat build-up and reduced braking efficiency.
03:02	Typical signs of this occurring are the car pulling to one side when braking and uneven pad or rotor wear.
03:09	These issues can all be easily confirmed by a visual inspection.
03:13	We're looking for one pad that will be significantly more worn than the other side.
03:18	Often this issue starts as a result of the weather boots that are designed to prevent water and dirt ingress into the slides becoming damaged or split, so inspecting these is always a good idea.
03:29	The fix for this issue depends on the severity of the problem.
03:32	If it's minor, the slider pins can be removed, cleaned with a wire brush and brake clean and then reinstalled with some fresh anti-seize.
03:40	If the damage is more substantial, the pins or even the entire caliper may need to be replaced.
03:46	Another common problem is damage to the pistons or their seals.
03:49	Often the two go hand in hand as an imperfect piston surface will in turn damage the seal it's running against.
03:56	This causes fluid to get past the seal compromising hydraulic pressure and leading to reduced braking force and possible brake failure.
04:04	This sort of damage can be caused by debris in the brake fluid or it can be caused by damage to the dust seals in the caliper that are designed to keep the dirt from making its way between the piston and the caliper bores.
04:15	On this basis it's always worth a thorough visual inspection of the dust seals during a pad change.
04:20	These issues can be identified in a few different ways.
04:24	Visible fluid leakage is an obvious giveaway with wet oily residue around the caliper piston area, backing plate or inside the wheel.
04:32	A drop in master cylinder reservoir fluid level is also a sure sign that fluid is finding its way out of the system.
04:38	So, if no other leaks are obvious then there's a good chance a scored or damaged piston and its seal will be the culprit.
04:45	Again depending on the severity of the issue there's a few different solutions to this problem.
04:50	If it's mild the seal itself can be replaced, but this will only work if the piston and bore surface are still smooth and uniform.
04:58	So, it requires careful inspection or we'll just end up having to pull everything apart again when the same issue with a new seal occurs a few weeks later.
05:06	Damage like this can be dealt with at home however it's often going to require the bore and the brake caliper to be honed to achieve a perfectly smooth surface.
05:15	And this is usually better left to a brake specialist who can restore and rebuild the caliper for a minor cost.
05:21	Let's quickly summarize the key points in this module.
05:24	Brake calipers convert hydraulic pressure into mechanical force, forcing the brake pads against the rotors.
05:30	Calipers are broken down into fixed multi-piston types which are common on performance oriented vehicles and floating types which are common on lower end vehicles.
05:39	Floating calipers use sliding pins and can suffer from flex and uneven pressure.
05:44	A common issue with these calipers is the sliding mechanism becoming partially jammed or entirely seized.
05:50	Fixed calipers incorporate pistons onto both sides of the caliper and offer superior rigidity making them ideal for high performance application.