Brake calipers are one of the essential components of a disc brake system. So when the pads are replaced, do you give the calipers the attention they deserve?
Most would agree that any caliper that's leaking, is damaged, has a frozen piston or is causing uneven pad wear obviously needs attention whether it's time to replace the pads or not.
But what about calipers that have no obvious problems? Do you leave them alone or do you rebuild or replace them?
Those who subscribe to the "don't fix it unless it's broke" school of repair philosophy say they're doing customers a favor by leaving the calipers alone. Consumer advocate groups that are hypersensitive about "unnecessary" brake work also agree that a "hands-off" policy is best unless there is a valid reason for rebuilding or replacing the calipers. The Motorist Assurance Program (MAP) guidelines also say caliper rebuilding or replacement isn't necessary unless there's an obvious problem. But there's another side to the issue.
Use Brings Wear
Brake calipers, like any other mechanical component, wear and corrode with age. Every time the brakes are applied, the back-and-forth motion of the caliper pistons produces a slight amount of wear. But what causes the most problems is moisture contamination of the brake fluid. By the time brake fluid has been in service for two years, it can contain as much as 3 percent water - enough to produce visible corrosion in the caliper bores and on steel pistons.
As the surface of the pistons become rough, they scour the seals with every application of the brakes. Before long, the seals begin to leak. The fluid contaminates and ruins the linings, causing uneven braking or grabbing. And if the leak is bad enough, a loss of pedal and/or brake failure may result.
Even if a caliper isn't leaking, it's still aging inside. Rubber piston seals and dust boots age with time and exposure to heat. Besides keeping the fluid where it belongs, piston seals help retract the pistons when the brakes are released. When a piston moves out, it twists the square cut seal slightly. This helps pull the piston back when the brakes are released.
But as a seal ages and loses elasticity, it doesn't do as good a job of pulling back the piston. Consequently, the pads start to drag resulting in reduced fuel economy, possible brake pull and/or accelerated or uneven pad wear.
When boots get old, they often crack or split, allowing dirt and water to enter the piston bore area. The result can be accelerated seal wear, piston corrosion and sticking.
Damage Often Hidden
But even if the caliper dust seals and piston seals are still in relatively good condition, the calipers are often full of corrosion and gunk.
Calipers are a low spot in the brake system so sediment typically settles in the piston bores. When you push back a piston to replace a set of pads, you shove the contaminated fluid back towards the master cylinder. And, as we all know, it doesn't take much gunk to cause problems in a master cylinder or ABS hydraulic modulator unit.
One alternative here is to use a brake hose clamp (not Vice-Grips) to block off the brake hose to the caliper. Then open the bleeder screw before you push back the piston. This will allow the old, dirty fluid to escape out the bleeder screw rather than back towards the master cylinder.
It adds an extra step, but you have to loosen the bleeder screws anyway to flush and bleed the system, right? So doing it before you push in the pistons can minimize the risk of creating any problems that weren't there before you serviced the brakes.
Here's another tip: when you're flushing or bleeding the calipers, replace the bleeder screws with new ones and put a dab of synthetic brake grease on the threads to prevent them from seizing. This will save somebody some grief the next time the bleeder screws have to be opened.
Do a First Class Job
>If you want to do a first class brake job, minimize the risk of a comeback and maximize the life of the brakes, then recommend rebuilding or replacing the calipers for preventive maintenance.
Leaving the calipers alone is no guarantee they won't leak or experience problems six months down the road - especially if the vehicle has a lot of miles on it. In fact, leaving them alone may be asking for trouble.
As the pads wear, the caliper pistons move gradually outward. This exposes more of the piston to environmental contamination - especially if the dust boots fit poorly, leak or are cracked. So the outer area of steel pistons is usually rusted. If the pistons are shoved back into the caliper bores when new pads are installed, any corrosion that's on the pistons will be forced past the seals. And if the exposed surface of the pistons is rusted and pitted, it won't take be long before the seals start to leak.
Even plastic pistons can cause problems if dirt has build up on the piston surface. Any roughness or contamination here will eventually cause problems if it comes into contact with the piston seals.
Cause For Concern
Yet some shops are fearful that replacing or rebuilding calipers without obvious cause may be seen as an attempt to pad the repair bill. In California, the Bureau of Auto Repair is especially sensitive to consumer concerns about replacing parts "unnecessarily."
According to one caliper supplier, this has had a chilling effect on caliper sales in that state. The number of calipers being replaced in California is down about 40 percent compared to a few years ago.
In the rest of the country, it's a different story. Caliper sales are up. What's more, according to one recent aftermarket survey, nearly two-thirds of the shops doing brake work are installing loaded caliper assemblies when the calipers are replaced. The rest either buy bare calipers or rebuild their customer's old calipers.
Making the Decision
Whether you rebuild a caliper yourself or replace it with a remanufactured caliper or loaded caliper assembly - one that comes complete with pads and hardware - will depend on the condition of the caliper, how much your customer is willing to spend, and your own repair preference.
Any caliper that is cracked, damaged, has worn mounting or slide surfaces, elongated pin or guide holes, bore damage or severe bore corrosion should be replaced.
If only one caliper needs replacing, the new caliper should have the same type of piston (steel or phenolic) as the one on the opposite side. Steel and phenolic conduct heat at different rates, so a difference side-to-side might allow the fluid behind a steel piston to run hotter than the fluid behind a phenolic piston increasing the risk of fluid boil and pedal fade.
Many caliper suppliers are now following the OEM lead and using the same type of pistons that came in the OEM calipers. This should reduce the risk of a piston mismatch if only one caliper is replaced, and the remaining caliper is still the original.
Balanced Friction
If you're installing a loaded caliper assembly, also make sure the friction material is the same side-to-side. A difference in friction characteristics side-to-side can cause the vehicle to pull toward the more aggressive side.
Many suppliers of loaded calipers are now using "application specific" friction materials instead of more universal friction material that fits a wider variety of applications. Application specific friction materials are designed to closely match the braking characteristics of the OEM linings.
This helps assure "like-new" brake performance and decreases the risk of mismatched friction if only one caliper is replaced - unless the pads have been replaced before with some other type of linings.
Do It Yourself?
If you're rebuilding a caliper yourself and it has steel pistons, chances are the pistons will be corroded. The temptation is to clean them up with sandpaper and reuse them - but don't!
Sanding will knock off any protective nickel or chrome plating that remains setting the stage for even more corrosion. Replace the pistons if they're corroded or rough.
With phenolic pistons, check the fit of the piston in the caliper bore. Some older pistons have a tendency to swell, which can cause sticking. Replace any piston that does not fit properly in its bore. The piston should also be replaced if the sealing surface is nicked, scratched or cracked.
For best results, use the same type of replacement piston (steel or phenolic) as the original.
Most caliper bores will show signs of corrosion and pitting. As long as the bore isn't too bad, it can be cleaned up by lightly sanding with fine grade (#600 grit or finer) crocus cloth. The bore should be lubricated with brake fluid and polished with a circular motion to smooth out minor imperfections.
Honing with a drill-powered brake hone may be necessary to restore a more badly worn or corroded caliper. But if you have to increase the inside diameter of the bore by more than about .002 inches, the caliper is too far gone to be rebuilt. You'll have to replace it.
NOTE: These guidelines apply to cast iron and steel calipers only. You should not attempt to rebuild an aluminum caliper because the bore in an aluminum caliper has an anodized surface to protect against corrosion. Sanding the bore would destroy the thin anodized coating leaving the caliper vulnerable to corrosion, leakage and piston sticking. So if the bore is rough or pitted, replace the caliper with a new one or a remanufactured caliper that has been sleeved with stainless steel.
Don't use anything other than brake cleaner or brake fluid to clean the caliper bores or pistons. Petroleum or mineral based solvents can leave a residue that will attack and damage rubber seals. For reassembly, use brake fluid or a small amount of silicone brake grease - never ordinary chassis grease!
Check All Hardware
Another important area that deserves attention are the caliper slides and mounting hardware. Calipers must be free to slide back and forth to center themselves over the rotor. If the slides, mounting bushings or pins are badly corroded, the caliper can hang up causing uneven braking and pad wear.
To prevent problems here, clean and inspect the caliper mounts, replace the hardware and apply high temperature synthetic brake grease to the caliper mounts, slides, guide pins and bushings. Synthetic grease that contains moly solids will last longer than other types of brake grease. Synthetic grease with moly solids or shims can also be applied to the backs of the brake pads to dampen vibrations and suppress noise.
Other items that deserve close scrutiny include the brake hoses (replace any that are cracked, bulging, leaking or damaged), steel brake lines (replace any that are leaky, damaged or severely corroded), the wheel bearings (check for looseness, and regrease and adjust if they are the serviceable type on an older rear-wheel drive vehicle), and the brake rotors (check thickness, runout and condition).
Rear Locking Calipers
A growing number of front-wheel drive cars today have four wheel disc brakes, and many of these have locking rear calipers for a parking brake.
Overhauling a locking rear caliper is not an easy job because the self-adjusting mechanism inside the piston is difficult to disassemble, clean, lubricate and reassemble correctly.
In many instances, the parts are too badly corroded to be reused anyway, and replacement parts may not even be available. So replacing a locking rear caliper with a new or remanufactured unit may be your best option if the caliper is not working properly.
If you do attempt to rebuild a locking caliper, be sure to lubricate the self-adjusting mechanism with synthetic brake grease prior to reassembly. This will keep the adjuster working freely and help protect it against further corrosion.
As a rule, vehicles with four wheel disc brakes tend to have a slightly lower brake pedal than those with a conventional front disc/rear drum arrangement. This is because the rear pads have to travel a further distance when the brakes are applied.
This condition can be aggravated if the rear caliper pistons are out of adjustment or the self-adjusters are frozen and leave too much space between pad and rotor. This can also happen if you replace a caliper and forget to adjust the piston to eliminate excess play between pads and rotor (which should be less than 1/16 inch).
Working the parking brake lever will usually take the play out of an adjuster. If the brakes don't adjust, the self-adjusting mechanism is frozen and the caliper needs to be overhauled or replaced.
The reverse can also happen. A rear caliper can drag if you install a new set of pads and there isn't sufficient play in the self-adjuster for the pads to clear the rotor. To back off the self-adjuster on GM and Ford brakes, the piston must be screwed back into its bore - which usually requires a special tool. If the self-adjuster fails to back off, then the caliper will need to be overhauled or replaced.
Don't Forget Parking Brake
Adjusting the parking brake cable is also important for the locking caliper to function correctly. Too tight and there may not be sufficient travel to work the self-adjusters and/or the brakes may drag. Too loose and the parking brake may not hold the vehicle.
To adjust the parking brake cable on a locking caliper, release the parking brake then loosen the cable turnbuckle. Pump the brake pedal several times to make sure there is normal clearance between pads and rotor. Tighten the cable turnbuckle until the levers on the calipers just begin to move (zero slack in the cable).
Rotate the wheel to make sure the pads are not dragging. Then push either caliper lever as far away from the cable as it will go while watching the lever on the opposite side.
If it moves, the cable is too tight and should be backed off slightly. Repeat this procedure for both sides. The final adjustment position should lock the brakes within four to seven clicks when engaging the parking brake.
