I’m a mechanic and I know the feeling when a job turns to crap and you lose your flow. But don’t panic, you’re in the right place and about 5 minutes from now you’ll understand what the problem is and how to fix it.
Top 4 reasons a cars brake caliper won’t go in:
- Incorrect wind-back procedure
- Binding caliper pins
- Seized caliper piston
- Collapsed brake hose
In this post, you’ll learn why your car’s brake caliper won’t go in, how to diagnose the root cause and how you can fix it.
How The System Works
Your car’s brakes are still operated by good old-fashioned technology – Hydraulics. They have evolved over the years, but they’ve been add-on’s like ABS, Brake Assist, Active braking, Radar technology. Brake systems are safety-critical kit and as the current system is tried and tested, I don’t expect we’ll move away from the basic concept of the mechanical hydraulic set-up.
Brake components include:
- Fluid – Brake fluid, quantity and quality is important.
- Brake booster – Employed to help the operator apply the brakes with little effort
- Master cylinder – Compresses the fluid pushing out the pistons when activated by the foot brake
- ABS modulator & pump – Brake manifold with integrated pump and control module (computer), used to rapidly apply and release fluid pressure causing the calipers to pulse the brakes.
- Brake lines and hoses – Carry the pressurized fluid to the brake calipers.
- Front Calipers – Front calipers come in two basic flavors floating and fixed. More on this below. The calipers job to apply force to the brake pad.
- Rear Calipers – Rear calipers vary as some cars integrate the parking brake and the caliper. And others again employ electronic parking brake. Either-way, rear calipers require special attention when working on them. More on this below.
- Rotors – Rotors or Discs are fixed to the hub and turn with the wheel. The caliper sits over the rotor helping to hold the pads close to the rotor read for activation.
- Pads – The pads are held against the rotor as default position and are forced against the rotor when the brakes are applied.
- Shoes – Shoes aren’t so common anymore and that’s a good thing. Replacing brake pads generally isn’t difficult, replacing shoes isn’t a fun experience without suitable tools.
Incorrect Wind Back Procedure
If you are working on a rear caliper that refuses to retract, check that you are following the correct service procedure. Rear calipers are different than fronts and require a different procedure.
Rear calipers won’t simply push home, the piston must be turned and pushed. A simple tool known as a wind-back tool is employed to turn and at the same time push the rear caliper pistons in.
Check out the repair tools I use including a wind back tool here on the Brake repair tools page.
Parking brakes now commonly come in two flavors:
- Manual – cable operated
- EPB – electronic push button parking brake
Retracting Rear Caliper with Manual Parking Brake
The rear calipers usually integrate the parking brake by fitting a brake lever and cable to the caliper. The manual parking brake obviously needs to be released before the removal procedure.
To retract the rear caliper:
Use a wind-back tool to turn and push the piston simultaneously. Some calipers will turn clockwise and some anti-clockwise. Keep turning and pushing until the piston retracts fully.
You can check out a wind back tool along with all the brake tools I use here on the Brake repair tools page.
Retracting Rear Caliper With EPB
The EPB brake uses a motor at each wheel or a single motor with cables to the caliper actuators as per a manual setup. Whichever type you have, the actuators will need to be placed into the service position.
This usually requires a scan tool to wind back the EPB actuators. You can check out the scan tool I use here on the Auto electrical repair tools page.
But it is possible to hot-wire the motors to retract them. You can read about that procedure here “EPB won’t release”.
After retracting the actuators, the piston is retracted similarly to the manual setup. Reactivating the EPB requires activating the parking brake a couple of times.
Binding Brake Caliper
A binding brake caliper is applicable to floating calipers which are fitted to most cars today. Only high-end or classic cars are fitted with fixed calipers. The difference between them is I’ll expect you’ve guessed, one is fixed and the other is free to move.
I say a floating caliper is free to move, but it only moves by a few mm. The floating caliper uses a single-piston which means to apply both pads, the caliper must move the outboard pad closer to the rotor. It does this by using the power of the piston to slide the whole caliper inboard.
To allow the caliper to float or slide, they use pins and bushings. Problems usually arise when the caliper’s pins corrode or bushings break down and cause the caliper to bind instead of slide.
How to diagnose?
Open the fluid reservoir before using a suitable screwdriver to push the brake piston into the caliper (Rear caliper use wind-back tool). Grab the caliper and rock it forward and back. If there’s no movement at all, you found your problem.
How to repair?
Remove the caliper and attempt to remove the pins from the brake carrier. In some cases the pins are bolts and when they become seized inside the brake carrier, it makes removal impossible without cutting equipment. If that is the case the carrier and bolts will need to be replaced.
The more common floating caliper setup will allow for caliper removal even with frozen sliding pins. With the caliper removed and suspended by a bungee.
Remove the pins from the carrier if possible and clean them using a wire brush and sandpaper. Use a small amount of anti-seize or copper grease to help the pins slide. You’ll find all these products and tools here on the Brake repair tools page.
Check the pin weather seals, a displaced or torn seal is often the root cause of the corrosion. In other cases, it may be impossible to remove the pins. If corrosion is too bad go ahead and replace the carrier and pins and bushings (not all calipers will have bushings).
Seized Caliper Piston
The caliper piston is what makes the whole system work. Without a free moving caliper, you’ll notice other symptoms like:
- Car hard on gas
- Feels slower than normal, pressing the gas pedal a little further
- Smoke from the wheel
- Hot smell of brakes
- Car pulls to one side of the road
- Single wheel is covered in excessive brake dust
How to diagnose?
Open the fluid reservoir before using a screwdriver to push back the piston (Rear caliper – use wind-back tool). If the piston fails to retract, suspect a frozen caliper, but one other possibility remains a collapsed brake hose.
To complete the diagnosis, we’ll need to open the brake caliper bleed nipple. (Be be mindful, after opening the bleed nipple the system will need to be bled before the brakes are usable.)
Check out the brake bleed procedure on this post “Car brakes won’t bleed”.
Go ahead and open the nipple, while pushing on the piston with a screwdriver, if fluid shoots from the bleed nipple and the piston now retracts, the flexible brake hose is faulty and needs to be replaced. Replace all the hoses at once as it’s likely the other hoses are also breaking down internally.
If on the other hand, the fluid didn’t shoot from the bleed nipple and the piston didn’t retract – your caliper is frozen and needs to be replaced. I would recommend replacing both on the same axle (both front or both rear), new pads, and a brake fluid change.
Common Causes Of Frozen Calipers
Bad brake fluid is the usual cause of caliper failure. Brake fluid attracts moisture (hygroscopic) and the moisture inside the brake system starts to pit and corrode the metal components. eventually causing the pistons to seize in the cylinder.
Brake fluid needs to be changed every 3 years for a trouble-free hydraulic system. Calipers are expensive but other components may be a ton more expensive to buy and fit like brake master cylinder or ABS modulator.
You can check out all the tools I use in this repair including workshop manuals here on the Brake repair tools page and if you need brake calipers check out the Amazon link below.Amazon Brake Calipers
Can a stuck caliper fix itself? A stuck or seized caliper will not repair itself and will need to be replaced immediately. A frozen caliper causes brake imbalance which is a safety hazard known as brake steer.