Fitting a new set of brake pads is a nice simple Saturday morning kind of job…. except it’s not! It’s turned into a giant turd of a job.
The most common reason new brake pads won’t fit – Corrosion on the caliper carrier bracket. Other causes include:
- Excessive paint on the brake pad arms
- Wrong pads
- Wrong pad orientation
- Caliper piston not retracted
Pads that won’t fit is usually a pretty simple problem to solve, and in this post, we’ll look at the most likely reason and how you can fix them.
Warning, some cars are fitted with dynamic braking systems. These systems can be dangerous to work on without disabling them first. Check if your car is fitted with a brake assist system.
Brake Caliper Carrier
Most modern cars use a free-floating brake caliper set-up. The calipers are free to move laterally across the caliper carrier. This free movement offers more evenly braking force over both sides of the rotor.
The caliper is fixed to the carrier by two sliding pins. The pins are lubed and allow for smooth caliper action.
The pads sit on the carrier with the brake pad arms in a rail. The rail holds the pads snugly in place and guides it to the rotor as the brake pedal is pressed.
Problems arise when corrosion builds up on the carrier rail. Corrosion can cause all sorts of braking problems, including:
- Noisy brakes
- Hard brake pedal
- Ineffective braking
- Sticking brake caliper
- Smoke from brake caliper
- Excessive brake pad wear
- Uneven brake pad wear
- Brake steering issues
And when it comes to fitting a new set of pads, you may find them difficult to fit. And you’ve guessed it, the corrosion needs to be cleaned, and the rails need some copper grease.
I removed this carrier just to show what it looks like, but you can do a perfectly good job cleaning it on the car. The copper grease helps the pads move smoothly along the rail and prevents brake squeal.
The tools you’ll need:
- Dust mask
- Wire brush
- Small scraper
- Copper grease
Before cleaning, you’ll need a mask. Brake dust is dangerous to the lungs. When there’s a lot of brake dust on the calipers, I wet the whole area with water using a spray bottle. Help keep the dust down.
The cleaning procedure involves scraping, sanding, and checking your work by fitting the old brake pad, not the new one, because the rust and crap will contaminate it. When checking, the pad should move freely across the rail. If so, go ahead and add some copper grease. You’ll find links to the tools and consumables I use here on the Brake repair tools page.
When applying the grease, less is more, too much grease will contaminate the rotors & pads, and your brakes will be crap.
Some brake pad carriers will also employ brake pad retaining clips. These guys are important, they keep the pad in place, and just off the rotor, help reduce brake noise, extends pad life, and keep them cooler.
New pads don’t always come with replacement clips, and so old ones are often reused. As they age, unsurprisingly, they become bent out of shape, which can cause fitting issues.
If your clips are old and bent, treat your brakes to a new set.
Excessive Brake Pad Paint
What does excessive brake pad paint mean? It means the brake pads have too much paint on the arms and consequently won’t fit in the carrier rails.
I know this because I worked as a technician for GM Canada in a large dealership that did first-class work and used only OEM parts.
The pads were made in Mexico and were in GM branded packaging. Although the pads were top quality, they still needed to be filled – Chevy Colt or Cadi, didn’t matter.
The problem was excessive black paint on the metal pad arms, right where they meet the carrier rail.
The solution is simple, check your pads for excessive paint and, using a small file, remove the paint from the metal pad arms, file a little, and test. Removing too much material will cause the pad to become loose in the carrier, and that will cause brake noise.
The pads should be snug in the rail but not tight. When you’re happy with the fit, use a small amount of copper grease to keep things moving smoothly.
Wrong Pad Type
Wrong parts don’t often happen today. Parts guys are usually pretty good at their job. When I was an apprentice, most of my time was spent running to and from the parts store.
As S**t flows downhill, I soon found it was more efficient to have the old part in my hand to compare before leaving the shop.
But wrong parts can happen, so check carefully the old and new pads, use Vernier calipers or tape measure if needed.
Having your chassis number to hand when ordering parts saves miscommunication errors.
Wrong Pad Orientation
Removing pads is easy, but sometimes you forget or just didn’t pay attention to which pad came from where. Taking photos when stripping is a great tip because it’s easy to forget.
Most brake calipers will have identical pads. You could use the inner or outer and left side of the car or right. However, some will have a specific pad for the inner and outer. But be mindful some could also have inner, outer, left, and right sides of the car. When they are left and right specific, the pads will likely be marked “L” and “R”.
I had an apprentice once. I’m not going to name names, “god bless him” he fitted a new set of calipers and was having difficulty fitting the pads that were marked L and R.
It turned out the pads were on the correct side alright, but the calipers weren’t, it could happen to a bishop.
Caliper Piston Extended
Before attempting any brake repairs, make sure it’s safe to do so. Some cars are fitted with brake assist. It’s a pre-charged braking system that can cause injury. Check and see if your vehicle is fitted with a dynamic brake assist system. If it has, disables it.
The pads won’t fit because the piston in the caliper hasn’t retracted far enough. The piston needs to be pushed all the way home. Front caliper pistons are usually easy to retract. A channel lock or c-clamp will do the job or pry them back using a longish screwdriver.
The proper tool is called a wind-back tool, and while it isn’t necessary for front pads, it is a useful kit.
Remove the brake fluid reservoir cap before forcing the caliper piston home, preventing fluid overflow.
Fitting rear pads aren’t as easy. First off, if you have an electronic parking brake (Push button), you’ll need a service tool.
The handheld tool communicates with the parking brake control unit and puts it into service mode. After the repairs, the service mode will need to be turned off.
Service tools aren’t as expensive as you might think. You can check out the tools I recommend on the “Brake repair tools page” and if you need brake parts, check out the Amazon link below.Amazon Brake Parts
Rear calipers won’t just push back like front calipers. Instead, they need to be screwed and pushed at the same time.
You’ll need a tool like the Orion Motor Tech wind back kit, it’s perfect for beginners, and it’s universal. It covers all vehicles and is conveniently sold and delivered by Amazon.com, Nice! I wrote a post about retracting rear calipers, and you can check it out here – Rear caliper won’t depress.
Should brake pads fit tight? Brake pads should fit snugly in the brake caliper carrier but should slide freely.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.