The single most important safety feature in your GMC Terrain is a good set of brakes. If your brake pedal is going to the floor, it indicates that there is a serious problem in the braking system.
When the pedal goes to the floor, it’s usually caused by a bad master cylinder, leaking brakes, bad brake shoes (if equipped with rear drums), and a few other reasons. We’ll go further into depth on each below.
The brakes are a hydraulic system that takes the energy that you exert on your Terrain’s brake pedal, multiplies it via the brake booster, and uses it to stop the vehicle. If any part of this system goes bad, the brake pedal can go to the floor.
We don’t recommend driving anywhere with a brake system that is compromised. If the vehicle still can stop, it’s not guaranteed that the problem won’t get worse.
Symptoms
- Increased Stopping Distance
- Brake Light On
- Brake Fluid Under Vehicle
Terrain Brake Pedal Goes to Floor: Causes + Diagnosis
Below we have listed five common reasons why your GMC Terrain’s brake pedal may be hitting the floor.
Items 1 and 2 are what you want to look at if there is a brake leak. Items 3, 4, and 5 are reasons why the pedal could sink to the floor with no leak at all.
1. Fluid Leak
A brake fluid leak is one of the most common reasons that the brake pedal would go to the floor. It also happens to be the easiest to check. All you have to do is take the lid off of the master cylinder reservoir and check the fluid level.
If the brake fluid is low, filling it back up is not going to fix the problem. The system needs bled. This is due to the fluid in the lines being replaced by air whenever it leaks out. It’s highly likely there is a leak, which you’ll need to find.
If you’ve recently had brake work done, and the pedal is going further to the floor than it used to, you may need to bring it back to the shop and have the brake system bled.
Diagnosis
- Fill the brake reservoir back up with the appropriate brake fluid for your vehicle.
- Pump the brakes for a few minutes with the Terrain’s engine running (check the fluid level from time to time, always put the lid on the master cylinder, you don’t want more air entering the system).
- Look behind all four wheels. You should see fluid on the ground by one of them. It’s highly unlikely that a brake line itself is bad. It’s much more likely that the problem is with a caliper or wheel cylinder.
- Jack up the vehicle and remove the wheel in question. Always use a jack stand for safety reasons.
- If it’s a disc brake in question, inspect the caliper. It’s likely to have a leak at the caliper seals at the piston(s). If it is a drum brake look at the wheel cylinder. This is a very common point of brake failure.
- Replace as needed.
- Bleed the Brake System.
2. Bad Master Cylinder
The master cylinder is the part of the braking system that presses the fluid into the caliper or brake shoes. When it goes bad, it loses pressure causing the brake pedal to go to the floor. It’s easy to find.
Diagnosis
- Locate the master cylinder. It’s always on the firewall right about where you would expect it to be in relation to the brake pedal on the other side.
- Inspect the master cylinder to see if there is fluid leaking from it. If there is, that’s proof positive that it needs replaced.
- Replace the master cylinder if needed.
- Bleed the Brake System.
Keep in mind that if the master cylinder is low on fluid, that fluid has to be going somewhere. Don’t give up until you find it.
3. Bad Brake Fluid
Brake fluid can go bad just like any other fluid. When this happens it gets darker in color.
Diagnosis
Good = Clear to Light Gold Color
Bad = Chestnut through Black Color
The best way to check this is to pull a little out with a medicine dropper. Compare it to some new fluid that GMC recommends for your Terrain. If the color is way off, that indicates that it should be changed.
Brake fluid can go bad for a number of reasons. It can get too hot. It can get moisture in it. When this happens you’ll get a soft pedal that can go toward the floor. If you hit the brakes a few times and the pedal hardens up, that indicates some air is trapped in the lines or that the fluid is bad.
4. Bad Shoes (Drum Brakes Only)
Brake shoes are only found on drum brake equipped vehicles. There will never be a drum brake on front of a modern vehicle. A shoe that is worn down too far will cause the pedal to sink closer to the floor than it normally would. This would be something to look at if there was no fluid leak detected.
Diagnosis
- Jack up the Terrain. Use a jack stand for safety.
- Pull the wheel.
- Pull the drum off. This is easy to do. It should pull right off.
- Inspect the shoes. If they look like they are about worn out replace them.
Tip: If you do replace the shoes, jack up the vehicle and pull both drums off. You can use the other wheel as a reference for spring placement. If you don’t have two jack stands, make sure to take a few good pictures of how everything looked before disassembly. A good pair of needle nose pliers can help when doing this job.
5. Wheel Bearing (Disc Brakes)
This is not as likely as the items listed above, but a bad wheel bearing can cause the brake pedal to go to the floor as the rotor has different geometry in relation to the caliper. This increase in air gap can cause the pedal to sink to the floor.
If there is a fluid leak this would not be the problem. You should hear and feel a wheel bearing that is this bad, just keep that in mind. Here’s more on diagnosing a bad wheel bearing.
Bleeding Brakes
If it ended up being a brake leak that caused the problem, and you’ve replaced the part in question, you’ll need to bleed the brake system. There are two ways to do this. You can get a one man bleeding tool, or you can use a friend to pump the brakes while you do each wheel. Here’s more on that.
Conclusion: GMC Terrain Brake Pedal Hits Floor
There are a lot of reasons why your Terrain’s brake pedal may go to the floor. With enough time and patience, you can find the cause yourself. If you don’t feel comfortable doing that, have a professional look at it right away. A weak brake pedal is not something you want to trust with your life.